In-Clinic Calibration of a Kerma-Area Product Meter at Different Radiation Qualities for the Assessment of Skin Doses In...

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Title:
In-Clinic Calibration of a Kerma-Area Product Meter at Different Radiation Qualities for the Assessment of Skin Doses Incurred during Interventional Fluoroscopic Procedures
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1 online resource (44 p.)
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english
Creator:
Borrego, David
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University of Florida
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Gainesville, Fla.
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Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Biomedical Engineering
Committee Chair:
Bolch, Wesley E
Committee Members:
Gilland, David R
Hintenlang, David E

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Subjects / Keywords:
anthropometric -- dap -- dose -- fluoroscopy -- interventional -- kap -- phantoms -- psd
Biomedical Engineering -- Dissertations, Academic -- UF
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Biomedical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

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Abstract:
The growing use and increasing complexity ofinterventional fluoroscopic procedures has raised public health concernsregarding radiation exposure to both the patient’s skin and internal radiosensitiveorgans. Current dosimetry options available to clinicians and physicians failto account for the dynamic nature of fluoroscopic procedures and anthropometricdifferences in-patient size. The University of Florida skin dose mapping andorgan software overcome these challenges by making use of the Radiation DoseStructured Report and the UF hybrid adult patient-dependent series ofcomputational phantoms; however, it still relies on measurements from thekerma-area product meter. The kerma-area product meter is only accurate towithin ±35% to account for uncertainties in determining patient skin dose. Inorder to address the inherent uncertainty introduced into the skin dosesoftware from the ionization chamber, calibration coefficients were introduced.The calibration coefficients show strong energy dependence and can be predictedwith knowledge of the tube voltage and amount of filtration material in thebeam. The skin dose mapping software is able to cull for those variables,calculate the calibration coefficient, and finally apply the corrections in itscalculation of dose. Overall, this study was able to show that many of theclinical challenges encountered in dose reconstructions may be overcome toeventually provide physicians with accurate real-time skin dose information tobetter help them manage patient risk.
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In the series University of Florida Digital Collections.
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Includes vita.
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Includes bibliographical references.
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Description based on online resource; title from PDF title page.
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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.
Statement of Responsibility:
by David Borrego.
Thesis:
Thesis (M.S.)--University of Florida, 2012.
Local:
Adviser: Bolch, Wesley E.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2013-12-31

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lcc - LD1780 2012
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UFE0045112:00001


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1 IN CLINIC CALIBRATION OF A KERMA AREA PRODUCT METER AT DIFFERENT RADIATION QUALITIES FOR THE ASSESSMENT OF SKIN DOSES INCURRED DURING INTERVENTIONAL FLUOROSCOPIC PROCEDURES By DAVID BORREGO A THESIS PRESENTED TO THE GRADU ATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2012

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2 2012 David Borrego

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3 To my mother and sister for their steadfast support in my endeavors and their display of unconditional love

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4 ACKNOWLEDGMENTS Sincere thanks to my advisor and mentor, Dr. Wesley Bolch, for his guidance and encouragement through the past couple years. I thank Dr. Daniel Siragusa for allowing the use of his equipment and valuable feedback through the course of the project. I thank Dr. Kevin Johnson for his hard work in obtaining IRB approval and overall know how with working on the PACS system and extracting RDSR. Thank you to Dr. David Hintenlang and Dr. David Gilland for their input, guidance, and serving as my instructors throughout my graduate school career. Thank you, Dr. Perry Johnson for laying down the groundwork.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 6 LIST OF FIGURES ................................ ................................ ................................ .......... 7 LIST OF ABBREVIATIONS ................................ ................................ ............................. 8 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 11 Interventional Fluoroscopy ................................ ................................ ...................... 11 Need for Comprehensive Dosimetry ................................ ................................ ....... 11 Li mitations in IR dosimetry ................................ ................................ ............... 13 University of Florida skin dose mapping software ................................ ............ 15 Kerma Area Product Meter ................................ ................................ ..................... 18 2 MATERIALS AND METHODS ................................ ................................ ................ 20 Site and Materials ................................ ................................ ................................ ... 20 Calibration Set Up ................................ ................................ ................................ ... 20 Determination of Calibration Coefficients ................................ ................................ 21 Implementation of Calibration Coefficients into Skin Dose Mapping Software and Testing ................................ ................................ ................................ .......... 22 3 RESULTS AND DISCUSSION ................................ ................................ ............... 29 Calibration Coefficients ................................ ................................ ........................... 29 Skin Dose Sof tware ................................ ................................ ................................ 30 4 CONCLUSION AND FUTURE WORK ................................ ................................ .... 41 LIST OF REFERENCES ................................ ................................ ............................... 42 B IOGRAPHICAL SKETCH ................................ ................................ ............................ 44

