ESTRO 2025 - Abstract Book

S1932

Clinical - Urology

ESTRO 2025

1337

Digital Poster Dose volume histogram-based comparison for late rectal bleeding in moderate hypo vs. standard fractionated radiotherapy in prostate cancer. Michał Posiewnik 1 , Dominik Malecki 2 , Pawel Czajkowski 1 1 Medical Physics, Gdynia Oncology Center, Gdynia, Poland. 2 Radiotherapy, Katowice Oncology Center, Katowice, Poland Purpose/Objective: In this study we have retrospectively analyzed and compared dosimetric quantities of radiotherapy plans that were created for patients with prostate cancer. Patients were treated with either standard (2 Gy per fraction to 76Gy) or moderate hypo-fractionated radiotherapy (2.5 Gy per fraction to 70Gy). General and group statistics were analyzed with respect to rectal bleeding toxicity as explained later. Material/Methods: In our study rectal bleeding toxicity endpoint, was recognized as a situation where, during first 2 years after radiotherapy [1] patient at least once but was subject of endoscopic plasma coagulation therapy [2] (APC). To analyze the whole cohort, hypo-fractionated dose schedules were converted to 2-Gy equivalent schedules (EQD2) using the Withers formula [3] using α/β = 3Gy. We have checked the difference in toxicity outcome between groups (called mHypo and standard group respectively). To compare groups, we have visualized it using mean DVH’s of rectum and its statistics were analyzed using Welch's t -test first for RAP [cc] volume and for DVH (Dose Volume Histogram) parameters. Further differences in geometrical and planning related characteristics of the groups were assed using created graphs of rectal dose volumes (V60[cc] – V75[cc]) plotted against RAP [cc] volume.

Results: