ESTRO 2025 - Abstract Book

S1914

Clinical - Urology

ESTRO 2025

1 Radiation Oncology, Sunnybrook Odette Cancer Centre, Toronto, Canada. 2 Radiation Oncology, Alfred Health, Melbourne, Australia Purpose/Objective: Recent RCTs have demonstrated the efficacy of five-fraction stereotactic body radiation therapy (SBRT) for prostate cancer. Single-arm prospective trials have been performed for SBRT of fewer than five fractions. However, no comparative evidence is available between these regimens. We compare outcomes of two- and five-fraction prostate SBRT using prospective data for patients with intermediate-risk disease. Material/Methods: This individual patient data meta-analysis evaluated intermediate-risk prostate cancer from four prospective trials of prostate SBRT (two trials each of two- and five-fraction). The primary endpoint was the cumulative incidence of biochemical failure (BCF). Secondary endpoints included the cumulative incidence of distant metastases (DM) and patient-reported quality of life (QoL). Results: 199 patients met eligibility criteria: 143 (72%) in the five-fraction and 56 (28%) in the two-fraction cohort. The median follow-up was 9.4 years. There was no significant difference in BCF with a five-year cumulative incidence of 3.6% (95% CI 0-8.6%) in the two-fraction and 6.0% (95% CI 1.8-10.2%) in the five-fraction cohort (p=0.73). At eight years, the cumulative incidence was 6.4% (95% CI 0-13.8%) in the two-fraction cohort and 9.5% (95% CI 3.8%-15.2%) in the five-fraction cohort. Fractionation was not significant for BCF on univariate analysis (p=0.72). No significant difference in DM was found. ). At five years, the incidence was 0% (95% CI 0-0%) in the two-fraction cohort and 2.2% (0-4.6%) in the five-fraction cohort (Supplementary Figure 1). At eight years, the cumulative incidence was 3.7% (95% CI 0-11.0%) in the two-fraction cohort and 2.2% (95% CI 0-4.6%) in the five-fraction cohort. We found no difference in acute and late urinary or bowel QoL. Conclusion: We report the first prospective comparison of two- and five-fraction SBRT as well as extended median follow-up overall with the longest median follow-up for SBRT less than 5 fractions. We found no significant difference in efficacy; or urinary or bowel QoL. This meta-analysis further encourages the potential for two-fraction SBRT to be a standard of care option for intermediate-risk prostate cancer. Poster Discussion RE-START: a national registry including patients undergoing reirradiation after previous RT for prostate cancer. A study on behalf of AIRO. Giulio Francolini 1 , Barbara A Jereczek-Fossa 2,3 , Giulia Marvaso 2,3 , Federico Mastroleo 2,3 , Eugenio Cammareri 2,3 , Daniela Alterio 4 , Marcin Miszczyk 5,6 , Fabio Matrone 7 , Alessandra donofrio 7 , Luca Triggiani 8 , Vittorio Morelli 8 , Liliana Belgioia 9,10 , Elisa D'angelo 11 , Rosario Mazzola 12 , Rossana Ingargiola 13 , Antonella Fontana 14 , Alberto Cacciola 15 , Esmeralda Scipilliti 16 , Saverio Caini 17 , Vanessa Di Cataldo 1 , Pietro Garlatti 1 , Michele Aquilano 18 , Niccolò bertini 1 , Giulio Frosini 1 , Lorenzo Livi 1 1 Radiation Oncology, Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Florence, Italy. 2 Division of Radiation Oncology, European Institute of Oncology IRCCS, Milan, Italy. 3 Department of Oncology and Hemato oncology, University of Milan, Milan, Italy. 4 Division of Radiotherapy, IEO European Institute of Oncology, Milan, Italy. 5 Department of Urology, Comprehensive Cancer Center, Medical University of Vienna, Vienna, Austria. 6 Collegium Medicum- Faculty of Medicine, WSB University, Dąbrowa Górnicza, Poland. 7 Division of Radiation Oncology, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, Italy. 8 Radiation Oncology Unit, ASST Spedali Civili, Department of Medical and Surgical Specialties, Radiological Sciences and Public Health, University of Brescia, Keywords: stereotactic body radiotherapy, prostate, SABR 1021