S1252
Clinical - Urology
ESTRO 2026
Patricia Salgado Gonzàles 4 , Gianluisa Sicignano 1 , Ruggiero Ruggeri 1 , Filippo Alongi 1 1 Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria Cancer Care Center, Negrar di Valpolicella, Italy. 2 Medical Physics Unit, IRCCS Ospedale Sacro Cuore Don Calabria, Negrar di Valpolicella, Italy. 3 Department of Radiation Oncology, Hospital Universitario 12 de Octubre, Madrid, Spain. 4 Oncologia Radioterapàpica, Hospital Universitario Fundaciòn Jimènes Dìa, Madrid, Spain Purpose/Objective: Salvage radiotherapy (sRT) is commonly used for locoregional prostate cancer (PC) relapse. Modern technology like adaptive RT (ART) can help to improve safety and accuracy of those treatments. Ethos system uses daily imaging and artificial intelligence to adjust treatment plans based on daily anatomy. This might set a new standard in the setting of sRT, balancing efficacy with reduced adverse events. We report a preliminary analysis of tolerability. Material/Methods: This is a prospective study (NCT05884632) evaluating the tolerability and efficacy of adaptive hypofractionated sRT in PC. Eligible patients ( ≤ 80 years old, PSMA-PET-CT confirmed M0) received 20 daily fractions up to 59 Gy for macroscopic relapse and 55 Gy for biochemical-only relapse. When indicated, pelvis was included with dose of 45 Gy. The treatment was administered using the daily adaptive AI-powered Ethos system. Primary endpoint was acute gastrointestinal (GI) tolerability, assessed via CTCAE v5.0. Secondary end-points included genitourinary (GU) tolerability, quality of life (QoL by EORTC QLQ- C30, EPIC), late events and biochemical failure. Adverse events and QoL data were collected at baseline, at second and last treatment week and every 3 months thereafter. Results: 86 patients with minimum 3 months follow-up were included in this analysis. Median age was 66 years (IQR 62-72), and the mean PSA before RT was 0.41 (0.11-2 ng/ml). 50 (58.1%) patients had a biochemical relapse and 36 (41.9%) a macroscopical relapse. The pelvis was included in 41 cases (47.7%). Overall 15 patients (17.4%) had a G2 event (either GI and GU). In particular, 4 acute G2 proctitis (4.7%), 5 G2 diarrhea (5.8%). G2 GU toxicity was: cystitis (4.7%), hematuria (1.2%), urinary incontinence (5.8%), urinary retention (1.2%). No G ≥ 3 events occurred. There was no difference in incidence for GI acute G1 (0.93), G2 (0.17), and GU G1 (0.35), and G2 (0.72) between treatment doses. Late GI tolerability was: G1 1.2%, G2 1.2%. Late GU tolerability was: G1 7%, G2 2.3%. At 9 months of follow-up mean PSA was 0.07 ng/ml (SD 0.13). QoL analysis at baseline and at 3 months documented a mean increase in fatigue (11.47 versus 16.43),
insomnia (13.98 versus 19.32), but a maintainance of the global health status (summary score: baseline 92.68 versus 91.98 at 3 months). Conclusion: Preliminary data seems to show minimal acute toxicity. CT-based adaptive moderate hypofractionated radiotherapy might be beneficial in the PC postoperative setting. A longer follow up is needed to confirm these data and evaluate late toxicity. Keywords: Prostate cancer, adaptive radiotherapy, salvage Prostate reirradiation using stereotactic body radiotherapy (SBRT) on daily-adaptive 1.5T MR- linac versus conventional linac Luca Nicosia, Michele Rigo, Chiara De-Colle, Andrea Gaetano Allegra, Niccolò Giaj-Levra, Carolina Orsatti, Edoardo Pastorello, Francesco Ricchetti, Andrea Romei, Nicola Bianchi, Riccardo Filippo Borgese, Antonio De Simone, Davide Gurrera, Stefania Naccarato, Gianluisa Sicignano, Ruggero Ruggieri, Filippo Alongi Department of Advanced Radiation Oncology, IRCCS SacroCuore Don Calabria Hospital Cancer Care Center, Negrar di Valpolicella, Italy Digital Poster 3174 Purpose/Objective: Re-irradiation of intraprostatic recurrence following primary radiotherapy for prostate cancer represents a clinical challenge, requiring a delicate balance between effective tumor control and minimizing dose to surrounding organs at risk. Technological advancements in radiotherapy have enabled more precise dose delivery, and among these, magnetic resonance-guided radiotherapy (MRgRT) with MR-linac systems offers superior soft tissue visualization and real-time adaptive planning compared to conventional linear accelerators (linacs). However, robust comparative data assessing the clinical impact of MR- linac versus conventional linac-based re-irradiation in this setting remain limited. This study aims to evaluate the feasibility, safety, and early efficacy of MR-linac re- irradiation compared to conventional image-guided radiotherapy (IGRT) techniques in patients with intraprostatic recurrence after definitive prostate radiotherapy. Material/Methods: Patients with exclusive prostate local relapse detected with PSMA PET/CT were treated with prostate reirradiation on MRL or CL. Treatment dose was 30 Gy in 5 fraction delivered every day or every other day. Androgen-deprivation therapy was administered in case of disease recurrence after prostate re-SBRT
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