Salvage Brachytherapy for Recurrent Prostate Cancer after Definitive Radiation Treatment and Factors That May Impact Outcomes

Abstract

Salvage low-dose-rate (LDR) brachytherapy is a potential treatment option for patients with locally recurrent prostate cancer following primary radiation therapy. Here we report our single institution outcomes and toxicity when utilizing LDR brachytherapy in the salvage setting. Nineteen patients with biopsy-proven locally recurrent prostate cancer underwent salvage LDR brachytherapy under transrectal ultrasound guidance utilizing 103 Pd to 120 Gy from August 2010 through February 2018. Prostate-specific antigen (PSA) failure was determined utilizing the Phoenix (nadir+2) definition. Toxicity was graded using Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and patient reported questionnaires including the Expanded Prostate Cancer Index Composite (EPIC) and American Urological Association (AUA). Median follow-up was 41 months. The 4- and 5- year PSA relapse-free survival (RFS) following salvage treatment were 78.9% and 68.4%, respectively. Androgen deprivation therapy was utilized in conjunction with salvage treatment in 7 patients (37%). On univariate analysis, 5- year PSA relapse was associated with both patients who experienced early failures after initial definitive treatment (p=.012), or if the patient had received stereotactic body radiation treatment (SBRT) (p=.005) prior to salvage treatment. Of the four patients who were treated following a biopsy-proven recurrence after initial SBRT treatment, two patients (50%) experienced PSA failure at a median of 9 months after their salvage treatment. AUA and EPIC scores showed a significant increase at one-month follow-up after salvage brachytherapy (p = .023) and returned to baseline within six months. Three patients (16%) experienced Grade 3 acute or late urinary toxicity, five patients experienced Grade 2 acute urinary toxicity, and one patient experienced Grade 2 acute rectal toxicity. Post-implant dosimetry did not predict for toxicity. There were no Grade 4 or 5 toxicities. LDR brachytherapy is a viable treatment option in the salvage setting with minimal morbidity. While longer follow-up is needed, early failures from initial radiation treatment and prior SBRT may portend for worse outcomes following salvage LDR brachytherapy.