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6 LIST OF TABLES Table page 2 1 Properties of the KAP meter installed in the Siemens Artis Zee system. ............ 25 2 2 Radcal chamber 10x6 6 used for the DIAMENTOR meter calibration in the Siemens Artis Zee fluoroscopic unit. Chamber was last calibrated on 18 Sep 2012. ................................ ................................ ................................ .................. 26 2 3 Summary of irradiation settings for calibration of DIAMENTOR meter. .............. 27 2 4 Summary of the ten RDSR cases used for the testing of skin dose mapping software. ................................ ................................ ................................ ............. 28 3 1 Results of the skin dose mapping software for a select group of high dose interventional fluoroscopic procedures. ................................ .............................. 40

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7 LIST OF FIGURES Figure page 2 1 The Siemens Medical Solutions Artis Zee angiographic bi plane system. (Photo courtesy of Siemens http://www.medical.siemens.com. Last accessed October, 2012). ................................ ................................ ................................ ... 23 2 2 Calibration set up of KAP meter for the Siemens Artis Zee system. (Photo courtesy of David Borrego). ................................ ................................ ................ 24 3 1 Measurements of KAP for the installed DIAMENTOR meter and reference chamber taken at a tube current of 200 mA and pulse width of 300 ms with 0.1 mm of copper filtration over a period of three months. ................................ 32 3 2 A best fit plane over measured calibration factors for two different beam filtrations over a range of tube currents and voltages. Only the tube voltage and filtration influence the calibration factor. ................................ ...................... 33 3 3 KAP readings corresponding to the DIAMENTOR installed in the Siemens Artis Zee system with no filtration. ................................ ................................ ...... 34 3 4 KAP readings made by the reference chamber at isocenter for the given radiation qualities with no beam fil tration. ................................ ........................... 35 3 5 Calculated calibration coefficients with no tube filtration for the installed DIAMENTOR. ................................ ................................ ................................ ..... 36 3 6 Calibration coef ficients for each tube filtration available to the Siemens Artis Zee system. ................................ ................................ ................................ ........ 37 3 7 Results from the skin dose mapping software before (A) and after (B) applying the calibration coefficients f or the KAP meter for a patient undergoing a selective angiograph of celiac and superior mesenteric artery. .... 38 3 8 A comparison of peak skin doses from the skin dose software against cumulative reference air kerma values obtained directly from the RDSR of the ten select patients. ................................ ................................ ........................ 39

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8 LIST OF ABBREVIATIONS ALRADS Advanced Laboratory for Radiation and Dosimetry Studies CD Cumulative dose DAP Dose area product FDA Fo od and Drug Administration ICRP International Commission on Radiological Protection IEC International Electrotechnical Commission IR Interventional Radiology KAP Kerma area product NCRP National Council on Radiation Protection PSD Peak skin dose VIR Vascul ar Interventional Radiology

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9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science IN CLINIC CALIBRATION OF A KERMA AREA PROD UCT METER AT DIFFERENT RADIATION QUALITIES FOR THE ASSESSMENT OF SKIN DOSES INCURRED DURING INTERVENTIONAL FLUOROSCOPIC PROCEDURES By David Borrego December 2012 Chair: Wesley Bolch Major: Biomedical Engineering The growing use and increasing complexi ty of interventional fluoroscopic procedures has raised public health concerns regarding radiation exposure to both the clinicians and physicians fail to account for the dynamic nature of fluoroscopic procedures and anthropometric differences in patient size. The University of Florida skin dose mapping and organ software overcome these challenges my making use of the Radiation Dose Structured Report and the UF hybrid a dult patient dependent series of computational phantoms; however, it still relies on measurements from the kerma area product meter. The kerma area product meter is only accurate to within 35% to account for uncertainties in determining patient skin dose. In order to address the inherent uncertainty introduced into the skin dose software from the ionization chamber, calibration coefficients were introduced. The calibration coefficients show strong energy dependence and can be predicted with knowledge of th e tube voltage and amount of filtration material in the beam. The skin dose mapping software is able to cull for those

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10 variables, calculate the calibration coefficient, and finally apply the corrections in its calculation of dose. Overall, this study was a ble to show that many of the clinical challenges encountered in dose reconstructions may be overcome to eventually provide physicians with accurate real time skin dose information to better help them manage patient risk.

