VALIDATION OF IN-HOUSE DOSE CALCULATION SOFTWARE FOR SUPERFICIAL X-RAY THERAPY. A Thesis. Presented to the. Faculty of. San Diego State University

Transcription

1 VALIDATION OF IN-HOUSE DOSE CALCULATION SOFTWARE FOR SUPERFICIAL X-RAY THERAPY A Thesis Presented to the Faculty of San Diego State University In Partial Fulfillment of the Requirements for the Degree Master of Science in Medical Physics by Christopher Daniel Johnstone Summer 2013

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3 iii Copyright 2013 by Christopher Daniel Johnstone All Rights Reserved

4 iv DEDICATION For my parents.

5 Research is what I m doing when I don t know what I m doing. Wernher von Braun v

6 vi ABSTRACT OF THE THESIS Validation of In-House Dose Claculation Software for Superficial X-Ray Therapy by Christopher Daniel Johnstone Master of Science in Medical Physics San Diego State University, 2013 To model the kilovoltage (kv) x-ray source of a superficial x-ray unit and to validate a rapid and accurate in-house software (kvdosecalc) tool for computing absorbed radiation dose from superficial x-ray therapy energies. To validate kvdosecalc, we measured central axis percent depth-doses (PDDs) and profiles using an Xstrahl 150 x-ray system (Gulmay Medical Inc.). We also compared the measured and calculated PDDs to those from the British Journal of Radiology Supplement 25 (BJR 25). The Xstrahl source was characterized as a point spectral source with varying spatial fluence, and this source model was used in kvdosecalc to compute absorbed radiation dose at points of interest (POIs). The spectrum was derived by inputting half-value layers (HVLs) and kvps into third party software Spektr and SpekCalc. Doses for the PDDs and profiles were measured using 2, 5, and 15 cm cone sizes at 80, 120, 140, and 150 kvp energies in a scanning water phantom (IBA Blue Phantom 2 ) using Scanditronix Wellhofer farmer-type and compact chambers of volumes 0.65 and 0.13 cc, respectively. The percent difference in the computed PDD doses compared with our measurements range from -4.76% to 4.78% with an overall mean percent difference and standard deviation of 1.52% and 0.74%, respectively. The percent difference between our PDD measurements and those from BJR 25 range from % to 15.7% with an overall mean percent difference and standard deviation of 4.94% and 2.10%, respectively; showing that our measurements agree much better with kvdosecalc than BJR25. The range in percent difference between kvdosecalc and measurement for profiles was -5.89% to 5.92% with an overall mean percent difference and standard deviation of 1.35% and 1.42%, respectively. The results demonstrate that using our source model, kvdosecalc can rapidly and accurately compute absorbed radiation dose for superficial x-ray therapy. The results demonstrate that using our source model, kvdosecalc can rapidly and accurately compute absorbed radiation dose for superficial x-ray therapy. An instruction manual for kvdosecalc is also accompanied.

7 vii TABLE OF CONTENTS PAGE ABSTRACT... vi LIST OF TABLES... ix LIST OF FIGURES...x ACKNOWLEDGEMENTS... xiii CHAPTER 1 INTRODUCTION Introduction to Superficial Radiation Therapy The Need for Clinical Dose Monitoring Introduction to Kvdosecalc Equipment and Techniques for Experimental Measurements BEAM CHARACTERIZATION Source Modeling Half-Value Layer Measurements Phantom Modeling and Dose Computation EXPERIMENTAL MEASUREMENTS Percent Depth Dose British Journal of Radiology Supplement Profiles Absolute Dose RESULTS AND VALIDATION Percent Depth Dose British Journal Of Radiology Supplement Profiles CONCLUSION...36 REFERENCES...38 APPENDIX A PERCENT DEPTH DOSE AND ABSOLUTE DOSE TABLES...41

8 B INSTRUCTION MANUAL FOR KVDOSECALC...49 viii

9 ix LIST OF TABLES PAGE Table 1.1. Added Filtration and Half-Value Layers...5 Table 2.1. Central-Axis Halve-Value Layers Computed with Equation Table 3.1. Absolute Dose Measurements and Calculations for 5 cm Applicator Diameter...24 Table 3.2. Absolute Dose Measurements and Calculations for 2 cm Applicator Diameter...25 Table 3.3. Absolute Dose Measurements and Calculations for 15 cm Applicator Diameter...25 Table A.1. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD...42 Table A.2. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD...43 Table A.3. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD...43 Table A.4. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD...44 Table A.5. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD...44 Table A.6. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD...45 Table A.7. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD...45 Table A.8. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD...46 Table A.9. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD...46 Table A.10. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD...47 Table A.11. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD...47 Table A.12. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD...48

10 x LIST OF FIGURES PAGE Figure 1.1. Xstrahl 150 unit with IBA Blue Phantom Figure 2.1. Relative x-ray output exiting 2 cm applicator in the (a) crossline and (b) inline off-axis directions...10 Figure 2.2. Relative x-ray outputs exiting 5 cm applicator in the (a) crossline and (b) inline off-axis directions...11 Figure 2.3. Relative x-ray outputs exiting 15 cm applicator in the (a) crossline and (b) inline off-axis directions...12 Figure 2.4. In-air central and off-axis halve-value layer setup Figure 2.5. Inline direction toward anode...15 Figure 2.6. Crossline off-axis halve-value layers for 15 cm applicator diameter Figure 2.7. Inline off-axis halve-value layers for 15 cm applicator diameter Figure 2.8. Image of kvdosecalc s virtual water phantom for 15 cm applicator Figure 3.1. Percent depth dose setup Figure 4.1. PDDs at 80 kvp for the 2, 5, and 15 cm diameter applicators Figure 4.2. PDDs at 120 kvp for the 2, 5, and 15 cm diameter applicators Figure 4.3. PDDs at 140 kvp for the 2, 5, and 15 cm diameter applicators Figure 4.4. PDDs at 150 kvp for the 2, 5, and 15 cm diameter applicators Figure 4.5. Transverse dose profile at (a) 80 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators. Note off-axis distances not to scale in the percentage difference plots Figure 4.6. Transverse dose profile at (a) 120 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators Figure 4.7. Transverse dose profile at (a) 140 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators Figure 4.8. Transverse dose profile at (a) 150 kvp with percentage dose differencesfor the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators Figure B.1. Interface for kvdosecalc Figure B.2. Files for kvdosecalc Figure B.3. Homogeneous water phantom code Figure B.4. Hounsfield unit table input....56

11 Figure B.5. Cross section input Figure B.6. Material composition input Figure B.7. Minimum and maximum density input Figure B.8.. Calculation region input...60 Figure B.9. Calculation region of homogeneous water phantom Figure B.10. Phantom folder Figure B.11. MATLAB interface for Spektr Figure B.12. Spektr 2.1 interface Figure B.13. Saving acquired spectrum Figure B.14. Non-uniform spectra calculation in MATLAB Figure B.15. Non-uniform spectra from MATLAB to Excel Figure B.16. SpekCalc interface Figure B.17. Dose calculation point of interest Figure B.18. Editing energy-angle distribution Figure B.19. Inputting spectrum into kvdosecalc Figure B.20. Saving inputted spectrum...68 Figure B.21. Inputting non-uniform spectra Figure B.22. Inputting virtual source parameters Figure B.23. Coordinate system of virtual phantom Figure B.24. Inputting uniform beam fluence Figure B.25. Inputting non-uniform beam fluence Figure B.26. Inputting beam fluence Figure B.27. Highlighting beam fluence...75 Figure B.28. Pasting beam fluence into kvdosecalc. Click the green Proceed button Figure B.29. Saving virtual source Figure B.30. Inputting trajectories Figure B.31. Points of interest setup Figure B.32. Pasting points of interest in Notepad Figure B.33. Copying dose results Figure B.34. Pasting dose information into Excel Figure B.35. Dose information extraction xi

12 xii Figure B.36. Displaying results Figure B.37. Updating directory in Project_SetUp file Figure B.38. Lung phantom CT scan uploaded in kvdosecalc....83

13 xiii ACKNOWLEDGEMENTS I would first like to acknowledge my thesis adviser Dr. Mauro Tambasco. Without the opportunity you gave me to have my internship at the Tom Baker Cancer Centre in Canada, I would have never had the chance to undertake such a wonderful project. Without your patience and guidance throughout all of my questions, I would have not been able to accomplish this thesis. I would like to thank Dave and Marilee Paterson for being the greatest host family imaginable during my two-month stay in Canada, you both helped me feel at home while I started my thesis in a different country, and I will visit you soon! I would like to thank Yannick Poirier and Dr. Alexei Kouznetsov for spending so much time trying to teach me how to use "DoseCalc." I appreciate the time and energy you guys invested in me. I look forward to seeing you again in Montreal this summer for COMP. I would also like to thank Dr. Richard LaFontaine for the countless hours and late nights that you spent helping me with my experimental measurements, and for allowing me to use all of the equipment at the Naval Medical Center San Diego. Without you, I would not have been able to conduct my experiments. I hope the tons of data I collected was interesting for you! I also thank Dr. Theodore St. John for assisting in my measurements and Lt. Larry Burns for always helping to fill the scanning water phantom. I also would like to thank Dr. Usha Sinha and Dr. Carlos Bazan for being on my committee. Lastly, I would like to thank my mother, Angie Johnstone. All throughout my life you have always helped me proofread my work, and I thank you for proofreading my thesis as well. You have always believed in me, have always pushed me to be better, and have always turned my gibberish into something intelligible. You are the best editor I know.

14 1 CHAPTER 1 INTRODUCTION This chapter provides an introduction into superficial radiation therapy treatment and introduces the clinical feasibility of a novel dose computational software tool to rapidly monitor patient dose. 1.1 INTRODUCTION TO SUPERFICIAL RADIATION THERAPY Superficial radiation therapy utilizes kilovoltage (kv) x-rays as a method for the treatment of tumors and various benign and malignant skin lesions on or near the surface of the skin. With a 150 peak kilovoltage (kvp) as compared to standard 6 to 20 megavoltage (MV) linear accelerator (LINAC) treatments, superficial therapy is a low-energy option. The MV tube potential of LINACs create x-rays that penetrate deep into the body for the treatment of deep-seated lesions, whereas superficial kv x-rays have enough energy to transcend only a few centimeters past the skin s surface. In a therapy unit, a cathode filament is heated to produce electrons that are accelerated by microwave technology in a part of the unit called a wave guide. The wave guide allows the accelerated electrons to collide with a tungsten anode. The interactions of the electrons with the tungsten anode result in the production of x-rays, with approximately 1% of interactions resulting in x-rays while the other 99% is dissipated into heat. 1 The released x-rays are emitted isotropically, thus for the x-rays to be useful, they are collimated to be released in a single direction. The x-ray beam emitted takes the shape of the collimated applicator as it leaves the therapy unit toward the patient. Superficial therapy utilizes contact therapy where the base of the applicator (varying from 1 to 20 cm in diameter) is in contact with the patient s skin. The applicators vary in diameter to allow the x-ray beam to contain a circular cross section equivalent to the size of area being treated. The patient lies or sits underneath the beam on a couch as the patient is positioned by fiducial markers used as a point of reference for treatment.

15 2 Superficial kv x-ray therapy is ideal for treating superficial lesions such as basal and squamous cell carcinoma, keloid scars, mycosis fungoides, psoriasis, benign plaques and other dermatological conditions. 1.2 THE NEED FOR CLINICAL DOSE MONITORING The exponential drop-off in energy deposition and the fact that the maximum energy deposition occurs at the surface makes superficial therapy a good method to spare underlying normal tissues. However, high atomic number (Z) body tissue such as bone absorb a much larger amount of radiation at lower energies (E), proportional to through photoelectric absorption. 2 Photoelectric interactions dominate with high Z materials at energies below 250 kvp. 3 In the superficial energy range, one can see the vast increase of bone dose compared to water-like tissue to be a factor of over five times larger (Z for bone and water-like tissue are ~13 and ~7.5, respectively 4 ). Furthermore, a recent study from Qi et al. 5 showed that skin dose from superficial kv therapy treatments to areas close to bone such as the forehead, chest wall, and kneecap can be as much as 7.8% greater than previously thought due to backscatter at the bone interface. For the skin, prescribed superficial therapy doses for an entire treatment can be as high as 45 Gy (4.5 Gy/fraction), 6 45 to 70 Gy, 7 and 40 to 85 Gy, 8 given in daily fractions ranging from 8 to 17 fractions. For unique cases of basal cell carcinomas with lesions less than 3 cm, 9 treatment composed of a single fraction of up to 18 Gy may be given. 10 These Gy/fraction treatments are large enough to cause an acute radiotherapy reaction, especially if the doses given are accidentally larger than prescribed, possibly leading to erythema of the skin characterized by desquamation, oozing, crusting of the lesion, skin de-pigmentation, skin atrophy, telangiecasia, and hair loss. 6 In some cases, tissue dose may unwantedly go beyond their radiation tolerances which can lead to an increased risk of stochastic effects such as secondary cancers and the development of normal tissue complications. 11 Thus, with the high absorbed dose from superficial therapy procedures, there is a need for a clinically feasible method for monitoring patient dose to both the area being treated and the underlying normal tissues. Monitoring patient dose would allow the radiation therapy team to ensure treatment areas are getting the dose that is intended, and that tissues do not go beyond their radiation tolerances, as too much dose may lead to tissue

16 3 complications and an increased risk secondary cancers. To the author s knowledge, there is no commercialized way to both quickly and accurately determine the amount of absorbed dose a patient will receive clinically from a superficial therapy treatment. Monte Carlo simulation is the only accurate method for computing absorbed x-ray dose, but its setup time and computational intense nature makes it impractical for clinical use. 1.3 INTRODUCTION TO KVDOSECALC Kouznetsov and Tambasco 12 have developed a novel dose calculation software (kvdosecalc) that quickly and accurately computes radiation dose to meet the need to clinically monitor patient dose. The software uses a computational algorithm based on using deterministic and stochastic computational methods to solve the Linear Boltzmann Transport Equation. These calculations take into consideration the un-scattered, first-scattered and multi-scattered components of the x-ray beam and calculate dose at a point of interest (POI) within seconds. The percent difference between kvdosecalc and standard Monte Carlo N- Particle Transport Code and EGSnrc is within 1.45%. The absorbed doses can be computed using CT voxel data from a patient s CT scan, or from a virtual phantom is created by using MATLAB and saved as a DICOM (Digital Imaging and Communications in Medicine) format. This study will compare kvdosecalc to experimental measurements for superficial x- ray therapy energies, and the ultimate aim of this and future work will be to incorporate the software into radiation treatment planning to help monitor and/or modify patient treatment plans. In a study by Oudee et al., 13 an in-house dose calculation software was developed for intensity-modulated radiation therapy (IMRT) for six MV photon beams. While Oudee et al. developed software for dose computation validation based on CT-patient data using water and heterogeneous phantom measurements, they did not investigate superficial energies, which is the focus of this study. In a separate study by Thomas et al. 14, a dose calculation software was produced for helical tomotherapy for use as an additional check or replacement for modeling patient radiation absorption. Thomas et al. utilized both programming software MATLAB and DICOM files to write their dose calculations software with fast and accurate voxel

17 4 computations through segmentation methods. Likewise, their study only took into consideration MV LINAC energies for helical tomotherapy and not superficial kv energies. Zhan et al. 15 specifically took into consideration superficial kv energies for their superficial information management and dose calculation system. Zhan et al. developed a web-based method for creating a database for clients to access and store patient data for superficial dose calculations. Unlike kvdosecalc s novel method of computing dose through deterministic and stochastic computations, the dose computation program of Zhan et al. calculates dose by computing the in-air method described in AAPM TG To validate kvdosecalc as a potential software to quickly and accurately monitor patient dose, this study will compare kvdosecalc s dose results to that of experimental percentage depth dose (PDD) and profile dose measurements. To do this, we characterize the x-ray source, which is crucial input for accurately computing absorbed dose using kvdosecalc. This characterization involves measuring the half-value layer (HVL), kvp, and beam fluence for modeling the x-ray source of a superficial x-ray unit. This method of using kvp and HVL as the main techniques to generate spectra has been validated previously for a cone beam CT (CBCT) imaging machine. 16 Additionally, kvdosecalc s PDD results will be compared to PDDs given in the British Journal of Radiology Supplement 25 (BJR 25). 17 PDD and absolute dose tables are included in Appendix A, and Appendix B contains the instruction manual for kvdosecalc. 1.4 EQUIPMENT AND TECHNIQUES FOR EXPERIMENTAL MEASUREMENTS The superficial x-ray therapy unit used in this study is an Xstrahl 150 x-ray system (Gulmay Medical Inc.), and the measurements were performed at the Naval Medical Center San Diego (NMCSD). The Xstrahl is the only kv x-ray therapy machine still in production. The Xstrahl 150 unit at the NMCSD contains output limits consisting of a tube voltage and current range of 10 to 150 kv and 0 to 30 ma, respectively, and a maximum power output of 3 kilowatts. The unit s x-ray tube specifications include a minimum and maximum HVL of 0.2 mm Al and 1.0 mm Cu (13 mm Al equivalent), respectively, 0.8 ±0.1 mm Be internal filtration, focal spot size of 7.5 mm, and a tungsten target (30-degree angle).

18 5 The unit contains a myriad of applicator cones ranging from 1.5 to 15 cm in base diameters. 80, 120, 140, and 150 kvp energies were examined in this study. All four energies were measured with the 2, 5, and 15 cm applicator diameters containing a source to surface distance (SSD) of 15, 15, and 25 cm, respectively. This study utilizes calculated HVLs based on a three-point semi-logarithmic interpolation technique with data from experimental HVL measurements to obtain a more accurate HVL than the nominal values. The added filtrations and HVLs for each examined energy is shown in Table 1.1. Table 1.1. Added Filtration and Half-Value Layers Energy (kvp) Added Filtration Calculated HVL (mm Al) Nominal HVL (mm Al) mm Al mm Cu mm Al mm Cu mm Al mm Cu Al Ion chambers used are the Accredited Dosimetry Calibration Laboratory (ADCL) calibrated Scanditronix Wellhofer FC65-G farmer-type ion chamber (0.65 cc), serial # E001225, for the 5 and 15 cm applicator diameter PDD and HVL measurements, and the Scanditronix Wellhofer CC13 compact chamber (0.13 cc), serial # 10164, for the 2 cm applicator diameter PDD measurements, and for the 2, 5, and 15 cm profile measurements. The electrometer used for all measurements is the DOSE-1 (IBA Dosimetry) electrometer coupled with OmniPro-Accept 7 dosimetry software. The scanning water phantom used for the measurements is the Blue Phantom 2 (IBA Dosimetry). The Xstrahl 150 used at the NMCSD clinically operates at 140 and 150 kvp at 10 mas, delivering approximately 250 cgy per fraction on average for 20 fractions per patient, five days a week. The Xstrahl 150 unit and the IBA Blue Phantom 2 is shown in Figure 1.1. PDD and profile measurements for superficial units have been measured in previous work, but for different superficial therapy units other than the Xstrahl 150. In all of these studies, it was difficult to properly compare PDD, profile, and absolute dose measurements (when applicable), as the therapy units considered have different inherent and external filtration, and operated at different mas and scanning times, which can change the spectrum

19 6 Figure 1.1. Xstrahl 150 unit with IBA Blue Phantom 2. and fluence of a given technique. Additionally, there were few techniques that matched the kvp, HVL, SSD, and applicator sizes of this study, making direct comparisons difficult. In a study by Jurado et al., 17 a Pantak Therapax SXT 150 was used, with their "Filter 4" (80 kvp, 2.27 mm Al HVL) being the only comparable technique used for comparison to the PDDs and absolute dose measurements of this study. The "Filter 4" PDDs for their 2, 5, and 15 cm applicators was comparable to our technique of 80 kvp and 2.06 mm Al HVL for the same applicator diameters and SSDs. The percentage difference between the PPDs computed by kvdosecalc and those measured by Jurado et al. 17 were within 1.98%. Jurado et al. 17 also measured an absolute dose of 291 cgy/min with "Filter 4" and a 3 cm applicator diameter, whereas our same technique at an equivalent applicator diameter yielded 268 cgy/min, a percentage difference of 7.9%. Due to variations in spectra between different superficial machines and the different ionization chambers used at superficial energies, there are difficulties when comparing our results with other studies. 19 This is further shown in a study by Natto 19 showing a percentage difference between superficial machines to be within 8.8% when comparing similar beam qualities and PDDs.

20 7 In the study by Evans et al., 18 the performance of the Gulmay D3300 therapy unit was assessed, including PDDs and profile measurements. No techniques they used were close enough to compare with our study. Profile measurements by Jurado et al,. 17 Evans et al., 18 Natto, 19 and Aukett et al. 20 contained a pattern of results consistent with the expected heel effect and profile shapes as in this study.

21 8 CHAPTER 2 BEAM CHARACTERIZATION This chapter discusses techniques used to create a virtual source in kvdosecalc for dose computation. Also examined, are techniques used to create virtual phantoms in kvdosecalc that model the water phantom used in our experimental measurements. 2.1 SOURCE MODELING To compute x-ray dose accurately, it is necessary to know the spatial fluence and spectral distribution of photons originating from the x-ray source. In this study, we determined these source characterization parameters for the Xstrahl 150 x-ray system (Gulmay Medical Inc.). Following Poirier et al., 22 we modeled the spectral aspect of the source from measurements of HVL and kvp. Spatial variations of the spectra also needed to be characterized because the energy spectrum varies in position due to the heel effect effecting inline direction (along anode-cathode tube direction) and both inherent and added filtration. The heel effect consists of a reduction of x-ray intensity towards the anode, producing a higher absorption of x-rays that pass through a greater thickness of the angled anode target. 23 Measurements were made in the inline and crossline (perpendicular to inline) directions. The 2 cm applicator used in this study was small enough to assume a uniform spectral distribution (spatial distribution of fluence was measured) exiting the base of the applicators without compromising the accuracy of kvdosecalc s computations for all energies. This held true for the 5 cm applicator as well except for the inline direction at 140 and 150 kvp. The 15 cm applicator was too large to make this assumption, thus the varying spectrum exiting the base of the applicator were considered through off-axis HVL measurements. Varying spatial beam intensities exiting the base of all three cones were measured. To model the spectral and spatial fluence of the source, the source is defined by the planar fluence as a function of separation of variables shown in Equation 2.1.,,, (2.1)

22 9 The parameter, represents the beam spectrum where variations are assumed to only be in the transverse (x) direction of the beam. The heel effect s presences is only found along this direction. represent the relative photon distribution taken to vary independently in the transverse (x) and (y) directions, respectively. A photon distribution calibration constant is represented by, relating kvdosecalc s computed dose to experimentally measured relative dose. The spatially-varying fluence represented by can be measured by in-air dose measurements through Equation 2.2,,,. (2.2), represents the in-air Kerma for a beam described by fluence,,. We simplify our source model so the spectrum, only varies with energy, thus allowing the isolation of our one-dimensional fluencies as shown in Equation 2.3,,,,,, (2.3) On account that the integral in Equation 3 only depends on energy, the spectrum, from the fluence,, stays inside the integral, resulting in the fluence being derived conventionally by measureable values only, as shown in Equation 2.4,,,, (2.4) This now allows for the spatially-varying fluence to be simply produced by relative dose and spectrum measurements. Through these measurements, fluence is calculated and input into kvdosecalc to model our x-ray source. The relative x-ray output of the emitted photons were measured in-air along the crossline and inline directions along the base of the 15 cm applicator. Measurements were made every 0.25 cm in the 2 cm applicator and every 0.5 cm in both the 5 and 15 cm applicators. Standard deviations of our beam fluence measurements are represented as error

23 10 bars in these figures, with less than a 2% deviation within 75% of the profile and up to 10% at the applicator edge. These cross-sectional spatial intensities exiting the base of the applicators were used to model the varying beam fluence in kvdosecalc. The results are displayed in Figures Figure 2.1. Relative x-ray output exiting 2 cm applicator in the (a) crossline and (b) inline off-axis directions, normalized along the central-axis at 0 cm. The vertical lines represent experimental uncertainty.

