S2150
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Imaging Radiat Oncol, vol. 23, pp. 97–102, Jul. 2022, doi: 10.1016/j.phro.2022.07.001.[2] [2] O. A. Houlihan et al., ‘A Randomized Feasibility Trial of Stereotactic Prostate Radiation Therapy With or Without Elective Nodal Irradiation in High-Risk Localized Prostate Cancer (SPORT Trial)’, Int J Radiat Oncol Biol Phys, vol. 117, no. 3, pp. 594–609, Nov. 2023, doi: 10.1016/j.ijrobp.2023.02.054. Keywords: dose accumulation, outcome, DIR Assessment of Breast Cancer IGRT Protocol Choice through EPID Transit Dosimetry and SGRT Signal Analysis Elisabetta Cagni 1 , Farah Jadallah 2 , Laura Verzellesi 1 , Giulia Paolani 1 , Francesco Braglia 1 , Ayman El Ouati 1 , Andrea Botti 1 , Valeria Trojani 1 , Roberto Sghedoni 1 , Adriana Barani 1 , Daniele Lambertini 1 , Daniele Bertoni 3 , Alice Zamagni 3 , Cinzia Iotti 3 , Mauro Iori 1 , Marco Esposito 4 1 Medical Physics Unit, Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, Italy. 2 Master of Advanced Studies in Medical Physics, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy. 3 Radiation Oncology Unit, Azienda USL-IRCCS di Reggio Emilia, Digital Poster 3098 Reggio Emilia, Italy. 4 Medical Physics Unit, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy Purpose/Objective: Breast cancer represents one of the largest cohorts in radiotherapy, involving relatively young patients with high long-term survival. This highlights the need for accurate treatment delivery and verification while minimizing additional radiation exposure from image- guided radiotherapy (IGRT) [1]. This study evaluated the feasibility of using electronic portal imaging device (EPID)-based three-dimensional (3D) transit in-vivo dosimetry (IVD) to assess the dosimetric accuracy of breast radiotherapy, combined with surface-guided radiotherapy (SGRT) for monitoring setup and intrafraction accuracy. Different IGRT scheduling protocols were analyzed, and correlations between SGRT metrics and EPID-IVD results were explored. Material/Methods: Fifty-five breast cancer patients were retrospectively analyzed: 35 treated with an ultra-hypofractionated regimen (26 Gy/5 fractions) and 20 with a standard hypofractionated regimen including a simultaneous integrated boost (40.5–48 Gy/15 fractions). All plans were delivered using IMRT tangential fields. Patients underwent either daily CBCT-IGRT or scheduled CBCT- IGRT (first three fractions and weekly thereafter), as determined by the radiation oncologist. Each patient underwent three EPID-IVD acquisitions (first, middle,
predictors of GU AE were found with accumulated dose. No planned rectum metric was significant in predicting GI AE. However, accumulated rectum V24Gy-V35Gy(cc), V26Gy-V35Gy(%), D10% and D15% were significant in predicting GI AE.Bladder V23Gy(%) and rectum V30Gy(cc) produced the highest AUC within planned DVHs. Patients with GU AE had higher (fig.1) planned median bladder V23Gy: 24.7% (22.4%– 27.9%) vs 17.9% (14.6%–20.7%), and GI AE rectum V30Gy: 5.99cc (3.91cc–9.65cc) vs 2.12cc (1.02cc– 3.20cc).
GU AE was predicted with an AUC of 0.75 (0.57-0.88) and 0.76 (0.57-0.88) with planned and accumulated bladder dose (fig.2). GI AE was predicted with an AUC of 0.66 (0.48-0.85) and 0.71 (0.51-0.88) using planned and accumulated rectum dose.
Conclusion: Structure-guided dose accumulation identified stronger predictors of GI AE compared to planned dose. No improvement was observed in predicting GU AE. Future work will include alternative deformable registration methods and potentially evaluate urinary substructures to improve GU AE predictions. References: [1] [1] A. L. K. Ong et al., ‘Dose-volume analysis of planned versus accumulated dose as a predictor for late gastrointestinal toxicity in men receiving radiotherapy for high-risk prostate cancer’, Phys
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