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Organ and Effective Dose Coefficients for Common Computed Tomography Protocols Using the UF/NCI Family of Computational Reference Phantoms

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Title:
Organ and Effective Dose Coefficients for Common Computed Tomography Protocols Using the UF/NCI Family of Computational Reference Phantoms
Creator:
Stepusin, Elliott J
Place of Publication:
[Gainesville, Fla.]
Florida
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University of Florida
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english
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1 online resource (120 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Biomedical Engineering
Committee Chair:
BOLCH,WESLEY EMMETT
Committee Co-Chair:
HINTENLANG,DAVID ERIC
Committee Members:
RILL,LYNN NEITZEY
Graduation Date:
5/3/2014

Subjects

Subjects / Keywords:
Abdomen ( jstor )
Arithmetic mean ( jstor )
Bone marrow ( jstor )
Cadavers ( jstor )
Computerized axial tomography ( jstor )
Dosage ( jstor )
Dosimetry ( jstor )
Estimated cost to complete ( jstor )
Human organs ( jstor )
Skin ( jstor )
Biomedical Engineering -- Dissertations, Academic -- UF
computed -- dose -- dosimetry -- modulation -- phantom -- tomography
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bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Biomedical Engineering thesis, M.S.

Notes

Abstract:
Due to the rapid growth of computed tomography (CT) examinations in the United States, there is a need for accurate CT size-specific organ dosimetry that accounts for tube current modulation (TCM). Past studies validate the use of a slice-by-slice CT dosimetry methodology for the Toshiba Aquilion ONE scanner that can accurately account for TCM, and can be implemented for a multitude of exam types. Physical anthropomorphic phantom dosimetry data was used a basis to further validate this algorithm for different size reference phantoms. The average magnitude of percent error in the computed dose to all in-field organs of torso exams when compared to measured values was 8.5%. For head exams, the average magnitude in percent error of in-field organ doses was 6.9%. This methodology was then applied to The University of Florida Family of Reference Hybrid Phantoms across a wide range of clinically relevant scan protocols. This data provides age and gender-specific organ dose calculations that can be scaled by average effective mAs to calculate absolute organ dose. Additionally, effective dose coefficients in units of microsievert per milligray-centimeter were calculated for each reference hybrid phantom, as well as a reference dose coefficient. These coefficients, when applied to the physical phantom data show a relative error in effective dose of 14.6% and 12.5% for the reference and phantom-specific coefficients, respectively. Calculating effective dose using the millisievert per average effective mAs for each phantom yielded an average dosimetric error of 6.4%. ( en )
General Note:
In the series University of Florida Digital Collections.
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Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2014.
Local:
Adviser: BOLCH,WESLEY EMMETT.
Local:
Co-adviser: HINTENLANG,DAVID ERIC.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2015-05-31
Statement of Responsibility:
by Elliott J Stepusin.

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UFRGP
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Applicable rights reserved.
Embargo Date:
5/31/2015
Resource Identifier:
908645512 ( OCLC )
Classification:
LD1780 2014 ( lcc )

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O RGAN AND EFFECTIVE DOSE COEFFICIENTS FOR COMMON COMPUTED TOMOGRAPHY PROTOCOLS USING THE UF/NCI FAMILY OF COMPUTATIONAL REFERENCE P HANTOMS By ELLIOTT JAMES STEPUSIN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2014

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2014 Elliott James Stepusin

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To my mom and dad, for everything

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4 ACKNOWLEDGMENTS Firstly, I would like to thank Dr. Wesley Bolch for giving me the opportunity to do this research and his guidance as a teacher and mentor throughout my undergraduate and graduate career. I thank my committee members Dr. Lynn Rill and Dr. David Hintenlang for their support both in the classroom and towards my research I thank my research colleagues for all their hard work and dedication that has contributed to this project Firstly I thank Dr. Dan Long for his major contributions to this project and its fundamental basis Without his mentorship and guidance this project would not be possible I thank Kayla Ficarrotta for conducting the physical phantom measurements used in this research I thank Choonsik Lee and Amy Geyer for her work towards creating the UF/NCI Library of Hybrid Computational Phantoms and associated 3D modeling help I thank Dr. Michael Wayson for his work tabulating and calculating material compositions for their use in computational dosimetry I thank Dr. Manuel Arreola and his research group of Dr. Thomas Griglock, Dr. Lindsay Sinclair, Anna Mench, and Becky Lamoureux for access to their cadaver dosimetry data I also thank my office mates, class mates, and friends for making my research enjoyable to conduct and for helping make every day in the off ice memorable Most importantly I want to thank my family I thank my sister Rebecca for all the love and friendship she gave to me while we grew up together I will remember you forever I thank my brother Paul for his love and always looking out for me Lastly, I thank my parents Paul and Nancy for loving me and providing for me, without you, none of this would be possible.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ .......... 9 LIST OF ABBREVIATIONS ................................ ................................ ........................... 11 A BSTRACT ................................ ................................ ................................ ................... 13 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 15 1.1 Ov erview of Computed Tomography ................................ ................................ 15 1.2 Patient Dose and Associated Risks of Computed Tomography Exams ............ 16 1.2.1 Patient Dose ................................ ................................ ............................ 16 1.2.2 Stochastic and Deterministic Effects ................................ ....................... 16 1.3 Computed Tomography Dose Optimization Techniques ................................ ... 17 1.3.1 Protocol Standardization ................................ ................................ ......... 17 1.3.2 Tube Current Modulation ................................ ................................ ......... 19 1.3.3 Iterative Reconstruction ................................ ................................ ........... 20 1.4 Computed Tomography Patient Dosimetry ................................ ....................... 20 1.4.1 Methods and Limitations of Current Dosimetry ................................ ........ 20 1.4.2 Methods and Limitations of Computational Dosimetry ............................. 22 1.4.3 Need for Size Specific Dosimetry that Accounts for Automatic Tube Current Modulation ................................ ................................ ........................ 22 2 CO MPLETION AND VALIDATION OF A MONTE CARLO BASED SLICE BY SLICE DOSIMETRY METHODOLOGY FOR THE TOSHIBA AQUILION ONE SCANNER ................................ ................................ ................................ .............. 24 2.1 Cr eation and Validation of a Toshiba Aquilion ONE Custom Source Subroutine in MCNPX TM ................................ ................................ ...................... 24 2.1.1 Custom Source Subroutines ................................ ................................ .... 24 2.1.2 Source Tilt ................................ ................................ ............................... 24 2.2 Toshiba Aquilion ONE Specific Dosimetry Methods ................................ ......... 26 2.2.1 Methodology ................................ ................................ ............................ 26 2.2.2 Tube Current Capping and Exam Over Ranging ................................ ..... 28 2.3 Physical Phantom Validation ................................ ................................ ............ 29 2.3.1 Physical Phantom CT Dosimetry ................................ ............................. 29 2.3.2 Torso Exams ................................ ................................ ........................... 31 2.3.3 Head Exams ................................ ................................ ............................ 33

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6 3 ANALYSIS OF SIZE SPECIFIC PHANTOM MATCHING USING CADAVER DOSIMETRY DATA ................................ ................................ ................................ 47 3.1 Hybrid Computational Phantom Matching ................................ ......................... 47 3.1.1 Height, Weight, and BMI Matching ................................ .......................... 47 3.1.2 Effectiv e Diameter Matching ................................ ................................ .... 48 3.2 Cadaver Matched Phantom Dosimetry ................................ ............................. 49 3.2.1 Comparison of Organ Dose for Cadaver Matched Phantoms ................. 49 4 ORGAN AND EFFECTIVE DOSE COEFFICENT ESTIMATES FOR HEAD AND TORSO EXAMS ON THE ICRP 89 BASED REFERENCE HYBRID COMPUTATIONAL PHANTOMS ................................ ................................ ............ 55 4.1 UF Family of Reference Hybrid Phantoms ................................ ........................ 55 4.2 Dosimetry Methods ................................ ................................ ........................... 56 4.2.1 Common Torso Exam Types ................................ ................................ ... 56 4.2.2 Special Dosimetry Considerations ................................ ........................... 58 4.2.3 Effective Dose and Effective Dose Coefficient Calculations .................... 60 4.2.4 Head and Brain Exam Methodology ................................ ........................ 61 4.3 Final Organ and E ffective Dose Coefficient Estimates ................................ ...... 62 4.3.1 Torso and Head Exam Organ Dose Data ................................ ................ 62 4.3.2 Torso Exam Effective Dose Coefficients ................................ ................. 63 4.3.4 Comparison of Effective Dose Calculations ................................ ............. 64 5 CONCLUSIONS AND FUTURE WORK ................................ ................................ 90 5.1 Conclusions ................................ ................................ ................................ ...... 90 5.2 Future Work ................................ ................................ ................................ ...... 90 5.2.1 Improvement of Methodology for the Calculation of Average Effective mAs ................................ ................................ ................................ ............... 90 5.2.2 Expand Dosimetry to the UF/NCI Library of Hybrid Computational Phantoms ................................ ................................ ................................ ...... 91 APPENDIX A COMPLETE PHYSICAL PHANTOM VALIDATION DOSIMETRY DATA ................ 92 UFADM CAP Exams ................................ ................................ ............................... 92 UF15F CAP Exams ................................ ................................ ................................ 93 UF10MF CAP Exams ................................ ................................ .............................. 94 UFADM Head Exams ................................ ................................ .............................. 95 UF10MF Head Exams ................................ ................................ ............................ 95 B COMPLETE CADAVER DOSIMETRY DATA ................................ ......................... 96 Cadaver IV Exams ................................ ................................ ................................ .. 96 Cadaver V Exams ................................ ................................ ................................ ... 97 Cadaver VI Exams ................................ ................................ ................................ .. 98

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7 Cadaver VII Exams ................................ ................................ ................................ 99 C COMPLETE REFERENCE PHANTOM DOSIMETRY DATA ............................... 101 UFADM Organ Dose and Effective Dose Coefficient Estimates ........................... 101 UFADF Organ Dose and Effective Dose Coefficient Estimates ............................ 103 UF15M Organ Dose and Effective Dose Coefficient Estimates ............................ 105 UF15F Organ Dose and Effective Dose Coefficient Estimates ............................. 106 UF10MF Organ Dose and Effective Dose Coefficient Estimates .......................... 108 UF05MF Organ Dose and Effective Dose Coefficient Estimates .......................... 109 UF01MF Organ Dose and Effective Dose Coefficient Estimates .......................... 111 UFNBMF Organ Dose and Effective Dose Coefficient Estimates ......................... 112 Head Exam Organ Dose Estimates for All Reference Phantoms ......................... 115 Brain Exam with Tilt Organ Dose Estimates for All Reference Phantoms ............. 115 LIST OF REFERENCES ................................ ................................ ............................. 116 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 120

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8 LIST OF TABLES Table page 2 1 Validation results for y axis rotation of the CT source subroutine. ...................... 41 2 2 Validation results for x axis rotation of the CT source subroutine. ...................... 42 2 3 Over ranging estimates for different exam types for the Toshiba Aquilion ONE Scanner. ................................ ................................ ................................ .... 43 2 4 Example mA values for different amounts of scanner over ranging. ................... 44 2 5 Detailed scan parameters for all physical phantom CT measurements. ............. 45 2 6 Average magnitude of percent error of in field organ doses for all phy sical phantom measurements. ................................ ................................ .................... 46 3 1 Scan parameters for all cadaver exams used in the phantom matching study. .. 52 3 2 Average magnitude of percent error of in field organ doses for the cadaver to matched phantom data. ................................ ................................ ...................... 53 3 3 Average magnitude of percent error for specific in field organs over all cadaver exams. ................................ ................................ ................................ .. 54 4 1 Common CT exam protocols and parameters based on SNIP data. .................. 83 4 2 Sensitivity study for *F6 and *F8 derived organ doses across four exam ranges and four different starting particles. ................................ ........................ 84 4 3 CTDI body phantom measurements and associated CTDI w values. .................. 85 4 4 Absolute organ dose estimates for 120 kVp head exams across all reference phantoms. ................................ ................................ ................................ ........... 86 4 5 Absolute organ dose estimate for 120 kVp brain exams with tilt across all reference phantoms. ................................ ................................ ........................... 87 4 6 Effective Dose Coefficients for the reference phantoms across different protocols and beam energies. ................................ ................................ ............ 88 4 7 Comparison of effective dose estimates for the physical phantom data. ............ 8 9

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9 LIST OF FIGURES Figure page 2 1 Excerpt of Fortran 90 code from the Toshiba Aquilion ONE custom source subroutine. ................................ ................................ ................................ .......... 36 2 2 A visualized MCNPX TM geometry showing five rotated CTDI body phantoms in the xz plane. ................................ ................................ ................................ ... 37 2 3 A visualized MCNPX TM geometry showing five spheres situated in the yz plane. ................................ ................................ ................................ .................. 38 2 4 A visual representation of a slice by slice li brary applied to a computational phantom. ................................ ................................ ................................ ............ 39 2 5 A comparison of slice specific mA values with and without mA capping for a given exam range. ................................ ................................ .............................. 40 3 1 A visualization of diameter measurements being made on a computational phantom. ................................ ................................ ................................ ............ 51 4 1 Visual representation of the Lesser Trochanter anatomical landmark. ............... 67 4 2 Visual representation of the Top of the Iliac Crest anatomical landmark. ........... 68 4 3 Visual representation of the Top of Kidney anatomical landmark. ...................... 69 4 4 Visual representation of the Dome of Diaphragm anatomical landmark. ............ 70 4 5 Visual representation of the Thoracic Inlet anatomical landmark. ....................... 71 4 6 Visual representation of the Chin anatomical landmark. ................................ ..... 72 4 7 Example of brain reference points needed for gantry tilt and exam range calculations. ................................ ................................ ................................ ........ 73 4 8 Comparison of relative organ doses for a 120 kVp Chest Abdomen Pelvis exam. ................................ ................................ ................................ .................. 74 4 9 Comparison of relative organ dose for a 120 kVp Chest Abdomen exam. ......... 75 4 10 Comparison of relative organ dose for a 120 kVp Abdomen Pelvis exam. ......... 76 4 11 Comparison of relative organ dose for a 120 kVp Chest exam. ......................... 77 4 12 Comparison of relative organ dose for a 120 kVp Abdomen exam. .................... 78 4 13 Comparison of relative organ dose for a 120 kVp Pevlis exam. ......................... 79

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10 4 14 Comparison of relative organ dose for a 120 kVp Head exam. .......................... 80 4 15 Comparison of relative organ dose estimates for a 120 kVp Brain exam. .......... 81 4 16 Comparison of relative organ doses for the UFADM Chest Abdomen Pelvis exam at differe nt energies. ................................ ................................ ................. 82

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11 LIST OF ABBREVIATIONS A Abdomen exam AAPM American Association of Physicists in Medicine AIDR AP B BEIR VII BMI BTES C CA CAP CDC CT CTDI DICOM DLP ED EDC H ICRP kVp LAT LTES Adaptive Iterative Dose Reduction abdomen pelvis exam anterior posterior view brain exam Biological Effects of Ionizing Radiation Report Number Seven Body mass index bone tissue equivalent substitute chest exam chest abdomen exam chest abdomen pelvis exam Center for Disease Control computed tomography Computed Tomography Dose Index Digital Ima ging and Communication in Medicine dose length product effective diameter Effective Dose Coefficient head exam The International Commission on Radiological Protection peak kilovoltage lateral view lung tissue equivalent substitute

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12 mAs MCNPX NAS NCRP NHANES NRPD NURBS OSLD P PMMA ROI SID SNIP STES TCM UF01MF UF05MF UF10MF UF15F UF15M UFADF UFADM UFNBMF milliampere second Monte Carlo N Particle eXtended National Academy of Sciences National Council on Radiation Protection and Measurements National Health and Nutrition Examination Study National Radiation Protection Board non uniform rational B spline optically stimulated luminesc ent dosimeter pelvis exam poly methyl methacrylate region of interest source image distance Standard Names for Imaging Procedures soft tissue equivalent substitute tube current modulation one year old hermaphrodite phantom Un iversit five year old hermaphrodite phantom University of Florid ten year old hermaphrodite phantom Un fifteen year old female phantom year old male phantom phantom n ew born hermaphrodite phantom

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13 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Mast er of Science O RGAN AND EFFECTIVE DOSE COEFFICIENTS FOR COMMON COMPUTED TOMOGRAPHY PROTOCOLS USING THE UF/NCI FAMILY OF COMPUTATIONAL REFERENCE P HANTOMS By Elliott James Stepusin May 2014 Chair: Wesley E. Bolch Major: Biomedical Engineering Due to the rapid growth of computed tomography (CT) examinations in the United States, there is a need for accurate CT size specific organ dosimetry that accounts for tube current modulation (TCM) Past studies validate the use of a slice by slice CT dosimetry meth odology for the Toshiba Aquilion ONE scanner that can accurately account for TCM, and can be implemented for a multitude of exam types Physical anthropomorphic phantom dosimetry data was used a basis to further validate this algorithm for different size reference phantoms The average magnitude of percent error in the computed dose to all in field organs of torso exams when compared to measured values was 8.5% For head exams, the average magnitude in percent error of in field organ doses was 6.9% Thi s methodology was then applied to The University relevant scan protocols This data provides age and gender specific organ dose calculations that can be scaled by average e ffective mAs to calculate absolute organ dose Additionally, effective dose coefficients in units of microsievert per milligray centimeter were calculated for each reference hybrid phantom, as well as a reference

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14 dose coefficient These coefficients, whe n applied to the physical phantom data show a relati ve error in effective dose of 14. 6 % and 12. 5 % for the reference and phantom specific coefficients, respectively Calculating effective dose using the millisievert per average effective mAs for each phant om yielded an average dosimetric error of 6. 4 %.