24 Figure 2.2. Relative x-ray outputs exiting 5 cm applicator in the (a) crossline and (b) inline off-axis directions, normalized along the central-axis at 0 cm. The vertical lines represent experimental uncertainty. 11

25 Figure 2.3. Relative x-ray outputs exiting 15 cm applicator in the (a) crossline and (b) inline off-axis directions, normalized along the central-axis at 0 cm. The vertical lines represent experimental uncertainty. 12

26 13 The 2 and 5 cm applicator relative dose measurements were obtained using a Scanditronix Wellhofer CC13 compact chamber (0.13 cc), while the 15 cm applicator fluence was obtained by Xstrahl s commissioning data which utilized a PTW (Model 31010) cc ion chamber and a DOSE-1 (IBA Dosimetry) electrometer for all measurements. Since the spectral and spatial distributions mainly affect dose readings off-axis, these adjustments were only applied for profile measurements and not to the central-axis PDD measurements -- thus for our PDD measurements we approximated the beam as having a single spectrum and spatial intensity over its entire cross-section. Change in spectra was quantified through off-axis HVL measurements in both the crossline and inline directions relative to our x-ray tube as described in Section 2.2. To generate the spectra, we used two types of computational software: Spektr developed by Siewersden, 23 based on the approach by Boone et al., 24 and SpekCalc, developed by Poludniowski. 25 These programs calculate spectra by polynomial interpolation between multiple x-ray output measurements from varying beam qualities. This gives us generated x- ray spectra by inputting kvp, HVL, internal, and external filtration. SpekCalc was utilized for the 80 and 150 kvp beams and Spektr for 120 and 140 kvp beams (our measured HVLs were too low for Spektr to generate spectra at 80 and 150 kvp). We then input the generated spectra and measured spatial fluencies into our dose calculation software kvdosecalc to create our virtual source. 2.2 HALF-VALUE LAYER MEASUREMENTS Central and off-axis HVLs of the Xstrahl unit at the Naval Medical Center San Diego were calculated. The measurements were made using a Scanditronix Wellhofer CC13 cylindrical ion chamber (0.13 cc), serial number 10164, and an ADCL-calibrated Scanditronix Wellhofer FC65 farmer-type ion chamber (0.65 cc), serial number E001225, and a DOSE-1 (IBA Dosimetry) electrometer. Both central and off-axis HVL measurements were acquired using the TG-61 protocol in-air for narrow beam geometries. 22 Figure 2.4 illustrates our setup. To obtain the true HVL from only the primary beam with as little scatter as possible, we placed the chamber at the bottom of the IBA Blue Phantom 2 tank without water, 50 cm from the source. We conducted off-axis HVL measurements inside the empty water tank to utilize IBA s outstanding positioning accuracy (certified ± 0.1 mm

27 14 Figure 2.4. In-air central and off-axis halve-value layer setup. maximum deviation). 26 We measured off-axis every 3 cm out to 18 cm in both the positive and negative directions for both the inline and crossline directions. The inline direction and Heel effect are shown in Figure 2.5. To shield against scatter, we placed approximately a 3 cm slab of lead at the base of the applicator. The slab contained a cutout across its length to allow for both central and off-axis HVL measurements, and held up by metal rods that rested across the top of the water tank. We measured the output of the open beam, then added millimeter thicknesses of aluminum (Al) until we obtained Al thicknesses that were both below and above the actual HVL, and recorded the corresponding outputs and Al thicknesses.

28 15 Figure 2.5. Inline direction toward anode. The inline direction and Heel effect are along the Cathode/Anode direction. The crossline direction is in the same plane and perpendicular to the inline. Note that the relative dose is exaggerated to show the Heel effect. Due to setup limitations, central-axis HVLs were measured at a stationary distance of 50 cm from the source instead of the TG-61 recommended 100 cm. We used a three-point semi-logarithmic interpolation technique 27 using Equation 2.5 for both central and off-axis HVL calculations Equation 2.5 interpolates HVL with doses,, corresponding to an unfiltered beam and a beam filtered by aluminum thickness of T 1 and T 2, respectively. The central-axis HVLs computed with Equation 5 are shown in Table 2.1. (2.5)

29 16 Table 2.1. Central-Axis Halve-Value Layers Computed with Equation 1 Energy (kvp) Thicknesses in mm of Al T 1 T 2 HVL All central-axis HVL measurements are within a ±0.20 mm Al standard deviation determined by three measurements at each depth. Off-axis half-value layer measurements were then taken to test for spectrum uniformity and to model the beam profile for kvdosecalc. The measurements show any off-axis variation in the spectrum. Figure 2.6 and Figure 2.7 illustrate off-axis HVL curves for the 80, 120, 140, and 150 kvp measurements with the 15 cm applicator diameter in the crossline and inline directions, respectively. The Heel effect is shown to be present only in the inline direction at 140 and 150 kvp. This occurs at the larger field size of the 15 cm applicator. It is only slightly present in the 5 cm applicator, and it is non-existent in the 2 cm applicator. Inline off-axis HVL standard deviations for our measurements were as high as approximately 0.40 mm Al near the edges of the applicators and reduced to approximately 0.20 mm Al towards the center of the applicators. Crossline off-axis HVL standard deviations for our measurements were as high as approximately 0.30 mm Al near the edges of the applicators and reduced to approximately 0.20 mm Al toward the center of the applicators. These standard deviations are represented as error bars in Figure 2.6 and Figure PHANTOM MODELING AND DOSE COMPUTATION For our PDD and profile dose calculations in kvdosecalc, we used MATLAB to construct a rectangular homogeneous water phantom of size 19.4 x 41.2 x 32.4 cm, saving the phantom in DICOM format. The material composition of the water and dimensions of the phantom were reproduced in kvdosecalc and consisted of 512 x 512 x 108 voxels (~28.3 x 10 6 total), each of size ~0.081 x 0.81 x 0.30 cm 3. Our virtual water phantom is shown in Figure 2.8. Hounsfield unit (HU) ranges were mapped to the physical density

30 17 Figure 2.6. Crossline off-axis halve-value layers for 15 cm applicator diameter. The vertical lines represent experimental uncertainty. Figure 2.7. Inline off-axis halve-value layers for 15 cm applicator diameter. The vertical lines represent experimental uncertainty.

31 18 Figure 2.8. Image of kvdosecalc s virtual water phantom for 15 cm applicator. Grey region is water, green line begins calculation region. ranges of vacuum and phantom material (water). Vacuum and water were assigned a material composition by inputting the elements and corresponding nuclear densities of each respective material. The macro cross-sections were calculated using the ENDF/B-VI micro cross-section library. 28 The material composition of water was calculated based on its elemental composition of two hydrogen and one oxygen along with its atomic density of ~0.1 x atoms/cm 3. The material composition of the vacuum was approximated to have an atomic density of ~0.0 atoms/cm 3. The phantom for our PDD and profile measurements was also composed of water. Dose computation in kvdosecalc was carried out by the method described by Kouznetsov and Tambasco. 12 Dose is computed at a POI through a dose calculation

32 19 algorithm that considers the primary and scattered components of the superficial x-ray beam through deterministic and stochastic calculations, respectively. The primary beam is composed of the un-scattered portion of the beam. The scattered portion of the beam is divided into single and multiple-scattered particles. The scatter component of dose is computed by Monte Carlo techniques utilizing only photoelectric, coherent, and incoherent Compton scattering interactions. Our dose computation algorithm works for only kv energies because it does not model electron transport (i.e., the charged particle interactions) that occurs at higher MV energies. The dose computations were from a single stationary point source x-ray projection directly above the virtual phantom, along its central axis, at SSDs of 15 cm for the 2 and 5 cm applicators and 25 cm for the15 cm applicator. In this study, circular field sizes were collimated at 2, 5, and 15 cm diameters and 5 10 particles were used to calculate dose. Data collected using 5 10 and particles when compared to 1 10 particles showed a computational accuracy in dose varying by less than 1% and ~3%, respectively. Based on a four Intel Core TM CPU at 3.20 GHz, an average time of 24 s is required to compute dose at a POI. 17

33 20 CHAPTER 3 EXPERIMENTAL MEASUREMENTS This chapter discusses the measurements used for the experimental validation of kvdosecalc. This includes PDD and profile measurements. Our experimental PDD and profile measurements were used as the benchmark for validation. Included are absolute dose measurements and calculations, and PDD calculations from the British Journal of Radiology Supplement 25 (BJR 25). 3.1 PERCENT DEPTH DOSE The PDD measurements along the central axis were taken in the IBA Blue Phantom 2 scanning water phantom (certified ± 0.1mm positioning accuracy) 27 using the same ion chambers and electrometer as our HVL measurements, ADCL-calibrated FC65 farmer-type ion chamber (0.65 cc) for the 5 and 15 cm applicator diameters, the CC13 cylindrical ion chamber (0.13 cc) for the 2 cm applicator diameter, and a DOSE-1 (IBA Dosimetry) electrometer. The ion chambers were centered based on preliminary off-axis beam-intensity readings. The center of the beam was acquired by off-axis dose measurements at a 1 cm depth using OmniPro-Accept 7 software. The chamber was placed in-between the 50% relative dose readings of each side of the profile curve. To simulate actual patient setup, all measurements were taken with the applicators in contact with the water s surface. The PDD measurements were taken from 1 to 10 cm depths in 1 cm increments. We starting recording at a 10 cm depth since it is optimal for limiting unwanted water movement that may skew readings. This was repeated with the 2, 5, and 15 cm applicator diameters at 80, 120, 140, and 150 kvp, with a 10 mas tube current and 0.5 s scan time. The PDDs were taken as the average of three measurements, with an average measurement uncertainty of all measured points to be 0.27%. The setup was taken down and recreated for all measurements with the 5 cm applicator, to acquire a setup uncertainty of 2.09%. When these uncertainties are added in quadrature, it represents a total dose uncertainty of 2.11%. Figure 3.1 illustrates our PDD setup. Due to setup limitations, we were unable to position the chambers for

34 Figure 3.1. Percent depth dose setup. 21

35 22 surface dose readings. To obtain the surface dose, we curve-fitted our PDDs using MATLAB polynomial extrapolation using function polyfit(x,y,n) to extend the PDDs back to the surface. 3.2 BRITISH JOURNAL OF RADIOLOGY SUPPLEMENT 25 The PDDs contained in the BJR 25 are used as a comparison to experimentally measured PDDs of superficial x-ray therapy, and will be used in comparison to PDDs calculated by kvdosecalc. We compared the same techniques (HVL, kvp, SSD, and applicator size) for our experimentally measured PDDs with the approximate HVLs and kvps (±50 kvp ) of the BJR 25 as well. The PDDs contained within the BJR 25 are only approximations, as they were compiled over eight institutions and averaged together using different superficial and orthovoltage machines with the majority of data taken from the British Journal of Radiology Supplement 11 (BJR 11) and the British Journal of Radiology Supplement 17 (BJR 17), 17 which were published in 1972 and 1983, respectively. 3.3 PROFILES Profile measurements were made to validate the accuracy of kvdosecalc for off-axis dose calculations. All profile measurements used the same setup as the PDD measurements, but they were taken at a constant depth of 1cm in the IBA Blue Phantom 2 scanning water phantom. We used the same CC13 cylindrical ion chamber (0.13 cc) as in the PDD measurements. The CC13 was used for all three applicator diameters, as a smaller chamber gives greater accuracy for the high dose gradient regions of profile measurements. The same electrometer DOSE-1 (IBA Dosimetry) and Omnipro-Accept 7 software was also used to collect the data. Measurements were tested at 80, 120, 140, and 150 kvps with the 2, 5, and 15 cm applicator diameters. For the 2, 5, and 15 cm applicator diameters, measurements were taken from -3 to +3, -5 to +5, and -12 to +12 cm, respectively, in both the crossline and inline directions with the inline in the direction of the heel effect. Measurements were taken every 0.5 cm in the relatively flat central regions of the profiles and every 0.1 cm in the high dose gradient regions near the ends of the applicator. Measurements were normalized to the central-axis beam output for all profiles. The profiles were taken as the average of three measurements, with an average measurement uncertainty of all measured points to be 0.32%.