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11 CHAPTER 1 INTRODUCTION Interventi onal Fluoroscopy Interventional fluoroscopic procedures use ionizing radiation to visualize human anatomy and physiology in real time. These images aid physicians in guiding surgical instruments though blood vessels and other pathways in the body to the si te of interest. This radiologic technique was born from diagnostic angiography and its development was lead by Charles Dotter in the early 1960s. Since then, interventional fluoroscopy has expanded greatly in many different medical field s owing to its adv antages over surgical procedures and improved patient care. Interventional fluoroscopic procedures have reduced the need for more invasive surgical procedures reducing the morbidity and mortality of numerous diseases 1 In contrast to invasive surgical procedures, interventional radiology requires only a small incision to be made for the introduction of instruments into the body greatly reducing the risks of infections, complications, and recovery times. Need for Compr ehensive Dosimetry The growing use and increasing complexity of interventional fluoroscopic procedures, however, has resulted in public health concerns regarding both deterministic risks of skin damage and, particularly for younger patients, stochastic can cer risks to irradiated tissues and radiosensitive organs. Tracking and documenting patient specific skin and internal organ dose has been specifically identified for interventional fluoroscopy where extended irradiation times, multiple projections, and re peat procedures can lead to some of the largest doses encountered in both radiology

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12 and cardiology. Furthermore, in procedure knowledge of localized skin doses can be of significant clinical importance to help physicians better manage patient risk. The ef fective dose per capita within the United States has risen by a factor of six from 1980 to 2006 primarily driven by the increased use of ionizing radiation in diagnostic imaging Fluoroscopically guided procedures have doubled in frequency from 1996 to 200 0, and as the number of procedures per capita has increased so has the ir complexity, with many requiring longer procedure times 2 Such an increase in the use of ionizing radiation has prompted strong recommendations from the scientific, medical, and legislative communit ies to encourage patient specific tracking of medical doses for inclusion in medical records. The state of California has already led the way by passing SB 1237, which requires radiation dose from computed tomo graphy (CT) to be included in patient medical records. The Center for Devices and Radiological Health (CDRH) of specifically ad dressing doses incurred during fluoroscopically guided interventions 3 The effective dose estimated for interventional procedures range s from 10 300 mSv, well above those for radiographic images, CT, and nuclear medicine exam inations. In February 2011, the National Council on Radiation Protection and Measurement (NCRP) released its Report No. 168. This comprehensive document includes 31 recommendations, ten of which relate to patient dose monitoring and documentation 4 The significance of these recommendations highlights one of the primary concerns of the interventional physician the management of radiological risk and specifically the management of radiation induced skin injury.

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13 The effects of radiation damage to the skin can range from transient erythema and epilation to severe dermal atrophy, induration, and ulceration with the latter often requiring surgical intervention 5 Considerable effort s have been de voted toward the prevention of such injuries through intensive training of residents, the development of dose reducing imaging systems and an overall increase in physician awareness. While these efforts have reduced the incidence of injury, any damage that does occur is almost always unanticipated, yet in many cases is avoidable had prior knowledge of peak skin dose and approaching thresholds been available. Due to the current lack of automated skin dose monitoring, this type of information is being denied to the physician who must then r ely on indirect dose metric s along with their clinical experience to manage patient risk 6 Additionally, The Joint Commission has specifically identified prolonged fluoroscopy use with a cumulative peak skin dose s > 15 Gy to a single field as a sentinel event requiring root cause analysis and a comprehensive response 7 A root cause analysis places a huge burden on clinical staff to rec onstruct skin dose when a sentinel event is thought to have occurred. The lack of direct and real time automated skin dose monitoring system in the clinic thus limits both the quality of patient care and the efficiency of the interventional unit for design ing better safeguards. Limitations in IR dosimetry To address public health concerns and those expressed by the scientific community a variety of dose tracking systems have been developed to indirectly or directly quantify the cumulative organ and local skin dose in real time or as a post procedure report The methods include the use of total fluoroscopy time, kerma area product, cumulative air kerma at the reference point, and the use of both point dosimeter or film dosimetry.

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14 Fluoroscopy timers are the simplest and only dose metric employed by most interventional fluoroscopic units for clinical radiation management. Despite being the most commonly used dose metric it is also arguably the most inadequate estimator of dose. The timer works by emitting an audible alert every five minutes of cumulative fluoroscopic time. This metric completely disregards important dose parameters such as radiation quality, fluoroscopic dose rate, image acquisitions and their contributions to anthropometric variation s in patient size 8 The air kerma area product, more commonly known as the dose area product, is defined as the air kerma integrated over the beams area. This metric may be directly measured with the use of an ionization chamber installed in the fluoroscopic unit or through tabulated parameters of irradiation techniques. The cumulative kerma area product (or KAP) is a better indicator of maximum skin dose than total fluoroscopy time; however, the KAP fails to account for field non uniformity effects and the field size 8,9 An extension of the KAP is the cumulative air kerma at the reference point, (K a,r ), which displays the reference air kerma de fined relative to the isocenter of the imaging system, KAP and K a,r fail to account for the dynamic nature of fluoroscopically guided procedures and have allowable uncertaint ies of up to 35% 8 Thermoluminescent dosimeters (TLD), optically stimulated luminescence (OSL) chips, and diodes as point dosimeters can provide a direct measure of dose under proper calibration and when applied prio r to the procedure on the patient s skin. Both TLDs and OSLs fail to provide real time dosimetry but may be used for retrospective

