S1200
Clinical - Urology
ESTRO 2026
Conclusion: Five-fraction SBRT for localized prostate cancer demonstrated excellent biochemical control and low adverse events using advanced IGRT in real-world conditions. The incidence of acute GU adverse events was higher in DIL boost subgroup. No statistically significant difference for bRFS or late adverse events
adverse events (hematuria). Acute GI grade ≥ 2 adverse events occurred in 2 patients (1%), but no grade 3 adverse events were observed. Two-year cumulative late grade ≥ 2 GU and GI adverse events were 11.83% (95% CI, 7.64-18.08) and 2.83% (95% CI, 1.19-6.66), respectively, with no late grade ≥ 3 GU or GI adverse events. No statistically significant difference for bRFS and late adverse events between each RT machine. MR-Linac with DIL boost shows statistically higher acute GU grade ≥ 2 incidence compared to other arms (15% vs. 0-4%, p=0.02).
between each radiotherapy machine. Keywords: Prostate, SBRT, Machine
Digital Poster 1909 Predictive factors of bladder filling variability in CBCT-guided prostate VMAT Meriem Skouri, Zeineb Naimi, Raouia Ben Amor, Awatef Hamdoun, Roua Toumi, Raja Oueslati, Lotfi Kochbati Radiation Oncology Department, Abderrahmen Mami Hospital, Ariana, Tunisia Purpose/Objective: Maintaining a consistent bladder volume during prostate radiotherapy is essential for dosimetric accuracy. This study aimed to identify the main predictive factors of bladder filling variability in CBCT- guided prostate radiotherapy. Material/Methods: Patients with localized or locally advanced prostate cancer, referred for definitive prostate radiotherapy, between September 2022 and April 2024, were prospectively enrolled in this study. All patients were planned for CBCT-guided VMAT, with a prescription dose of 76 Gy in 38 fractions. A comfortably full bladder was required prior to planification and to each treatment session. For this goal to be achieved, patients were asked to empty their bladder, then drink water, until full bladder sensation was reached. To assess bladder volume variability during treatment, the bladder was delineated on all 38 CBCT scans acquired for each patient. Water intake at planification and during treatment, prostate and bladder volumes on the planning CT, and treatment timing were recorded. Additional clinical characteristics including age, diabetes, history of TURP, creatinine clearance, baseline IPSS score, urinary tract involvement and daily water intake were collected. ANOVA and multiple linear regression analyses were performed to identify the predictive factors of bladder volume variability. Results: Forty patients were included with a mean age at diagnosis of 69 (54-79) years. Water intake prior to planification was 1255 (350 – 2000) ml. Mean planning CT bladder volume was 344.8 ± 146.9 ml. During treatment, bladder volume decreased by -120.7 ml (- 30.9%), with variability increasing significantly between the 25th and the 38th fractions (p<0.001). Daily inter-
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