ESTRO 2025 - Abstract Book

S2074

Clinical - Urology

ESTRO 2025

3846

Digital Poster Evaluating Target Volume in Prostate Cancer Radiotherapy: How Much is Too Much? Grzegorz Matuszny 1 , Paweł Grządziel 2 , Mateusz Gajek 1 , Aleksandra Napieralska 1,3 , Wojciech Majewski 1 1 Radiotherapy, National Institute of Oncology, Gliwice, Poland. 2 Radiotherapy Planning, National Institute of Oncology, Gliwice, Poland. 3 Radiotherapy, National Institute of Oncology, Kraków, Poland Purpose/Objective: This retrospective study evaluated the impact of target volume (clinical-CTV and planning-PTV) on the incidence and severity of early radiation-induced bladder (GU) and rectal (GI) toxicity in prostate cancer patients treated with moderately hypofractionated radiotherapy (MHRT). Material/Methods: Sixty-eight consecutive patients irradiated with MHRT (70 Gy in 28 fractions) in years 2022 and 2023 were included in the study. Toxicity was evaluated using a modified RTOG scale, with grade 2 (G2) divided into G2a (mild symptoms, pharmacological preventive treatment) and G2b (more severe symptoms, pharmacological treatment and/or modifications necessary). Statistical analysis included logistic regression and ROC curves. Results: Median CTV was 85cm 3 (IQR 64-102cm 3 ) and PTV was 176cm 3 (IQR 154-211cm 3 ). Early ≥G2 GU toxicity was observed in 31 patients (42.6%). Early ≥G2b GU toxicity occurred in 14 patients (20.6%) and G3 GU toxicity was noted in 2 patients (2.9%) Early ≥G2 GI toxicity was observed in 7 patients (10.29%), while ≥G2b GI toxicity in 2 patients (2.9%). No statistically significant associations were observed between early ≥G2 GI toxicity and the CTV (p=0.666) or PTV (p=0.956). However, a trend indicating an increased incidence of ≥G2 GU toxicity with rising CTV (p=0.085) and PTV (p=0.072) was observed. A borderline significant impact was observed between the CTV and ≥G2b GU toxicity (p=0.054), with a statistically significant impact of PTV (p=0.018). ROC analysis indicated a threshold volume of CTV >112cm 3 (p=0.064) and PTV >218cm 3 (p=0.028) best differentiated patients with early ≥G2b symptoms. Incidence of ≥G2b GU toxicity was 14.5% for CTV ≤112cm3 and 46.1% for CTV >112cm 3 . In Figure 1, the percentage of patients experiencing ≥G2b GU toxicity is shown as a function of the CTV in patients with large prostate.