ESTRO 2025 - Abstract Book

S2605

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

2316

Digital Poster Development and evaluation of polycrystalline semiconductor dosimeter for quality assurance application in high-dose-rate brachytherapy Jin-Beom Chung 1 , Moo-Jae Han 1 , Sang-Won Kang 1 , Jae-Sung Kim 1,2 1 Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea, Republic of. 2 Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea, Republic of Purpose/Objective: This study aims to develop and evaluate polycrystalline semiconductor dosimeters (PSDs) to establish a digital quality assurance (QA) system for high-dose-rate (HDR) brachytherapy. Material/Methods: PSDs were fabricated using four polycrystalline materials: mercury(II) iodide (HgI ₂ ), lead(II) iodide (PbI ₂ ), lead(II) oxide (PbO), and thallium(I) bromide (TlBr). To evaluate the performance of the fabricated dosimeters, dosimetric parameters, including reproducibility, dose-response linearity, distance dependence, and angular dependence, were measured using an Iridium-192 (Ir-192) radioisotope source and compared with corresponding parameters measured from a parallel-plane ion chamber. For reproducibility, each PSD was irradiated 10 consecutive times. Dose-response linearity was assessed for doses ranging from 0.1 to 10 Gy. Distance dependence was evaluated by administering a dose of 1 Gy at source-to-dosimeter distances ranging from 1 to 12 cm, in increments of 0.25 cm. Angular dependence was assessed by positioning the PSDs 1 cm below the Ir-192 source and measuring signals at angles of 15°, 30°, and 45° relative to the reference angle of 0°, where the PSD's central axis was parallel to the source. Signals measured at 15°, 30°, and 45° were normalized to those measured at 0°. Results: The PSD using PbO demonstrated the best reproducibility, with a coefficient of variation of 0.85%, and showed a minimal difference of -0.03% compared to the ion chamber. Other PSDs also achieved excellent reproducibility, with relative standard deviations within 1.5%. For dose-response linearity, all PSDs achieved an R² value of 0.9993 or higher, outperforming the ion chamber, which had an R² value of 0.9983. Regarding distance dependence, the slope of the power function and the distance of 50% intensity (D ₅₀ ) were analyzed in comparison to the ion chamber. The PSD with PbI ₂ exhibited the closest agreement, with a slope difference of 0.103 and a D ₅₀ difference of 0.003 cm. For angular dependence, the PSD using PbI ₂ demonstrated the least attenuation, with a 13.2% reduction in signal intensity at 45° compared to 0°. Conclusion: The findings of this study indicate that PbI ₂ is the most suitable material for PSDs when compared with the ion chamber in terms of measurement characteristics. Furthermore, this study provides valuable insights into optimizing semiconductor materials for various applications in HDR brachytherapy QA.

Keywords: dosimeter, brachytherapy

2328

Digital Poster Equivalent square fields in small elongated MLC-shaped fields Antonella Fogliata 1 , Antonella Stravato 2,3 , Marco Pelizzoli 1 , Francesco La Fauci 1 , Pasqualina Gallo 1 , Andrea Bresolin 1 , Luca Cozzi 1 , Stefano Tomatis 1 , Marta Scorsetti 1,4 , Giacomo Reggiori 1 1 Radiosurgery and Radiotherapy Department, IRCCS-Humanitas Research Hospital, Milan, Italy. 2 Medical Physics, A.O. San Giovanni-Addolorata, Rome, Italy. 3 Medical University, UniCamillus, Rome, Italy. 4 Department of Biomedical Sciences, Humanitas University, Milan, Italy