36 23 The setup was taken down and recreated for all measurements with the 5 cm applicator, to acquire a setup uncertainty of 2.15%. When these uncertainties are added in quadrature, it represents a total dose uncertainty of 2.17%. 3.4 ABSOLUTE DOSE Absolute dose measurements were acquired based on the TG-61 protocol for the x- ray beam dosimetry of kv radiotherapy units. 22 The absolute dose (cgy) was measured for the Xstrahl unit. The same FC65 farmer-style ion chamber (0.65 cc) was used for the 5 cm applicator diameter as well as the same DOSE-1 (IBA Dosimetry) electrometer. The chamber was placed 0.43 cm from the base of the cone, then inverse square corrected to get the absolute dose at the surface to obtain maximum dose at d max = 0 cm. The chamber was set up in-air inside the empty IBA Blue Phantom 2 water tank to utilize IBA s outstanding positioning accuracy (certified ± 0.1 mm maximum deviation). 26 Table 3.1 contains the acquired and calculated correction factors, absorption coefficients, electrometer readings, and final dose rate (cgy/min) for the 5 cm diameter applicator at 80, 120, 140, and 150 kvp. Since the effective area of the ion chambers is recommended at its center for superficial energies, 22 and the top of the ion chamber was touching the bottom of the cone applicator, we applied an inverse square correction to get the average electrometer reading at the bottom of the cone, correcting the cm SSD to 15 cm SSD. Our setup was the same as our PDD measurements, except in-air with the chamber stationary at the base of the applicator. The electrometer readings were taken as the average of three measurements, with an average measurement uncertainty of all measured points to be 0.43%. The setup was taken down and recreated for all measurements with the 5 cm applicator, to acquire a setup uncertainty of 2.29%. When these uncertainties are added in quadrature, it represents a total dose uncertainty of 2.33%. The absolute dose to water was calculated from TG-61, displayed in Equation 3.1,,, (3.1) where M is the free in-air electrometer reading corrected for recombination, polarity, temperature and pressure, and electrometer correction factors. is the air-kerma calibration factor for the given beam quality, is the backscatter factor (BSF),, is the chamber

37 24 Table 3.1. Absolute Dose Measurements and Calculations for 5 cm Applicator Diameter Electrometer Energy (kvp) Recombination Correction Polarity Correction BSF N k (10-9Gy/C) Reading Avg.(10 C -9 ) µ Output (cgy/min) Corrected Output (cgy/min) stem correction factor accounting for the change in photon scatter from the chamber stem between the calibration measurement, and is the ratio for water-to-air of the mean mass energy-absorption coefficients averaged over the incident photon spectrum. 16 The center of the sensitive air cavity of the ionization chamber was placed at the reference depth of 2.0 mm (as close to the applicator surface as possible). The depth of 2.0 mm was inversesquare corrected to get the surface dose at 0 cm. The electrometer reading was corrected for temperature, pressure, ion recombination, and the polarity effect. The temperature recorded at the day of the measurement was 19.2 degrees Celsius with a 0.50 min scan time, and the pressure was 757 mmhg, giving a temperature and pressure correction (TPC) factor of For the 2 and 15 cm applicator diameters, the CC13 cylindrical ion chamber (0.13 cc) and FG65 farmer-type ion chamber (0.65cc) were used, respectively. The corrected output of the 2 and 15 cm applicator diameters were obtained by Equation 3.2,,, (3.2) where CO 2,15, BSF 2,15, and O 2,15 are the corrected outputs, backscatter factors, and outputs of the 2 and 15 cm diameter applicators, respectively. Likewise, CO 5, BSF 5, and O 5 are the corrected output, backscatter factor, and output of the 5 cm diameter applicators, respectively. Absolute dose for the 2 and 15 cm applicators are derived from the 5 cm applicator and corrected for field size by Equation 2.3, by the ratio of the 2 and 15 cm applicator s BSFs and outputs to the 5 cm applicator s BSF and output. The dose rates resulting from the application of Equation 2.3 for the 2 cm applicator diameter are 80.86, , 79.30, and cgy/min for the 80, 120, 140, and 150 kvps, respectively. For the

38 25 15 cm diameter applicator, the resulting dose rates were , , , and cgy/min for the 80, 120, 140, and 150 kvps, respectively. The average electrometer readings are inverse square corrected from cm SSD to 15.0 cm SSD. Since these are the maximum dose rates, the tables in Appendix A map these dose rates to each respective PDD to give the dose rates at each depth along the central axis. Table 3.2 and Table 3.3 contain the 2 and 15 cm absolute dose measurements and calculations. Table 3.2. Absolute Dose Measurements and Calculations for 2 cm Applicator Diameter Energy (kvp) BSF N k (10-9Gy/C) Electrometer Reading Avg. (10-9 C) µ Output (cgy/min) Corrected Output (cgy/min) Table 3.3. Absolute Dose Measurements and Calculations for 15 cm Applicator Diameter Energy (kvp) BSF N k (10-9Gy/C) Electrometer Reading Avg. (10-9 C) µ Output (cgy/min) Corrected Output (cgy/min)

39 26 CHAPTER 4 RESULTS AND VALIDATION This chapter displays the results of the experimental measurements and the dose computations of kvdosecalc for validation. This includes PDDs, BJR 25, and profile results in comparison to kvdosecalc. 4.1 PERCENT DEPTH DOSE The relative percent depth dose data generated from kvdosecalc coincided with our scanning water phantom measurements within a percent difference range of -4.76% to 4.78%, and with an overall mean percent difference and standard deviation of 1.52% and 0.74%, respectively (Figure 4.1-Figure 4.4). These results show good agreement between measurement and kvdosecalc. 4.2 BRITISH JOURNAL OF RADIOLOGY SUPPLEMENT 25 The percent difference between our gold standard PDDs of experimental measurement and those from BJR 25 range from -6.64% to 14.77% with an overall mean percent difference and standard deviation of 3.36% and 2.23%, respectively, showing that kvdosecalc agrees twice as better to measurement than the BJR 25. The authors suspect the reasoning to be because the PDD data from the BJR 25 was compiled and averaged over eight separate institutions, using only approximate HVL and kvp (±50 kvp) with much of the data reused from the BJR 11 (1972) and BJR 17 (1983). Furthermore, the compiled data provided by BJR 25 is not machine specific (composed of varying internal and external filtrations, HVL and kvp, which can change the spectrum of the beam), whereas the results we attained with kvdosecalc were generated from modeling the x-ray source of the specific machine used to make our measurements. BJR 25 s (1996) re-measurement comparisons were stated as being off by as much as 20% with its best agreement being within 10%. 16 It s also stated that, The depth dose data given in the present tables are average values for the reference HVLs and the need for direct measurement must again be stressed if higher

40 Figure 4.1. PDDs at 80 kvp for the 2, 5, and 15 cm diameter applicators. 27

41 Figure 4.2. PDDs at 120 kvp for the 2, 5, and 15 cm diameter applicators. 28

42 Figure 4.3. PDDs at 140 kvp for the 2, 5, and 15 cm diameter applicators. 29

43 Figure 4.4. PDDs at 150 kvp for the 2, 5, and 15 cm diameter applicators. 30

44 31 accuracy is needed. 16 Therefore, kvdosecalc yields a higher PDD accuracy than the BJR 25. Our PDDs, PDDs of the BJR 25, kvdosecalc, and corresponding dose in cgy/min are shown Appendix A. 4.3 PROFILES The transverse profile data generated by kvdosecalc compared to the measurements has a percent difference ranging from -5.89% to 5.92% with an overall mean percent difference and standard deviation of 1.35% and 1.42%, respectively, except for regions outside of the applicators in the high dose gradient regions. The authors believe that this is due to the fact that these regions lie in very high dose gradient regions where the 0.13 cc ion chamber is too large to accurately measure the rapidly changing profile dose due to volume averaging effects. Since the chamber has a relatively large region, the chamber effectively averages measured charge over its entire measurement volume, which will not correctly represent the actual dose that is being delivered at its center, and this volume averaging effect can profoundly affect the profiles. 29 Hence, dose readings in these regions could not be accurately compared to our gold standard of experimental measurements. We did not have available a smaller chamber calibrated for superficial energies, thus a smaller chamber could not be used for a higher degree of accuracy. Furthermore, at the very ends of the profiles in the low dose gradient regions at less than 10% relative dose, our error was within experimental measurement. The maximum difference in dose in these areas are within 4.7 cgy/min (based on our absolute dose measurements coupled to our transverse profile measurements). This difference may be due to the fact that the signal to noise ratio at such low energies makes precise measurements extremely difficult. Also, the combined HVL and spatial fluencies modeled at the edges of the applicators yielded relatively high deviations (+/-0.4 mm Al HVL combined with a 10% beam intensity deviation). Together, these differences can affect dose by up to 7 cgy/min in these regions of 10% relative dose and lower. This makes it extremely difficult to accurately measure dose in regions outside of the applicators without a chamber calibrated for superficial energies. Nonetheless, our results show good agreement and validation of off-axis dose calculations for kvdosecalc, displayed in Figure

45 Figure 4.5. Transverse dose profile at (a) 80 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators. Note off-axis distances not to scale in the percentage difference plots. 32

46 Figure 4.6. Transverse dose profile at (a) 120 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators. Note off-axis distances not to scale in the percentage difference plots. 33

47 Figure 4.7. Transverse dose profile at (a) 140 kvp with percentage dose differences for the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators. Note off-axis distances not to scale in the percentage difference plots. 34

48 Figure 4.8. Transverse dose profile at (a) 150 kvp with percentage dose differencesfor the (b) 2 cm, (c) 5 cm, and (d) 15 cm applicators. Note off-axis distances not to scale in the percentage difference plots. 35

49 36 CHAPTER 5 CONCLUSION Superficial radiation therapy is a low-energy option for the treatment of various skin lesions and dermatological conditions. The low penetrability of x-rays from this mode of treatment is ideal for depositing the majority of radiation at the surface of the skin with relatively less radiation penetrating the underlying normal tissues. Since photoelectric interactions are greatly increased in bone at these low superficial energies, as well as high doses per fraction administered at the skin's surface, great care must be taken into monitoring patient dose during treatments to avoid accidental overdose to normal tissues. Monte Carlo simulation is the only high accuracy method in simulating patient dose for kv energies, but it is computationally intense, which makes it impractical for routine clinical use. Examined in this study is the in-house computation software kvdosecalc, which meets this need for clinically monitoring patient dose by calculating dose at POIs within seconds. It may be utilized to plan, verify, and monitor dose to the patient, and thereby ensure target coverage while avoiding excessive dose in unwanted regions. This study has demonstrated that kvdosecalc can rapidly and accurately compute radiation dose for superficial x-ray therapy. Our validation on dose accuracy was shown through our relative central-axis PDD measurements in water for three different applicator diameters (2, 5, and 15 cm) at four different energies (80, 120, 140, and 150 kvp). We have shown that the central-axis PDD agreement between kvdosecalc and measurement is within a percent difference and standard deviation of 1.52% and 0.74%, respectively, with a percent difference range of -4.76% to 4.78%. Compared to the central-axis PDDs measured in BJR 25, measured PDDs had a percent difference and standard deviation of 3.63% to 2.23%, respectively, with a percent difference range of -6.64% to 14.77%. This shows that kvdosecalc is twice as accurate to experimental measurement than the BJR 25. Absolute dose measurement were also taken and shown to be in good agreement to previously published data. 17 Transverse profile measurements in water compared to kvdosecalc resulted in a percent difference and standard deviation of 1.35% and 1.42%, respectively, with percent

50 37 difference range of -5.89% to +5.92% within the applicator. The authors believe that the percent differences near and outside of the applicator edges are due to the chamber volume averaging effect in these very high dose gradient regions. 30 Due to the unavailability of a smaller chamber calibrated for superficial energies, comparisons to measurement in these regions could not be done. This makes accurate dose measurements in high dose gradient regions extremely difficult. 30 Collectively, these results show a validation of kvdosecalc s dose computation accuracy and bring us closer to our goal of creating an accurate patient-specific dose computation system for superficial x-ray therapy procedures. Future work will focus on further experimental validation using anthropomorphic and heterogeneous phantoms.

