ESTRO 2025 - Abstract Book

S2086

Clinical - Urology

ESTRO 2025

3993

Digital Poster Outcomes and Toxicity of a Third Radiotherapy Course for Prostate Cancer Local Recurrence: A Retrospective Analysis Costantino Putzu 1,2 , Federico Mastroleo 1,2 , Mattia Zaffaroni 1 , Maria Giulia Vincini 1 , Dario Zerini 1 , Giovanni Carlo Mazzola 1 , Ekaterina Milovanova 1,2 , Chiara Lorubbio 1,2 , Federica Cattani 3 , Ottavio De Cobelli 4,2 , Gennaro Musi 4,2 , Giuseppe Petralia 5,2 , Giulia Marvaso 1,2 , Barbara Alicja Jereczek-Fossa 1,2 1 Department of Radiotherapy, European Institute of Oncology, IEO IRCCS, Milan, Italy. 2 Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy. 3 Unit of Medical Physics, European Institute of Oncology, IEO IRCCS, Milan, Italy. 4 Department of Urology, European Institute of Oncology, IEO IRCCS, Milan, Italy. 5 Department of Radiology, European Institute of Oncology, IEO IRCCS, Milan, Italy Purpose/Objective: Re-irradiation is increasingly recognized as a viable and safe treatment option for prostate cancer (PCa) local recurrence. The aim of this study is to present the technical feasibility and efficacy of a third radiotherapy (RT) with stereotactic image-guided for PCa local recurrence. Material/Methods: Inclusion criteria were as follow: (1) histologically confirmed PCa; (2) patients with two previous course of radiotherapy, including external beam or brachytherapy, on prostate gland/prostate bed; (3) absence of > G2 toxicity from previous treatments; (4) restaging after biochemical recurrence performed by multiparametric magnetic resonance and/or Choline positron-emission-tomography (PET) and/or PSMA-PET with no distant metastasis. Cumulative maximum doses to rectum and bladder were calculated in EQD2 (α/β = 3) by considering the maximum dose received during previous treatments, when available, while when previous RT plans were not retrievable, the prescription dose was considered in a “worst - case scenario” approach. Since the absence of dose constraints for third reirradiation, Abusaris et al constraints minus 20% of the cumulative dose were considered (1). Acute and late genitourinary (GU) and gastrointestinal (GI) toxicities were evaluated according to CTCAE. Results: From May 2013 to January 2024, 18 and 5 patients received a third RT course on the radiological detectable intraprostatic/prostatic bed disease, respectively (Table1). Two patients were lost at first follow-up, one was lost after the first 3-months follow-up visit, two had follow-up < 12 months. Of the remaining 18 patients, median follow up was 48.52 (range: 13.9 – 133.2) months. At the time of the analysis, 5/18 (27.8%) are considered disease-free. For prostate gland, median biochemical recurrence free survival (BRFS) after first, second and third RT-course were 57.1 (IQR: 40.3 – 78.3) months, 30.6 (IQR: 16.7 – 48.2) months and 22.6 (IQR: 18.6 – 31.9) months, respectively. For prostate bed, median BRFS after first, second and third RT-course were 27.6 (IQR: 22.1 – 58.7) months, 17.6 (IQR: 15.7 – 27.1) months and 26.9 (IQR: 21.6 – 27.0) months, respectively. Regarding acute toxicities, 3 severe (≥ G3) genitourinary (GU) events were reported, while for late toxicities 4 severe GU events (2 resolved at last follow-up) and 1 severe GI event (persistent) were recorded. Dosimetric evaluation was performed considering cumulative dose received by organs at risk (Table2).