Single-Dose Focal Salvage High Dose Rate Brachytherapy for Locally Recurrent Prostate Cancer.

AIMS: To evaluate focal high dose rate (HDR) brachytherapy in locally recurrent prostate cancer.
MATERIALS AND METHODS: Patients with biochemical relapse after non-surgical primary treatment for localised prostate cancer were selected after a negative screen for metastatic disease. Template mapping biopsies combined with multiparametric magnetic resonance imaging were used to identify the location of the tumour and the focal clinical target volume. The planning aim dose prescription was 19 Gy. Outcome measures were biochemical relapse-free survival and toxicity using International Prostate Symptom Score and Common Terminology Criteria for Adverse Events (version 4.0) scores.
RESULTS: Between March 2013 and December 2018, 50 patients underwent salvage HDR brachytherapy. The median follow-up was 21 months (range 1-53). Biochemical progression-free survival at 2 and 3 years was 63% and 46%, respectively. On multivariate analysis, only prostate-specific antigen nadir ≤0.5 ng/ml post-salvage (P = 0.03, hazard ratio 0.04) was associated with biochemical progression-free survival. Relapse was associated with distant metastases in 11/13 patients in whom this was investigated. Late grade 3 genitourinary toxicities were gross haematuria (three patients), severe lower urinary tract symptoms (two patients), erectile dysfunction (one patient) and urethral stricture requiring surgery (four patients). No acute and late grade 4 or 5 genitourinary and no grade 3 or higher gastrointestinal toxicities were recorded.
CONCLUSIONS: Focal salvage HDR monotherapy achieves biochemical control in 46% of patients at 3 years with acceptable toxicity rates in selected patients. Biochemical relapse was related to a post-salvage prostate-specific antigen nadir of ≥0.5 ng/ml. Long-term outcomes are needed to assess the impact on the natural history of prostate cancer in these patients.