51 38 REFERENCES 1 J. E. Turner, Atoms, Radiation, and Radiation Protection, 3rd ed. (Wiley-Vch, Germany, 2007). 2 J. T. Bushburg, J. A. Seibert, E. M. Leidholdt Jr. and J. M. Boone, The Essential Physics of Medical Imaging, 2nd ed. (Lippincott Williams & Wilkins, Philadelphia, 2002). 3 M. F. Khan, The Physics of Radiation Therapy, 4th ed. (Lippincott Williams & Wilkins, Philadelphia, 2010). 4 L. Rock, et al., "Tissue inhomogeneity corrections for megavoltage photon beams," Report of Tast Group No. 65 of the Radiation Therapy Committee of the AAPM, Madison, WI, Z. Qi, et al., "In vivo verification of superficial dose for head and neck treatments using intensity-modulated techniques," Med. Phys. 36 (1), (2009). 6 V. Wolstenholme and J. P. Glees, "The role of Kilovoltage x-rays in the treatment of skin cancers," European Oncology Disease 1 (1), (2006). 7 M. Caccialanza, R. Piccinno, L. Kolesnikova, and L. Gnecchi, "Radiotherapy of skin carcinomas of the pinna: a study of 115 lesions in 108 patientsle," Int. J. Dermatol. 44 (6), (2005). 8 M. Caccialanza, R. Piccinno, D. Moretti, and M. Rozza, "Radiotherapy of carcinomas of the skin overlying the cartilage of the nose: results in 405 lesions," Eur. J. Dermatol. 13 (5), (2003). 9 S. Chan, A. Dhadda, and R. Swindell, "Single fraction radiotherapy for small superficial carcinoma of the skin," Clin. Oncol. (R. Coll. Radiol.) 19 (4), (2007). 10 M. Poulsen, "Merkel-cell carcinoma of the skin," Lancet. Oncol. 5 (10), (2004). 11 C. Land, "Estimating cancer risks from low doses of ionizing radiation," Science 209, (1980). 12 A. Kouznetsov and M. Tambasco, "A hybrid approach for rapid, accurate, and direct kilovoltage radiation dose calculations in CT voxel space," Med. Phys. 38 (3), (2011). 13 N. Oudee, S. Suriyapee, P. Tangboonduangjit, and S. Srisatit, "Development of in-house software to calculate dose for intensity-modulated radiation therapy based on lung CT-patient data," Asian Biomedicine 5 (5), (2011). 14 S. J. Thomas, K. R. Eyre, G. S. J. Tudor, and J. Fairfoul, "Dose calculation software for helical tomotherapy, utilizing patient CT data to calculate an independent threedimensional dose cube," Med. Phys. 39 (1), (2012). 15 L. Zhan, A. Fleck, R. Jiang, and Osei, "E. SU-E-T-729: A superficial information management and calculation system," Med. Phys. 38 (6), 3658 (2011).

52 39 16 Joint Working Party of the British Institue of Radiology and the Hospital Physicists' Association, in Central Axis Depth Dose Data for Use in Radiotherapy: 1996, 25 (British Institute of Radiology, London, 1996). 17 D. Jurado et al,. "Pantak Therapax SXT 150: performance assessment and dose determination using IAEA TRS-398 protocol," Br. J. Radiol. 78 (932), (2005). 18 P. A. Evans, A. J. Moloney, and P. J. Mountford, "Performance assessment of the Gulmay D3300 kilovoltage X-ray therapy unit," Br. J. Radiol. 74 (882), (2001). 19 S. S. A. Natto, "Performance characteristics of the Pantak Therapax-150 superficial x-ray treatment machine: measurements and calculations," Australasian Physics & Engineering Sciences in Medicine 25 (4), (2002). 20 R. J. Aukett, D. W. Thomas, A. W. Seaby, and J. T. Gittins, "Performance characteristics of the Pantak DXT-300 kilovoltage x-ray treatment machinee," Br. J. Radiol. 69 (824), (1996). 21 K. K. Fung and W. B. Gilboy, Anode heel effect on patient dose in lumbar spine radiography," Br. J. Radiol. 73 (869), (2000). 22 Y. Poirier, A. Kouznetsov, and M. Tambasco, "A simplified approach to characterizing a kilovoltage source spectrum for accurate dose computation," Med. Phys. 39 (6), (2012). 23 J. H. Siewerdsen, A. M. Waese, D. J. Moseley, S. Richard, and D. A. Jaffray, "Spektr: a computational tool for x-ray spectral analysis and imaging system optimization," Med. Phys. 31 (11), (2004). 24 J. M. Boone and J. A. Seibert, "An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kv," Med. Phys. 24 (11), (1997). 25 G. Poludniowski, F. Deblois, G. Landry, P. Evans, and F. Verhaegen, "F. SU-FF-I-60: SpekCalc: A free and user-friendly software program for calculating x-ray tube spectra," Med. Phys. 36 (6), 2472 (2009). 26 I. J. Das, et al., "Accelerator beam data commissioning equipment and procedures: Report of the TG-106 of the Therapy Physics Committee of the AAPM," Med. Phys. 35 (9), (2008). 27 A. L. Hill, "Short communication half value layer measurements to facilitate patient dose assessment for newer CT scanners using published normalized dose data," Br. J. Radiol. 72, (1999). 28 Members of the Cross Sections Evaluation Working Group, BNL , ENDF-6 Formats Manual, Data Formats and Procedures for the Evaluated Nuclear Data File, ENDF/B-VI and ENDF/B-VII (Brookhaven National Laboratory, Upton, NY, 2009). 29 D. A. Low, P. Parikh, J. F. Dempsey, S.Wahab, and S. Huq, "Ionization chamber volume averaging effects in dynamic intensity modulated radiation therapy beams," Med. Phys. 30 (7), (2003).

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54 41 APPENDIX A PERCENT DEPTH DOSE AND ABSOLUTE DOSE TABLES

55 The following tables give in-water central-axis percent depth doses (PDDs) of kvdosecalc s computations, our measurements, and those of the British Journal of Radiology Supplement 25 (BJR 25). Also included in the tables are corresponding absolute doses (cgy/min) for each respective PDD. The data in consideration in Table A.1-A.12 correlate to the PDD figures of section 4.1. Also, absolute dose was measured and calculated based on the methods described in section 3.5 of this study. Absolute dose was found for the 100% PDD for each respective technique (kvp, HVL, field size, and SSD), then mapped to each subsequent PDD of that technique and displayed in the following tables. Table A.1. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD 42 Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

56 Table A.2. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD 43 Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min) Table A.3. PDD and Absorbed Dose for 80 kvp, 2.06 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

57 Table A.4. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD 44 Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min) Table A.5. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

58 45 Table A.6. PDD and Absorbed Dose for 120 kvp, 4.18 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min) Table A.7. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

59 46 Table A.8. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min) Table A.9. PDD and Absorbed Dose for 140 kvp, 7.14 mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

60 47 Table A.10. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 2 cm Diameter Applicator at 15 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min) Table A.11. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 5 cm Diameter Applicator at 15 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

61 48 Table A.12. PDD and Absorbed Dose for 150 kvp, mm Al HVL, and 15 cm Diameter Applicator at 25 cm SSD Depth (cm) kvdosecalc Absolute Dose (cgy/min) Measurements Absolute Dose (cgy/min) BJR25 Absolute Dose (cgy/min)

62 49 APPENDIX B INSTRUCTION MANUAL FOR KVDOSECALC

63 50 The interface for dose calculation software kvdosecalc is illustrated in Figure B.1. The following is an instruction manual for the dose computational software kvdosecalc. This manual is the creation of Christopher Johnstone of San Diego State University, created for kvdosecalc as of version 7.1.1, which explains the usage of the dose computation software created by Dr. Alexei Kouznetsov of the Tom Baker Cancer Centre, Alberta, Canada. This manual is written in practical terms as to be of maximum use to those carrying out computations in kvdosecalc. This manual does not attempt to cover the software s wide diversity and usage in its entirety, as I did not create the program. The main goal would be to provide a reasonably detailed guide that could be expanded or modified to suit conditions of the user. The sections and steps of this manual are in the exact order the user must follow in using the software to avoid potentially frequent software errors. To obtain the software and its required files, or for any other inquiries, please contact Dr. Mauro Tambasco. 1 B.1 FILES FOR KVDOSECALC Dose computational software kvdosecalc utilizes x-ray beam spectra and field techniques to rapidly output dose. Once the required files are obtained, the user will open the folder kvdosecalc Files which contains all the necessary files the user will need, including the software itself. Figure B.2 displays all files inside the folder kvdosecalc Files which will be used throughout this manual To open latest version of kvdosecalc on a 64-bit Windows operating system, open folder DosesCalc 7_1_1 from June , then open DICOM_Viewer. To open kvdosecalc on a 32-bit Windows operating system, open folder DoseCalc 6_8_4 1 CPU+unsc bug fixed 32 Bit Compilation, then double click the file DICOM_Viewer.exe. In the Phantoms folder is where the user will keep any kvdosecalc phantom projects. 1 Mauro Tambasco, PhD., MCCPM. Assistant Professor/Medical Physicist, Associate Director, Department of Physics, San Diego State University. MTambasco@mail.sdsu.edu.

