PO0413

Salvage brachytherapy (BT) is gradually becoming the preferred treatment modality in cases of isolated local relapse following definitive irradiation for prostate carcinoma, given the high morbidity of the historical treatment option that is salvage prostatectomy. The aim of this study was to gather the experience of French centers with expertise in prostate BT as a salvage treatment. A large national retrospective cohort was set up, retrospectively recording all patients from 7 French centers treated with salvage BT between 2006 and 2022 for isolated local relapse after definitive radiotherapy. A total of 269 patients were included. Half of patients presented with high-risk disease at first treatment. The initial irradiation consisted in external beam radiotherapy (EBRT) for 77% of patients, EBRT + BT for 4% of patients and exclusive iodine 125 seeds BT for 19% of patients. EBRT was mostly a 3D technique (72%) and median dose to the prostate was 74Gy. 49% received androgen deprivation therapy at the time of first irradiation. Median interval between initial irradiation and relapse was 8 years. Median PSA at relapse was 3.9 ng/mL. 10% of patients were castrate-resistant at the time of salvage BT. Salvage BT was delivered with an iodine seeds LDR technique for 61% of patients and with a HDR technique for 39% of patients. 84% of patients were treated on the whole-gland, while the rest benefited from a more focal approach. For 40% of patients, ADT was associated to salvage BT. After a median follow-up of 57 months, 43% of patients presented with biochemical relapse. Median PFS was 39 months. Grade 3 GI and GU toxicity occurred in <1% and 10% of patients, respectively. One patient suffered from grade 4 urinary retention. Salvage BT yields promising control rates with a safe toxicity profile. Prospective data are needed to position salvage BT as a new standard.