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15 CHAPTER 1 INTRODUCTION 1.1 Overview of Computed Tomography Computed Tomography (CT) is a robust diagnostic imaging modality which is essential in modern medicine Sir Godfrey Hounsfield and Allan Cormack are each credited as the inventors of CT with their combined work being recognized for t he Noble Prize in Physiology or Medicine 1979 1 The mathematical basis for image reconstruction was originally laid out in 1917 by astrophysicist Johann Radon His work went largely unnoticed until the mid 1960s when Houns field and Cormack independently used his methodology along with the unique attenuation characteristics of tissue to create anatomical images Their research came to fruition in 1971 when the first clinical CT image was acquired of 2 Since then CT has seen great advances in technology and use, most notably helical scanning (late 1980s) and mult i slice scanning (late 1990s) 3 An estimated 85.4 million CT scans were performed in 2011 in the U.S., up 4% from 2010 4 Of these scans, an estimated 7 million CT exams were performed on pediatric patients 5 As the number of scans has increased so has the average effective whol e body dose to the U.S. population. In a 2006 report from the National Council on Radiation Protection and Measurements (NCRP), medical applications now account for 48% of total radiation exposure to the U.S. population, with 50% of the medical exposure a ttributed to CT imaging alone 6 7

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16 1.2 Patient Dose and Associated Risks of Computed Tomography Exams 1.2.1 Patient Dose The fundamental SI unit for radiation absorbed dose is the gray (Gy), defined as one joule (J) of energy absorbed per kilogra m (kg) of tissue mass Due to the varying spectrum of biological effects associated with an equal quantity of absorbed dose, we more commonly use a related dosimetry quantity, the equivalent dose Equivalent dose which is measured in sieverts (Sv), is th e product of absorbed dose in a specific organ (organ dose) and a weight factor based on radiation particle type 8 For CT, the only particle of interest is photons, which have a weighting factor w R of 1 .0 Patient dose from CT is a n issue of major concern in the medical physics community The increase in patient dose over the past 30 years has led to concerns for patient health A 2007 article in The New England Journal of Medicine outli ned these concerns in which the authors estimated that approximately 1.5 to 2.0% of all cancers in the U.S. were potentially caused by CT exams 9 Additionally, patient overdoses have been well documented in the media such as the Cedars Sinai incident in Los Angeles where 206 stro ke victims were exposed to eight times the normal radiation dose 10 Although overexposures should never occur, they are usually caused by poor training misuse of the CT scanner or improper protocol design 1.2.2 Stochasti c and Deterministic Effects Tracking and calculating patient dose is done mainly to predict the biological effects of radiation exposures Stochastic effects, such as cancer are radiation induced effects whose probability of occurrence in a population ar e proportional to the magnitude of the organ dose, and usually have no threshold dose value Deterministic effects, such as skin damage are effects whose severity is proportional to organ dose,

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17 and may or may not have a threshold dose 8 Common deterministic effects associated with CT exposures are lens cataracts and circulatory disease to the heart or brain 11 The threshold dose for these ailments is in constant debate with in the scientific community T he International Commission on Radiological Protection (ICRP) recently set the dose threshold for cataracts at 0.5 Gy, but some research has suggested it may be as low as 0.1 Gy if not zero 11 12 The primary stochastic effect associated with CT exposures is cancer The National Academy of Sciences (NAS) Biological Effects of Ionizing Radiation Report N o. 7 (BEIR VII) outlines organ specific cancer models for populations 8 These risk models are based primarily on the data obtained from the Japanese Bomb Survivors This data set is comprised of an ar ray of radiation particle type s over a large range of energies Many argue that these models are not just ified for exposures of photons in the diagnostic energy range (0 to 140 keV) especially at small exposure levels 13 The biggest rebuttal to using the BEIR VII report is its use of a linear no threshold model The Brenner ar ticle previously refer enced used organ equivalent doses of radiation for which the models are not significantly significant (< 100 mSv) There is not sufficient evidence to conclude there are observable effects below this threshold or if the dose response is even linear at the se low doses 14 For these reasons, new risk models must be created for CT exposures resulting from radiation epidemiology studies that directly target exposed patients 1.3 Computed Tomography Dose Optimization Techniques 1.3.1 Protocol Standardization There are many ways to optimize dose to the patient while maintain ing acceptable image quality such as technique charts and standardized protocols The

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18 major variables in a CT expos ure are tube potential helical pitch, and tube current The energy spectrum of x rays in a CT exam is a function of the inherent and added filtration, and the tube potential, usually 120 kVp (peak kilovoltage) for adults which can be lowered or raised based on the size and thickness of the patient Smaller pa tients who are less attenuating can be scanned at 100 kVp or even 80 k Vp with little impact on image quality Pitch is a unit less quantity that describes the relative movement of the table with respect to the fan beam width as a function of rotation 3 A pitch of 1.0 implies that for every rotation of the beam, the table has moved exactly one beam collimation width Furthermore, a pitch less than one is when the table is moving less th an one beam width per rotation The pitch, which affects the amount of projection data acquired for each slice impacts both image quality and patient dose Tube current which is measured in milliampere (mA), is proportional to the number of photons b ei ng generate d by the x ray tube Increasing the mA of an exam will increase image quality and patient dose, and vice versa Image quality is always the most important part of diagnostic imaging and should be the basis for dose optimization Choosing which ima ge quality is acceptable is difficult to determine as it is subjective in nature Nonetheless, some medical conditions require more or less image quality to yield a successful diagnosis Optimizing beam energy, pitch, tube current and beam thickness will lower patient dose while maintaining satisfactory images 15 Standardized protocols also lead to less confusion when ordering CT proc edure s as they decrease the chance of overdosing the patient either through the image itself or by way of avoiding re imaging The University of Florida Department of Radiology has created an elaborate set of protocols that can be used when ordering

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19 and administering CT exams T hese protocols are described by Standard Names for Imaging Procedures (SNIP s ) and are located on their departmental website 16 1.3.2 Tube Current Modulation Protocol adjustment is controlled mainly by the healthcare instituti on; nevertheless, many dose optimization methods are created by the CT vendors themselves One ma jor technique is tube current modulation ( TCM) 15 17 As the x ray tube rotates around the patient, the path length of the each incident photon in the fan beam geometry experiences a variable amount of tissue attenuation High attenuating a reas of the patient require a higher number of incident photons (via increa sed mA) than lower attenuating areas of the body Altering the tube current as a function of space and time can optimize patien t dose by ensuring the number of photons incident on the detector array at any given time is sufficient to produce a usable imag e There are three major types of TCM: angular, longitudinal, and combined Angu lar modulation changes the tube current as a function of angle relative to the patient. rior posterior (AP) thickness provides less tissue atten uation than the l ateral (LAT) thickness Modulating the beam s intensity, usually in a sinusoidal manner can offset these changes in attenuation Longitude modulation is dependent on anatomical regions of the body A low attenuating region of the body such as the neck can be imaged with less photons than high attenuating regions such as the pelvis Currently most vendors employ combined SURE Exposure (Toshiba America Medical Systems Inc. Tus tin, CA) technology which utilizes both angular and longitudinal dependent changes in attenuation Patient dose can be significantly lowere d using TCM and is used in almost every CT torso exam.

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20 1.3.3 Iterative Reconstruction The most recent form of dose r eduction is iterative image reconstruction Ever since its creation, CT has relied heavily on filtered back projection for image reconstruction This method is not completely accurate and requires a high amount of projection data to render a useful image Now that computer process ing power is much greater and more cost effective images can be reconstructed numerically in an iterative process 18 Thes significantly less projection data to be reconstructed Iterative reconstruction is currently (AIDR) technology th at is used in conjunction with TCM Although its presence is obvious, quantifying the dose savings from these exams has yet to be determined due to its recent emergence and inherent changes in image appearance 1.4 Computed Tomography Patient Dosimetry 1.4.1 Methods and Limitations of Current Dosimetry With multiple efforts being made to reduce patient dose attributed from CT scans it is equally as important to measure and quantify that dose Th e most basic metric for computing dose is the Computed Tom ography Dose Index (CTDI) The first iteration of CTDI shown in equation 1 1 represents the average absorbed dose along the z axis of a cylindrical acrylic phantom where N is the number tomographic sections in the scan and T is the number of data channels used in the scan 19 (1 1) To account for larger beam width s CTDI 100 was created which accounts for the dose over a 100mm region in the acrylic phantom This represents the average

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21 exposure over the 100 mm pencil ion chamber used for these measurements Finally, to compensate for higher doses at the peripheral l ocations of the phantom as well as the exam pitch, CTDI w and CTDI vol were created as shown in equations 1 2 and 1 3. (1 2) (1 3) The CTDI vo l can used to estimate absorbed dose across a material similar in composition to acrylic such as soft tissue In order to compensate for the changes in scan lengths, the dose length product (DLP) was defined as shown in E quation 1 4 20 (1 4) Even though CTDI and DLP are good indicators of scanner output and are used extensively in quality assurance testing they are still limited because patient size is never accounted for The American Association of Physicists in Medicine (AAPM) Tas k Group 204 report address ed this concern 5 This report utilizes effect ive diamete r which is shown in E quation 1 5 to scale the doses from CTDI vol to a more appropriate value for each patient which is shown in Equation 1 6 (1 5) (1 6) These scaling factor s which are a function of patient effective diameter, are very important in pedia tric dosimetry because traditional CTDI vol underestimates many of the values of organ dose in these smaller patients It should be noted that TCM is a shift variant technique and CTDI vol is not, because of this local dose cannot be assigned from the CTDI vol values outputted by the scanner 21 This makes TCM hard to account for using the CTDI vol and DLP model.

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22 1.4.2 Methods and Limitation s of Computational Dosimetry Another method for CT dosimetry is through the use of pre calculated organ dose libraries which are generated through Monte Carlo simulations Once the x ray tube spectrum and source geometry are mathematically defined, organ doses can be estimated through a Monte Carlo simulation using a computational anatomic phantom The Nat ional Radiation Protection Board (NRPD) in the United Kingdom and the National Research Center for Environment and Health in Germany created CT dose databases in 1991 22 23 These databases provided dosimetry data based on stylized phantoms and an array of CT sources and scan parameters Software programs such as CT Expo TM were created to provide an easy to use graphical user interface that interacts with the underlying database to provide patient dosimetry information 24 The advantages of these programs are that they provide dosimetry for a large set of scanners and for scan parameter s commonly seen in the clinic. One disadvantage of this methodology is that the Monte Carlo simulations were performed only on one 50 th percentile adult sty lized phantom It should be noted that TCM is not reflected in these dose libraries and mA modulation is nea rly impossible to account for retroactively Parameters such as patient age, height, and weight can be adjusted for using scaling factors but the se add considerable error to the dose estimate 1.4.3 Need for Size Specific Dosimetry that Accounts for Automatic Tube Current Modulation Relying on the scanner output for dosimetry has been shown to have large error s with some stationary exams report dose differences as high as 300% 25 With the growing concern in the media and the general public for the risks of CT, California

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23 passed B ill SB 1237 in 2010 and Texas passed Administrative Code 289.227 in 2013 requiring the inclusion of a CT exposure report in medical records for all exams 26 27 Additionally, The Joint Commission will re quire the inclusive of a CT exposure report starting July 1 st 2014 28 As noted above, slice based dose databases cannot accurately account for TCM much like CTDI vol A methodology proposed by Dr. Dan Long at the University of Florida in 2013 laid the foundation for creating dose databases that can indeed accurately account for TCM during CT procedures 29 He showed that increased the accuracy of organ doses as seen in matching of dosimeter measured organ doses in cadaver specimens The goal of this research is to finalize validation of this work using anthropomorphic phantoms that include an even wider range of beam energies and protocols on a Toshiba Aquilion ONE scanner Once completed this dosimetry algorith m is applied to the UF family of reference hybrid phantoms for common SNIP protocols to generate organ dose and effective dose estimates 30

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24 CHAPTER 2 COMPLETION AND VALIDATION OF A MONTE C ARLO BASED SLICE BY SLICE DOSIMETRY METHODOLOGY FOR THE TOSHIBA AQUILION ONE SCANNER 2.1 Creation and Validation of a Toshiba Aquilion ONE Custom Source Subroutine in MCNPX TM 2.1.1 Custom Source Sub routine s Previous work at the University of Florida and the University of California, Los Angeles demonstrated respectively the mathematical bases and measurements necessary to accurately model a CT scanner in a Monte Carlo radiation transport simulation 31 32 Th ese concepts along with the x ray spectrum generation code SPEKTR were used to model a Toshiba Aquilion ONE scanner at UF Health Shands Hospital in Gainesville Florida as outlined by Long et al 29 33 This scanner was modeled in MCNPX TM (Monte Carlo N Particle eXtended) version 2.70, which is a radia tion transport code developed at the Los Alamos National Laboratory The custom source subroutine was written in Fortran 90 and compiled on the University of Florida Hig h Performance Computing cluster The benefit of using a custom source subroutine is it allows for quick variations in input parameters such as source to image distance (SID), fan beam angle, helical pitch, starting angle, energy, filter, and spatial location The SID and fan beam angle for the Aquilion ONE scanner are 60 cm and 49.2 respectively. 2.1.2 Source Tilt The previously described source subroutine was capable of successfully modeling all major SNIP protocols with the exception of exams that u se gantry tilt Computational phantoms are inserted into the MCNPX TM geometry in the fo rm of voxel lattices, which are cuboid s containing a discrete number of voxels in each of the three spatial dimen sions These lattices must be aligned orthogonally with the Cartesian

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25 coordinate plane in the MCNPX TM geometry The previously described source subroutine is also aligned orthogonal to the xyz plane in MCNPX TM making a tilted CT scan impossible to model Due to the difficultly of rotating the actual xyz plane in MCNPX TM the source subroutine was rewritten to allow for a tilted helix geometry Using the rotation matrices sho wn in E quation s 2 1 and 2 2, the particle st arting position and direction (E quat ion 2 3) were rotated with respect to either the x or y axis. (2 1) (2 2) (2 3) To allow for rotation about both the x and y axis, angles that have negative values correspond to the x axis and positive values to the y axis Figure 2 1 shows an excerpt from the Fortran 90 code that depicts t he inclusion of these rotation vectors. Validating the proper geometrical rotation of the source was done in two ways. First, for the y axis rotation, a CTDI body phantom was modeled in MCNPX TM This phantom is defined as a 32 cm dia meter and 15 cm deep cylinder of poly methyl methacrylate (PMMA) This cylinder was rotated about the y axis at 0, 15, 90, 180, 270, and 330 degrees intervals and had a detector placed at five interior locations (center and four equally spaced peripheral locations) A 20 cm helix was centered around the body phantom and rotated at the same angles described above as shown in Figure 2 2 The dose to the detectors was co mputed in each of the five locations for each angle,

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26 and these outputs are shown in Tabl e 2 1 The average percent error in the doses relative to the non rotated phantom was less than 0. 1% Validation for the x axis was done by simply placing five 5 cm spheres around the yz plane and rotating a 20 cm helix around the four cardinal direction s as shown in Figure 2 3 The dose to the sp heres for each of the four helical locations is shown in Table 2 2 The average percent error in dose relative to the non shifted helix was less than 0.1% These results show a successful ability to rotat e the Aqulion ONE custom source subroutine around both the x and y axis. 2.2 Toshiba Aquilion ONE Specific Dosimetry Methods 2.2.1 Methodology Accurately modeling the output of the scanner although important, does not translate directly to patient dose In a clinical setting, a patient experience s a wide range of exam protocols and parameters Robust dosimetry that can accurately estimate doses for a wide range of protocols is possible with Monte Carlo simulations by use of a slice by slice organ dose li brary A slice by slice dosimetry library consists of a axis ( cranial caudal direction ) Separate MCNPX TM simulations are ru n at equally spaced z ax is locations for one single axial rotation with organ dose tallies for both in field and out of field organs Out of field organ doses are important to this dosimetry methodology as sc atter dose is a large contributor to the organ dose during a CT exam 21 Once populated, these slice libraries can be u sed to estimate organ doses for a specific imaging exam through summation of the organ dose contributions from ever y slice along the exam length On e issue with this approach is choosing how narrow to make your slices, as slices that are too wide will create exam