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15 analysis. Diodes can provide real time dose feedback; however, knowledge of correct placement to measure the peak skin dose i s required and is seldom a clinical possibility. Film dosimetry provides the advantage of not having to precisely estimate where the occurrence of the peak skin dose will manifest itself; rather only a general idea of location is needed. Dosimetry with the use of film can provide great spatial knowledge with regards to the dose distribution on the skin; however, most films only have a working range up to 2 Gy. The films working sensitivity leaves much to be desired for the complex interventional f luoroscopic procedures where the dose commonly exceeds the upper detection limits of the film. University of Florida skin dose mapping software In contrast to the previously mentioned dosimetry systems, the University of e for interventional fluoroscopy is unique by taking advantage of two innovations that increase the prospects for accurate automated dose monitoring. First, the software system makes use of the UF hybrid adult patient dependent series of computational phan toms. These models represent the best choice for medical dosimetry because they rely on anthropometric measurements to match the characteristics of individual patients 10 Secondly, the introduction of the Radiation D ose Structured Report (RDSR) allows the software to address directly the dynamic nature of interventional procedures. Anthropometric phantoms. The UF Advanced Laboratory for Radiation and Dosimetry Studies (ALRADS) has developed hybrid phantoms and pioneer ed the methods for patient phantom matching, whereby individuals are computationally matched to a similar hybrid phantom based on anthropometric parameters. For skin dose calculations, the primary factor affecting dose is the calculation of the source to

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16 s lead to different estimations of peak skin dose. By correctly matching a patient to a the accura cy of skin dose estimates is greatly improved 6 Radiation dose structured report. For accurate dose reconstruction a wealth of irradiation parameters are needed. Included in these conditions are exposure parame ters (kVp, mAs, filtration material, filtration thickness, and KAP/K a,r ) and geometry factors (source to skin distance, field size, field position, rotation, angulation, and table location). The challenge presented in fluoroscopy is that the irradiation co nditions are not typically standardized and change often during a given fluoroscopic procedure. There is the principal need for a system that monitors the irradiation conditions and produces an automated report, preferably in real or near real time. In re sponse to this pressing need for standardization, The DICOM Committee published Supplement 94 to the DICOM standard. This update provided a framework for dose reporting by creating the RDSR. The RDSR records all pertinent exposure conditions and geometry factors needed for a dose reconstruction, save field size. Furthermore, the RDSR report stands as an independent DICOM object that is updated at the completion of each irradiation event during a fluoroscopic procedure. The application of phantom patient m atching through the use of patient dependant hybrid phantoms provides one solution for a two part problem. The RDSR provides a framework to overcome the second challenge faced in dose reconstruction algorithms and that is the dynamic nature of intervention al procedures. While the use of hybrid patient dependent phantoms will increase the accuracy of current dosimetry

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17 methods, the development and recent release of the RDSR will make them practical for the clinic. Algorithm. The skin dose mapping software is written in PYTHON, an open source scientific programming language that allows for a robust graphical user interface and 3 Dimensional visualization techniques. The module Pydicom, a DICOM compatible reader for PYTHON, is used to extract geometric informati on and dose parameters found within the RDSR and populates a 2 Dimensonal array structure where each row is filled with the parameters corresponding to a single irradiation event. The information extracted from the RDSR is transformed into peak skin dose w ith the dose mapping algorithm. This algorithm is then able to incorporate a variety of different phantom types to account for individual variations in patient body morphometry. The only requirement is that the phantom be voxelized prior to use. The voxeli zation of the phantom allows for the 3 phantom coordinate system is then aligned with that of the Siemens Artis Zee system installed within the Department of Radiology at Sh ands Jacksonville Medical Center. Assuming a supine orientation with the tube located beneath the table, the posterior skin of the phantom rests at the tube isocenter. The position of the isocenter in relation to the head of the table is predetermined. The the table is then used to locate the phantom longitudinally. The patient is assumed to lie in the middle of the table and a correction can be applied for any lateral displacement. Any shifts in table height, l atitudinal, and longitudinal positions as identified by the RDSR are applied to the phantom. The primary and secondary angles are then used in

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18 correspondence with the source to isocenter distance to determine the xyz location of the source relative to the phantom. Unit vectors are then calculated from the origin, tube location, and in the direction of each xyz skin location. These unit vectors are then separated based on their position either inside or outside the irradiation filed. To differentiate betwee n skin locations on the entrance and exit sides of the phantom, the source to skin distance for each location is determined to be within the beam is compared with the minimum source to skin distance. The program then rejects all unit vectors outside the ir radiation projection and all non entrance side skin locations. The dose is then calculated for each skin affected area according to Equation 1. (1) The backscatter factor, BF, is selected from ICRU Report 74, the ratio of mass en ergy en skin en air is determined from the NIST Physical Reference Data Library, and e represents table attenuation. The peak skin dose is then calculated as the maximum of these doses after the dose from each irradiation event has been summed at each skin location 6 Kerma Area Product Meter As previously indicated, current dosimetry techniques in interventional radiology fail to account for the dynamic nature of these procedures and anthropometric variation in the population. The University of Florida skin dose mapping software addresses both these issues; however, it still relies on measurements from the KAP and K a,r Both the KAP and K a,r are measured with the use of a plane parallel transmission ionization chamber which need only be accurate to 35% 8 The tolerance is allowed to be broad in

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19 order to account for uncertainties in determining patient skin dose and variation in tissue biological response to dose. In order to address the inherent uncertainty introduced into the skin dose software from the ionization chamber calibration coefficient s are introduced. The purpose of this study was to first develop a method for an in clinic calibration of the Siemens Artis Zee kerma area product meter. The calibration coefficient would need to take into account the strong dependence of the kerma area product meter on the energy spectrum of the x ray beam. Furthermore, issues have been raised over fluoroscopic units not reporting the true reading from the kerma area product meter but rather a convoluted reading accounting for tube positioning and irradiation conditions. These proprietary algorithms needed to be investigated before a suc cessful calibration could be achieved. Secondly, based on the meters interdependence of irradiation parameters this study developed an algorithm that would be able to calculate the calibration coefficient for each irradiation event with the use of the RDS R and apply the correction factors to the skin dose mapping software.

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20 CHAPTER 2 MATERIALS AND METHODS Site and Materials The Division of Vascular and Interventional Radiology at Shands Jacksonville was selected for the in clinic calibration of a KAP mete r. This facility is equipped a Siemens Medical Solutions Artis Zee bi plane angiography system, Figure 2 1, which includes software for the generation of RDSR. This facility performs the full range of peripheral vascular interventions, as well as non vascu lar interventional procedures performing approximately 14,000 procedures each year. The Siemens Artis Zee is equipped with the DIAMENTOR M4 KDK DAP/Dose Meter featuring a transmission ion chamber that can measure air kerma air kerma rate, and air kerma area product simultaneously during radiographic and fluoroscopic procedures. Table 2 1 list the specifications of the KAP meter installed. To calibrate the KAP meter in the Siemens Artis Zee a Radcal 10x6 6 chamber, ion chamber digitizer 9660A, and Accu Dose 2186 dosimeter system was used. The ionization chamber was selected for its relative flat energy response over the beam quality range of interest and dose rate sensitivity. A summary of the detectors specifications can be found in Table 2 2. Calibrat ion Set Up The calibration coefficients of the KAP meter were measured with the use of the RADCAL ionization chamber placed at isocenter with the axis of the cylindrical chamber parallel to the axis of rotation for the C arm. The chamber was held free in a ir with the use of a stand and a minimum clearance of 10 cm was provided between the chamber and tabletop. The position of the chamber may be verified by rotating the C arm about the axis of rotation while acquiring images. If the chamber is at isocenter t he image of

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21 the chamber will translate but no rotation should be visible. The system is then set at maximum SID with the radiation field collimated so that un irradiated margins are seen on all sides of the field and C arm at 90 o see Figure 2 2. With no w edges in place an image of the ionization chamber is acquired under set up conditions to determine the radiation field size. Before performing the remaining measurements the detector array was removed and replaced with a lead insert to protect the integri ty of the system form unnecessary radiation. The Siemens Artis Zee system is then set in service mode and the chamber is irradiated under the desired irradiation qualities. Alternatively, if service mode is unavailable loading phantoms may be used to achi eve the desired radiation qualities. The reference value for the kerma area product (KAP ref ) was calculated as a product of the measured air kerma, k a ,r at isocenter of the x ray beam and the field area, A, at isocenter, Equation 2. (2) KAP meter reading. Determination of Calibration Coefficients The KAP meter for the Siemens Artis Zee machine was calibrated for radiation incident on the chamber using x ray tube voltages from 40 120 kVp and at 5 different tube filtrations of 0.1, 0.2, 0.3, 0.6, and 0.9 mm of Cu and also at tube voltages with no filtration. The effects of tube current and pulse width were also observed at high mAs combinati ons to insure that the KAP meter was not being saturated. These measurements were repeated at one month intervals for four months to verify the reproducibility of the Siemens Artis Zee machine. One way ANOVA analysis was

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22 performed on these data to quantify the relationship between the calibration coefficients and how it relates to tube voltage, tube current, or filtration. Implementation of Calibration Coefficients into Skin Dose Mapping Software and Testing Calibration coefficient curves were developed as a function of tube voltage for each filtration and embedded into the skin dose mapping software. The algorithm in the skin dose mapping software was then modified to retrieve tube voltage and filtration information from the RDSR and calculates a calibrati on coefficient for each irradiation event. The calibration coefficient is then applied to correct the calculated skin doses. The changes made to the skin dose mapping software where tested on RDSR from ten patients that were marked with relatively high cu mulative reference air kerma values ( see Table 2 4 ) The RDSR were obtained through an IRB protocol with Shands Jacksonville Hospital from The Division of Vascular and Interventional Radiology. Procedure information along with patient height and weight wer e also obtained under this IRB protocol. The patient height and weight information was used to select patient dependant hybrid phantoms from the UF Adult Hybrid Computational Phantom Series.

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23 Figure 2 1 The Siemens Medical Solutions Artis Zee angiograp hic bi plane system ( Photo courtesy of Siemens http://www.medical.siemens.com Last acc essed October, 2012 )

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24 Figure 2 2. Calibration set up of KAP meter for the Siemens Artis Zee system ( Photo courtesy of David Borrego )

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25 Table 2 1. Properties of the KAP meter installed in the Siemens Artis Zee system. DIAMENTOR M4 KDK Measuring Range D 2] 0.1 999,999 2 /s] 0.1 30,000 Dose [mGy] 0.01 10000 Dose rate [mGy/s] 0.01 999,999 Irradiation time [s] 1s 999min Digital Resolution 2] 0.01 2 /s] 0.01 Dose [mGy] 0.001 Dose rate [mGy/s] 0.001 I rradiation time Ranges of Use DAP rate 0.005 2 /s Tube voltage 50 100 kVp Temperature 10 40 o C

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26 Table 2 2 Radcal chamber 10x6 6 used for the DIAMENTOR meter calibration in the Siem ens Artis Zee fluoroscopic unit. Chamber was last calibrated on 18 Sep 2012. Chamber 10x6 6 Min Rate 20 nGy/s Max Rate 17 R/s 149 mGy/s Min Dose 100 nGy Max Dose 59 kR 516 Gy Calibration Accuracy 4% at 60 kVp and 2.8 mm Al HVL Expo sure Rate Dependence pulses Energy Dependence 5%, 30 keV to 1.33 MeV Construction Polycarbonate walls and electrode conductive graphite interior coating; 6.0 cm 3 active volume

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27 Table 2 3. Summa ry of irradiation settings for calibration of DIAMENTOR meter. Filtration Material Filtration Thickness (mm) Tube Voltage (kVp) Tube Current (mA) Pulse width (ms) Focal spot size None N/A 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 200 300 Small Cu 0.1 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 100, 200, 300, 400, 500, 600 300, 600, 800, 1000 Small, Medium, Large Cu 0.2 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 200 300 Small Cu 0.3 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 100, 200, 300, 40 0, 500, 600 300, 600, 800, 1000 Small, Medium, Large Cu 0.6 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 500 600 Small Cu 0.9 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120 500 600 Small

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28 Table 2 4. Summary of the ten RDSR cases used for the testing o f skin dose mapping software. RDSR Procedure Age Sex Height (cm) Weight (Kg) Patient Dependant Phantom Cumulative K a,r (mGy) 1106 Endovascular stent graft repair of abdominal aortic aneurysm 72 M 177.8 117.9 [180cm/120kg] 8475.86 1193 Superior mesenteric artery stent placement 62 M 170.2 72.6 [170cm/75kg] 8406.56 1124 Bilateral uterine artery embolization 35 F 157.5 70.8 [160cm/70kg] 8191.52 1025 AAA stent graft repair 76 M 175.3 113.4 [175cm/115kg] 7581.00 1141 Cecostom tube replacement 24 M 134.6 59. 0 [135cm/60kg] 6464.27 1325 Abdominal angiography; angioplasty of the superior mesenteric artery; stenting of celiac artery origin and bilateral renal arteries 63 M 175.3 73.5 [175cm/75kg] 6375.54 1166 Selective angiograph of celiac and superior mesenter ic artery 81 M 175.3 89.8 [175cm/90kg] 6300.49 1150 Endovascular stent graft repair of abdominal aortic aneurysm 79 M 182.9 72.6 [180cm/75kg] 5856.81 1313 TIPS placement from right hepatic vein to right portal vein 50 F 165.1 72.6 [165cm/75kg] 5818.54 1 322 Diagnostic arteriography of the lower abdomen/pelvis; embolization of left internal iliac artery and inferior mesenteric artery 19 M 177.8 71.2 [175cm/70kg] 5273.03

