Lab 5 Dose Calculation Algorithms.docx (2)

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Course Title: Radiation Therapy Devices Course Number: BME 704 Semester/Year (e.g.F2016) F2023 Instructor Dr. Victor Yang Teaching Assistant Quentin Currier-Moritsugu Assignment/Lab Number: 5 Assignment/Lab Title: Dose calculation algorithms : Submission Date Monday November 6th 2023 Due Date: Tuesday October 7th 2023 Student LAST Name Student FIRST Name Student Number Section Signature* Chalhoub Nourhan 500982281 2 N.C Butler Tori 500920088 2 T.B *By signing above you attest that you have contributed to this written lab report and confirm that all work you have contributed to this lab report is your own work. Any suspicion of copying or plagiarism in this work will result in an investigation of Academic Misconduct and may result in a “0” on the work, an “F” in the course, or possibly more severe penalties, as well as a Disciplinary Notice on your academic record under the Student Code of Academic

BME704 | Radiation Therapy Devices Lab 5 Department of Electrical, Computer, and Biomedical Engineering Program: Biomedical Engineering BME704: Radiation Therapy Devices Lab 5: Dose calculation algorithms 2

BME704 | Radiation Therapy Devices Lab 5 Name:_____________________ Student #:___________________ Location: Engineering computer lab ENG 412 Objectives: - Perform a manual patient dose calculation for a single field, perform corrections for patient contour and heterogeneities References: - reference text: Chapter 6 Instructions: During the lab, the answers to the questions have to be directly filled into this instruction document. Extra time will be given, where the student must hand in their completed solutions at the beginning of the next scheduled laboratory time. *Note this is an individual lab assignment, and a department cover page must be included. 3

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BME704 | Radiation Therapy Devices Lab 5 Part A. Correction-based dose calculation Use the tabulated data provided in the appendix to answer these questions. 1. Figure 1 illustrates a homogeneous container of water is irradiated by a 4 MV photon beam. The surface of the water is located 100 cm from the radiation source (SSD = 100 cm). The area of the beam at the surface of the water is 10x10 cm 2 . A dose of 100 Gy has been prescribed to the 100% dose point. Calculate the dose values (in Grays) at 1 cm intervals inside the region outlined by the dashed lines on Figure 1. Write the dose values on Figure 1. In the space below, show an example of how you calculated the dose at one of the points. 4

BME704 | Radiation Therapy Devices Lab 5 2. The same beam is irradiating a patient in the configuration shown in Figure 2. For now, we will assume that the patient is composed uniformly of water. Use the inverse-square law correction of Equation 1 to correct for the increase h in the source to surface distance. Refer to the Figure 12.14 for definition of d and h . If necessary, interpolate between data in the tables. Calculate the dose values in the first row on Figure 2. In the space below, show an example of how you calculated the dose at one of the points. (1) 𝐷 ???? = 𝐷 ? ( ) ??𝐷+1 ?𝑚 ??𝐷+1 ?𝑚+ℎ ( ) 2 5

BME704 | Radiation Therapy Devices Lab 5 What effect does increasing or decreasing the source to patient surface distance have on the dose at a given depth? Why? As the distance between the source and the patient increases, the dose administered to the patient decreases. Conversely, reducing the distance increases the dose in accordance with the inverse square law, illustrating the inverse relationship between distance and dose. 3. Figure 3 illustrates a slice through a patient showing a region of lung tissue (density = 0.3 g/cm 3 ) below the patient surface. We will now take into account the different radiological properties of lung and water. a. Do you expect the dose in regions below the lung to be higher or lower than when the lung is replaced by water? Why? The expectation of when dose is in the lung would be greater than when it's in water due to the lower density of lung tissue. Consequently, fewer particle interactions and attenuations occur in the presence of lungs as opposed to water. 6

