Late toxicity after single dose HDR prostate brachytherapy and EBRT for localized prostate cancer: Clinical and dosimetric predictors in a prospective cohort study.

PURPOSE: To describe the genitourinary (GU) and gastrointestinal (GI) late toxicity profile and to analyse the clinical and dosimetry outcomes predictors of the combination of EBRT and high-dose-rate (HDR) prostate brachytherapy (BT) for localized prostate cancer. MATERIALS AND METHODS: Between January 2012 and May 2017, 210 patients were included in a prospective protocol. Treatment consisted in HDR-BT (15 Gy single fraction) plus 3DCRT (37.5 Gy/15 fractions). Univariate and multivariate logistic regressions were used to analyse the impact of variables on late toxicity. RESULTS: Median age was 71 (56-82), 12.4% of patients had low, 44.3% intermediate and 41% high-risk prostate cancer. Median prostate volume was 28.4 cc. Median V100, V150, V200 were 98.2%, 27% and 7.4% respectively. Median urethra Dmax, rectum D1cc and D2cc, were 113.5%, 62.2%% and 54.2% respectively. After a median follow-up of 41 months (5-75) late G2 GU and GI late toxicity was observed in 14.8% and 5.2% of patients respectively. Late G3 GU and GI toxicity occurred in 0% and 1% of patients respectively. There were no outcome correlations with late G ≥ 2 GU toxicity on univariate analysis. Previous cardiovascular comorbidity (p = 0.042), and dose to the rectum D2cc (p = 0.016) and D1cc (p = 0.017) were associated with G ≥ 2 GI toxicity. Multivariate analysis showed that rectum D1cc (HR11.56; 95%CI 1.4-92.1; p = 0.021) and prior history of cardiovascular disease (HR3.6; 95%CI 1-12.9; p = 0.045) remained independent predictors of G ≥ 2 GI toxicity. CONCLUSIONS: There is a low incidence of late GU and GI morbidity using single fraction HDR-BT and hypofractionated EBRT. Previous cardiovascular disease and dose to the rectum were observed to correlate with GI toxicity.