ESTRO 2025 - Abstract Book

S2115

Clinical - Urology

ESTRO 2025

4286

Digital Poster PSMA-Targeted Focal Stereotactic Re-Irradiation in Two Fractions for Recurrent Prostate Cancer Post Definitive Radiation Therapy Liat Hammer 1 , Ron Lewin 1 , Jacob Mattout 1 , Maoz Ben-Ayun 1 , Lev Tzvang 1 , Sergey Dubinski 1 , Ilana Weiss 1 , Yaacov R Lawrence 1,2 , Zvi Symon 1,2 1 Radiation Oncology, Sheba Medical Center, Ramat Gan, Israel. 2 Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel Purpose/Objective: While a five-fraction salvage SBRT is recommended for prostate re-irradiation, it remains controversial and is linked to a higher risk of adverse events compared to initial radiotherapy. We propose the delivery of two fractions, 9 Gy each, through intensified hypo-fractionation, and report the feasibility, toxicity, and early outcomes of 68Ga-PSMA PET/CT-directed salvage focal re-irradiation using this approach . Material/Methods: Between July 2022 and November 2023, 17 patients with isolated prostate cancer recurrence post-definitive radiation were treated at our institution. Each patient underwent 68Ga-PSMA PET/CT following biochemical recurrence by Phoenix criteria or repeated PSA increase. Recurrence was confirmed in 53% by prostate biopsy and 35% by multiparametric MRI. We administered focal SBRT of 18 Gy in two fractions to PSMA-avid areas with a 3-5 mm prostate margin on alternate days, guided by fiducial markers. Hydrogel spacer (29%) or endorectal balloon (71%) placement was required. Concurrent androgen deprivation therapy was given to 88% of patients for a median of six months (range, 4-21). Toxicity was evaluated using the Common Terminology Criteria for Adverse Events v5. Results: The median follow-up was 11.9 months (range, 3-18), with a median interval of 4.3 years (range, 0.6-15.6) between primary radiation and salvage SBRT. The median patient age was 73.1 years (range, 66-89), and PSA levels at re irradiation were 1.87 ng/ml (range, 0.02-7.1). Only one patient had a biochemical recurrence confirmed by 68Ga PSMA PET/CT. No patients experienced acute or late gastrointestinal toxicity, and 23.5% reported no adverse events. Acute GU toxicity grades 1 and 2 were seen in 41.2% and 11.8%, respectively. Late GU toxicity grades 1 and 2 occurred in 41% and 35%, with cystitis and urinary incontinence as the main toxicities. No grade 3 or 4 toxicities were observed. Conclusion: With a limited follow-up, PSMA-directed salvage focal re-irradiation using SBRT of 18 Gy in two fractions is feasible and shows acceptable toxicity. No gastrointestinal or high-grade toxicities were reported, demonstrating promising short-term biochemical control in a selected patient cohort.

Keywords: Re-Irradiation, SBRT, Prostate

4287

Digital Poster Results of the UPRATE trial (NCT05361902): reducing seminal vesicle PTV-margin to 5mm by combining online adaptive SBRT and intra-fraction tracking Victor J. Brand, Maaike T.W. Milder, Femke E. Froklage, Miranda E.M.C. Christianen, Kim C. de Vries, Mischa S. Hoogeman, Luca Incrocci Department of Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands