S1215
Clinical - Urology
ESTRO 2026
2 Department of Radiation Oncology, Ba ş kent University Faculty of Medicine, Ankara, Turkey. 3 Department of Radiation Oncology, Iskenderun Gelisim Hospital, Hatay, Turkey. 4 Department of Radiation Oncology, Gazi University Faculty of Medicine, Ankara, Turkey Purpose/Objective: To determine whether a simultaneous integrated boost (SIB) to intraprostatic lesions (IPLs) improves oncologic outcomes in unfavorable intermediate-risk prostate cancer (UIR-PCa) patients treated with image- guided dose-escalated radiotherapy (RT) and short- term androgen deprivation therapy (ADT). Material/Methods: This retrospective study included 194 patients with NCCN-defined UIR-PCa treated between 2010–2023. Eighty-seven patients (44.8%) received SIB (86 Gy to IPL) and 107 (55.2%) received standard-dose RT (78 Gy). All underwent image-guided IMRT/VMAT and short-term ADT (median 6 months). Outcomes included biochemical relapse-free survival (bRFS), distant metastasis-free survival (DMFS), and prostate cancer-specific mortality (PCSM). Kaplan–Meier and Fine–Gray analyses assessed outcomes. Model discrimination and clinical utility were evaluated using time-dependent ROC, calibration, and decision-curve analysis (DCA). Toxicities were graded per RTOG/EORTC criteria. Results: After a median follow-up of 105.5 months (IQR 80.4– 130.6), 8-year bRFS and DMFS for the cohort were 93.7% and 95.7%, respectively. No differences were observed between SIB and non-SIB groups for bRFS (93.5% vs 93.6%, p = 0.36) or DMFS (94.6% vs 96.7%, p = 0.15). Fine–Gray analysis showed no increased risk of PCSM with SIB (SHR = 1.54 × 10 ⁻ ⁵ , p < 0.001); cumulative PCSM incidence was slightly lower in the SIB arm (p = 0.037). At 96 months, the model’s AUC was 0.74 (95% CI 0.69–0.79). DCA revealed nearly identical net-benefit curves for base and SIB-augmented models, and calibration plots demonstrated strong agreement between predicted and observed probabilities. Late grade ≥ 2 genitourinary and gastrointestinal toxicities were rare, with 8-year rates of 2.7% vs 1.9% (p = 0.47) and 0.9% vs 1.7% (p = 0.15) for SIB and non-SIB groups, respectively.
Conclusion: In UIR-PCa treated with image-guided dose-escalated RT and short-term ADT, adding SIB did not improve biochemical or metastatic control but achieved excellent disease-specific survival and minimal toxicity. These findings support the safety of SIB but suggest limited incremental benefit over standard-dose regimens. Keywords: prostate cancer, intermadiate risk, radiotherapy Digital Poster Highlight 2159 Dose–response for late urinary incontinence after prostate cancer radiotherapy integrating α/β estimates, bladder volume effects, and patient factors Gianluca Villa 1 , Tiziana Rancati 1 , Eliana Gioscio 1 , Sofia Spampinato 2 , Barbara Avuzzi 3 , Barbara Noris Chiorda 3 , Alessandro Cicchetti 1 , Fabio Badenchini 4 , Francesco Fiorino 1 , Valeria Casanova Borca 5 , Andrea Botti 6 , Angelo Maggio 7 , Marcella Palombarini 8 , Tommaso Giandini 9 , Alessio Pierelli 10 , Elisabetta Garibaldi 11 , Domenico Cante 12 , Pierfrancesco Franco 13 , Elisa Villa 14 , Giuseppe Girelli 15 , Claudio Degli Esposti 16 , Cinzia Iotti 17 , Vittorio Vavassori 14 , Claudio Fiorino 18 , Cesare Cozzarini 19 1 Data Science Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy. 2 Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam, Rotterdam, Netherlands. 3 Radiation Oncology Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy. 4 Genito-Urinary Oncology Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy. 5 Medical Physics Unit, ASL TO4 Ospedale di Ivrea, Ivrea, Italy. 6 Medical Physics Unit, AUSL- IRCCS di Reggio Emilia, Reggio Emilia, Italy. 7 Medical Physics Unit, Candiolo Cancer Institute, FPO- IRCCS, Candiolo (TO), Italy. 8 Medical Physics Unit, Ospedale Bellaria, Bologna, Italy. 9 Medical Physics Unit, Fondazione IRCCS Istituto Nazionale dei Tumori,
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