1218 - Outcomes of Risk-Stratified and Intensified Salvage Re-Irradiation in Local Recurrence : A Prospective Cohort Comparison
Presenter(s)
C. Belliveau1, M. Barkati1, C. Lambert1, M. C. Beauchemin1, G. Delouya1, D. Taussky1, D. Béliveau-Nadeau1, M. K. Benhacene-Boudam1, B. Nicolas1, D. Duplan2, S. Clavel2, L. Igidbashian2, A. S. Gauthier-Pare2, G. Mok2, D. H. A. Nguyen3, B. Bahoric4, T. M. Niazi4, and C. Menard5; 1Département de radio-oncologie, Centre Hospitalier de l'Université de Montréal (CHUM), Montréal, QC, Canada, 2Département de radio-oncologie, Centre Intégré de Santé et de Services Sociaux de Laval, Laval, QC, Canada, 3Département de radio-oncologie, Hôpital Maisonneuve-Rosemont, Montreal, QC, Canada, 4Department of Radiation Oncology, Jewish General Hospital, McGill University, Montreal, QC, Canada, 5Département de radio-oncologie, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montréal, QC, Canada
Purpose/Objective(s):
Re-irradiation using focal high dose rate (HDR) brachytherapy for infield prostate recurrences has minimal toxicity but limited disease control. We hypothesized that risk adapted intensification, using focal HDR for low risk (LR) and combined HDR with stereotactic radiotherapy (sRT) for high risk (HiR) patients, would safely improve outcomes.Materials/Methods:
Patients were prospectively enrolled (NCT03378856) in sequential cohorts: C1 (pre algorithm) and C2 (intensified algorithm). C1 received focal HDR; pelvic RT was added for N+. In C2, intensification was risk-stratified: LR patients (PSA <7, <T3b, N0, concordant imaging/pathology, >3-year RT interval) received focal HDR (15 Gy x2 weekly); HiR (not meeting LR criteria) received focal HDR (13–15 Gy x1) plus sRT to the entire prostate ± pelvis if N+. HiR EQD2 targets (a/ß 1.4) were >120 Gy to the tumor, >66 Gy to the prostate, >46 Gy to the pelvis, increasing to >80 Gy to N+. Isolated seminal vesicle (SV) recurrences received sRT alone (aim EQD2 >75 Gy). Patients were staged with MRI ± PSMA-PET, followed by systematic and targeted biopsies. Endpoints were treatment-related toxicity (CTCAE v5) and Failure-Free Survival (FFS; PSA nadir + 2ng/mL or radiologic progression) in patients with >6 months’ follow-up. C1 patients were retrospectively risk-stratified using the C2 algorithm for comparison. Survival was assessed using Kaplan Meier and Cox proportional hazards regression. Stabilized inverse probability treatment weighting (IPTW) adjusted for T/N stage, PSA, hormonal therapy (HT), Gleason, and RT interval (ASMD <0.10).Results:
A total of 97 patients were enrolled (C1 n=41, C2 n=56 (n=23 LR, n=28 HiR, n=5 SV)) between May 2018 and October 2025; C2 beginning in May 2022. Salvage RT doses are summarized in Table 1. PSMA-PET use was 60% in C1 vs 96% in C2; adjuvant HT was 78% vs 69%. Among patients with = 6 months of follow-up (C1, n=41; C2, n=48), median follow-up was 66 months (range 30–80) and 24 months (range 10–40), respectively. In C2, these included 23 LR, 20 HiR, and 5 isolated SV recurrences. At 24 months, cumulative Grade 2/3 toxicity was 44%/0% in C1 vs 38%/2% in C2 (ns). Eugonadal rates (testosterone = 5.2 ng/mL) were similar (93% in C1 vs. 94% in C2), while FFS was 78% in C1 vs 96% in C2 (HR 0.27; 95% CI 0.06–1.27; p=0.08), with consistent findings after IPTW adjustment. Stratified analysis showed hazard reductions in both intensified LR (HR 0.16; p=0.14) and HiR (HR 0.31; p=0.15) groups compared to reclassified controls.Conclusion:
Risk-adapted and intensified salvage RT is well tolerated and achieved promising early disease control across risk groups, supporting its premise as an effective strategy. Limitations include the sequential, non-randomized cohort design and low event count, warranting further prospective validation. Table 1.| C1 (n=41) | C2 (n=56) | p | |
| Median EQD2 (a/ß 1.4) to Primary Tumor (IQR) | 110 Gy (110) | 137 Gy (130–137) | <0.01 |
| Treatment volumes | |||
| Entire Prostate Treated | 3 (7%) | 28 (50%) | <0.01 |
| Nodal Tumor Treated | 4 (10%) | 6 (11%) | 1 |