ESTRO 2025 - Abstract Book

S393

Brachytherapy - Urology

ESTRO 2025

113 (95.9%) patients underwent focal therapy; 5 (4.2%) had whole gland treatment. 15 (12.7%) patients were on ADT at the time of salvage.

Results: Median follow-up was 33.5 months (0-102 months). Median time to relapse was 60 months (0-NR months). 7 deaths were reported, all had metastatic disease at time of death. Median RFS was 30 months (0-NR months).

50 (42%) patients had biochemical and/or radiological relapse. Relapse sites included bone (n=11), lymph nodes (n=15), pelvis (n=3), intra-prostatic (n=19) and visceral (n=2). Of 19 intra-prostatic recurrences, 15 were in-field. Recurrence within the re-irradiated volume therefore represented 12.7% of the total salvage cohort; local control probability was 83.8%. Late gastrointestinal toxicity data was available for 76 patients. 6 patients developed fistula requiring urinary and/or bowel diversion; all occurred in the context of peri-rectal spacer insertion. There were no ≥ grade 3 toxicities in patients without spacer. 1 patient developed rectal cancer 7 years later. Late genitourinary toxicity data was available for 78 patients; 24.3% developed ≥ grade 3 toxicities. The CTV ranged from 2.4cm 3 -49.16cm 3 . There was no difference between volume irradiated and late genitourinary toxicity (H(3) = 1.37, p= 0.71). Time to first relapse demonstrated a statistically significant relationship with risk of relapse post salvage (χ2, df = 1, p=0.002). There was no association between NCCN risk groups for predicting response (χ2, df = 6, p= 0.17) nor between PSA nadir of <0.2 as compared to ≥0.2 and time to relapse (χ2, df = 1, p = 0.77). Conclusion: The local probability control rate was 83.8% with a 5-year relapse free survival of 30%. Treatment is well tolerated even in the context of previous radiation treatment. Time to relapse from first diagnosis may help to predict risk of secondary relapse post salvage treatment. Future work will aim to determine predictors of outcome to inform decision making for salvage brachytherapy.

Keywords: salvage brachytherapy, prostate cancer