ESTRO 2025 - Abstract Book

S2147

Clinical - Urology

ESTRO 2025

4653

Digital Poster Outcomes of PSMA PET/CT-Based Salvage Radiotherapy and Hormonal Therapy in Post-Surgical Prostate Cancer Relapse Berardino de Bari Department of Radio-oncology, Réseau Hospitalier Neuchâtelois, La Chaux-de-Fonds, Switzerland Purpose/Objective: This study retrospectively evaluates the clinical course of 57 patients who underwent PSMA PET/CT imaging prior to salvage radiotherapy (RT) for relapse of previously operated prostate cancer. It aims to assess the therapeutic impact, efficacy, and predictors of success for a PSMA PET/CT-guided treatment approach. Material/Methods: A total of 57 patients with documented post-surgical prostate cancer relapse were included. The median age at surgery was 65 years (range: 50 – 75), and at relapse, 68 years (range: 52 – 77). Patients underwent PSMA PET/CT (18 fluorine: n=50, 68-gallium: n=7) before RT for disease assessment and treatment planning. Median PSA at relapse was 0.79 ng/ml (IQR: 0.55 – 0.84). RT volumes and doses included: CTV pelvis (median: 50 Gy, range 45-54), CTV prostatic bed (median: 66 Gy, range: 64-70), GTV PET-positive nodal regions (median: 60 Gy, range: 54 – 66, usually delivered in 25 fractions with a Simultaneous Integrated Boost during the pelvic irradiation), and GTV macroscopic relapse in the prostatic bed areas (median: 70 Gy, range: 68 – 74), delivered with a standard fractionation sequential boost). Respective PTV were obtained by adding 5mm to the GTV and the CTV described above. Daily CBCT were performed to verify the seup of the patients.Hormonal therapy was administered for a median duration of 24 months (range: 6 – 36). Outcomes included disease-free survival (DFS), overall survival (OS), biochemical-relapse free survival (BRFS), and toxicity rates. Results: Over a median follow-up of 48 months (range: 24 – 72), the 3-year OS rate was 88% (95% CI: 80 – 96), BRFS was 72% (95% CI: 63 – 81), and DFS was 68% (95% CI: 59 – 77). Toxicity was minimal, with G1 acute bowel toxicity in 16 patients and G2 in 4. G1 acute cystitis was observed in 27 patients with no G2 urinary toxicity. Late proctitis and bowel toxicity were rare (3 cases each, always G1), and late GU toxicity was mostly absent (G1 cystitis: 10 cases, G1 obstruction: 3 cases). Conclusion: PSMA PET/CT should be integral in restaging relapsing prostate cancer. This approach demonstrated favorable OS, DFS, and BRFS rates in a high-risk cohort with minimal toxicity.

Keywords: PSMA PET/CT, prostate cancer, salvage radiotherapy