ESTRO 2025 - Abstract Book

S2027

Clinical - Urology

ESTRO 2025

better outcomes for selected patients [1]. In a prospective cohort of patients we observed long clinical relapse free survival with ENRT and PET guided simultaneous integrated boost (SIB) [2]. Here we report the results of a mono institutional analysis of patients treated with ENRT and PET-guided SIB (ENRT group) vs PET guided directed RT (MDT group). For patients with repeated treatments for subsequent LN relapse, only the first treatment was considered for this analysis. Material/Methods: From 02/2005 to 10/2023, 254 patients were treated for PET+ LNs: 209 (776 LNs) with ENRT and 45 (57 LNs) with MDT. The median number of metastases was 2 (1-32) for ENRT patients and 1 (1-4) for MDT patients. [11C]-Choline PET/CT was used for 193 patients and [18F]-PSMA PET/CT for 61 patients. Concomitant MDT treatments for synchronous metastases were considered together, as a single treatment, when delivered by means of different treatment plans, for different LN levels. ENRT median biological equivalent dose (BED) considering α/β = 1.5 for prostate cancer was 115.7 Gy, PET-guided SIB BED was 162.8 [IQR 150.4, 167.64] Gy, and MDT median BED was 198.33 [150.00, 230.00] Gy. Results: Median follow up was 111.9 months IQR[63.37-152.66] for the ENRT group and 42.94 months IQR[31.34-61.19] for the MDT group. Biochemical relapse in the ENRT group was 61.7% vs 62.2% in the MDT group. To balance the differences only patients with up to 4 LNs were considered (maximum number of LNs in the MDT group). Five-year biochemical relapse-free survival was 42.2 % in ENRT group, vs 16.5% in MDT group (p=0.011) (See Fig.1). No statistically significant differences were observed for clinical relapse-free survival and overall survival. Late gastro intestinal grade≥2 toxicity was 5.3% (ENRT) vs 0% (MDT), late genito - urinary grade≥2 toxicity was 17.3 vs 2.2%, due to, above all, prostate bed irradiation.

Conclusion: Better biochemical relapse-free survival was observed with ENRT+SIB vs MDT considering up to 4 positive lymph nodes. ENRT toxicity was higher, but acceptable. ENRT could save/delay a significant number of patients from starting the treatment with androgen receptor pathway inhibitors [3], enabling savings for healthcare systems.