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29 CHAPTER 3 RESULTS AND DISCUSSIO N Calibration Coefficients Figure 3 1 shows the re producibility of measurements taken by the reference chamber and KAP meter. Both ionization chambers were exposed to 200 mA for 300 ms pulses with 0.1mm of copper filtration. These measurements were taken over a period of three months during which the KAP meter drifted by no more than 3%. The Radcal chamber measurements were within 2%. The small amount of variation in the measurements is surprisingly low given the uncertainties introduced by set up and determination of radiation field size. These results a re advantageous for the adoption of calibration coefficients by demonstrating that the installed KAP while lacking accuracy is still precise. Measurements covering a wide range of parameters for 0.1 and 0.3 mm of copper where made to help design the calib ration procedure. Figure 3 2 shows how the calibration factor relates to the tube current and tube voltage. The beam filtration and tube current are statistically significant in the determination of the calibration factor while the tube current is not. No effects of saturation of either chamber were seen at high currents and voltages, in fact heat issues with the anode were the limiting factor in achieving higher outputs from the unit. These results indicate that only the tube voltage need be varied at each filtration to understand the behavior of the KAP meter. Figure 3 3 shows the measured KAP values from the installed meter for 0.0 mm of copper filtration. A change in tube current yields a proportionate increase in the KAP value and no signs of saturation are evident at higher outputs. Figure 3 4 is the analogous version for the reference chamber. To calculate the calibration factors for 0.0

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30 mm of copper filtration regression lines were fitted to the data and the quotient of them yielded the calibration fa ctors seen in Figure 3 5. This figure illustrates that calibration factors can be described knowing only the tube voltage and inherent filtration of the incoming beam. This procedure was repeated for all filtrations to derive calibration coefficient curves Figure 3 6, plots the calibration coefficients for all possible filtrations. For beams filtered with 3 mm or less of copper the calibration coefficient is monotonically decreasing. For harder beams, as seen with 0.6 mm and 0.9 mm, the behavior of the cal ibration coefficient is reversed which is consistent with previous studies. 11 13 In either case, the calibration coefficient is always less than unity indicating that the reported KAP an d K a,r are overestimating dose to the patient. Skin Dose Software The skin dose mapping software was updated to include the calibration coefficients. Figure 3 7 (a) has mapped the skin dose on a patient dependant hybrid phantom for a male undergoing a sel ective angiograph of the celiac and superior mesenteric artery. Before applying the correction factors this patient has a higher calculated peak skin dose than the cumulative reference air kerma; however, after taking into account the uncertainty in the KA P meter the peak skin dose drops by about 25%, Table 4 1. Figure 3 7 (b) shows the skin dose map after correcting for the KAP meter. Though rare, two effects contributed to the high peak skin dose. This procedure was static and not much panning was perform ed allowing for the dose to be concentrated on one spot. Secondly, the IEC defines the reference air kerma at a location 15 cm from the isocenter; therefore, if the outer body contour lies beyond this point on the side closest to the tube the ca lculated dose will be higher than the registered reference air kerma. Relying only on the reference air kerma fails to

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31 provide a good peak skin dose estimate or a sp atial distribution of the dose. Both of these shortcomings are addressed in the skin dose m apping software and are further illustrated in Figure 3 8. This figure shows both the corrected and uncorrected peak skin dose plotted against the cumulative reference air kerma provided by the RDSR along with a linear fit that corresponds to a one to one relationship between cumulative reference air kerma and peak skin dose. This figure suggests that there is no correlation between these data.

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32 Figure 3 1. Measurements of KAP for the installed DIAMENTOR meter and reference chamber taken at a tube curren t of 200 mA and pulse width of 300 ms with 0.1 mm of copper filtration over a period of three months

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33 Figure 3 2. A best fit plane over measured calibration factors for two different beam filtrations over a range of tube currents and voltages. Only the tube voltage and filtration influence the calibration factor.

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34 Figure 3 3. KAP readings corresponding to the DIAMENTOR installed in the Siemens Artis Zee system with no filtration.

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35 Figure 3 4. KAP readings made by the reference chamber at isocenter for the given radiation qualities with no beam filtration.

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36 Figure 3 5. Calculated calibration coefficients with no tube filtration for the installed DIAMENTOR.

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37 Figure 3 6. Calibration coefficients for each tube filtration available to the Siemens Artis Zee system.

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38 Figure 3 7. Results from the skin dose mapping software before (A) and after (B) applying the calibration coefficients for the KAP meter for a patient undergoing a selective angiograph of celiac and superior mesenteric artery.

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39 Fig ure 3 8. A comparison of peak skin doses from the skin dose software against cumulative reference air kerma values obtained directly from the RDSR of the ten select patients.