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27 lengths too long or too short, but choosing slices that are too narrow will greatly increase computational time and statisti cal imprecision at larger distance s from the rotation center As stated in Long et al, this dosimetry method choose s slice thickness es equal to the beam width of the scanner in 64 slice mode, which is 3.2 cm (64 x 0.5 mm) 34 To allow for more resolution in exam start and end, these slices are spaced every 1.6 cm throughout the phantom s z axis. The remaining important CT parameters are energy, filter, tube current, and pitch Because there are discrete energy and filter combinations for the CT scanner the energy spectrum for each of the twelve combinations were computed separately using the SPEKTR code and hard coded within the source subroutine These combinations were 80, 100, 120, and 135 kVp all with small, medium and large bowtie filters For each phantom, the organ dose library must be simulated at each of the relevant energy filter combina tions for that patient size Tube current, which is assumed proportional to dose and pitch are accounted for after the MCNPX TM simulations 3 MCNPX TM outputs tallies as a function of t he number of starting particles, a nd has no time or output relevance this must be done manually This is accomplished by creating normalization factors for each energy, filter, and collimation thickness for the scanner With the assumption that tube out put is proportional to tube current, these normalization factors are tabulated as photons per mAs as shown in Equation 2 4. (2 4) Multiplying gives dose (mGy) per tube current time product (mAs) The final step is assigning an

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28 mAs value to the exam, this is done using the average effective mAs, as shown in Equation 2 5. (2 5) The average effective mAs which has units of milliampere second must be calculated for each exam Need ed for this value is the average mA from the exam of interest as well as the rotation time and exam pitch Finally, to account for tube current modulation, each average effective mAs is scaled by the normalized relative attenuation seen by the x ray beam for the slice of interest This is calculated by averaging the inverse of dose from each of eight equally spaced detectors around the phantom at each z position A more in depth description of this methodology can be found in Dr. and is visually represented in Figure 2 4 34 2.2.2 Tube Current Capping and Exam Over Ranging When specifically modeling the T o shiba Aquilion ONE parameters such as mA capping (max allowed tube current) and over ranging ( tube traversing more patient anatomy than seen in the reconstructed image ) must be characterized For larger patients, the tube current is inherently higher F or safety and technical reasons, a maximum tube current is specified by the vendor, in the case of the Aquilion ONE, this max is set to 500 mA Although uncommon for most patients, this protocol was incorporated into this dosimetry methodology b y capping the mA for each slice I t should be noted that this cap must be applied to the tube current (mA) and not the average effective mAs Because the area under the mA plot is proportional to the entire exam s output, the mA removed from each sl ice must be rea ssigned This is done by

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29 redistributing the excess mA from the exam even ly throughout the remaining slices An example of an mA map before and after capping is shown in Figure 2 5. As outlined in Dr ner c ollects projection data in a longer exam region than depicted by the image set 35 Equivalent dose to organs that lie at either end of the visible exam range could be greatly under estimated when this effect is not mode led Additionally, over ranging is dependent on the exam type and it is not consistent for all exams d issertation gives over ranging estimates for different exam types and slice thicknesses the most relevant estimates for this research a re shown in Table 2 3 Incorporating these values into a slice by slice dosimetry methodology requires two assumptions First, that the mA to the over ranged slices i s the same as the first and last slice in the exam range respectively This assumption is made because no data is available from the scanner indicating what the mA was during the over ranging portion of the scan Secondly, it is assumed that the length of the over range is in an integer multiple of slices This is one limitation to using a slice by slice library but is unavoidable For over ranging that happens in a no n is weighted based on the length of the over ranging length in the library Table 2 4 shows examples of mA distribution s for select over ranging values. 2.3 Physical Phantom Validation 2.3.1 Physical Phantom CT Dosimetry Monte Carlo simulations by nature are estimates, and hold very little physical relevance until they are physically val idated The first step to validating the Toshiba Aquilion ONE dosimetry methodology outlined in this chapter was with cadaver specimens Three cadaver specimens of varying body mass indexes (BMI) were

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30 scanned using four common SNIP protocols: chest abdomen pelvis (CAP), chest (C), abdomen (A), and pelvis (P) A computational twin of each cadaver was generated using 3D DOCTOR TM (Able Software Corp., Lexington, MA) and inputted into an MCNPX TM geometry Organ dose estimates for the four exams were estimated and compared to the measured doses inside the cadaver specimens 35 The average magnitude of percent error in organ dose for the twelve cadaver protocol combinations was around 12% 34 Undesirable factors such as post mortem material and density changes were difficult to model accurately using this dosimetry methodology The promising results of the study however, prompted validation through the use of physical anthropomorphic phantoms which were previously created at the University of Florida 36 Three anthropomorphic phantoms representing an adult male (UFADM), a fifteen year old female (UF15F), and a ten ye ar old hermaphrodite (UF10MF) reference phantom were scanned To expand the parameters to which the dosimetry me thodology could be validated different energy exams as well as head and brain protocols were included in this study, a detailed list of these scan pa rameters are listed in Table 2 5 Dosimetry was performed using optically stimulated luminescent dosimeters (OSLD) at UF Health Shands Hospital by Kayla Ficarrotta, a detailed outline of her methodology can be found 37 One major advantage of using a physical phantom for validation is that the compu tational phantom has already been created, and all organs are fully segmented This decreases the error caused my manual segmentation, as well as material and density uncertainties The computational reference phantom associated with each of the physical phantoms were modified using Rhinoceros TM (McNeel North America,

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31 Seattle, WA) version 5.0, a non uniform rat ional B spline (NURBS) modeling and rendering software The outer body contour of each phantom was scaled to match circumference measurements take n from the CT image sets of each scanned physical phantom The motivation for this scaling was to offset any minor volume differences in the anthropomorphic phantom Next, each phantom was voxelized using a custom MATLAB TM (The Mathworks Inc., Natick, MA ) script that converts the NURBS model of each phantom into a discrete number of numerically tagged voxels, where each tag represents a unique tissue in the phantom The physical phantoms used in this study consist of only four materials: soft tissue equi valent substitute (STES), bone tissue equivalent substitute (BTES), lung tissue equivalent substitute (LTES), and air For the MCNPX TM simulations each tag from the computational phantom was assumed to be one of these four materials, with their densities and material compositions consistent with ICRP Report Publication 89 38 2.3.2 Torso Exams Each of the UFADM, UF15F, and UF10MF anthropomorphic phantoms were scanned using the CAP protocol at UF Health Shands Hospital for various energies as shown in Table 2 5 The resu lts from the cadaver study show no dependence of the TCM algorithm on exam protocol; consequently, for this reason only the CAP exam was performed fo r the torso studies where TCM is the m ost complex To model this exam, the previously mentioned TCM algorithm was employed on each of the computational phantoms associated with these three physical phantoms Starting from the neck of each phantom, 3.2 cm axial exams were simula ted every 1.6 cm down the phantom axis through the legs Ea ch of these axial scans collected *F6 (energy deposition in MeV/g) tallies in MCNPX TM for each of the organs measured in the

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32 physical phantoms 39 A more in depth description of how slice ranges were determined for the computational phantom s is found in section 4.2.1 Each axial exam was accompanied by eight additional MCNPX TM runs where attenuation was measured using *F6 tallies as outlined in Long et al 34 These eight measur ements were used to calculate a relative attenuation value for that slice which was later normalized for the exam range and applied to the energy deposition tallies for each organ Equation s 2 6 and 2 7 show how the organ dose was estimated using this alg orithm. (2 6) (2 7) Organ doses were calculated and compared to the measured doses from the physical phantoms The percent error for each organ dose was calculated using Eq uation 2 8 and the average magnitude for percent error for each exam was calculated using Equation 2 9. (2 8) (2 9) The average magnitude of percent error and range of errors for the six CAP exams were 8.5% and (5.5% to 11.2%) respectively T hese individual values are l isted in Table 2 6 Organ to organ dose comparisons for each exam are listed in Appendix A.

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33 Thes e results further validate the TCM algorithm as they show very consistent organ doses across all three phantoms at different energies for each of the 15 organs of interest The error in these studies can be attributed to multiple factors such as the dosimetry methodology, the source su broutine, or the physical phantom construction dose using a sum of axial exams Accordingly the beam is centered at discrete points throughout the patient and is not co ntinuous Additionally, TCM happens dyn amically as a function of time during a CT procedure, and this algorithm is assuming the changes in mA are a function of each individual slice This algorithm is preferential towards z axis modulation although the a ttenuation is measured radially around the patient Assumptions made on the e nergy spectra and beam profile in the source subroutine could have provided additional error Physical phantoms, although far superior to cadaver specimens in terms of segmentat ion, are not exact physical representations of their computational twins Volume, density, and material composition can fluctuate throughout the phantom Also, the assembly of the phantom which is done in section s can cause minor air gaps to form through out the phantom which can impact the tube current modulation in ways that differ from the computational approximation 2.3.3 Head Exams Another important clinical application of CT is for imaging of the head and brain For this reason, additional measurements were made on the UFADM and UF10MF physical phantom A detailed breakdown of these exams and their para meters are found in Table 2 5 Head exams exhibit different techniques than torso exam s, most notably the abse nce of TCM as the head has a relatively consistent thickness throughout the scan length To increase detail and lower noise, exam collimation is

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34 lowered (32 x 0.5mm), energy is held constant at 120 kVp, tube current is constant at 270 mA and pitch is lowered to 0.656 These changes make dosimetry easier to model as they no longer require a slice by slice approach In general, organ dose s from head exams are calculated by averaging the organ doses from different helical exams that properly model the e xam range, collimation, and pitch Small organs and peripheral organs such as the thyroid and lens of the eye have a higher dependence on starting angle 29 For this reason, eight equally space d starting angles from 0 to 315 were used and averaged for each head exam Exams that are modeled using a slice by slice method are multiplied by averag e effective mAs, which is appropriate because the organ dose contributions are calculated one slice at a time Head exams are modeled in MCNPX TM as a helix so they must be multiplied by the total effective mAs which is derived in Equation 2 10. (2 10) Pitch is already taken into account during the calculation of average effective mAs so it does not need to be divided out in this case The methodology for choosing the exam range and modeling the gantry tilt is described in detail in section 4.2.4 The CT image sets for physical phantom exams were used as a basis for where to start each exam in the c omputational phantoms The overall average error which was calculated as the average magnitude of all in field organ doses for the four head and brain exam s was 6.9% as shown in Table 2 6 A detailed comparison of each organ dose is shown in Appendix A.

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35 As expected, the average error for head exams was less than that of torso exams Additional sources of error for these exams arise from the selection of the exam start and end as they were done by manually viewing the image sets Over ranging was accou nted for by simply adding to the viewable length of the exam 35 One source of error reduction from the torso exams was the use of a helical source and not t he sum of multiple axial exams, where the latter assumes discrete locations of starting particles throughout the z axis, unlike a continuous helical source.

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36 Figure 2 1. Excerpt of Fortran 90 code from the Toshiba Aquilion ONE custom source subroutine

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37 Figure 2 2. A visualized MCNPX TM geometry showing five rotated CTDI body phantoms in the xz plane.

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38 Figure 2 3 A visualized MCNPX TM geometry showing five spheres situated in the yz plane.

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39 Figure 2 4. A visual representation of a slice by slice library applied to a computational phantom A) Constant mA exam. B ) Weighted mA exam.

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40 Figure 2 5. A comparison of slice specific mA values with and without mA capping for a given exam range

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41 Table 2 1. Validation results for y axis rotation of the CT source subroutine. Dose to Detector as a function of Rotation Angle [jerks*/(gram x starting particle)] Hole Location 0 15 90 180 270 330 Center 6.58E 29 6.58E 29 6.58E 29 6.59E 29 6.58E 29 6.59E 29 3 o'clock 1.12E 28 1.12E 28 1.12E 28 1.12E 28 1.09E 28 1.12E 28 6 o'clock 1.12E 28 1.12E 28 1.09E 28 1.09E 28 1.09E 28 1.12E 28 9 o'clock 1.09E 28 1.09E 28 1.09E 28 1.09E 28 1.12E 28 1.09E 28 12 o'clock 1.09E 28 1.09E 28 1.12E 28 1.12E 28 1.12E 28 1.09E 28 Average 1.11E 28 1.11E 28 1.10E 28 1.10E 28 1.10E 28 1.11E 28 1 jerk=1E9 Joule

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42 Table 2 2. Validation results for x axis rotation of the CT source subroutine. Dose to Detector as a function of Rotation Angle [jerks*/(gram x starting particle)] Detector Location 0 90 180 270 0 1.49E 28 1.96E 31 2.93E 32 2.14E 31 90 2.02E 31 1.49E 28 1.87E 31 3.23E 32 180 3.22E 32 1.92E 31 1.49E 28 1.86E 31 270 1.78E 31 3.46E 32 1.89E 31 1.49E 28 Center 3.03E 31 3.00E 31 3.07E 31 3.13E 31 Average 3.00E 29 3.00E 29 3.00E 29 2.99E 29 1 jerk = 1E9 Joule

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43 Table 2 3. Over ranging estimates for different exam types for the Toshiba Aquilion ONE Scanner. CAP* C* A* P* H** B** Over Range Estimate (cm) 3.2 3.2 6.1 6.1 2.6 2.6 # of Organ Range Rotations 1.0 1.0 1.9 1.9 2.5 2.5 Slice collimation = 64 x 0.5 mm ** Slice collimation = 32 x 0.5 mm

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44 Table 2 4 Example mA values for different amounts of scanner over ranging. Over Range Distance (number of slices) 0.7 1 1.3 1.7 2 2.2 Last Slice (mA) 100 100 100 100 100 100 Over Ranging First Over Range Slice (mA) 70 100 100 100 100 100 Second Over Range Slice (mA) 0 0 30 70 100 100 Third Over Range Slice (mA) 0 0 0 0 0 20

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45 Table 2 5 Detailed scan parameters for all physical phantom CT measurements. CAP Exam Head Exam Brain Exam Parameter UF10MF UF15F UFADM UF10MF UFADM UF10MF UFADM Tube Current Modulation Yes Yes Yes No No No No Collimation 0.5 mm x 64 0.5 mm x 64 0.5 mm x 64 0.5 mm x 32 0.5 mm x 32 0.5 mm x 32 0.5 mm x 32 Energy (kVp) 100, 120 120, 135 120, 135 120 120 120 120 Exam Start Thoracic Inlet Thoracic Inlet Thoracic Inlet Chin Chin Base of Brain Base of Brain Exam End Lesser Trochanter Lesser Trochanter Lesser Trochanter Skull Vertex Skull Vertex Skull Vertex Skull Vertex Filter Large Large Large Small Small Small Small Gantry Tilt () 0 0 0 0 0 9.5 9.5 mA 150*, 120* 140*, 120* 140*, 110* 270 270 270 270 Pitch 0.828 0.828 0.828 0.656 0.656 0.656 0.656 Rotation Time (s) 0.5 0.5 0.5 0.75 0.75 0.75 0.75 Exam mA is Variable due to Tube Current Modulation, Reported Value is Average mA from CT Image Set

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46 Table 2 6 Average magnitude of percent error of in field organ doses for all physical phantom measurements. Average Magnitude of In Field Organ Doses Exam Average Error (%) Error Range (%) Chest Abdomen Pelvis UF10MF 100 kVp 8.8 7.4 ( 4.3, 25.4) UF10MF 120 kVp 11.2 4.5 (2.1, 19.6) UF15F 120 kVp 8.7 4.3 ( 14.3, 13.9) UF15F 135 kVp 9.4 6.3 ( 21.1, 12.1) UFADM 120 kVp 7.6 4.0 ( 13.9, 16.2) UFADM 135 kVp 5.5 3.4 ( 10.7, 10.1) Head UF10MF 120 kVp 6.5 5.0 ( 13.6, 8.2) UFADM 120 kVp 6.4 5.2 ( 1.6, 15.4) Brain with Tilt UF10MF 120 kVp 8.6* UFADM 120 kVp 6.0* Only one infield organ: brain

