ESTRO 2025 - Abstract Book

S2602

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Conclusion: While the film manufacturer reports an optimal dose range of 200-1000cGy (EBT4) and 400-4000cGy (EBT-XD), both models may be suitable for MBRT dosimetry with peak doses up to 7000cGy and valley doses as low as 150cGy, with a trend to higher accuracy for EBT-XD. The measurements on the patient-specific phantom highlight the feasibility of in-vivo MBRT dosimetry, which will be critical for future comparison with Monte Carlo calculations.

Keywords: Gafchromic film, minibeam radiotherapy

References: 1.

Grams MP, Mateus CQ, Mashayekhi M, Mutter RW, Djonov V, Fazzari JM , et al. Minibeam Radiation Therapy Treatment (MBRT): Commissioning and First Clinical Implementation. Int J Radiat Oncol Biol Phys 2024 doi 10.1016/j.ijrobp.2024.06.035. 2. Ma CM, Coffey CW, DeWerd LA, Liu C, Nath R, Seltzer SM , et al. AAPM protocol for 40-300 kV x-ray beam dosimetry in radiotherapy and radiobiology. Med Phys 2001; 28 (6):868-93 doi 10.1118/1.1374247. 3. Howard ME, Herman MG, Grams MP. Methodology for radiochromic film analysis using FilmQA Pro and ImageJ. PLoS One 2020; 15 (5):e0233562 doi 10.1371/journal.pone.0233562.

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Digital Poster Effectiveness of testicular shielding in reducing radiation exposure during rectal cancer treatment Karan Jangbahadoer Sing, Jeroen Buijsen, Jurjen Puls, Gloria Vilches-Freixas Radiotherapy, Maastro, Maastricht, Netherlands Purpose/Objective: Preoperative or postoperative external beam radiation therapy is a key component in the multimodal treatment of rectal cancer. The incidence of rectal cancer in younger populations is on the rise, as noted by recent studies [1] . While the testicles are often located outside the primary radiation field, scattered radiation can still impact them, posing a risk to male fertility due to the testicles' high radiosensitivity. Doses above 500 mGy can lead to fertility issues, while cumulative doses exceeding 2 Gy can cause significant damage. This project investigates the effectiveness of testicular shielding in reducing radiation exposure to the testicles during rectal cancer treatment. Material/Methods: The experimental setup involved a phantom simulating the pelvic and pubic region, with water-filled containers mimicking the legs. A 4 cm-thick lead shielding was used to cover the scrotum. CT and CBCT scans were performed on the phantom with and without the shielding, and a treatment plan was developed following clinical guidelines. Testicular doses were measured using a Farmer ionization chamber during both imaging and radiation treatment.

Results: