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

Abstract

To evaluate focal high dose rate (HDR) brachytherapy in locally recurrent prostate cancer. Patients with biochemical relapse after non-surgical primary treatment for localized prostate cancer were selected after a negative screen for metastatic disease. Template mapping biopsies combined with multiparametric MRI were used to identify the location of the tumor and the focal clinical target volume. The planning aim dose prescription was 19Gy. Outcome measures were biochemical progression free survival (bPFS) and post treatment gastrointestinal (GI) & genitourinary (GU) toxicities using CTCAE v4.0 scores. Between March 2013 and December 2018, fifty-seven patients were included in this study. Median follow-up was 21 months bPFS at 2 and 3 years were 61% and 48%, respectively; median time to biochemical failure (BF) was 17 months. On multivariate analysis, the bPFS was best predicted by PSA nadir ≤0.5 ng/ml post-salvage (p<0.0001, hazard ratio 33.82), PSA doubling time ≥ 12 months post-salvage (p=0.01, hazard ratio 0.05) and primary PSA (p=0.01, hazard ratio 2.98). Late grade 3 GU toxicities were gross hematuria (5%), severe lower urinary tract symptoms (4%), erectile dysfunction (2%), and urethral stricture requiring surgery (5%). No acute and late ≥grade 4 GU and ≥grade 3 GI toxicities were recorded. Focal salvage HDR monotherapy is an effective treatment with acceptable toxicity rates in selected patients. Strong predictors of biochemical control in this study were PSA nadir post- salvage ≤ 0.5 ng/ml, PSA doubling time post salvage≥ 12 months and presenting PSA. Long term outcomes are needed to assess the impact on the natural history of prostate cancer in these patients.