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40 Table 3 1. Results of the skin dose mapping software for a select group of high dose interventional fluoroscopic procedures. RDSR Procedure Sex Patient Dependant Phantom Cumulative k a,r Dose (mGy) Peak Skin Dose w/o Calibration (mGy) Peak Skin Dose w/ Calibration (mGy) 1106 Endovascular stent graft repair of abdominal aortic aneurys m M [180cm/120kg] 8476 5788 4292 1193 Superior mesenteric artery stent placement M [170cm/75kg] 8407 8704 6301 1124 Bilateral uterine artery embolization F [160cm/70kg] 8192 7773 5770 1025 AAA stent graft repair M [175cm/115kg] 7581 10631 7718 1141 Cec ostom tube replacement M [135cm / 60kg] 6464 6700 5072 1325 Abdominal angiography; angioplasty of the superior mesenteric artery; stenting of celiac artery origin and bilateral renal arteries M [175cm/75kg] 6376 5517 4134 1166 Selective angiograph of celi ac and superior mesenteric artery M [175cm/90kg] 6300 6904 5163 1150 Endovascular stent graft repair of abdominal aortic aneurysm M [180cm/75kg] 5857 5457 4087 1313 TIPS placement from right hepatic vein to right portal vein F [165cm/75kg] 5819 14243 103 59 1322 Diagnostic arteriography of the lower abdomen/pelvis; embolization of left internal iliac artery and inferior mesenteric artery M [175cm/70kg] 5273 5300 3971

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41 C HAPTER 4 CONCLUSION AND FUTURE WORK This study shows that it is possible to generate calibration coefficients for the KAP meter through in clinic testing of its performance. The calibration coefficients are dependant only on the tube voltage and amount of filtration. Both of these parameters are contained in the RDSR for each irradiation event. The skin dose mapping software is then able to cull these variables, calculate the calibration coefficient, and finally apply the corrections in its calculation of peak skin dose. This study is a small step in testing the hypothesis that in procedu re mapping of local skin doses, and post procedure documentation of internal organ doses, received by patients undergoing fluoroscopically guided interventions are clinically feasible and can take into account individual variation in patient body morphomet ry and dynamic nature of these procedures. Future work will put the skin dose mapping software through rigorous physical validation of its results and prepare it for clinical trials within the next two years.

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42 LIST OF REFERENCES 1. J.R. Dun can, S. Balter, G.J. Becker, J. Brady, J.A. Brink, D. Bulas, M.B. Chatfield, S. Choi, B.L. Connolly, R.G. Dixon, J.E. Gray, S.T. Kee, D.L. Miller, D.W. Robinson, M.J. Sands, D.A. Schauer, J.R. Steele, M. Street, R.H. Thornton, R.A. Wise, "Optimizing radiat ion use during fluoroscopic procedures: proceedings from a multidisciplinary consensus panel," J. Vasc. Interv. Radiol. 22 425 429 (2011). 2. NCRP, "Ionizing radiation exposure of the population of the United States," National Council on Radiation Protect ion and Measurement, NCRP Report No. 160 (2009). 3. FDA, "Initiative to reduce unnecessary radiation exposure from medical imaging," Center for Devices and Radiological Health, US Food and Drug Administration (2010). 4. NCRP, "Radiation dose management for fluoroscopically guided interventional medical procedures," National Council on Radiation Protection and Measurement, NCRP Report No. 168 (2010). 5. S. Balter, J.W. Hopewell, D.L. Miller, L.K. Wagner, M.J. Zelefsky, "Fluoroscopically guided interventional procedures: a review of radiation effects on patients' skin and hair," Radiology 254 326 341 (2010). 6. P.B. Johnson, D. Borrego, S. Balter, K. Johnson, D. Siragusa, W.E. Bolch, "Skin dose mapping for fluoroscopically guided interventions," Med. Phys. 38 5490 5499 (2011). 7. The Joint Commission, "Sentinel event policies and procedures," (2012). 8. S. Balter, "Methods for measuring fluoroscopic skin dose," Pediatr. Radiol. 36 Suppl 2 136 140 (2006). 9. K. Chida, H. Saito, H. Otani, M. Kohzuki, S. Takaha shi, S. Yamada, K. Shirato, M. Zuguchi, "Relationship between fluoroscopic time, dose area product, body weight, and maximum radiation skin dose in cardiac interventional procedures," AJR Am. J. Roentgenol. 186 774 778 (2006). 10. 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," Med. Phys. 38 1008 1017 (2011). 11. P. Toroi T. Komppa, A. Kosunen, "A tandem calibration method for kerma area product meters," Phys. Med. Biol. 53 4941 4958 (2008). 12. P. Toroi, T. Komppa, "Effects of radiation quality on the calibration of kerma area product meters in x ray beams," Phys. Med. Biol. 53 5207 5221 (2008).

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43 13. P. Toroi, T. Komppa, "The energy dependence of the response of a patient dose calibrator," Phys. Med. Biol. 54 N151 6 (2009).

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44 BIOGRAPHICAL SKETCH David Borrego was born to Adolfo and Martha Borrego in Las Vegas, NV. Shortly thereafter, David and his family moved to Medellin, Colombia where he would spend the next nine years of his life. David would not return back to the United States until the mid the junior high level in Sewickley, PA. From an early age David took an interest in the natural sciences and mathematics. This interest led David to pursue a Bachelor of Sc ience in Nuclear Engineering from the University of Florida Curr ently, David is on track for a doctoral degr ee in medical physics from the Department of Biomedical Engineering at the University of Florida.