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47 CHAPTER 3 ANALYSIS OF SIZE SPECIFIC PHANTOM MATCHING USING CADAVER DOSIMETRY DATA 3.1 Hybrid Computational Phantom Matching 3.1.1 Height, Weight, and BMI Matching In the past, one downside of using Monte Carlo methods for CT dosimetry was the lack of diversity in phantom sizes Traditionally, scaling factors are applied to dose estimates to accoun t for changes in patient size T his technique increases accuracy of organ dose but still carries some error The UF/NCI Library of Computational Phantoms was created to allow for a more precise selection of a computational phantom 40 This 351 phantom library consists of adult and pediatric phantoms of varying heights and weights based on circumferential an d anatomical data obtained from the Center for (NHANES) As shown in Long et al, one method for patient matching is through height, weight and BMI matching 34 Choosing the phantom from the library with the closest height and weight allows for increased accuracy in CT dosimetry For patients that lie outs ide of the libraries height and weight range, the phantom with the closest size parameter is chosen between two phantoms, BMI is used as the determining factor for patient matching, the calculation for BMI is shown in Equation 3 1. (3 1) Ma tch ing patient specific phantom s to a phantom in the library yielded an average error in organ dose of 11%, as opposed to 29% for a reference hybrid phantom, and 35% for a reference stylized phantom 34

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48 3.1.2 Effective Diameter Matching to muscle ratio Two people of similar heights and weight could po tentially have two drastically different body diameters In CT because of the dependence of patient shape on TCM, it was believed that matching a phantom based on effective diameter measurements would yield more accurate dosimetry To further investigat e the effects of patient matching for this dosimetry algorithm, each of the 31 patient specific phantoms used in the Lo ng et al and Johnson et al studies were matched to a phantom based on three effective diameter (ED) measurements 34 41 For simplicity and increased accuracy, the effective diameters were calculated at three easy to identify skeletal landmarks: top of iliac crest, bottom of sternum, and top of the sternum These effective diameter measurements were made in Rhinoceros TM 5. 0 for the patient specific phantoms as well as the relevant computational phantoms in the library; a visual depicting how these measurements were made is shown in Figure 3 1 The patient specific phantoms were then matched using Equation 3 2; the phantom in the library with the lowest value was considered the match. (3 2) Once matched, each of the computational phantoms had organ doses calculated for four different exam protocols (CAP, C, A, and P) and were compared to the same organ doses from the patient specific phantoms. Overall, the average magnitude of percent error in organ dose for these phantoms was 12%, slightly worse than matching based on B MI For this reason, BMI

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49 matching is used for all future dosimetry because it supplies the most accurate CT dosimetry and relies on information that is more easily obtained in a clinical setting. 3.2 Cadaver Matched Phantom Dosimetry 3.2.1 Comparison of O rgan Dose for Cadaver Matched Phantoms The final measure for error in this dosimetry algorithm is matching cadaver specimens to a computational phantom compared to that of a computational twin, one whose body morpho metry and organ placement resemble the cadavers true anatomy The purpose of that study was to validate the dosimetry methodology, and for that reason changes in patient size were minimized The phantom matching study was performed to show there is alwa ys inherent error in matching a patient to a computational phantom, which for CT dosimetry errors were shown to be around 11% Matching a cadaver specimen to a computational phantom would allow for an all encompassing measurement of error as the robustnes s of the dosimetry algorithm as well as the random fluctuations in patient size and relative organ locations are accounted for. Cadaver organ dose data for four cadaver specimens were obtained by Dr group at the University of Florida fo r this study These four cadavers: Cadaver IV, Cadaver V, Cadaver VI, and Cadaver VII have BMI s of 17.4, 27.1, 43.8, and 33.5 respectively Cadavers IV, VI, and VII were scanned using CAP, C, A, and P protocols and Cadaver V was scanned using both a CAP and C protocol, all with TCM Table 3 1 shows the associated scan parameters for all of the cadaver examinations used in this study Each of these four cadavers w as matched using the height, weight, and BMI metric described above to a phantom in the library Slice by slice dosimetry with attenuation weighting factors was applied to each of the four

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50 phantoms and organ doses were calculated f or each of the scan parameters A ach phantom is described in section 4.2.1 The average effective mAs (Equation 2 5) for these exams were derived from the imag e based average mA shown on their respective CT image sets. The overall magnitude in percent error for organ dose comparisons for all of the cadaver specimens to their matched computationa l phantoms was 19.3% A complete breakdown of percent erro r for each phantom and exam type is found in Table 3 2, and 3 Appendix B shows specific organ to organ comparisons for every cadaver exam These average errors represent the total error from the dosimetry methodology and the matching of a pat ient to a computational phantom Dosimetry associated with CTDI vol or DLP, even when scaled by patient size, is still associated with a population of people, and assigned effective dose or organ doses are not tailored to an individual One advantage of this study is that it provides more insight on the error associated with ass igning organ doses to one specific patient, not a population Consistency between the four cadavers of varying sizes str engthens the validation of the TCM algorithm and patient matching schemes.

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51 Figure 3 1. A visualization of diameter measurements be ing m ade on a computational phantom. A) A nterior posterior B) Lateral

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52 Table 3 1. Scan parameters for all cadaver exams used in the phantom matching study. Scan Parameter Cadaver IV Cadaver V Cadaver VI Cadaver VII Chest Abdomen Pelvis kVp 120 120 120 120 Rotation Time (s) 0.5 0.5 0.5 0.5 Pitch 0.828 0.828 0.828 0.828 Length (mm) 635 700 700 600 Eff mAs 154 302 302 302 Image Eff mAs 85 187 253 255 Focal Spot Small Large Large Large Collimation (mm) 0.5 x 64 0.5 x 64 0.5 x 64 0.5 x 64 Chest kVp 120 120 120 120 Rotation Time (s) 0.5 0.5 0.5 0.5 Pitch 1.484 1.484 1.484 1.484 Length (mm) 360 360 360 360 Eff mAs 95 169 169 169 Image Eff mAs 56 125 149 155 Focal Spot Large Large Large Large Collimation (mm) 0.5 x 64 0.5 x 64 0.5 x 64 0.5 x 64 Abdomen kVp 120 120 120 Rotation Time (s) 0.5 0.5 0.5 Pitch 0.828 0.828 0.828 Length (mm) 250 300 300 Eff mAs 133 302 302 Image Eff mAs 79 241 252 Focal Spot Large Large Large Collimation (mm) 0.5 x 64 0.5 x 64 0.5 x 64 Pelvis kVp 120 120 120 Rotation Time (s) 0.5 0.5 0.5 Pitch 0.828 0.828 0.828 Length (mm) 250 250 250 Eff mAs 151 302 302 Image Eff mAs 98 259 241 Focal Spot Small Large Large Collimation (mm) 0.5 x 64 0.5 x 64 0.5 x 64

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53 Table 3 2. Average magnitude of percent error of in field organ doses for the cadaver to matched phantom data. In Field Organ Dose Average Percent Errors (%) Exam Type Cadaver 4 Cadaver 5 Cadaver 6 Cadaver 7 Average (Exam Type) Chest Abdomen Pelvis 21.3 13.3 18.8 20.3 18.4 Chest 11.0 14.6 19.9 10.2 14.0 Abdomen 24.3 --18.0 21.4 21.2 Pelvis 8.2 --37.9 40.7 28.9 Average (Cadaver) 17.8 13.0 21.8 21.4 19.3* Overall Percent Error Calculated as Average of All Individual Organ Dose Errors

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54 Table 3 3. Average magnitude of percent error for specific in field organs over all cadaver exams Organ Percent Error (%) Thyroid 28.8 24.8 Breast 12.1 8.0 Lung 18.4 8.0 Liver 20.1 16.1 Stomach 19.2 11.2 Small Intestine 25.0 15.9 Colon 25.7 18.2 Ovary 25.1 15.2 Skin (in field) 9.0 6.7

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55 CHAPTER 4 ORGAN AND EFFECTIVE DOSE COEFFICENT ESTIMATE S FOR HEAD AND TORSO EXAMS ON THE ICRP 89 BASED REFERENCE HYBRID COMPUTATIONAL PHANTOMS 4.1 UF Family of Reference Hybrid Phantoms The UF Family of Reference Hybrid Phantoms was created to allow accurate computational dosimetry with high anatomical precision that could represent an entire population 30 A reference individual represents the 50 th percentile height and weight of an entire population ICRP Publication 89 provides these values for males and females at the ages of: new born (UFNBMF) one year old (UF01MF) five year old (UF05MF) ten year old (UF10MF) fifteen year old (UF15MF) and adult (UFADMF) 42 In addition to these values, reference organ masses, tissue compositions, and tissue densities are provided for th e ir use in dosimetry calculations Theses phantoms were created and modeled in Rhinoceros TM 4.0 and scaled to the appropriate height, weight, and organ masses Each organ in the phantom is tagged with a numerical value that can later be assigned a materi al composition, density, and volume in MCNPX TM In order to have a relevant skin dose, each phantom must be voxelized in the xy plane at reference skin thickness which is provided in ICRP Publication 89 If the z extent of the voxel is also at skin thickness, the 3D array containing the voxe ls will become too large, slowing down dosimetry calculations It has been shown that roughly 55 million total voxel elements provide accurate phantom dosimetry in MCNPX TM This number, along with the known thic kness of skin in the x and y direction was used to calculate an optimal z thickness for each of the reference phantoms 43 Once voxelized, each phantom must have all their material tags assigned to specific material volum es, densities, as well as material compositions in MCNPX TM

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56 Previous work by Dr. Michael Wayson at the University of Florida tabulated all relevant blood inclusive material compositions and densities from ICRP Publication 89 43 The se materials are age and gender specific which means they must be custom tailored for each phantom This was done using a custom MATLAB TM script that read in each voxel file that calculated the volume of each organ based on the voxel dimensio ns and voxel count, and assigned the appropriate material card for each organ These values were attached to each phantom lattice file (an MCNPX TM compatible voxel structure) for their use in dosimetry. 4.2 Dosimetry Methods 4.2.1 Common Torso Exam Types O ne major advantage of CT over radiography is its soft tissue contrast a s well as a 3D depiction of patient anatomy 3 For these reasons CT is extensively used for imaging the torso of the patient The most common exam protocols for torso imaging are chest abdomen pelvis (CAP), chest abdomen (CA), abdomen pelvis (AP), chest (C), abdomen (A), and pelvis (P) exams Table 4 1 shows a complete breakdown of these protocols and their associated SNIP recommended parameters For each of the torso exams the recommended beam collimation is 3.2 cm (64 x 0.5 mm) For this reason a 3.2 cm slice thickness and a 1.6 cm slice spacing was used for all dosimetry calculations. Each exam st art and end is based on an anatomical reference point which is easy to identify on the CT console after a scout exam has been taken of the patient The interpretation of this parameter can vary from technologist to technologist as it is not an exact scien ce Determining these scan regions on a computational phantom is done in a similar fashion Each voxelized phantom binary file (numerical structure of the

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57 voxel array) can be visualized using the software tool ImageJ TM (National Institute of Health, Beth esda Maryland) Once viewed in the xy markers can be identified, and their accompanying slice location can be denoted Fi gures 4 1 through 4 6 shows the visualized anatomical landmarks listed in Table 4 1 Once the discr ete slice number was determined for each landmark, the spatial extent of these landmarks was calculated by Equation 4 1. (4 1) These locations were than compared to the center of each axial slice in the dose library to determine which slice range was most appropriate for that exam For the UFNBMF, slice spacing of 0. 4 cm was used due to the highly compressed anatomy in the z direction so as to allow for more exam length resolution The specific attenuation weightin g factors for each exam range were calculated by normalizing the relative attenuation number associated with each slice in the range to 1 .0 as shown in Equation 4 2. (4 2) each organ and summed over the exam range, giving total organ dose per mAs. Effective dose was also calculated f or each exam in accordance with ICRP Publication 103 44 Each organ absorbed dose was converted to its equivalent dose using a photon radiation weighting factor of 1.0 Effective dose was calculated as the

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58 sum of the product of each organ dose and its respective tissue weighting factor as defined in ICRP Publication 103. 4.2.2 Special Dosimetry Considerations Additional methods must be applied to calculate the organ dose for active marrow, shallow marrow, and skin For each axi al location of the beam an F4 tally (average flux) with energy bins of: 0 10, 10 15, 15 20, 20 30, 30 40, 40 50, 50 60, 60 80, 80 100 and 100 150 keV were calculated for each bone site in the respective phantom Active marrow and shallow marrow (bone endosteum) dose can be calculated by multiplying these flu ence values by pre calculated dose response functions for each bo ne site at each energy bin and then summing their contributions shown in Equation 4 3 45 Dose per axial slice for both red bone marrow and shallow marrow were the n calculated by weighting each dose by the marrow fract ion of each bone site based on the age of the phantom shown in Equation 4 4 (4 3) ( 4 4 ) Once calculated for each slice, these organ doses are weighted and summed just like the rest of the organ doses. Skin dose receives special treatment because of the difference in its MCNPX TM calculation relative to its physical meaning MCNPX TM calculates dose as energy deposited in an organ per unit mass of that organ For a given exam range, a different

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59 amount of skin is irradiated so dividing by the total mass of all skin in the body will underestimate the peak skin dose This was offset computationally by calculating the number of skin voxels present in the exam range and dividing it by the total number of skin voxels This conversion factor renormalizes the MCNPX TM skin d ose to the irradiated skin dose as shown in Equation 4 5. (4 5) The exam range of inter est inclu des the predicted over ranging for that exam protocol One assumption made by doing this is that no skin outside the exam range was irradiated, which is not the case Scattered irradiation inside the patient could leave the exam range and be absorbed in skin Skin dose will be overestimated in this case as energy deposited to a large r volume of skin will be used for the organ dose calculation This assumption is valid because the vast majority of skin dose is from the un collided beam entering the patie nt especially from low energy x rays It is unlikely that an internally scattered photon would interact with skin due to its minimal thickness relative to the path length of the photon leaving the body Although useful for peak skin dose reporting, whol e body skin dose must be used for the calculation of effective dose. Another assumption made about skin dose is that all secondary electrons created from photons are locally deposited For all other organs this assumption is valid due to the very limited range of electrons in the diagnostic energy range relative to the spatial size of organs Skin thickness is on the order of millimeters so this assumption must be tested To do this, a sensitivity analysis was performed testing the relative doses from *F6 (energy deposition, no electron transport) tallies and F8 (pulse

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60 height in MeV, with electron transport) tallies in MCNPX TM Additionally, the number of starting partic les was varied to see the reliability of a *F6 organ dose calculation An overall percent error of 0.15% was shown across four exam ranges and four starting particle amounts, as shown in Table 4 2 For the purposes of CT dosimetry, *F6 tallies are deemed appropriate for skin dose calculations. 4.2. 3 Effective Dose and Effective Dose Coefficient Calculations Effective dose is defined as tissue weighted sum of the equivalent doses in all specified tissues and organs of the body, shown in Equation 4 6 44 (4 6) In this equation w T represents the tissue weighting factor presented in ICRP Publication 103, and equivalent dose is the absorbed dose multiplied by the photon radiation weighting factor of 1.0 Effective dose for a given exam protocol is calculated by weighting each organ dose contribution for that exam and summing over all organs It should be noted that the in field skin dose is reported as it has more clinical relevance, but effective dose was calculated using whole body skin dose as it is more appropriate for the dosimetry models. In order to have a meaningful value of effective dose all organs must be accounted for even if they were not tallied during the dosimetry calculation Resultantly, o ut of field organs not included in the dosimetry were given an organ dose of zero In field organs that were not accounted for were assigned the average dose of the organs that were in fi eld for that exam. Another useful metri c for CT dosimetry is a n e ffective dose coefficient (EDC) sometimes called a k factor, which h as units of Sv per mGy cm 46 These coefficients

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61 allow for the quick conversion of the scanner reported DLP into effective dose Creating effe ctive dose coefficients for the Toshiba Aquilion ONE Scanner requires CTDI w measurements at relevant energy, filter, and collimation combinatio ns, and these are shown in Table 4 3 34 To convert effective dose per mAs to a n effective dose coefficient Equation 4 7 was used. (4 7) Pitch is included to convert CTDI w into CTDI vol and exam length is calculated as the number of slices multiplied by the slice thickness Exam range does not include over ranging because it only accounts for viewable slices. 4.2.4 Head and Brain Exam Methodology As stated earlier, head and brain exams are simulated u sing a helical exam due to the absence of TCM Scan ranges are determined in the same fashion as torso exams when no gantry tilt is used For exams with gantry tilt, special accommodatio n s are made to model this for each phantom The motivation behind doing a tilt ed CT exam is to minimize the dose to the lens and salivary glands 47 The tilt angle is determined manually by the CT technologist for each patient based on their diagnostic need as well as the scout image A region of interest (ROI) can be manually def ined at a chosen angle after the head has been imaged laterally This makes predicting these angles and exam ranges subjective Using recommendation s from a CT technologist and examples in published literature, these ROIs were determined for each phantom manually 47 48 Using a visualized central coronal slice from the MCNPX TM geom etry, four reference points were made in each phantom in the yz plane Points one and three