64 Figure B.1. Interface for kvdosecalc. 51

65 52 Figure B.2. Files for kvdosecalc. B.2 EDITING VIRTUAL PHANTOM The first step in kvdosecalc is to open one of the following three virtual phantoms, or use your own CT scan as described at the end of Section B.2. If creating your own virtual phantom, the pre-made phantoms to use and edit are located inside your Phantoms folder. Square homogeneous water phantom in a vacuum named "Phantom Hobo." Circular water phantom in air named "Phantom Archie." Square heterogeneous phantom in air composed of water, bone, and lung named "Phantom Bob." These phantoms may be used as is or used as a template to modify and create the user's own phantoms to fit his/her specific projects. If the user would like to use the phantoms as is, skip to Section B.3. If the user would like to edit these phantoms, knowledge of the programming software MATLAB is required, and the following m-files located in the spectramod folder must be opened in MATLAB. For square homogeneous water phantom "Phantom Hobo", open m-file waterdicomwriter.m. For circular homogeneous "Phantom Archie," open m-file

66 53 roundhomodicomwriter.m. For square heterogeneous "Phantom Bob," open m-file heterodicomwriter.m. How kvdosecalc creates the material composition of the three virtual phantoms is by taking an existing CT scan and changes the values in the pixels of the scan into Hounsfield Units (HU) to match the material composition in the phantom that the user wants. This creates a predetermined voxel size, slice thickness, and pixel-to-hu algorithm that the user will use to change the material composition of the virtual phantom. It loads up every image/slice, from 0 to 108 (for example), creates a matrix Z (i,j) which contains the pixel values of every slice, then changes the pixel values of every Z (i,j) value into HU units. Figure B.3 shows the file waterdicomwriter.m open in MATLAB as an example (refer to the corresponding virtual phantom coordinate system at the end of step 6 in Section B.7). Edit this code to modify the square homogeneous water phantom. To change the HUs go to the for loop starting in line 12. The loop i=1:m and j=1:n are the x and y coordinates of the virtual phantom. This is where the user can change the parameters of the virtual phantom by adding and removing information as needed. For example, lines 14 and 15 set every pixel position equal to and above y=256 to 1024 (Z (i,j) ), and line 17 sets every pixel position below y=256 to 24 (Z (i,j) ). Equation B.1 converts pixels into HUs, (B.1) where HU is the Hounsfield Unit, Z (i,j) is the pixel value, and 1024 is a constant. To simulate water, we need a HU of 0, thus Z (i,j) =1024. Likewise, to simulate air, we need a HU of -1000, thus Z (i,j) =24. If the material composition of the phantom needs to be changed, look up its respective HU, solve for Z (i,j) and input Z (i,j) s pixel value into line 15. If the user would like to add additional slabs to create a heterogeneous phantom, add elseif statements in the same for loop and insert the appropriate Z (i,j) for each material, as shown in the heterogeneous phantom file heterodicomwriter.m. For the circular phantom roundhomodicomwriter.m, the exact same steps apply, except the size of the circular phantom changes by the size of the radius. For instance, instead of the if i<(256) in the square phantom, it is if r<(188) in the circular phantom.

67 54 Figure B.3. Homogeneous water phantom code. The user also has the ability to change the slices of the virtual phantom in the z direction. The user must change the for loop on line 6 from k=0:107 to k=54, for example. It is very important to note that the user must change line 2 to match the path name exactly to the file location where the virtual phantom is located on the user s computer. This includes not removing \CT after the path name. If this is not done, the phantom will not work properly. The user must also include ' before and after the file name for kvdosecalc to compile the code. Equation B.2 and Equation B.3 convert actual cm positions into pixels of the x and y coordinates in the virtual phantom,., (B.2)

68 ,., 55 (B.3) where Z (i,j) is the pixel value equivalent to 0 cm in your phantom, l is the length in cm, d is the depth in cm, and is the factor that changes cm into pixels in kvdosecalc s x-y coordinate system, which changes based on your specific CT data (this number can be found in kvdosecalc inside the Frame tab, and under the Value column to the right where it says Pixel Spacing ). This is a phantom-specific factor for the amount of cm per pixel based on the phantom voxel size. The user also has the option to upload CT scans to use as a phantom. To open a CT scan, the steps in Section B.3 should be followed. The process in using a CT scan is the same to the steps in using a virtual phantom as discussed in this manual. The HUs of your CT scan will automatically be read by kvdosecalc to create the material compositions of your phantom. B.3 OPENING PROGRAM AND PHANTOM SETUP After the user has a virtual phantom to use, it must now be opened in kvdosecalc Open kvdosecalc folder (refer to Section B.1). Click on DosesCalc 7_1_1 from June (for only a 64-bit computer), or click on DoseCalc 6_8_4 1 CPU + bug fixed 32 Bit Compilation (for a 32-bit computer). Click DICOM_Viewer to open kvdosecalc. Once kvdosecalc is open, click on the DICOM tab in the upper left corner. This is where the user opens his/her phantom setup file. 5. In the DICOM tab, locate the phantom folder of interest, such as "Phantom Hobo," and click OK. Bypass the remainder of this section (except for step 19) if using one of the virtual phantoms without editing its setup, as these pre-made phantoms already have their setups completed. Continue with this section if the user would like to make changes to the virtual phantom s setup. To start with a unedited phantom setup, go into the Phantoms folder and click on the specific phantom to be used. Once opened, create a new folder called Backup. This will be where the user will save backup files of the phantom. While still inside the phantom folder, scroll down to the end of the files and delete the file labeled Project_Setup.ser. Not having the setup file will allow the user to edit the phantom s setup

69 56 from scratch, which is what we are about to go over. You may also open a CT scan to use as a phantom by opening the folder containing the CT files. The next step in kvdosecalc is to setup the virtual phantom. The following steps must be completed in the exact order, or the user may run into program errors With the virtual phantom open in kvdosecalc, click the HU Table tab to input HUs. Open the HU Density Table tab in kvdosecalc. The left box contains the HUs of your choice to input, and the right colomn corresponds to mapping those HUs to a specific density of the materials in your phantom (these density numbers will be used in step 12 of this section). After inputting the HUs and corresponding densities, press Fill The Grid and hit OK. It should look like Figure B.4. Note that it is extremely important to save the phantom setup every time changes are made. This will save the hardships of losing any previously inputted data. To save the virtual phantom, exit the program by pressing the Exit button on the top right of the main screen. The prompt Update Current Project will pop up, click "Yes." Reopen the program and continue. Figure B.4. Hounsfield unit table input. Click on the Materials tab to the left of the red Exit button. In this tab the user will reach one of the quirks of the program, where the user must click on any boxes in the Cross Sections Types followed by pressing the Draw button. This is illustrated in Figure B.5.

70 57 9. Figure B.5. Cross section input. Click Material Composition Cross Sections Library tab to input Materials. 10. For example, if a solid water phantom is to be made, type Water in the Materials Composition area. Now enter the molecules of the material, such as 1-H and 8-O for water, by clicking on the elements in the Nuclides Table. As another quirk of the program, you first have to click on a blank box, then the element you wish to choose. This is illustrated in Figure B After clicking on the blank box and then the element, a window will pop up asking to input the nuclide density. This information is found by opening the Phantom Setup.xlsx Excel file, then go to the Materials page inside the file; it will give the densities of the elements to input. After inputting the density, press OK and then do the same for further elements. 12. Click on the green Save Material Composition button to save your created materials when done. Now repeat the same process for additional materials the user wishes to create. Note that if the user wishes to create a vacuum, input VACUUM in capitals in the Material Composition box and input the elements for water (another quirk of the system). 13. Click the Close Dialog Button. To save the phantom press the Exit tab, then click Yes when the Update Current Project window pops up. Reopen program to continue. (It is crucial that the user exits out to save before moving on). When back in the main program menu, click on the lower Materials tab that is to the left of the Virtual tab. This is shown in Figure B.7. In here, input the Minimum and Maximum density ranges of each respective material (the numbers you inputed from the HU Table tabe from step 7). These densities are the values below and above the material density of each respective material, and used by kvdosecalc to distinguish between the different materials.

71 58 Figure B.6. Material composition input. Figure B.7. Minimum and maximum density input. This information can be found by opening the Phantom Setup.xlsx Excel file, then go to the Materials page inside the file; it will give the densities of the elements. The Minimum value for one material must be the Maximum value of the next material. This is because there can t be any gaps in densities from one material to the next. When inputting the Minimum and Maximum densities, left click the box and input the numbers

72 for all blank boxes. Only after filling in all the boxes, press Enter and a window will pop up saying Change Density Regions? Click Yes. The density of VACUUM is really not the g/cm 3 displayed (inputting VACUUM automatically puts its density to ~0.01 g/cm 3 regardless of what is displayed). 14. The user must now save the phantom setup once again by pressing the Exit tab and clicking Update Current Project when it pops up. The user will be exited out of the program. 15. Before continuing to step 15, go to Section B.4 to learn how to save a backup of your phantom setup. This will save the user from having to create the same phantom more than once if something accidentally gets erased or changed. After saving a backup, proceed to step 1 of this section. 16. After saving a backup of the virtual phantom s setup, reopen kvdosecalc. 17. On the upper left, click on the tab labeled DICOM and locate the virtual phantom folder to reopen the phantom setup. Once open, click on the View tab to load your phantom as illustrated in Figure B The Upper and Lower boxes are the range of slices from 0 to 108. To use slices towards the center, input 90 for Upper and 18 for Lower. After inputting the slice ranges, click on the checkboxes to the left to save them. 19. The Calculation Region is the area where dose will be calculated (enter entire phantom area). Input the outer borders of the phantom in the x and y directions. It is not a bad idea to have a region slightly larger than your phantom. Figure B.9 illustrates this region. The Calculation Region is slightly larger than the Phantom to make sure dose is computed near the edges of the phantom. As an example, the pre-made homogeneous phantom s calculation region has a Top X (far left edge of phantom) located at , Bottom X (far right edge of phantom) at 205.7, Top Y (slightly above phantom surface) at 142.5, and Bottom Y (bottom of phantom) at The user must now input the values for their respective phantom. These values are found by hovering the curser around the virtual phantom, with the pixel number appearing in blue at the top left of the virtual phantom image. After finding these values, click on the question marks in the Calculation Region box and input the values. When done, click the checkbox to the left to save the calculation region. 59

73 60 Figure B.8.. Calculation region input. Figure B.9. Calculation region of homogeneous water phantom.

74 61 In the Slice # box, enter the slice (0 to 108) to be used for dose calculations and press Enter. Use 54 to use the middle slice. Checking in the Source Drawing box will display where the particles are being absorbed in the phantom. Now save the phantom setup before continuing. Exit the program by pressing the Exit button on the top right of the main screen. The user will be prompted to Update Current Project, click "Yes." Then reopen kvdosecalc and the phantom setup file to continue. B.4 BACKING UP VIRTUAL SETUP Saving a backup of the virtual setup is vital in case the setup file becomes corrupted by program errors. It will save the user time from needing to recreate the setup. This will be the same process the user will use to save backup files for the virtual spectrum and virtual source Enter the DoseCalc Files folder followed by the Phantoms folder to enter the specific phantom folder of interest. Once in the user s specific phantom folder, scroll down until you find the Project_SetUp.ser Folder as illustrated in Figure B.10. Copy the Project_SetUp.ser file and paste it in your Backup folder. In your Backup folder, rename the file to describe the phantom s setup, for example, Project_Setup 100kVp 5HVL.ser. Giving it a specific name makes it easy to see exactly what techniques that setup has when opening it at a later time. The user has now finished saving a backup of the virtual setup. When opening a backup file, you must copy it from the Backup folder, paste it back to the original setup file location, delete the old Project_SetUp.ser, and rename the backup file back to Project_SetUp.ser. Then go open kvdosecalc and load your virtual setup like before. (If the file is not back in the original location, not named exactly Project_SetUp.ser or if the old setup file is not deleted, then kvdosecalc will not open it). Figure B.10 also illustrates a typical phantom folder with the respective phantom s CT scan files of its 108 slices, project setup, collision source file, and its backup folder.

75 62 Figure B.10. Phantom folder. B.5 ACQUIRING SPECTRUM The user will now acquire a spectrum to input as a virtual source in kvdosecalc. The user will utilize kvp and HVL of the x-ray source of interest. There are two programs the user may use to acquire the beam spectra, Spektr in combination with MATLAB, and SpekCalc. Spektr is used if the user has the kvp and mm Al filtration but trying to find the case SpekCalc is used. A uniform spectrum using Spektr will be examined, next a varying spectrum (step 5) using Spektr, and lastly SpekCalc (steps 6 and 7) will be examined. Once HVL is found, Spektr can then calculate beam spectra for energies under 150 kvp. For energies of 150 kvp to 300 kvp, SpekCalc is used. Spektr cannot compute spectra for energies with relatively low HVL Determine the kvp. Use Spektr to find the HVL (if HVL is known, skip to step 3). Open MATLAB and always input the proper path to the Spectramod folder by inputting the path name in the Current Folder box and open Spektr by typing the command spektr in the command window as shown in Figure B.11. Figure B.11. MATLAB interface for Spektr.

