Salvage brachytherapy for locally recurrent prostate cancer after definitive radiotherapy – a multicentric French cohort by the SFRO brachytherapy group

BACKGROUND AND PURPOSE: Salvage brachytherapy (BT) after definitive irradiation for prostate cancer is gaining increasing interest, although many areas of uncertainty remain. MATERIALS AND METHODS: We established a large national retrospective cohort including all patients treated with salvage prostate BT for isolated prostatic local relapse after definitive radiotherapy between 2006 and 2022 in seven French expert centers. RESULTS: A total of 266 patients were included. At initial diagnosis, 42 % of patients presented with high-risk disease. Primary irradiation consisted of external beam radiotherapy (EBRT) in 78 % of cases, most commonly delivered with a 3D conformal technique (51 %), with a median dose of 74 Gy. Median PSA at relapse was 3.7 ng/mL. Salvage BT was performed using low-dose-rate (LDR) permanent iodine seed implantation in 63 % of patients and high-dose-rate (HDR) brachytherapy in 37 %. Seventy percent of patients were treated with whole-gland irradiation, while the remainder received a focal approach. In 34.5 % of cases, androgen deprivation therapy (ADT) was combined with salvage BT. After a median follow-up of 60.1 months, 135 (50.7 %) of patients experienced biochemical relapse. Median biochemical progression-free survival (bPFS) was 40.0 months. On multivariate analysis, initial risk group (high-risk: HR = 1.64, 95 % CI [1.13-2.37], p = 0.008), BT technique (HDR: HR = 2.14, 95 % CI [1.41-3.26], p = 0.0004), and treated volume (focal vs. whole-gland: HR = 2.14, 95 % CI [1.23-3.73], p = 0.007) were significantly associated with bPFS. Late grade 3 gastrointestinal and genitourinary toxicities occurred in 3 % and 14 % of patients, respectively. CONCLUSION: Salvage BT provides encouraging disease control with an acceptable toxicity profile. Careful patient selection remains essential.