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62 determine the needed source subroutine tilt to image the brain and miss the lens of the eye Point two lies at the base of the brain at the theoretical center of the helix Point four represents the end of the exam range as well as the t heoretical center of the helix From these four points, exam tilt and exam range can be determined as shown in Figure 4 7 and associated Equations 4 8 and 4 9 (4 8 ) (4 9 ) These two values can be incorporated into the source subroutine for each exam to su ccessfully model a tilted helical geometry Additionally, as stated earlier, all head and brain exams are the average of eight MCNPX TM simulations taken at varying starting angles. 4.3 Final Organ and E ffective Dose Coefficient Estimates 4.3.1 Torso and Head Exam Organ Dose Data For each of the ref erence phantom s, organ dose estimates were calculated for each of the protocols as listed in Table 4 1: CAP, CA, AP, C, A, P, H, and B In addition to organ dose estimate s, an effective dose in mSv is listed per mAs This value is calculated by weighting each individual organ dose by its ICRP 103 weighting factors As stated earlier, out of field organs that were not calculated were assigned an organ dose of zero, and in field organs that were not calculated were assigned the average dose of all in fi eld organs Every phantom was ru n at 120 kVp as it is the most clinically used energy Additionally, any clinically relevant energy for that sized patient was ru n for completeness All organ dose data (per mAs) is listed in Appendix C Overall, the data f ollows the anticipated trend of increasing organ dose as patient size decreases 5 49

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63 The only exception to this rule is with the 15 year male reference phantom who for certain exa m protocols had higher relative dose s than the 15 year female reference phantom This is believed to have happened because of the presence of breast in the female, which helps shield certain organs such as the lungs, heart, and thymus These changes in organ dose impact the effective dose a s the shielded organs have higher tissue weighting factors Absolute organ doses were not included due to the uncertainty in calculating average effective mAs Average effective mAs is strongly dependent on the protocol, the vendor, as well as the noise tolerated by the radiologist or the healthcare institution. The average dose in the head and brain exams was higher than that of torso exams as expected 47 48 Effective dose is much lower for brain exams due the lack of in field organs with significant tissue weighting factors Orga n doses as well as effective dose per mAs are listed in Appendix C Due to the consistency in head and brain protocols, example absolute dose calculations are shown in Table 4 4 and 4 5 The SNIP protocols as well as the Image Gently TM recommended head reduction factors were used to calculate absolute organ dose 50 For the brain exam with ti l t the UF01MF and UFNBMF reference phantoms are excluded due to the clinical feasibility of a tilted exam on such very young patient s A visual comparison of relative organ dose for each reference phantom across all protocols is shown in Figures 4 8 through 4 15 Figure 4 16 shows relative organ do ses for a CAP exam on the UFADM phantom across three different energies. 4.3.2 Torso Exam Effective Dose Coefficients Using Equation 4 7, effective dose coefficients were calculated for each reference phantom for each exam type and beam energy A referenc e effective dose

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64 coefficient was calculated as the average of the adult male and adult female coefficients as done traditionally, Table 4 6 lists all effective dose coefficients for the reference phantoms 46 The value of the coefficient increases as a function of decreasing patient size but re mains consistent over different beam energies These values should level out clinically as DLP decreases for smaller patients. 4.3.4 Comparison of Effective Dose Calculations Traditionally effective dose coefficients are not created for specific ages and genders they are age and gender averaged per the definition of effective dose To test the validity of these coefficients as well as assigned effective dose per average effective mAs values a comparison was completed using the physical phantom data For each of the physical phantom scans a scanner reported DLP is given The effective dose for a given exam was calculated by summing the product of measured organ dose s by their respective tissue weighting factor Once again, in field organs that were not measured were assumed to be the average of all in field organs, and out of fields organs not measured were assumed to have zero dose One exception to this was for the calculation of the dose to active bone marrow and endosteum dose Previously the assumption was made that in field organs could be assigned the average dose of all measured in field organs, this does not apply to red bone marrow due to its different density and material composition To compensate for this, Monte Carlo data from the c omputational phantoms was used to estimate the active marrow dose in the physical phantoms On average, for all CAP exams of the UFADM the red marrow dose was 65% of the average of all in field organs and 55% for the UF15F and UF10MF The s e weighting fa ctor s were applied when estimating the red bone marrow dose for the physical phantoms.

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65 Using this as a benchmark four different effective dose calculations were calculated and compared as shown in Table 4 7 The ethod is the product of t he report ed scanner DLP and the reference coefficient for that energy specific dose estimate factor (AAPM Report No. 204) for that phantom and the reference coefficient The SSDE weighting f actors are actually intended for CTDI vol the assumption was made that these could be applied to DLP as it is a direct result from the scanner predicted CTDI vol value rted DLP and the age and gen der specific coefficient for that energy previously The average magnitude s of percent err or in effective dose compared to the measured effecti ve dose in the respective physical phantom for these four methods are 23.0%, 14.6%, 12.5%, and 6.4 % respectively. The traditional DLP M ethod yielded the highest error in effective dose, which is expect ed as patient size is never taken into account In contract, t he SSDE Method resulted in a more accurate effective dose estimate as the patient size was taken into account The reported DLP is based on a 32 cm PMMA CTDI phantom which is much larger than each of the three scanned phantoms The Age Gender Method yielded slightly better results than the SSDE Method This preliminary data implies the practicality of doing age and gender specific effective dose coefficients for clinical dosimetry It should be noted that this method has not be rigorously tes ted on p atients that are not exactly of reference size The SSDE Method may be more accurate for a patient who se size is between two reference phantoms The most accurate way of

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66 estimating effective dose was multiplying the average effect mAs by the calc ulated effective dose per mAs As seen in the previous cadaver and physical phantom validation studies, a CT image based average effective mAs is a consistent means of predicting patient organ dose as well as the effective dose

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67 Figure 4 1. Visual representation of the Lesser T rochanter anatomical landmark.

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68 Figure 4 2. Visual repre sentation of the T op of the I liac C rest anatomical landmark.

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69 Figure 4 3. Visual representation of the Top of Kidney anatomical landmark.

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70 Figure 4 4. Visual representation of the Dome of Diaphragm anatomical landmark

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71 Figure 4 5. Visual representation of the Thoracic Inlet anatomical landmark.

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72 Figure 4 6. Visual representation of the Chin anatomical landmark.

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73 Figure 4 7. Example of brain refere nce points need ed for gantry tilt and exam range calculations A) Four spatial points required for calculations. B) Projected tilted ROI.

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74 Figure 4 8. Comparison of relative organ doses for a 120 kVp Chest Abdomen Pelvis exam.

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75 Figure 4 9. Comparison of relative organ dose for a 120 kVp Chest Abdomen exam.

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76 Figure 4 10. Comparison of relative organ dose for a 120 kVp Abdomen Pelvis exam.

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77 Figure 4 11. Comparison of relative organ dose for a 120 kVp Chest exam.

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78 Figure 4 12. Comparison of relative o rgan dose for a 120 kVp Abdomen exam.

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79 Figure 4 13. Comparison of relative organ dose for a 120 kVp Pevlis exam.

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80 Figure 4 14. Comparison of relative organ dose for a 120 kVp Head exam.

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81 Figure 4 15. Comparison of relative organ dose estimates for a 120 kVp Brain exam.

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82 Figure 4 16. Comparison of relative organ doses for the UFADM Chest Abdomen Pelvis exam at different energies.

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83 Table 4 1. Common CT exam protocols and parameters based on SNIP data. Protocol Name Filter Exam Start Exam End Rotation Time mA Pitch Collimation Chest Abdomen Pelvis CAP L Thoracic Inlet Lesser Trochanter 0.5 s TCM* 0.828 64 x 0.5mm Chest Abdomen CA L Thoracic Inlet 2cm below Illiac Crest 0.5 s TCM* 0.828 64 x 0.5mm Abdomen Pelvis AP L Dome of Diaphragm Lesser Trochanter 0.5 s TCM* 0.828 64 x 0.5mm Chest C L Thoracic Inlet Top of Kidneys 0.5 s TCM* 1.484 64 x 0.5mm Abdomen A L Dome of Diaphragm 2cm below Illiac Crest 0.5 s TCM* 0.828 64 x 0.5mm Pelvis P L Illiac Crest Lesser Trochanter 0.5 s TCM* 0.828 64 x 0.5mm Head H S Chin Skull Vertex 0.75 s 270** 0.656 32 x 0.5mm Brain B S Base of Brain (angled) Skull Vertex 0.75 s 270** 0.656 32 x 0.5mm *mA is variable due to automatic tube current modulation **mA for UFADM and UF10MF physical phantom

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84 Table 4 2. Sensitivity study for *F6 and *F8 derived organ doses across four exam ranges and four different starting particles. Exam Range Particles *F6 Dose (mGy) *F8 Dose (mGy) Percent Different (%)* 1 1.00E+07 14.39 14.37 0.09 2.00E+07 14.39 14.37 0.18 5.00E+07 14.39 14.38 0.06 1.00E+08 14.39 14.36 0.21 2 1.00E+07 12.39 12.36 0.29 2.00E+07 12.39 12.38 0.07 5.00E+07 12.39 12.37 0.23 1.00E+08 12.40 12.39 0.10 3 1.00E+07 14.39 14.37 0.09 2.00E+07 14.39 14.37 0.18 5.00E+07 14.39 14.38 0.06 1.00E+08 14.39 14.36 0.21 4 1.00E+07 12.71 12.70 0.06 2.00E+07 12.71 12.68 0.18 5.00E+07 12.70 12.67 0.22 1.00E+08 12.70 12.68 0.17 Error calculated as 100 [(F6 Dose F8 Dose) / F6 Dose]

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85 Table 4 3. CTDI body phantom measurements and associated CTDI w values. CTDI Position Measured Air Kerma (mGy) for 100 mAs/rot Energy (kVp) Filter Collimation (mm) Center 3 o'clock 6 o'clock 9 o'clock 12 o'clock CTDI W 80 M 16 0.24 0.57 0.54 0.56 0.57 2.84 32 0.43 1.02 0.95 0.99 1.00 2.51 L 16 0.25 0.66 0.61 0.63 0.64 3.17 32 0.45 1.16 1.07 1.12 1.13 2.80 100 M 16 0.54 1.13 1.06 1.09 1.10 5.70 32 0.96 1.99 1.86 1.92 1.94 5.01 L 16 0.57 1.30 1.21 1.24 1.26 6.40 32 1.00 2.29 2.13 2.18 2.21 5.62 120 M 16 0.96 1.86 1.74 1.79 1.80 9.50 32 1.68 3.24 3.04 3.11 3.14 8.28 L 16 1.00 2.15 2.00 2.03 2.06 10.66 32 1.74 3.74 3.50 3.55 3.60 9.31 135 M 16 1.36 2.53 2.38 2.42 2.45 13.02 32 2.34 4.37 4.11 4.18 4.23 11.24 L 16 1.41 2.93 2.74 2.77 2.81 14.65 32 2.42 5.07 4.73 4.77 4.85 12.64 Calculated as [(1/3)*Dose center + (2/3)*Dose peripheral ]*(100mm/Collimation)

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86 Table 4 4. Absolute organ dose estimates for 120 kVp head exams across all reference phantoms. Estimated Organ Dose from 120 kVp Toshiba Head CT Exam (mGy) Organ UFADM UFADF UF15M UF15F UF10MF UF05MF UF01MF UFNBMF Brain 40.0 47.8 49.7 52.4 54.5 57.4 48.5 53.3 Lens 53.2 55.8 64.7 63.3 60.1 61.1 53.0 53.6 Submaxillary 54.1 62.8 54.2 57.3 61.3 59.6 54.8 55.7 Parotid 60.9 61.9 60.6 64.6 69.4 61.4 59.6 54.8 Sublingual 58.6 50.3 56.7 56.4 58.0 57.4 53.7 54.8 Thyroid 8.5 9.3 7.0 9.7 12.6 29.1 49.3 61.2 Skin (in field) 58.6 61.4 61.9 63.9 63.8 64.0 56.7 61.3 Effective Dose (mSv) 1.9 2.0 2.0 2.1 2.3 3.0 3.6 4.1 Parameter Exam Length (cm) 22.1 21.3 21.0 21.2 19.2 19.2 20.2 20.2 Average Effective mAs 309 309 309 309 309 287 266 229 Based on Image Gently TM Brain Reduction Factor

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87 Table 4 5. Absolute organ dose estimate for 120 kVp brain exams with tilt across all reference phantoms. Estimated Organ Dose from 120 kVp Toshiba Brain CT Exam (mGy) Organ UFADM UFADF UF15M UF15F UF10MF UF05MF Brain 34.8 40.1 42.8 45.9 46.3 44.6 Lens 7.2 4.9 12.7 9.4 7.5 10.2 Submaxillary 1.9 2.3 3.1 4.5 3.8 3.7 Parotid 2.3 3.1 3.4 4.3 3.3 3.8 Sublingual 0.8 1.5 1.3 1.7 1.6 1.8 Thyroid 0.4 0.6 0.5 0.7 1.2 1.4 Skin (in field) 49.1 54.6 54.4 60.0 56.6 55.4 Effective Dose (mSv) 0.9 1.0 1.0 1.1 1.1 1.1 Parameter Exam Length (cm) 12.3 11.3 11.6 11.2 11.3 11.3 Average Effective mAs 309 309 309 309 309 287* Based on Image Gently TM Brain Reduction Factor

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88 Table 4 6. Effective Dose Coefficients for the reference phantoms across different protocols and beam energies. Effective Dose Coefficient cm) Phantom kVp CAP CA AP C A P Reference* 100 15.14 17.45 15.65 33.51 19.64 8.97 120 16.14 18.57 16.69 35.62 20.88 9.62 135 16.63 19.10 17.19 36.64 21.48 9.95 UFADM 100 14.19 16.65 14.79 31.05 19.04 9.82 120 15.10 17.71 15.73 33.05 20.23 10.41 135 15.55 18.23 16.18 34.02 20.81 10.70 UFADF 100 16.08 18.26 16.50 35.97 20.25 8.12 120 17.18 19.42 17.65 38.20 21.53 8.84 135 17.71 19.98 18.21 39.26 22.14 9.20 UF15M 100 18.09 20.25 19.42 35.14 23.49 14.45 120 18.88 21.16 20.26 36.83 24.51 14.95 UF15F 100 19.32 21.94 19.09 41.23 23.84 11.27 120 20.24 22.88 20.06 43.06 24.88 11.96 UF10MF 100 24.89 29.51 25.29 54.25 33.62 17.26 120 25.63 30.34 26.05 55.89 34.53 17.77 UF05MF 80 37.67 45.40 36.90 80.14 44.03 27.15 120 37.73 45.54 37.05 80.35 44.34 26.95 UF01MF 80 56.10 59.56 58.87 119.79 65.37 43.54 120 54.94 58.55 54.71 116.66 64.23 42.46 UFNBMF 80 86.40 97.85 91.40 185.40 111.35 58.36 120 79.74 91.98 83.13 169.69 105.38 53.77 Average of UFADM and UFADMF

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89 Table 4 7. Comparison of effective dose estimates for the physical phantom data. Parameter Unit UF10MF UF15F UFADM Energy kVp 100 120 120 100 120 135 AE mAs mAs 90.58 70.65 85.75 165.46 86.96 68.24 DLP mGy cm 297.90 350.90 620.50 675.20 580.80 616.60 SSDE* --1.71 1.71 1.52 1.30 1.30 1.30 Weighted DLP mGy cm 510.30 601.09 942.03 877.76 755.04 801.58 Measued Effective Dose mSv 8.20 10.32 12.05 11.28 10.54 11.47 Effective Dose Coefficient cm 15.14 16.14 16.14 15.14 16.14 16.63 Age Gender EDC cm 24.89 25.63 20.24 14.19 15.10 15.55 Effective Dose per AE mAs mSv/mAs 0.097 0.166 0.138 0.065 0.114 0.160 Average DLP Method Calculated Effective Dose mSv 4.51 5.66 10.02 10.22 9.38 10.25 Percent Difference** % 45.02 45.14 16.88 9.41 11.04 10.57 23.0 15.8 SSDE Method Calculated Effective Dose mSv 7.73 9.70 15.21 13.29 12.19 13.33 Percent Difference** % 5.81 6.03 26.19 17.76 15.65 16.26 14.6 7.1 Age Gender Method Calculated Effective Dose mSv 7.41 8.99 12.56 9.58 8.77 9.59 Percent Difference** % 9.60 12.88 4.25 15.07 16.76 16.37 12.5 4.4 AEF Method Calculated Effective Dose mSv 8.81 11.73 11.87 10.71 9.92 10.89 Percent Difference** % 7.46 13.60 1.51 5.07 5.83 5.06 6.4 3.7 *SSDE Values from AAPM Report No. 204 **Calculated as 100*[(Calculated Measured)/Measured]

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90 CHAPTER 5 CONCLUSIONS AND FUTURE WORK 5.1 Conclusions This study finalizes the validation of the Toshiba Aquilion ONE CT dosimetry methodology Th e addition of source tilt, over ranging considerations, mA capping and physical phantom data confirms this methodology as a viable and accurate means of CT dosimetry in a future patient d ose tracking system Slice based organ dose libraries can be used to generate different exam protocols with no sacrifice in accuracy Additionally, tools for calculating effective dose such as effective dose coefficients and effective dose per mAs values were calculated and compared There is a clear need for size specific dosimetry as well as dosimetry that accounts for TCM. 5.2 Future Work 5.2.1 Improvement of Methodology f or the Calculation of Average Effective mAs The end result of this work was organ dose estimates per mAs To as sign an absolute dose to these exams, an average effective mAs for that patient and exam must be provided The most accurate way to calculate this value is through the averaging of the exam mA displayed in the Digital I maging and Communication in Medicine (DICOM) header of each CT image in an exam This is equivalent for the use of effective dose coefficients that require the scanner report ed CTDI vol or DLP. For retrospective dosimetry, or dosimetry on an exam where ave rage mA, CTDI vol or DLP are unknown, estimates of these values must be made Predicting these values is difficult due to vendor specific and healthcare institution specific protocols that are tailored to different parameters It is possible that trends based on patient size, exam energy, and exam range exists in this data Obtaining a large data

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91 set of CT image sets with those parameters known would allow for the better retrospective prediction of average mA, CTDI vol or DLP. 5.2.2 Expand Dosimetry to th e UF/NCI Library of Hybrid Computational Phantoms W ith a large emphasis on size specific dosimetry and a trend for organ dose accuracy to increase when patient size is accounted for in the Monte Carlo simulations, it would be beneficial to expand this dosi metry methodology to the UF/NCI Library of Hybrid Computational Phantoms The phantom matching study using height weight and BMI matching and effective diameter matching both show ed a significant reduction in error when a patient is matched to a size specific phantom This CT dosimetry methodology could be expanded to these phantoms for use in a CT dosimetry software program similar to CT Expo TM or an in clinic software program that generates organ doses on the fly using the CT image set.

