S1672
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Orzechowska 1 , Sebastian Maleszka 1 , Seweryn Jakubowski 1 1 Medical Physics, Oncology Center, Bydgoszcz, Poland. 2 Department of Oncology and Brachytherapy, Collegium Medicum Nicholas Copernicus University, Toruń, Poland. 3 Physical Department, Kazimierz Wielki University, Bydgoszcz, Poland Purpose/Objective: In vivo verifcation of the dose delivered remains still an unsolved dosimetric issue in several radiotherapy activities (e.g. brachytherapy, IOeRT and MRgART). Conventional detectors cannot be used for this purpose due to their specific limitadtions. The aim of the study was to design a safe dosimetric detector for use in patient specific quality assurance systems (PSCA), resistant to magnetic fields as well as aplicable in brachtherapy and intra-operative radioterapy. Material/Methods: In this work we propose the solution based on the known scintillation crystal of cerium-doped garnet (GAGG:Ce and others) attached with an optical fiber as a fully resisant dosimeter, capable for QA as well as point dose in vivo dosimetry in brachyterapy, IOeRT and in Linac-MR adaptive radiotherapy. The prototype device was cross-calibrated with an 0.6cc Farmer type ionization chamber according to IAEA TRS 398 recomendations. The scheme of detector is shown in
Conclusion: Single-spot film dosimetry is effective for studying high-LET dose response and for evaluating the impact of range shifters on spot characteristics. While TPS and measurements agree in most regions, film under- response becomes significant near the Bragg peak, where LET increases sharply. Additional measurements at multiple energies would be required to fully parameterize quenching for clinical applications, but the correlation of the product LET_fluence × TPS dose with dose difference suggests that this quantity may provide a practical descriptor for future empirical correction models for EBT-XD film. References: The internship that permitted this work was funded by the ENEN2PLUS Project.Guan, F., Wang, X., Yang, M., Draeger, E., Han, D., Iga, K., ... & Chen, Z. (2023). Dosimetric response of Gafchromic™ EBT ‑ XD film to therapeutic protons. Precision radiation oncology, 7(1), 15-26.Resch, A. F., Heyes, P. D., Fuchs, H., Bassler, N., Georg, D., & Palmans, H. (2020). Dose ‑ rather than fluence ‑ averaged LET should be used as a single ‑ parameter descriptor of proton beam quality for radiochromic film dosimetry. Medical Physics, 47(5), 2289-2299. Keywords: Protontherapy, Radiochromic, LET Digital Poster Highlight 3842 A prototype of a universal in vivo FOD detector for a wide range of applications: brachytherapy, nuclear medicine, external-beams including Linac- MR Janusz Winiecki 1,2 , Yuriy Zorenko 3,1 , Sandra Witkiewicz- Lukaszek 3 , Bogna Sobiech 1,3 , Paulina Michalska 1,3 , Natalia Wiśniewska 1 , Eliza Gunia 1 , Agnieszka
Fig.1a whereas Fig.1b,c,d show it’s very good characteristics in several clinical conditiones.
Figure 1. The scheme and funcional characteristic of the ptototype detector: a - over-all scheame of the measurement conditions; b - calibration curve for Ir- 192 brachytherapy, c- calibration curve for 6MV external beeam radiotherapy, d - EBRT 7MV witch external magnetic field 1.5 T. Due to its small size (approx. 1 mm), the detector has a nearly isotropic spatial response when used for brachytherapy purposes. For EBRT applications, a build-up overlay should be used - Fig. 2a), b).
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