Salvage Low Dose Rate Brachytherapy For Intraprostatic Local Prostate Cancer Recurrence Following Definitive External Beam Radiation Therapy

Intra-prostatic local recurrence following definitive external beam radiation therapy (EBRT) represents a significant challenge in prostate cancer (PCa) management. While salvage brachytherapy has been proposed as an ideal treatment modality in such scenarios, long term data on toxicity and outcomes remain limited. We sought to describe the safety and efficacy of salvage low dose rate (LDR) brachytherapy for local recurrence following definitive EBRT for PCa. We conducted a multi-institutional cohort design study utilizing data from two prospectively maintained institutional prostate cancer databases. Patients were included who underwent salvage LDR brachytherapy for localized intra-prostatic PCa recurrence following prior definitive EBRT. All patients underwent prostate biopsy to confirm intra-prostatic recurrence and only those patients with both negative bone scan and radiographic lymph node evaluation (e.g. CT, MRI, PET scan) were included. Failure free survival (FFS) was defined as the time from salvage LDR implant until the time of biochemical (based on Phoenix criteria) or clinical failure; patients without recurrence were censored at the time of non-PCa death. Overall survival (OS) was defined as the time from salvage LDR implant until death. Toxicity was graded based on CTCAE criteria. Survival outcomes were determined using the Kaplan-Meier estimates. All patients signed informed consent for inclusion in this study. We identified 102 patients who met inclusion criteria. Median follow-up was 6.5 years. Median prior EBRT dose was 6840 cGy (range: 6000-8100 cGy) and median time from EBRT to salvage implant was 7.3 years. Palladium-103 was used in all cases and median implant D90 was 106.5 Gy. Most patients received combined androgen deprivation therapy (ADT) (94%) with median duration of ADT of 6.1 months. CTCAE G3+ toxicity occurred in 21 patients (21%). Of these, 20 experienced G3 GU toxicity and 3 experienced G3 GI toxicity; no grade 4/5 toxicity occurred. Urinary retention occurred in 17 (17%) patients. Five- and 10-year FFS estimates were 62.2% (95% CI 52.8-73.2%) and 51.3% (95% CI 35.6-62.1%), respectively. Five- and 10-year OS estimates were 83.2% (95% CI 76.0-91.1%) and 58.3% (95% CI 48.5-69.9%), respectively. Among patients previously treated with definitive EBRT, salvage LDR brachytherapy for localized intra-prostatic recurrence was safe with an acceptable rate of grade 3+ toxicity. Additionally, salvage LDR brachytherapy proved efficacious with 62% of patients remaining disease free at 5 years. Additional patients and longer follow-up are needed to confirm these results.