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92 APPENDIX A COMPLETE PHYSICAL PHANTOM VALIDATION DOSIMETRY DATA UFADM CAP Exam s 120 kVp Organ Doses (mGy) 135 kVp Organ Doses (mGy) Organ Calculated Measured Error (%)* Calculated Measured Error (%)* Thyroid 11.9 12.3 3.6 13.1 14.6 10.7 Lung 9.9 11.1 10.8 11.3 11.1 2.0 Thymus 10.1 11.1 9.1 11.5 10.8 6.6 Stomach 11.4 11.8 3.6 13.1 12.5 5.3 Liver 11.4 12.0 5.0 13.1 13.9 5.8 Gallbladder 11.1 10.6 5.2 12.9 13.5 4.3 Esophagus 8.6 10.0 13.9 10.0 10.6 5.2 Spleen 11.0 11.6 5.4 12.6 11.4 10.1 Kidneys 11.3 10.3 10.1 13.1 13.4 2.3 Pancreas 10.8 10.1 6.8 12.6 12.4 1.3 Colon 13.5 11.6 16.2 15.4 14.0 9.9 Small Intestine 11.8 11.1 5.9 13.6 12.7 6.9 Bladder 8.9 8.1 10.3 10.4 10.3 1.2 Prostate 7.8 7.3 6.3 9.1 9.2 1.1 Gonads 10.5 10.8 2.4 11.6 12.7 9.1 Average Magnitude: 7.6 4.0 Average Magnitude: 5.5 3.4 Error is calculated as follows: (calculated dose measured dose)/measured dose

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93 UF15F CAP Exam s 120 kVp Organ Doses (mGy) 135 kVp Organ Doses (mGy) Organ Calculated Measured Error (%)* Calculated Measured Error (%)* Thyroid 12.3 13.9 11.6 14.4 18.3 21.1 Lung 13.9 12.2 13.9 16.5 14.7 12.1 Thymus 12.4 11.7 6.0 14.7 14.6 1.1 Stomach 13.2 14.6 9.9 15.7 17.0 7.9 Liver 13.5 14.9 9.2 16.1 18.3 12.1 Gallbladder 12.3 14.0 12.2 14.8 17.5 15.6 Esophagus 11.6 12.1 4.6 13.9 14.8 6.1 Spleen 12.4 14.5 14.3 14.8 17.8 17.1 Kidneys 11.6 12.7 8.8 13.9 15.5 10.5 Pancreas 11.5 12.6 9.1 13.9 15.7 12.0 Colon 13.8 13.6 1.3 16.2 15.8 2.4 Small Intestine 12.6 14.6 13.9 15.0 17.2 12.8 Bladder 12.3 11.5 6.8 13.9 13.8 0.3 Gonads 11.2 11.3 0.5 13.1 13.2 0.6 Average Magnitude: 8.7 4.3 Average Magnitude: 9.4 6.3 Error is calculated as follows: (calculated dose measured dose)/measured dose

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94 UF10MF CAP Exams 100 kVp Organ Doses (mGy) 120 kVp Organ Doses (mGy) Organ Calculated Measured Error (%)* Calculated Measured Error (%)* Thyroid 8.7 9.0 3.0 13.4 12.1 11.0 Lung 10.7 8.7 22.5 14.0 12.0 16.2 Thymus 10.2 9.2 10.2 13.8 13.6 2.1 Stomach 10.3 9.8 5.2 13.7 12.2 12.0 Liver 10.3 10.1 2.2 13.5 12.0 12.3 Gallbladder 10.2 10.6 4.3 13.5 11.8 14.1 Esophagus 8.9 7.1 25.4 12.1 11.5 4.9 Spleen 9.7 9.6 0.4 12.7 11.2 13.4 Kidneys 9.4 8.9 6.1 12.4 11.8 5.4 Pancreas 9.6 8.8 8.6 12.7 11.7 8.2 Colon 10.7 9.3 15.2 13.7 11.5 19.6 Small Intestine 10.1 9.9 2.6 13.2 11.9 11.0 Bladder 9.3 8.9 4.7 12.1 10.7 13.3 Gonads 9.0 7.9 12.7 10.9 9.6 13.4 Average Magnitude: 8.8 7.4 Average Magnitude: 11.2 4.5 Error is calculated as follows: (calculated dose measured dose)/measured dose

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95 UFADM Head Exams 120 kVp Head Organ Doses (mGy) 120 kVp Brain with Tilt Organ Doses (mGy) Organ Calculated Measured Error (%)* Calculated Measured Error (%)* Brain 42.2 42.7 1.2 29.7 28.0 6.0 Lens 53.4 49.6 7.8 3.2 8.6 62.5 Submaxillary Gland 52.8 53.7 1.6 1.1 2.5 57.7 Parotid Gland 57.4 49.7 15.4 1.1 2.2 50.5 Sublingual Gland 54.1 51.1 5.9 0.5 2.4 79.6 Average Magnitude: 6.4 5.2 Average Magnitude**: 6.0 Error is calculated as follows: (calculated dose measured dose)/measured dose ** In Field Organs only: Brain UF10MF Head Exams 120 kVp Head Organ Doses (mGy) 120 kVp Brain with Tilt Organ Doses (mGy) Organ Calculated Measured Error (%)* Calculated Measured Error (%)* Brain 51.0 51.8 1.6 32.9 30.3 8.6 Lens 57.4 66.5 13.6 8.7 8.4 4.1 Submaxillary Gland 60.6 60.9 0.4 1.9 7.0 73.0 Parotid Gland 67.6 62.4 8.2 1.5 3.6 58.5 Sublingual Gland 56.4 61.7 8.6 0.9 2.8 67.6 Average Magnitude: 6.5 5.0 Average Magnitude**: 8.6 Error is calculated as follows: (calculated dose measured dose)/measured dose ** In Field Organs only: Brain

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96 APPENDIX B COMPLETE CADAVER DOSIMETRY DATA Cadaver IV Exams Chest Abdomen Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast 10.3 12.3 18.9 Lung 11.4 14.8 30.6 Liver 12.2 14.6 19.5 Stomach 11.0 14.5 31.7 Small Intestine 14.6 14.7 0.6 Colon 13.5 15.2 12.8 Ovary 8.5 12.1 43.4 Skin (in field) 17.0 14.8 12.7 Average Magnitude: 21.3 12.6 Error is calculated as follows: (calculated dose measured dose)/measured dose Chest Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast 8.5 8.4 1.8 Lung 8.7 10.1 15.6 Liver 9.9 8.2 17.6 Stomach 8.2 7.0 14.5 Small Intestine** 3.9 0.8 79.9 Colon** 2.5 0.4 82.9 Skin (in field) 10.0 9.5 5.3 Average Magnitude(In Field): 11.0 6.2 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Abdomen Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast 9.5 10.7 12.8 Lung 5.6 6.2 10.8 Liver 9.2 13.8 49.8 Stomach 9.7 13.7 41.4 Small Intestine 13.9 8.4 39.8 Colon 8.4 9.5 12.9

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97 Skin (in field) 13.4 13.8 2.8 Average Magnitude: 24.3 17.3 Error is calculated as follows: (calculated dose measured dose)/measured dose Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast** 0.4 0.0 87.7 Small Intestine 9.3 9.2 0.3 Colon 11.2 8.8 21.0 Ovary 11.8 12.8 8.5 Skin (in field) 16.6 17.1 3.0 Average Magnitude(In Field): 8.2 7.9 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Cadaver V Exams Chest Abdomen Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Lens** 1.2 0.3 74.9 Thyroid 19.7 18.8 4.6 Breast 24.8 21.0 15.4 Lung 18.8 23.4 24.7 Liver 20.3 23.0 13.3 Stomach 24.6 22.4 8.9 Small Intestine 28.6 23.9 16.5 Colon 27.5 24.7 10.1 Ovary 26.5 21.8 17.6 Skin (in field) 28.1 25.6 8.8 Average Magnitude(In Field): 13.3 5.7 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Chest Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Lens** 0.9 0.2 77.6 Thyroid 22.1 11.7 47.0 Breast 15.1 15.1 0.1 Lung 14.9 16.7 11.8

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98 Liver 12.5 14.4 15.6 Stomach 13.4 13.4 0.2 Small Intestine** 1.2 1.6 37.5 Colon** 4.5 1.4 69.8 Ovary** 0.3 0.1 65.5 Skin (in field) 18.9 16.5 12.6 Average Magnitude(In Field): 14.6 15.7 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Cadaver VI Exams Chest Abdomen Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Thyroid 31.0 13.1 57.7 Breast 25.0 18.2 27.3 Lung 21.9 18.1 17.3 Liver 22.8 22.6 0.9 Stomach 26.4 22.7 13.9 SI 29.4 22.6 23.1 Colon 26.4 24.6 6.9 Ovary 21.9 18.1 17.5 Skin (in field) 28.4 27.0 5.0 Average Magnitude: 18.8 15.9 Error is calculated as follows: (calculated dose measured dose)/measured dose Chest Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Thyroid 22.3 10 55.2 Breast 16.8 13.6 19.2 Lung 15.0 13.6 9.2 Liver 16.0 15.8 1.0 Stomach 12.3 15.6 26.8 Small Intestine** 7.9 4.2 47.3 Colon** 3.5 5.1 45.3 Skin (in field) 20.7 19.1 8.0 Average Magnitude(In Field): 19.9 17.8 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field

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99 Abdomen Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast 12.6 13.9 10.6 Lung 8.2 8.9 8.6 Liver 20.1 18.8 6.6 Stomach 22.4 19.0 15.2 Small Intestine 25.6 12.7 50.4 Colon 20.4 15.6 23.5 Skin (in field) 27.8 24.7 11.1 Average Magnitude: 18.0 14.2 Error is calculated as follows: (calculated dose measured dose)/measured dose Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast** 0.3 0.1 60.8 Small Intestine 5.8 7.9 35.3 Colon 14.0 7.1 49.2 Ovary 24.3 12.6 48.0 Skin (in field) 26.6 21.6 18.8 Average Magnitude(In Field): 37.9 12.3 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Cadaver VII Exams Chest Abdomen Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Thyroid 28.4 28.1 1.2 Breast 23.7 22.2 6.5 Lung 18.8 24.2 28.6 Liver 19.3 28.9 50.0 Stomach 24.4 29.4 20.4 SI 22.6 28.7 27.2 Colon 22.9 31.6 38.0 Ovary 22.0 20.3 7.9 Skin (in field) 28.8 29.8 3.3 Average Magnitude: 20.3 16.0 Error is calculated as follows: (calculated dose measured dose)/measured dose

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100 Chest Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Thyroid 21.2 19.8 6.9 Breast 16.6 15.2 7.9 Lung 14.5 16.7 15.4 Liver 15.1 17.8 17.6 Stomach 15.8 17.6 10.8 Small Intestine** 6.4 2.9 55.6 Colon** 2.7 2.8 2.9 Skin (in field) 20.6 20.2 2.3 Average Magnitude(In Field): 10.2 5.2 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field Abdomen Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Lung 6.5 8.4 29.4 Liver 18.2 23.6 29.5 Stomach 19.2 24.5 27.5 Small Intestine 22.7 18.8 17.1 Colon 19.4 23.0 18.4 Skin (in field) 28.1 26.4 6.2 Average Magnitude: 21.2 8.4 Error is calculated as follows: (calculated dose measured dose)/measured dose Pelvis Exam Organ Measured Dose (mGy) Calculated Dose (mGy) Perfecnt Error (%)* Breast** 0.2 0.1 69.5 Small Intestine 5.0 6.9 39.3 Colon 14.6 5.3 63.8 Ovary 23.8 15.9 33.0 Skin (in field) 27.9 20.5 26.5 Average Magnitude(In Field): 40.7 14.1 Error is calculated as follows: (calculated dose measured dose)/measured dose ** Not in field

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101 APPENDIX C COMPLETE REFERENCE PHANTOM DOSIMETRY DATA UFADM Organ Dose and Effective Dose Coefficient Estimate s Estimated Organ Doses from 100 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.064 0.073 0.001 0.075 0.001 0.000 Lung 0.065 0.065 0.028 0.067 0.022 0.000 Thymus 0.067 0.067 0.005 0.069 0.004 0.000 Stomach 0.075 0.075 0.071 0.064 0.066 0.004 Liver 0.077 0.076 0.072 0.069 0.067 0.003 Gall Bladder 0.068 0.067 0.065 0.040 0.061 0.009 Skin (in field) 0.079 0.077 0.059 0.078 0.081 0.083 Esophagus 0.054 0.055 0.025 0.056 0.022 0.001 Spleen 0.075 0.074 0.071 0.070 0.066 0.002 Kidney 0.072 0.069 0.070 0.022 0.063 0.025 Pancreas 0.067 0.065 0.064 0.024 0.059 0.014 Colon 0.087 0.078 0.084 0.009 0.072 0.051 SI 0.077 0.051 0.075 0.006 0.047 0.060 Bladder 0.061 0.004 0.060 0.000 0.004 0.061 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.074 0.074 0.047 0.075 0.039 0.001 Breast 0.073 0.074 0.067 0.076 0.059 0.000 Prostate 0.049 0.001 0.048 0.000 0.001 0.049 Testes 0.062 0.000 0.060 0.000 0.000 0.062 Active Marrow 0.039 0.025 0.030 0.018 0.014 0.019 Shallow Marrow 0.033 0.018 0.024 0.014 0.009 0.018 Effective Dose (mSv) 0.065 0.054 0.051 0.041 0.037 0.019 Exam Length (cm) 67.2 48.0 51.2 35.2 28.8 28.8 CTDI w (mGy/mAs) 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 14.19 16.65 14.79 31.05 19.04 9.82 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.105 0.119 0.002 0.122 0.002 0.000 Lung 0.115 0.116 0.050 0.118 0.039 0.001 Thymus 0.119 0.119 0.010 0.122 0.007 0.000 Stomach 0.134 0.134 0.127 0.115 0.118 0.008 Liver 0.136 0.136 0.127 0.121 0.118 0.007