76 After acquiring the HVL, type the "HVLfind()" command in the command window with parameters kvp and HVL. For example, type HVLfind(120,5.45). This will generate beam spectra for energies less than 150 kvp Figure B.12 illustrates Spekter 2.1 s interface. For energies of 150 to 300 kvp, proceed to step 7.With the spectrum output in MATLAB, copy and paste the spectrum into the Phantom Setup Excel file under a new sheet labeled Spectrum. It is a good idea to copy and save every new spectrum here for future use. This prevents the user from having to create the same spectrum again. After pasting the spectrum into the Phantom Setup Excel file, insert the intensity column to the right of the corresponding MeV energies (kvdosecalc only handles energy in MeV), always starting at MeV in MeV increments until reaching the respective kvp energy. (Remember, when copying the spectrum from MATLAB, copy all the beginning zeros up until the last non-zero number in the spectrum as illustrated in Figure B.13). This will properly line up the correct MeV energies with their respective spectrum intensities. If the MeV energies go one row past the end of the spectrum intensities, then the spectrum intensities match the MeV energies correctly. When using a varying spectra of changing HVL, follow steps 3 through 5 but use command spectruminterpt(x1,resolution,field size radius, kvp). Parameter x1 is a matrix of HVLs that correspond to the measured position (in cm) of each respective HVL in mm Al. Parameter resolution is the increment (in cm) of the spectra detail. This is illustrated in a simplified example in Figure B.14, where - 2.5, 0, and 2.5 are the positions of HVL measurements correlating to 7.08, 7.14, and 7.18 mm Al HVL, respectively, across a 5 cm diameter circular field size. The resolution is 0.5 cm, the field size radius is 2.5 cm, and is at 140 kvp. 63 Figure B.12. Spektr 2.1 interface.

77 64 Figure B.13. Saving acquired spectrum. Figure B.14. Non-uniform spectra calculation in MATLAB. To copy and paste the spectrum, click on the Workspace tab on the far right of the command window, and double click the ans matrix and follow the method in steps 4 and 5. Figure B.15 illustrates copying the spectra from MATLAB into Excel. Notice that once pasted to Excel, any intensity in the spectra smaller than ~1.0 x 10-6 must be changed to 1.0 x 10-6, as kvdosecalc does not handle small numbers properly. 6. Spectra ranging from 150 to 300 kvp will use SpekCalc. Go to the folder labeled SpekCalc and open the program. SpekCalc is more in depth than Spektr, as it asks the user for the kvp, minimum energy, theta (anode angle), and inherent and external filtration. The user is unable to set the HVL, thus the user must insert and tweak the required parameters to arrive at the needed HVL. 7. Once the user obtains the needed HVL, click View Data and highlight the spectrum as illustrated in Figure B.16. Notice that SpekCalc gives the spectrum energies in kev, therefore, those energies must be changed to MeV when pasting the spectrum into excel. To tweak the parameters to arrive at the required HVL, first input the kvp, set the minimum energy to 10% of the kvp, energy bin to 1, find and insert your specific unit s anode angle and inherent filtration, and don t change the Nf or P parameters. Then

78 65 Figure B.15. Non-uniform spectra from MATLAB to Excel. Figure B.16. SpekCalc interface.

79 proceed to tweak the Aluminum Thickness, Copper Thickness, etcetera, until the HVL is close. Then tweak Air Thickness to make very small HVL changes until the user arrives at the required first HVL. (It is extremely difficult to obtain both the first and second HVL in SpekCalc if the second HVL is known.) The user must now input the acquired spectra into kvdosecalc to create the virtual source. B.6 INPUTTING SPECTRUM The following steps must be completed in the exact order, or the user may run into program errors. Steps 1 through 12 are for inputting a uniform spectrum. Go to steps 13 through 15 for directions on inputting a non-uniform varying spectrum Open kvdosecalc (refer to Section B.1). Click DICOM tab to load file. Click View tab to load virtual Phantom. 4. Click Source tab (between the red Stop Dose and Exit tabs) to edit virtual source. Note that if the user is getting an error and can t get into the Source tab, click the Dose tab and make sure there are X,Y, and Z values for the dose calculation point of interest (POI) are inputed and not blank. The software won t let the user enter into the Source tab without these values inputted; it doesn t matter what is entered at this moment as long as the boxes are not empty. This is illustrated in Figure B.17 with zeros filling in the X,Y, and Z values In the Source tab, uncheck the box next to the red words Virtual Source to erase the previous virtual source. A virtual source cannot be loaded when inputting a new spectrum, or a program error will pop up when trying to save. In the Source tab, click the Energy-Angle Distrubutions tab to input spectrum. In the Energy-Angle Distributions tab, highlight the spectrum by clicking on the circled box in Figure B.18, followed by clicking the Edit Distribution. This allows the pre-existing spectrum to be modified. 66

80 67 Figure B.17. Dose calculation point of interest. Figure B.18. Editing energy-angle distribution. 8. After aquiring the spectrum from Section B.5, the user must now copy the spectrum from Excel, paste it into Notepad, and finaly copy and paste it into kvdosecalc. This is because kvdosecalc will not properly recognize the values if pasted from Excel. Paste the energies (in MeV) in the upper left box, and their corresponding intensities in the box to its right right, as shown in Figure B.19. Note that the energy column must have exactly one set of numbers more than the corresponding intensities column or a program error will pop up. Also, kvdosecalc does not interpret zeros correctly, so do not paste the zeros in the beginning or end of the intensity spectrum, and only paste their corresponding energies. For example, if the first non-zero intensity in the spectrum occurs at an energy of MeV for a 150 kvp experiment, only paste the energies to MeV and their corresponding intensities into kvdosecalc (The last energy at MeV will not have a corresponding intensity) Click Fill The Grid of Energies tab followed by the Sources tab. As shown in Figure B.20, in the Sources tab, click the very left of both circled boxes. This highlights the rows in blue. Then click the Save Source button on the top left of the program. (Make sure both rows are highlighted before clicking "Save Source.) Now exit the program by pressing the Exit button on the top right. You will be prompted to Update Current Project, click Yes. The user will now have to reopen kvdosecalc to now input the virtual source. Directions to input the virtual source are in Section B.7.

81 68 Figure B.19. Inputting spectrum into kvdosecalc. Figure B.20. Saving inputted spectrum.

82 Note that the user must exit out and Update Current Project before proceeding to inputing the virtual source, or kvdosecalc will not properly save the newly inputted spectrum For inputting a varying spectrum, follow steps 1 through 12, except enter only one intensity column when entering the spectrum intensities in step 8. This column may be any column from the many that were generated and pasted into Excel from Section B.6, step 5. In addition, the user must complete Section B.7 before finishing the input of the non-uniform, varying spectra (this is because the source parameters and beam fluence of Section B.7 need to be inputted before finally inputting the entire nonuniform spectra). Once Section B.7 is completed, the user can now input the non-uniform spectra. To do this, follow Section B.7, steps 1 through 5, and enter the Spectra tab. Inside this tab is where the user will input the non-uniform beam spectra. Copy the entire intensity spectra from Excel (user doesn't need to paste into Notepad for this input). As shown in Figure B.21, click the first intensity box and press shift+ctrl+down+right arrow keys to highlight the entire field in blue. Then press ctrl+v to paste (this may take a few tries). 69 Figure B.21. Inputting non-uniform spectra. The first column in Figure B.21 represents the energy in MeV and the first row represents the position of each respective intensity of the inputted spectra. The picture to the right illustrates the rotation of the virtual source above the plane of the virtual phantom. A

83 70 good check to make sure it is inputted correctly, is to scroll to the bottom right of the spectra and see if the very last intensity matches the number in Excel. If not, try again. It is an absolute must that the resolution (amount of columns in the X direction) in the "Spectra" tab is equal to the amount of columns of the beam fluence in the Planar Projection Params tab. If not, the spectra will be incorrect and an error will occur. This will occur if the user uses different measurement positions for calculating the spectra than used for the beam fluence. (Generating the spectra in MATLAB using the spectruminterpt() command changes the spectra resolution.) They must be the same. For example, if the user measures the beam fluence at the three positions of -2.5, 0, and 2.5 cm along the field size, the HVL must be measured at the exact same points of -2.5, 0, and 2.5 cm as well. Now repeat steps 10 and 11 in this section to save the completed spectra. The user may now move on to Section B.8 for dose calculations. B.7 INPUTTING VIRTUAL SOURCE The following steps must be completed in the exact order, or the user may run into program errors. 1. Open kvdosecalc (refer to Section B.1). 2. Click DICOM tab to load file. 3. Click View tab to load virtual phantom. 4. Click Source tab (between the red Stop Dose and Exit tabs) to edit virtual source. Note that if the user is getting an error and can t get into the Source tab, Click the Dose tab and make sure there are X,Y, and Z values for the dose calculation POIs are inputed and not blank. The software won t let the user enter into the Source tab without these values inputed, it doesn t matter what is entered at this moment as long as the boxes are not empty. Filling in the X,Y, and Z values with zeros works fine In the Source tab, check-in the box next to the red words Virtual Source" and a Edit Source button will appear right below it. Click the Edit Source Button. This will prompt the user to input the virtual source paramenters as shown in Figure B.22. Enter the axis of rotation, plane of rotation, arc angle, arc size, SAD, and the collimator jaw settings (field size).

84 71 Figure B.22. Inputting virtual source parameters. These settings shown in Figure B.22 are for a square homogeneous water phantom, where the axis of rotation (position of rotation for the virtual source relative to virtual phantom plane) is positioned over the center of the phantom (x=0 mm) and above the phantom s surface (y=152.2 mm) in the DICOM coordinate system. The plane of rotation is at the very center slice of the phantom (z=388 mm, which is at slice 54 of the 108 slices in the phantom). This setup is for a stationary source (arc size=0) that is directly above the plane of the phantom (arc start angle = 270 degrees). It also has a 30 cm SAD with a 5 cm diameter collimator (by inputting the field width and height in the x, +x, and -y, +y directions, respectively. The location of the source can be adjusted in the Arc Start Angle box, where 270 degrees is directly above the phantom plane and sweeps through 360 degrees clockwise around the phantom, which is the length of the sweep set in the Arc Size box. Change these parameters based on the user s experiment, or put the arc start angle at 270 degrees with an arc size of 0 degrees for a stationary source directly above the phantom. This is illustrated in the above figure. Note that inputting the z value as the coordinates of the center slice is best for accuracy (unless the user intends to calculate at a specific slice). Figure B.23 is a visual representation in kvdosecalc of the virtual phantom as previously described. The circle is the axis of rotation with respect to the plane of the virtual phantom. The coordinate system is drawn in the picture. The top left underlined numbers are the x, y, and z coordinates in mm

85 72 Figure B.23. Coordinate system of virtual phantom. (while the numbers next to them in brackets are the pixels in kvdosecalc s DICOM coordinate system) While still in the Source tab, click the Planner Projection Params tab to input the fluence distributions. To acquire a fluence distribution, the user needs to know the intensities at different points of the beam in the radial direction exiting the collimator (as it may vary due to the Heel Effect and scattering in the aperture). Create this distribution in Microsoft Excel to then paste into kvdosecalc. The user will also have to know the collimation of the aperture, whether it is spherical, square, or other and its diameter. 10. Open the Phantom Setup file, and create a new Excel sheet titled Fluence. For a circular fluence, set up the fluence distribution as in Figure B.24 (which assumes a single spectrum and flat field for simplicity), with a 4 cm diameter circular aperture. The 1 represents the uniform beam fluence exiting the collimator, while 1E-10 represents where the beam is collimated (~0 because kvdosecalc doesn t handle zeros well). This creates a circular fluence distribution.

