ESTRO 2025 - Abstract Book

S2015

Clinical - Urology

ESTRO 2025

2880

Digital Poster Re-irradiation for isolated local recurrence of prostate cancer: a monocentric experience

Maria Giulia Vincini, Mattia Zaffaroni, Eugenio Cammareri, Federico Mastroleo, Dario Zerini, Sabrina Clobiaco, Sofia Netti, Stefano Luzzago, Francesco Alessandro Mistretta, Sarah Alessi, Francesco Ceci, Giuseppe Petralia, Gennaro Musi, Federica Cattani, Sara Gandini, Ottavio De Cobelli, Giulia Marvaso, Barbara Alicja Jereczek-Fossa IEO, European Institute of Oncology, IRCCS, IEO, European Institute of Oncology, IRCCS, Milan, Italy Purpose/Objective: The aim of the present study is to evaluate the efficacy and safety of photon re-irradiation (reRT) for local relapse in prostate cancer (PCa) patients who previously underwent adjuvant/salvage radiotherapy (RT) following prostatectomy or curative RT. Material/Methods: Patients who underwent salvage reRT after previous adjuvant/salvage RT were retrospectively considered. ReRTwas performed with image-guided RT (RapidArc®, VERO®, and CyberKnife®). Primary endpoints were biochemical relapse-free survival (bRFS) and clinical relapse-free survival (cRFS). Univariate and multivariate Cox proportional hazard models were performed to investigate prognostic factors associated to CR and local relapse. The log-rank test was used to compare Kaplan — Meier curves. Wilcoxon rank sum test were used to investigate dosimetric factors associated to late toxicities. Results: A total of 120 patients were included. Cohort characteristics at primary treatment and at reRT are displayed in Table 1 . At a median follow-up of 4.7 years (IQR 2.1 – 5.7 years), 88 (73%) patients experienced BR, with a median time to BR of 1.3 years (95% CI 1.1-1.9 years), and bRFS rates at 1- and 2-year of 68% and 35%, respectively. CR was recorded in 69 patients: 17 experienced both intraprostatic relapse and metastatic relapse, 14 developed only metastatic relapse, and 38 had a local relapse only. Median time to CR was 3.0 years (95% CI 2.2 – 3.8 years) and the cRFS rates at 1- and 2-year were 89% and 63%, respectively. Polymetastatic relapse (>5 lesions) was reported in 16 patients. Seventeen patients developed castration resistant PCa. When stratifying patients according to ISUP grade (<3 vs >3) and time to first relapse (<57 months vs >57 months) KM curves for CR resulted significantly different (p=.012 and p<.001, respectively, Figure 1 ). One G2 acute GU event was recorded (bladder toxicity) and three G≥3 late GI events (two resolved at the last follow - up) and twelve G≥3 late GU events (seven resolved at the last follow-up) were reported. Only the maximum dose of bladder was found to be associated to late bladder toxicity. At last follow-up (available for 66 patients), 24 patients died, 13 were alive with no evidence of disease, while the remaining 29 were alive with disease.