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102 Gall Bladder 0.124 0.122 0.120 0.074 0.110 0.018 Skin (in field) 0.131 0.129 0.099 0.129 0.134 0.138 Esophagus 0.100 0.102 0.048 0.102 0.041 0.001 Spleen 0.133 0.132 0.125 0.124 0.116 0.005 Kidney 0.129 0.123 0.125 0.039 0.113 0.045 Pancreas 0.122 0.118 0.118 0.044 0.107 0.026 Colon 0.151 0.134 0.146 0.017 0.124 0.087 SI 0.138 0.091 0.134 0.012 0.084 0.107 Bladder 0.111 0.008 0.108 0.001 0.008 0.110 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.132 0.132 0.085 0.134 0.069 0.001 Breast 0.125 0.127 0.114 0.130 0.101 0.000 Prostate 0.090 0.002 0.087 0.000 0.002 0.090 Testes 0.101 0.001 0.098 0.000 0.001 0.101 Active Marrow 0.075 0.049 0.058 0.035 0.028 0.038 Shallow Marrow 0.061 0.034 0.046 0.026 0.017 0.035 Effective Dose (mSv) 0.114 0.096 0.091 0.073 0.066 0.034 Exam Length (cm) 67.2 48.0 51.2 35.2 28.8 28.8 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 15.10 17.71 15.73 33.05 20.23 10.41 Estimated Organ Doses from 135 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.141 0.159 0.004 0.164 0.003 0.000 Lung 0.161 0.163 0.070 0.166 0.055 0.001 Thymus 0.167 0.166 0.014 0.171 0.011 0.000 Stomach 0.189 0.188 0.178 0.161 0.166 0.012 Liver 0.191 0.190 0.178 0.170 0.165 0.010 Gall Bladder 0.177 0.173 0.169 0.104 0.156 0.026 Skin (in field) 0.179 0.175 0.134 0.176 0.183 0.188 Esophagus 0.143 0.145 0.068 0.146 0.058 0.002 Spleen 0.186 0.185 0.175 0.172 0.162 0.007 Kidney 0.182 0.173 0.176 0.056 0.158 0.064 Pancreas 0.174 0.167 0.167 0.062 0.152 0.037 Colon 0.208 0.185 0.202 0.024 0.170 0.121 SI 0.193 0.128 0.187 0.017 0.117 0.149 Bladder 0.157 0.012 0.153 0.001 0.011 0.156 Lens 0.001 0.001 0.000 0.002 0.000 0.000 Pericardium 0.184 0.185 0.118 0.187 0.097 0.002 Breast 0.173 0.176 0.157 0.180 0.139 0.001

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103 Prostate 0.127 0.004 0.124 0.000 0.003 0.127 Testes 0.135 0.001 0.131 0.000 0.001 0.136 Active Marrow 0.112 0.072 0.086 0.052 0.042 0.056 Shallow Marrow 0.089 0.050 0.067 0.038 0.025 0.050 Effective Dose (mSv) 0.160 0.134 0.126 0.102 0.092 0.047 Exam Length (cm) 67.2 48.0 51.2 35.2 28.8 28.8 CTDI w (mGy/mAs) 0.1264 0.1264 0.1264 0.1264 0.1264 0.1264 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 15.55 18.23 16.18 34.02 20.81 10.70 UFADF Organ Dose and Effective Dose Coefficient Estimate s Estimated Organ Dose from 100 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.068 0.071 0.004 0.068 0.004 0.000 Lung 0.082 0.085 0.044 0.081 0.046 0.000 Thymus 0.070 0.074 0.008 0.071 0.008 0.000 Stomach 0.076 0.079 0.070 0.063 0.073 0.002 Liver 0.079 0.082 0.072 0.068 0.075 0.001 Gall Bladder 0.065 0.068 0.060 0.050 0.062 0.002 Skin (in field) 0.084 0.085 0.084 0.084 0.087 0.089 Esophagus 0.066 0.069 0.035 0.065 0.036 0.000 Spleen 0.082 0.085 0.075 0.073 0.078 0.001 Kidney 0.075 0.076 0.070 0.021 0.072 0.005 Pancreas 0.066 0.068 0.062 0.038 0.063 0.003 Colon 0.077 0.069 0.072 0.005 0.061 0.032 SI 0.074 0.058 0.069 0.007 0.050 0.038 Bladder 0.080 0.005 0.075 0.000 0.004 0.072 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.087 0.091 0.057 0.086 0.060 0.000 Breast 0.076 0.079 0.069 0.075 0.072 0.000 Ovaries 0.067 0.008 0.064 0.000 0.005 0.060 Active Marrow 0.046 0.034 0.034 0.022 0.021 0.018 Shallow Marrow 0.045 0.032 0.032 0.022 0.018 0.018 Effective Dose (mSv) 0.070 0.059 0.054 0.044 0.044 0.012 Exam Length (cm) 64.0 48.0 48.0 32.0 32.0 22.4 CTDI w (mGy/mAs) 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 16.08 18.26 16.50 35.97 20.25 8.12

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104 Estimated Organ Dose from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.113 0.118 0.007 0.114 0.007 0.000 Lung 0.144 0.150 0.077 0.143 0.080 0.000 Thymus 0.124 0.129 0.015 0.124 0.015 0.000 Stomach 0.135 0.140 0.124 0.111 0.129 0.003 Liver 0.139 0.145 0.126 0.120 0.132 0.002 Gall Bladder 0.119 0.123 0.109 0.090 0.113 0.004 Skin (in field) 0.140 0.141 0.139 0.139 0.144 0.147 Esophagus 0.119 0.124 0.063 0.117 0.066 0.000 Spleen 0.141 0.147 0.130 0.126 0.135 0.002 Kidney 0.130 0.133 0.122 0.038 0.124 0.010 Pancreas 0.119 0.122 0.111 0.068 0.114 0.006 Colon 0.135 0.120 0.127 0.010 0.106 0.057 SI 0.132 0.104 0.123 0.013 0.089 0.067 Bladder 0.140 0.011 0.132 0.001 0.007 0.127 Lens 0.002 0.002 0.000 0.001 0.000 0.000 Pericardium 0.154 0.161 0.101 0.153 0.106 0.000 Breast 0.131 0.137 0.119 0.130 0.125 0.000 Ovaries 0.122 0.015 0.117 0.001 0.010 0.109 Active Marrow 0.088 0.065 0.065 0.042 0.040 0.034 Shallow Marrow 0.083 0.058 0.059 0.041 0.033 0.034 Effective Dose (mSv) 0.124 0.105 0.095 0.077 0.077 0.022 Exam Length (cm) 64.0 48.0 48.0 32.0 32.0 22.4 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 17.18 19.42 17.65 38.20 21.53 8.84 Estimated Organ Dose from 135 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.153 0.160 0.010 0.154 0.011 0.000 Lung 0.200 0.209 0.107 0.199 0.112 0.001 Thymus 0.172 0.179 0.021 0.172 0.022 0.000 Stomach 0.188 0.195 0.173 0.154 0.180 0.005 Liver 0.195 0.202 0.176 0.168 0.184 0.004 Gall Bladder 0.169 0.174 0.155 0.127 0.160 0.006 Skin (in field) 0.190 0.192 0.189 0.189 0.196 0.200 Esophagus 0.168 0.176 0.090 0.166 0.094 0.001 Spleen 0.195 0.202 0.179 0.174 0.186 0.004 Kidney 0.181 0.183 0.169 0.054 0.171 0.015 Pancreas 0.168 0.172 0.157 0.096 0.161 0.009

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105 Colon 0.188 0.166 0.176 0.015 0.147 0.079 SI 0.184 0.145 0.173 0.019 0.124 0.094 Bladder 0.195 0.015 0.183 0.001 0.010 0.176 Lens 0.002 0.002 0.001 0.002 0.001 0.000 Pericardium 0.215 0.224 0.142 0.213 0.149 0.001 Breast 0.182 0.190 0.165 0.181 0.173 0.000 Ovaries 0.174 0.023 0.166 0.001 0.015 0.154 Active Marrow 0.129 0.095 0.096 0.061 0.059 0.051 Shallow Marrow 0.119 0.083 0.085 0.059 0.046 0.049 Effective Dose (mSv) 0.173 0.146 0.133 0.107 0.108 0.031 Exam Length (cm) 64.0 48.0 48.0 32.0 32.0 22.4 CTDI w (mGy/mAs) 0.1264 0.1264 0.1264 0.1264 0.1264 0.1264 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 17.71 19.98 18.21 39.26 22.14 9.20 UF15M Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Doses from 100 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.096 0.096 0.003 0.092 0.003 0.000 Lung 0.090 0.090 0.041 0.085 0.041 0.000 Thymus 0.090 0.090 0.006 0.086 0.006 0.000 Stomach 0.094 0.091 0.089 0.046 0.087 0.005 Liver 0.096 0.095 0.090 0.063 0.089 0.003 Gall Bladder 0.086 0.084 0.082 0.039 0.080 0.004 Skin (in field) 0.087 0.087 0.088 0.086 0.089 0.093 Esophagus 0.077 0.077 0.033 0.072 0.033 0.000 Spleen 0.090 0.089 0.085 0.058 0.085 0.002 Kidney 0.079 0.074 0.076 0.015 0.072 0.011 Pancreas 0.076 0.072 0.073 0.014 0.070 0.009 Colon 0.095 0.055 0.093 0.003 0.062 0.064 SI 0.086 0.040 0.084 0.004 0.046 0.063 Bladder 0.076 0.002 0.072 0.000 0.002 0.077 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.102 0.102 0.057 0.096 0.056 0.000 Breast 0.086 0.086 0.078 0.082 0.078 0.000 Prostate 0.076 0.001 0.067 0.000 0.001 0.078 Testes 0.104 0.000 0.087 0.000 0.001 0.107 Active Marrow 0.045 0.027 0.034 0.019 0.017 0.021 Shallow Marrow 0.038 0.022 0.028 0.016 0.013 0.018 Effective Dose (mSv) 0.083 0.062 0.063 0.043 0.046 0.025

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106 Exam Length (cm) 67.2 44.8 48.0 32.0 28.8 26.0 CTDI w (mGy/mAs) 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 18.09 20.25 19.42 35.14 23.49 14.45 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.158 0.158 0.005 0.151 0.005 0.000 Lung 0.157 0.157 0.072 0.148 0.072 0.001 Thymus 0.156 0.156 0.012 0.149 0.012 0.000 Stomach 0.163 0.159 0.154 0.081 0.150 0.008 Liver 0.167 0.164 0.157 0.109 0.155 0.005 Gall Bladder 0.153 0.149 0.145 0.070 0.141 0.008 Skin (in field) 0.145 0.145 0.146 0.143 0.147 0.153 Esophagus 0.138 0.137 0.059 0.128 0.059 0.001 Spleen 0.156 0.153 0.147 0.100 0.145 0.004 Kidney 0.139 0.130 0.133 0.028 0.126 0.020 Pancreas 0.136 0.127 0.131 0.027 0.124 0.016 Colon 0.161 0.092 0.156 0.005 0.104 0.108 SI 0.150 0.070 0.146 0.007 0.079 0.109 Bladder 0.134 0.004 0.128 0.000 0.005 0.136 Lens 0.002 0.002 0.001 0.002 0.001 0.000 Pericardium 0.177 0.177 0.099 0.166 0.098 0.001 Breast 0.147 0.147 0.133 0.139 0.133 0.000 Prostate 0.132 0.001 0.116 0.000 0.001 0.134 Testes 0.171 0.001 0.143 0.000 0.001 0.175 Active Marrow 0.085 0.050 0.065 0.035 0.033 0.040 Shallow Marrow 0.070 0.040 0.052 0.029 0.025 0.034 Effective Dose (mSv) 0.143 0.107 0.109 0.074 0.079 0.044 Exam Length (cm) 67.2 44.8 48.0 32.0 28.8 26.0 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 18.88 21.16 20.26 36.83 24.51 14.95 UF15F Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Dose from 100 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.095 0.081 0.004 0.078 0.004 0.000 Lung 0.089 0.093 0.049 0.089 0.052 0.000

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107 Thymus 0.082 0.086 0.009 0.083 0.009 0.000 Stomach 0.088 0.092 0.082 0.076 0.087 0.005 Liver 0.091 0.095 0.084 0.083 0.089 0.004 Gall Bladder 0.078 0.080 0.072 0.067 0.076 0.006 Skin (in field) 0.087 0.085 0.095 0.089 0.094 0.097 Esophagus 0.074 0.075 0.038 0.072 0.040 0.001 Spleen 0.086 0.090 0.080 0.082 0.084 0.003 Kidney 0.080 0.081 0.075 0.040 0.077 0.018 Pancreas 0.075 0.077 0.070 0.051 0.073 0.010 Colon 0.096 0.084 0.090 0.008 0.080 0.066 SI 0.088 0.068 0.082 0.010 0.065 0.063 Bladder 0.081 0.004 0.081 0.000 0.004 0.079 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.102 0.107 0.072 0.103 0.077 0.001 Breast 0.086 0.090 0.078 0.086 0.083 0.000 Ovaries 0.070 0.006 0.072 0.001 0.006 0.070 Active Marrow 0.047 0.031 0.038 0.020 0.022 0.025 Shallow Marrow 0.043 0.028 0.034 0.019 0.019 0.022 Effective Dose (mSv) 0.080 0.067 0.062 0.050 0.052 0.020 Exam Length (cm) 60.8 44.8 48.0 32.0 32.0 25.6 CTDI w (mGy/mAs) 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 19.32 21.94 19.09 41.23 23.84 11.27 Estimated Organ Dose from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.154 0.132 0.008 0.128 0.008 0.000 Lung 0.155 0.161 0.085 0.155 0.090 0.001 Thymus 0.140 0.148 0.016 0.144 0.017 0.000 Stomach 0.153 0.159 0.143 0.132 0.150 0.010 Liver 0.158 0.164 0.145 0.143 0.153 0.007 Gall Bladder 0.139 0.143 0.129 0.118 0.135 0.011 Skin (in field) 0.144 0.140 0.157 0.148 0.156 0.162 Esophagus 0.131 0.134 0.068 0.128 0.072 0.001 Spleen 0.148 0.154 0.137 0.139 0.145 0.005 Kidney 0.139 0.141 0.131 0.071 0.134 0.031 Pancreas 0.135 0.137 0.125 0.091 0.130 0.019 Colon 0.162 0.140 0.152 0.014 0.135 0.112 SI 0.153 0.118 0.144 0.019 0.113 0.109 Bladder 0.142 0.008 0.142 0.001 0.007 0.138 Lens 0.002 0.002 0.001 0.002 0.001 0.000 Pericardium 0.176 0.185 0.125 0.178 0.132 0.001

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108 Breast 0.147 0.153 0.133 0.147 0.141 0.001 Ovaries 0.126 0.012 0.130 0.001 0.012 0.127 Active Marrow 0.090 0.059 0.072 0.038 0.042 0.047 Shallow Marrow 0.080 0.051 0.063 0.034 0.035 0.042 Effective Dose (mSv) 0.138 0.115 0.108 0.086 0.090 0.034 Exam Length (cm) 60.8 44.8 48.0 32.0 32.0 25.6 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 20.24 22.88 20.06 43.06 24.88 11.96 UF10MF Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Doses from 100 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.123 0.121 0.002 0.119 0.002 0.000 Lung 0.110 0.108 0.030 0.105 0.029 0.001 Thymus 0.113 0.112 0.007 0.109 0.007 0.000 Stomach 0.110 0.107 0.105 0.063 0.101 0.007 Liver 0.110 0.107 0.102 0.080 0.098 0.004 Gall Bladder 0.103 0.099 0.099 0.042 0.095 0.008 Skin (in field) 0.105 0.103 0.108 0.103 0.110 0.114 Esophagus 0.094 0.093 0.030 0.088 0.029 0.001 Spleen 0.108 0.106 0.102 0.083 0.099 0.004 Kidney 0.103 0.098 0.101 0.021 0.095 0.020 Pancreas 0.098 0.094 0.095 0.025 0.090 0.013 Colon 0.116 0.096 0.116 0.005 0.094 0.075 SI 0.110 0.074 0.109 0.005 0.073 0.085 Bladder 0.099 0.004 0.099 0.000 0.004 0.102 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.117 0.115 0.053 0.109 0.051 0.001 Breast 0.095 0.093 0.075 0.091 0.073 0.000 Prostate 0.089 0.001 0.089 0.000 0.001 0.092 Gonads 0.109 0.003 0.109 0.000 0.003 0.112 Active Marrow 0.052 0.033 0.037 0.024 0.017 0.025 Shallow Marrow 0.060 0.038 0.041 0.027 0.019 0.028 Effective Dose (mSv) 0.097 0.077 0.071 0.053 0.051 0.030 Exam Length (cm) 57.6 38.4 41.6 25.6 22.4 25.6 CTDI w (mGy/mAs) 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 24.89 29.51 25.29 54.25 33.62 17.26