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BME704 | Radiation Therapy Devices Lab 5 b. Using the TAR correction factor of equation 2, which corrects for the difference in radiological pathlength travelled by the x-rays, calculate the dose values in the region of interest. In the space below, show an example of how you calculated the dose at one of the points. (2) 𝐷 ???? = 𝐷× ?𝐴? ?1+ ρ?+?2 ( ) ?𝐴? ? ( ) where d1 is the distance from the surface to the top of the lung region, t is the thickness of the lung region, and d2 is the distance from the bottom of the lung region to the point at which the dose is calculated. Refer to the attached Figure 12.16 for an illustration of these quantities. 𝐷??? 𝑎? ????ℎ 1. 5?𝑚 = 95. 15 × ( ?𝐴?(1+0.3×1+0.5) ?𝐴? (2.5) ) = 95. 15 × ( ?𝐴?(1.8) ?𝐴? (2.5) ) = 95. 15 × 1.00 0.989 = 96. 2 𝐺? 𝑂?? 𝐴?𝑖?: 𝐷??? 𝑎? ????ℎ 0. 5?𝑚 = 95. 15 × ( ?𝐴?(1+0.3×1+0.5) ?𝐴? (2.5) ) = 95. 15 × ( ?𝐴?(1.8) ?𝐴? (2.5) ) = 95. 15 × 1.00 0.989 = 96. 2 𝐺? 𝐷??? 𝑎? ????ℎ 1. 5 ?𝑚 = 96. 10 × ( ?𝐴?(1.8) ?𝐴? (2.5) ) = 96. 10 × 1.00 0.989 = 97. 17 𝐺? 𝐷??? 𝑎? ????ℎ 2. 5 ?𝑚 = 72. 31 × ( ?𝐴?(1.8) ?𝐴? (2.5) ) = 72. 31 × 1.00 0.989 = 73. 11 𝐺? 𝐷??? 𝑎? ????ℎ 3. 5 ?𝑚 = 𝐷??? 𝑎? ????ℎ ?? 0. 5 ?𝑚 = 90. 7 × ( ?𝐴?(1+0.3×1+0.5) ?𝐴? (3.5) ) = 90. 7 × 0.98 0.957 = 92. 9 𝐺? 𝑂?? 𝐴?𝑖? 𝐷??? 𝑎? ????ℎ 0. 5?𝑚 = 90. 7 × ( ?𝐴?(1+0.3×1+0.5) ?𝐴? (3.5) ) = 90. 7 × 0.98 0.957 = 92. 9 𝐺? 𝐷??? 𝑎? ????ℎ 1. 5 ?𝑚 = 91. 15 × ( ?𝐴?(2.8) ?𝐴? (3.5) ) = 91. 15 × 0.98 0.959 = 93. 15 𝐺? 𝐷??? 𝑎? ????ℎ 2. 5 ?𝑚 = 69. 39 × ( ?𝐴?(2.8) ?𝐴? (3.5) ) = 69. 39 × 0.98 0.959 = 70. 91 𝐺? 7

BME704 | Radiation Therapy Devices Lab 5 c. Compare your dose values for part 1. What do you observe? Q 1 Q 3 Distance Depth = 2.5 cm (Gy) Depth = 3.5 cm (Gy) Depth = 2.5 cm (Gy) Depth = 3.5 cm (Gy) 0 95.15 90.7 96.2 92.9 0.5 95.15 90.7 96.2 92.9 1.5 96.10 91.15 97.17 93.15 2.5 72.31 69.36 73.11 70.91 In my observation, the dosages are higher for part 3 when the lung is present compared to using just water. Specifically, at a depth of 2.5 cm, the dose value is greater than that at a depth of 3.5 cm. d. What limitation(s) do you observe for the TAR correction method? TAR values are presented as whole numbers and are approximations (not precise) rather than incremental depth. This represents assumptions about the values at the intermediate depths 8

BME704 | Radiation Therapy Devices Lab 5 Appendix: Data Table 1: 4MV x-ray Percent Depth Dose curve for 10x10 cm 2 field (100 cm SSD) Depth (cm) Dose (%) 1.0 100.0 2.0 97.4 3.0 92.9 4.0 88.5 5.0 84.8 Table 2: 4MV x-ray Off-axis ratios for 10x10 cm 2 field (100 cm SSD) Off-axis distance (cm) Dose (%) Depth = 2 cm Depth = 3 cm Depth = 4 cm 0.0 100.0 100.0 100.0 1.0 100.0 100.0 100.0 2.0 102.0 101.0 101.0 3.0 50.0 52.0 52.0 4.0 5.0 5.0 5.0 5.0 1.0 1.0 1.0 Table 3: 4MV x-ray Tissue –air ratios for cm 2 field (100 cm SSD) Depth (cm) TAR 1.0 1.031 2.0 1.004 3.0 0.974 4.0 0.940 5.0 0.905 9

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BME704 | Radiation Therapy Devices Lab 5 10

BME704 | Radiation Therapy Devices Lab 5 11

BME704 | Radiation Therapy Devices Lab 5 Section and Total Mark Section Content Deductions(TA will circle relevant deductions) Part A. Correction-based dose calculation A-1 ) Problem (Total Marks=13) - Calculating the dose at different points - dose at the center (-1) - dose at each point, final value and steps to reach it (-1 each/-12 total) A-2 ) Problem (Total Marks=7) - Calculating the dose at different points - dose at the center (-1) - dose at each point, final value and steps to reach it (-0.5 each/-6 total) A-2 ) Discussion question (Total Marks=2) - Investigating the behavior of dose as a factor of distance - wrong or incomplete answer (-2) A-3-a ) Theory question (Total Marks=2) - Investigating the behavior of dose as a factor of different radiological tissues - wrong or incomplete answer (-2) A-3-b ) Problem (Total Marks=13) - Calculating the dose at different points - dose at the center (-1) - dose at each point, final value and steps to reach it (-1 each/-12 total) A-3-c ) Discussion question (Total Marks=1) - Investigating the behavior of dose as a factor of different radiological tissues - wrong or incomplete answer (-2) A-3-d ) Discussion question (Total Marks=1) - Discussion on the limitations - wrong or incomplete answer (-2) 12

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