86 73 Figure B.24. Inputting uniform beam fluence The top is where the user inputs the number of rows and columns of the fluence (17 by 17), its x1, x2, y1, y2 collimator settings and its source position (0,152.2,388). Insert the beam diameter in box A4 and put its negative radius in boxes B4 and A5. As an example, input =B in box C4 and =A in box A6 to add a 0.25 cm resolution along the length and width of the circular collimator. Highlight those boxes and drag them until you reach the positive radius. In this example, with a diameter of 4 cm, it goes from -2 to +2 in the x and y directions. When picking a resolution for a circular aperture, make sure to use a number that creates a symmetric fluence (17 rows and 17 columns for example). Sometimes an error will occur if the user uses over 50 rows and 50 columns. To create a circular aperature, input =IF(SQRT(B$4^2+$A5^2)>($A$4/2),10^- 10,1) into box B5, and then drag that box along the entire field. It tells Excel that if the beam is outside of the circle, input 1E-10, and if it s within the circle, input 1. For other shape applicators, edit the field in Excel to meet the needs of the experiment. 6. If the user wants to model a varying fluence for the beam instead of all 1s, after collimating the beam with 1E-10s (if needed), use the fluenceinterp(x1,res,fsize) function in MATLAB and then paste it into the Planner Projection Params tab in kvdosecalc (much the same way as with the spectrum in Section B.5). What kvdosecalc does with these different fluence numbers is normalize them to the maximum fluence when computing dose. A good way to model the non-uniform fluence is by experimentally measuring the relative percent dose in the inline and crossline directions in the plane of fluence with an ion chamber, and inputting it into Excel as shown in Figure B.25. Row 4 contains the crossline points of measurements in cm with their respective relative percent dose readings in row 5. Column A contains the inline points of

87 74 Figure B.25. Inputting non-uniform beam fluence. measurements with their respective relative percent dose readings in column B. To accomplish this, follow step 13 to create the circular collimation, and replace the 1 in the center box H11 with =(H$5*$B11)/100 and drag that box s code to all the boxes with 1s to replace with the non-uniform beam fluence, normalizing the largest dose at 100%. What this equation does is multiply each box by its respective inline and crossline percent dose measurements and normalizes to 100% (for example box D8 is 97.3x98.8/100). After obtaining a beam fluence in Excel, input the beam fluence into kvdosecalc. In kvdosecalc while still under the Planner Projection Params tab, double click one of the white boxes and a new window titled Rows/Columns Count will appear as shown in Figure B.26. Here, input the number of rows and columns of the beam fluence that the user created in Excel Next, in Excel, copy only the relative fluence (not the position numbers) as shown in Figure B.26. The user does not need to paste into Notepad for this input. Still in the Planner Projection Params tab, click on the first fluence box and press shift+ctrl+down+right arrow keys to highlight the entire field in blue as shown in Figure B.27. Then press ctrl+v to paste (this may take a few tries).

88 75 Figure B.26. Inputting beam fluence. 9. Figure B.27. Highlighting beam fluence. Now press Ctrl+v to paste the beam fluence into kvdosecalc, it should look like Figure B.28. Notice that it should look like the Excel file but with a different first column. The first column represents the energy in MeV and the first row represents the position of each respective intensity of the inputted beam fluence. A good check to make sure it is inputted correctly is to scroll to the bottom right of the pasted beam fluence and see if the very last fluence number matches the last number in Excel. If not, try again. 10. This will take the user back to the Sources tab. Now highlight both the top and bottom spectra by clicking the very left of both boxes as shown in Figure B.29, followed by clicking the Save Source button on the top left of the program. 11. Exit the program by pressing the Exit button on the top right. The user will be prompted to Update Current Project, click Yes.

89 76 Figure B.28. Pasting beam fluence into kvdosecalc. Click the green Proceed button. Figure B.29. Saving virtual source. 12. The user must now save a backup of the setup file with its specific virtual phantom and virtual source completed. This will save the hardships of needing to create the setup again from scratch in the event that the setup file becomes accidentally deleted or corrupted. This is explained in Section B.4 Backing Up Virtual Setup in this manual. The user will now have to reopen the program to input the non-uniform spectra as described in steps 13 through 15 in Section B.6 before calculating dose (unless the user is using a uniform spectrum; directions to calculate dose are in the following Section B.8). Note that you must exit and Update Current Project before proceeding to calculating dose for the program to properly save the newly finished virtual source. After reentering kvdosecalc, the beam fluence will have different values than the ones just inputted. This is normal, as kvdosecalc just normalizes the points for its calculations.

90 77 B.8 CALCULATING DOSE The following steps must be completed in the exact order, or the user may run into program errors Open kvdosecalc (refer to Section B.1). Click DICOM tab to load file. Click View tab to load Phantom. Click the Dose tab. Now to create a new collision source, uncheck the box next to the green words Collision Source. You will have a window pop up saying that File: ScatterdDICOM_Source_AnalogMCT Trajectories.bin will be deleted permanently! Click Yes. The user needs to delete the old collision source and create a new one everytime a new dose calculation is attempted or the software may not calculate the dose properly. We must now input the number of Trajectories. This is the number of particles that the virtual source uses to calculate dose. Notice that it is in units of thousands (K) in Figure B.30. Figure B.30. Inputting trajectories. For the best data, use 1,000 K trajectories. For quicker computations, 500 K trajectories is computed in a fraction of the time with approximately a 1% percent dose difference compared to 1,000 K particles. Beyond 1,000 K particles, results do not change noticeably. Do not change the Generations box; the optimal number is inputted automatically. (Just to see how kvdosecalc works for the first time, try using only 10 K particles for extremely fast dose computation times. Once the user is more comfortable using the software, try 500 to 1,000 K particles.) Input the number of trajectories in the white "K Trajectories" box. The three white "Dose" boxes from left to right represent the number of particles in the virtual beam that are un-scattered, single-scattered, and n-scattered, respectively. The best combination for the un-scattered, single-scattered, and n- scattered are 10% of the trajectories, 20% of the trajectories, and the same number as the trajectories, respectively.

91 9. Check the box next to the green words Collision Source to create your new collision source. A window will pop up saying No Scattered Source Found! Would you like to Create it? Click Yes. 10. The user will now input the POIs where dose will be calculated in the virtual phantom. The user must convert the amount of pixels in the phantom to distance in cm. Use an Excel file and set up the POIs as illustrated in Figure B.31. Insert the number into box A1. This is the number that converts pixels into cm. Input the depths you would like to calculate dose at. As in Figure B.31 for example, the depths are at 0, 0.5, 1, 2, and 3 cm at the center of the homogeneous water phantom (center being at x=256) in the center slice (z=54). 78 Figure B.31. Points of interest setup. To find the DICOM coordinates of 0, 0.5, 1, 2, and 3 cm, we use Equations B.2 and Equation B.3, which are restated here for convenience,,,.,., (B.2) (B.3) where Z (i,j) is the pixel value correlating to 0 cm, l is the length in cm, d is the depth in cm, and is the factor that changes cm into kvdosecalc s x and y coordinate system in pixels. To find y s pixel values (Z (i,j) ) for example, insert 0, 0.5, 1, 2, and 3 cm into y in Equation 6 and solve for each respective Z (i,j). This produces the values in column C. 11. Now with the complete x, y, and z pixel coordinates, the user must highlight the pixel values and paste them into Notepad as shown in Figure B.32. These pixel values correlate to depths in the y-direction of 0, 0.5, 1, 2, and 3cm in the center of the virtual phantom (x-direction) in the center slice (z-direction). Save this Notepad file in the Backup folder within its respective phantom folder. The file will be used to calculate dose at the POIs.

92 79 Figure B.32. Pasting points of interest in Notepad. 12. While in the main kvdosecalc menu, click on the Dose button with the X, Y, and Z boxes empty. This will cause a popup that reads, Error in Row:0; Col:1 ;, in the X TextBox. This is normal, click OK. This will prompt a window to pop up to load the recently saved Notepad file to calculate dose at the POIs specified in the Notepad file. After opening the Notepad file, kvdosecalc will automatically calculate the dose at all POIs specified in the Notepad file. Directions to display the results are in the following Section B.9. Note that kvdosecalc outputs calculated dose in units of MeV/g s. B.9 DISPLAYING RESULTS The following steps must be completed in the exact order, or the user may run into program errors After kvdosecalc has finished calculating dose from Section B.8, click on the small grey square circled in Figure B.33 located left of the rectangle labeled Parameter. This will highlight everything blue. Press ctrl+c to copy the highlighted area. This gives the user all the information on the un-scattered, firstscattered, and n-scattered events, each event s POI, computation time, and much more. The total dose at each POI is the most important information to extract. Open the Excel file named Spectrum.xlsm and go to the sheet named Data Extraction. Click on the first box A1 in the Data Extraction folder and press ctrl+v to paste the dose information from kvdosecalc into Excel. Find the Wrap Text button to clean up what you pasted. This is illustarted in Figure B.34. Using a Macro that is saved in the Data Extraction file (make sure to always Enable Macros if Excel so prompts the user), press ctrl+shift+r to extract only the most useful information. The new condensed information will appear to the right as shown in Figure B.35. Copy the "Total Dose" column. (This can only be completed in the "Data Extraction" Excel file.) Open the file named Measurements.xlsx.

93 80 Figure B.33. Copying dose results. Figure B.34. Pasting dose information into Excel. Figure B.35. Dose information extraction At the very top of the Excel file, for every experiment dose computation, label all the parameters used such as kvp, HVL, SSD, Apperature Diameter, and how may particles used. Input all the cm depths that kvdosecalc calculated in a column and have another column next to it titled PDD. Set it up as illustrated in Figure B.36.

94 81 Figure B.36. Displaying results With the "Total Dose" column copied in step 4, paste it into the Measurements.xlsx Excel file next to each dose's corresponding phantom depth. Note that the total dose from kvdosecalc is given in MeV/g s. 1 MeV/g = x10-10 Gy. The information in the above figure was normalized at 0 cm by inserting =H10/H$10*100 in box B3 (and then dragging down to box B7) to get the total PDDs in the above setup. Normalizing divides all the total doses at their specific cm depths by the maximum dose ( ) to obtain the relative PDDs. From there the user can create a PDD graph to visually represent the data for PDD comparisons. The data may also be organized into tables such as in the British Journal of Radiology Supplement 25. Off-axis dose profiles can be computed in kvdosecalc and graphed as well, along with any other dose calculation ideas the user may have. B.10 FUTURE VERSIONS OF KVDOSECALC In the event that kvdosecalc receives an update and/or upgrade, certain steps must be carried out before using the newest version.

95 When using a pre-existing virtual phantom, the file directory must be updated in the Project_Setup.ser file. If this is not done, the phantom will not open properly in the latest version. To do this, open the Project_Setup.ser file in Notebook. (Change the files to be searched for from Text Documents (*.txt) to All Files. Once the setup file is opened, search for the lines that are highlighted in Figure B.37. The first highlighted code is the directory containing the exact name of the current version of kvdosecalc to date. In order for the newest version to work with an existing setup file, replace the older version information, for example, DoseCalc ver &#39; Zero Primary Dose Bug Fixed&#39; from June at 12:24 with the latest version information. To obtain the new directory is by creating a copy of any phantom project, deleting the Project_SetUp.ser file, and opening that phantom in kvdosecalc. After openining kvdosecalc, press the exit button in the top right corner. This loads and saves a brand new Project_SetUp.ser file with the updated directory automatically inputted. Open the new setup file in Notepad, copy the new directory and paste it into the directory of the old setup file. (This is done to have a current phantom project to open into the latest version of kvdosecalc, or likewise, to open a phantom project in an older version of kvdosecalc.) If the user would like to create a new setup from scratch in an updated version of kvdosecalc, just follow the directions in step 3, then follow Sections B.2 through B.7 to set up the phantom. The second highlighted directory in Figure B.37 must always lead to the correct phantom folder path or the setup will not properly load. Figure B.38 illustrates a lung phantom CT scan uploaded in kvdosecalc. Figure B.37. Updating directory in Project_SetUp file.

96 Figure B.38. Lung phantom CT scan uploaded in kvdosecalc. 83