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10 9 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.197 0.194 0.005 0.191 0.004 0.000 Lung 0.189 0.186 0.051 0.179 0.050 0.001 Thymus 0.193 0.190 0.013 0.186 0.013 0.000 Stomach 0.189 0.184 0.180 0.108 0.172 0.012 Liver 0.189 0.184 0.174 0.137 0.167 0.008 Gall Bladder 0.179 0.172 0.172 0.074 0.164 0.015 Skin (in field) 0.172 0.170 0.179 0.169 0.181 0.187 Esophagus 0.164 0.161 0.053 0.153 0.051 0.002 Spleen 0.184 0.180 0.173 0.141 0.167 0.007 Kidney 0.177 0.168 0.173 0.038 0.162 0.035 Pancreas 0.172 0.164 0.166 0.044 0.157 0.023 Colon 0.194 0.159 0.193 0.009 0.156 0.126 SI 0.187 0.126 0.186 0.010 0.124 0.145 Bladder 0.170 0.007 0.170 0.001 0.007 0.175 Lens 0.003 0.003 0.000 0.003 0.000 0.000 Pericardium 0.199 0.196 0.091 0.187 0.088 0.002 Breast 0.160 0.157 0.126 0.152 0.123 0.001 Prostate 0.152 0.003 0.152 0.000 0.003 0.157 Gonads 0.182 0.007 0.182 0.001 0.006 0.187 Active Marrow 0.097 0.060 0.069 0.044 0.032 0.046 Shallow Marrow 0.107 0.068 0.074 0.047 0.035 0.051 Effective Dose (mSv) 0.166 0.131 0.122 0.090 0.087 0.051 Exam Length (cm) 57.6 38.4 41.6 25.6 22.4 25.6 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 25.63 30.34 26.05 55.89 34.53 17.77 UF05MF Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Doses from 80 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.063 0.062 0.002 0.062 0.001 0.000 Lung 0.062 0.061 0.015 0.059 0.015 0.000 Thymus 0.067 0.066 0.004 0.064 0.004 0.000 Stomach 0.061 0.060 0.059 0.037 0.056 0.002 Liver 0.062 0.061 0.058 0.043 0.056 0.001 Gall Bladder 0.059 0.057 0.055 0.015 0.053 0.003 Skin (in field) 0.060 0.065 0.061 0.058 0.059 0.064 Esophagus 0.051 0.050 0.016 0.048 0.016 0.000

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110 Spleen 0.062 0.060 0.057 0.046 0.055 0.001 Kidney 0.060 0.058 0.059 0.014 0.055 0.004 Pancreas 0.057 0.056 0.057 0.011 0.054 0.003 Colon 0.067 0.059 0.068 0.002 0.052 0.035 SI 0.063 0.052 0.062 0.002 0.043 0.038 Bladder 0.060 0.007 0.063 0.000 0.004 0.064 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.067 0.066 0.032 0.063 0.031 0.000 Breast 0.055 0.054 0.044 0.052 0.043 0.000 Prostate 0.062 0.003 0.054 0.000 0.002 0.055 Gonads 0.051 0.007 0.059 0.000 0.004 0.060 Active Marrow 0.020 0.015 0.013 0.010 0.007 0.007 Shallow Marrow 0.032 0.024 0.021 0.016 0.012 0.011 Effective Dose (mSv) 0.053 0.044 0.040 0.029 0.029 0.015 Exam Length (cm) 41.6 28.8 32.0 19.2 19.2 16.0 CTDI w (mGy/mAs) 0.028 0.028 0.028 0.028 0.028 0.028 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 37.7 45.4 36.9 80.1 44.0 27.1 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.188 0.186 0.007 0.183 0.006 0.000 Lung 0.203 0.200 0.053 0.193 0.051 0.001 Thymus 0.213 0.210 0.017 0.205 0.017 0.000 Stomach 0.209 0.204 0.199 0.126 0.190 0.007 Liver 0.210 0.206 0.195 0.144 0.187 0.006 Gall Bladder 0.207 0.201 0.193 0.054 0.182 0.013 Skin (in field) 0.189 0.202 0.191 0.180 0.186 0.201 Esophagus 0.174 0.172 0.059 0.163 0.057 0.001 Spleen 0.208 0.203 0.192 0.154 0.184 0.005 Kidney 0.207 0.200 0.201 0.050 0.188 0.017 Pancreas 0.200 0.194 0.198 0.041 0.186 0.014 Colon 0.215 0.188 0.218 0.009 0.164 0.111 SI 0.211 0.173 0.209 0.010 0.145 0.127 Bladder 0.198 0.028 0.206 0.002 0.018 0.207 Lens 0.002 0.002 0.001 0.002 0.001 0.000 Pericardium 0.223 0.219 0.109 0.208 0.105 0.002 Breast 0.180 0.178 0.144 0.172 0.139 0.001 Prostate 0.202 0.011 0.175 0.001 0.007 0.179 Gonads 0.168 0.025 0.194 0.001 0.016 0.195 Active Marrow 0.079 0.060 0.053 0.039 0.029 0.030

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111 Shallow Marrow 0.119 0.092 0.079 0.060 0.044 0.044 Effective Dose (mSv) 0.176 0.147 0.133 0.097 0.096 0.048 Exam Length (cm) 41.6 28.8 32.0 19.2 19.2 16.0 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 37.7 45.5 37.1 80.3 44.3 27.0 UF01MF Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Doses from 80 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.063 0.062 0.007 0.064 0.004 0.000 Lung 0.073 0.072 0.051 0.072 0.038 0.001 Thymus 0.063 0.062 0.014 0.063 0.008 0.000 Stomach 0.069 0.067 0.066 0.043 0.063 0.008 Liver 0.072 0.071 0.069 0.052 0.064 0.007 Gall Bladder 0.065 0.063 0.063 0.024 0.059 0.011 Skin (in field) 0.071 0.074 0.088 0.083 0.084 0.095 Esophagus 0.055 0.054 0.026 0.055 0.018 0.001 Spleen 0.075 0.073 0.071 0.067 0.066 0.003 Kidney 0.070 0.068 0.068 0.026 0.062 0.015 Pancreas 0.065 0.063 0.063 0.013 0.065 0.014 Colon 0.072 0.064 0.070 0.005 0.053 0.053 SI 0.068 0.056 0.066 0.004 0.044 0.055 Bladder 0.064 0.012 0.063 0.001 0.007 0.061 Lens 0.001 0.001 0.000 0.001 0.000 0.000 Pericardium 0.076 0.075 0.061 0.075 0.043 0.001 Breast 0.064 0.063 0.061 0.064 0.045 0.001 Prostate 0.051 0.005 0.050 0.000 0.003 0.049 Gonads 0.061 0.011 0.060 0.001 0.006 0.059 Active Marrow 0.031 0.027 0.024 0.020 0.015 0.010 Shallow Marrow 0.039 0.033 0.030 0.023 0.018 0.014 Effective Dose (mSv) 0.061 0.052 0.051 0.036 0.035 0.019 Exam Length (cm) 32.0 25.6 25.6 16.0 16.0 12.8 CTDI w (mGy/mAs) 0.028 0.028 0.028 0.028 0.028 0.028 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 56.10 59.56 58.87 119.79 65.37 43.54

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112 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.197 0.194 0.021 0.199 0.016 0.001 Lung 0.231 0.227 0.143 0.226 0.120 0.005 Thymus 0.202 0.200 0.040 0.203 0.030 0.002 Stomach 0.228 0.222 0.216 0.140 0.207 0.028 Liver 0.235 0.229 0.218 0.167 0.207 0.025 Gall Bladder 0.221 0.214 0.210 0.084 0.197 0.039 Skin (in field) 0.216 0.228 0.252 0.254 0.259 0.264 Esophagus 0.181 0.178 0.075 0.179 0.061 0.003 Spleen 0.237 0.232 0.218 0.208 0.207 0.013 Kidney 0.232 0.224 0.219 0.086 0.204 0.052 Pancreas 0.218 0.209 0.218 0.047 0.213 0.050 Colon 0.233 0.207 0.223 0.018 0.170 0.170 SI 0.225 0.185 0.216 0.016 0.148 0.179 Bladder 0.210 0.045 0.198 0.004 0.027 0.199 Lens 0.004 0.004 0.002 0.003 0.001 0.000 Pericardium 0.242 0.238 0.169 0.236 0.139 0.005 Breast 0.208 0.205 0.172 0.207 0.144 0.003 Prostate 0.167 0.021 0.163 0.002 0.013 0.160 Gonads 0.190 0.038 0.183 0.003 0.022 0.181 Active Marrow 0.115 0.099 0.082 0.072 0.055 0.036 Shallow Marrow 0.141 0.117 0.102 0.080 0.064 0.052 Effective Dose (mSv) 0.198 0.169 0.157 0.117 0.116 0.061 Exam Length (cm) 32.0 25.6 25.6 16.0 16.0 12.8 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 54.94 58.55 54.71 116.66 64.23 42.46 UFNBMF Organ Dose and Effective Dose Coefficient Estimates Estimated Organ Doses from 80 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.079 0.076 0.004 0.079 0.004 0.000 Lung 0.082 0.082 0.040 0.081 0.039 0.001 Thymus 0.079 0.081 0.009 0.078 0.008 0.001 Stomach 0.087 0.085 0.086 0.080 0.082 0.007 Liver 0.090 0.088 0.083 0.084 0.080 0.006 Gall Bladder 0.085 0.083 0.082 0.077 0.079 0.008 Skin (in field) 0.095 0.099 0.098 0.116 0.109 0.093 Esophagus 0.074 0.073 0.033 0.073 0.032 0.001

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113 Spleen 0.085 0.083 0.083 0.081 0.080 0.004 Kidney 0.088 0.084 0.087 0.060 0.082 0.028 Pancreas 0.082 0.088 0.095 0.073 0.091 0.009 Colon 0.091 0.086 0.091 0.053 0.085 0.038 SI 0.088 0.075 0.086 0.034 0.075 0.054 Bladder 0.080 0.019 0.085 0.005 0.027 0.075 Lens 0.003 0.003 0.001 0.003 0.001 0.000 Pericardium 0.089 0.088 0.045 0.088 0.044 0.001 Breast 0.077 0.076 0.069 0.076 0.067 0.001 Prostate 0.087 0.007 0.079 0.002 0.008 0.084 Gonads 0.073 0.003 0.072 0.001 0.004 0.072 Active Marrow 0.039 0.033 0.022 0.030 0.018 0.009 Shallow Marrow 0.043 0.037 0.024 0.033 0.019 0.010 Effective Dose (mSv) 0.075 0.064 0.059 0.056 0.048 0.019 Exam Length (cm) 25.6 19.2 19.2 16.0 12.8 9.6 CTDI w (mGy/mAs) 0.028 0.028 0.028 0.028 0.028 0.028 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 86.40 97.85 91.40 185.40 111.35 58.36 Estimated Organ Doses from 120 kVp Toshiba 64 Slice CT Exam (mGy/Average Effective mAs) Organ CAP CA AP C A P Thyroid 0.232 0.228 0.012 0.231 0.012 0.001 Lung 0.251 0.249 0.121 0.248 0.119 0.002 Thymus 0.240 0.248 0.029 0.239 0.029 0.001 Stomach 0.268 0.260 0.261 0.242 0.251 0.022 Liver 0.272 0.268 0.250 0.252 0.241 0.020 Gall Bladder 0.268 0.260 0.258 0.240 0.248 0.028 Skin (in field) 0.273 0.289 0.287 0.339 0.318 0.270 Esophagus 0.232 0.229 0.108 0.230 0.101 0.002 Spleen 0.259 0.251 0.250 0.242 0.241 0.012 Kidney 0.269 0.257 0.268 0.181 0.249 0.088 Pancreas 0.251 0.269 0.290 0.221 0.279 0.030 Colon 0.270 0.252 0.269 0.158 0.250 0.112 SI 0.269 0.228 0.260 0.102 0.228 0.162 Bladder 0.250 0.051 0.253 0.013 0.071 0.237 Lens 0.011 0.010 0.002 0.011 0.001 0.000 Pericardium 0.270 0.268 0.138 0.268 0.131 0.002 Breast 0.228 0.222 0.201 0.221 0.198 0.001 Prostate 0.263 0.025 0.236 0.008 0.027 0.254 Gonads 0.240 0.086 0.213 0.012 0.086 0.227 Active Marrow 0.132 0.112 0.078 0.101 0.060 0.031

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114 Shallow Marrow 0.141 0.121 0.080 0.110 0.062 0.032 Effective Dose (mSv) 0.230 0.199 0.179 0.170 0.152 0.058 Exam Length (cm) 25.6 19.2 19.2 16.0 12.8 9.6 CTDI w (mGy/mAs) 0.0931 0.0931 0.0931 0.0931 0.0931 0.0931 Pitch 0.828 0.828 0.828 1.484 0.828 0.828 EDC cm) 79.74 91.98 83.13 169.69 105.38 53.77

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115 Head Exam Organ Dose Estimates for All Reference Phantoms Estimated Organ Dose from 120 kVp Toshiba Head CT Exam (mGy/Effective mAs) Organ UFADM UFADF UF15M UF15F UF10MF UF05MF UF01MF UFNBMF Brain 0.129 0.155 0.161 0.169 0.176 0.200 0.183 0.233 Lens 0.172 0.181 0.209 0.205 0.195 0.213 0.200 0.234 Submaxillary 0.175 0.203 0.175 0.185 0.198 0.207 0.206 0.244 Parotid 0.197 0.200 0.196 0.209 0.225 0.214 0.224 0.240 Sublingual 0.190 0.163 0.184 0.183 0.188 0.200 0.202 0.240 Thyroid 0.027 0.030 0.023 0.031 0.041 0.101 0.185 0.268 Skin (in field) 0.190 0.199 0.200 0.207 0.207 0.223 0.213 0.268 Effective Dose (mSv) 0.006 0.007 0.006 0.007 0.007 0.010 0.013 0.018 Brain Exam with Tilt Organ Dose Estimates for All Reference Phantoms Estimated Organ Dose from 120 kVp Toshiba Brain CT Exam (mGy/Effective mAs) Organ UFADM UFADF UF15M UF15F UF10MF UF05MF Brain 0.113 0.130 0.139 0.148 0.150 0.155 Lens 0.023 0.016 0.041 0.030 0.024 0.036 Submaxillary 0.006 0.008 0.010 0.015 0.012 0.013 Parotid 0.008 0.010 0.011 0.014 0.011 0.013 Sublingual 0.003 0.005 0.004 0.006 0.005 0.006 Thyroid 0.001 0.002 0.002 0.002 0.004 0.005 Skin (in field) 0.159 0.177 0.176 0.194 0.183 0.193 Effective Dose (mSv) 0.003 0.003 0.003 0.004 0.004 0.004

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119 40 A.M. Geyer, The University of Florid a/National Cancer Institute Family of Hybrid Computational Phantoms Representing the Current United States Population of Male and Female Children and AdolescentsApplications to Computed Tomography Dosimetry (University of Florida, Gainesville, Fla, 2012) 41 P.B. Johnson, A. Geyer, D. Borrego, K. Ficarrotta, K. Johnson, W.E. Bolch, "The impact of anthropometric patient phantom matching on organ dose: a hybrid phantom study for fluoroscopy guided interventions," Medical physics 38 1008 1017 (2011). 42 International Commission on Radiological Protection Basic Anatomical and Physiological Data for Use in Radiological Protection: Reference Values ," 2003. 43 M. Wayson, COMPUTATIONAL INTERNAL DOSIMETRY METHODS AS APPLIED TO THE UNIVERSITY OF FLORIDA SERI ES OF HYBRID PHANTOMS ," University of Florida, 2012. 44 International Commission on Radiological, 2007. 45 P.B. Johnson, A.A. Bahadori, K.F. Eckerman, C. Lee, W.E. Bolch, "Response functions for computing absorbed dose to skeletal tissues from photon irrad iation -an update," Phys Med Biol 56 2347 2365 (2011). 46 W. Huda, K.M. Ogden, M.R. Khorasani, "Converting dose length product to effective dose at CT," Radiology 248 995 1003 (2008). 47 J.S.P. Tan, K.L. Tan, J.C.L. Lee, C.M. Wan, J.L. Leong, L.L. Chan, "Comparison of Eye Lens Dose on Neuroimaging Protocols between 16 and 64 Section Multidetector CT: Achieving the Lowest Possible Dose," American Journal of Neuroradiology 30 373 377 (2009). 48 D. Zhang, C.H. Cagnon, J.P. Villablanca, C.H. McCollough, D.D. Cody, M. Zankl, J.J. Demarco, M.F. McNitt Gray, "Estimating peak skin and eye lens dose from neuroperfusion examinations: Use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM Report No. 111, and ImPACT dosimetry tool values," Medical Phys ics 40 2013). 49 X. Tian, X. Li, W.P. Segars, E.K. Paulson, D.P. Frush, E. Samei, "Pediatric Chest and Abdominopelvic CT: Organ Dose Estimation Based on 42 Patient Models," Radiology 270 535 547 (2014). 50 Image Gently, "How to Develop CT Protocols for Chi ldren," 2007.

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120 BIOGRAPHICAL SKETCH Elliott James Stepusin was born in St Charles, Illinois to Paul and Nancy Stepusin in May 1990 He has two siblings, an older sister Rebecca and an older brother Paul He gr aduated from Celebration High School in 2008 and graduated cum laude with his Bachelor of Science in nuclear engineering sciences from the University of Florida in May 2012 He conducted undergraduate research during his junior and senior year as a part of the Univer He is currently pursuing a doctoral degree in medical physics from the Department of Biomedical Engineering at the University of Florida.