Salvage brachytherapy for locally-recurrent prostate cancer after radiation therapy: A comparison of efficacy and toxicity outcomes with high-dose rate and low-dose rate brachytherapy.

Background: Brachytherapy (BT) is widely used for salvage therapy in patients with biochemical failure (BF) after radiotherapy for prostate cancer (PCa). Although low-dose-rate (LDR) and high-dose-rate (HDR) BT are both used for salvage therapy, it is not clear whether there are any differences between these two approaches in terms of efficacy or toxicity in this setting. Therefore, we review the institutional experience of the members of the Urological Tumour Working Group (URONCOR) of the Spanish Society of Radiation Oncology (SEOR) to compare these two techniques.

Methods And Materials: Between 2001 and 2016, 119 patients with biopsy-proven, locally-recurrent PCa underwent salvage BT (LDR, n = 44; HDR, n = 75) after primary radiotherapy. Relapse-free survival (RFS) and cause-specific survival (CSS) after salvage therapy were analyzed. Toxicity was assessed according to the RTOG scale.

Results: Median follow-up after salvage BT was 52 months. Overall, the 5-year prostate-specific antigen (PSA) RFS rate was 71% (95% CI, 65.9%-75.9%). No significant between-group differences in RFS were observed (p = 0.063). Five-year CSS for the LDR- and HDR-BT groups were 96.5% and 93%, respectively. Overall, 38 patients (32%) developed biochemical progression (Phoenix definition) after salvage BT: 14 patients (32%) in the LDR group and 24 (32.5%) in the HDR group. On the multivariate analysis, the following variables were significantly associated with progression, time to BF from primary radiotherapy <30 months (p = 0.014); and post-salvage nadir PSA (p = 0.000). There were no significant between-group differences in toxicity. Overall, there were 13 cases of urethral stricture, 22 cases of urinary incontinence, and 13 cases of haematuria. Toxicity ≥grade 3 was observed in 23.5% of patients.

Conclusions: These findings show that both HDR-BT and LDR-BT yield comparable efficacy and toxicity outcomes in patients undergoing salvage treatment for locally-recurrent prostate cancer after primary radiotherapy. Predictors of worse outcomes after salvage BT were post-salvage nadir PSA and time to BF from initial radiotherapy.