Rates of rectal toxicity in patients treated with high dose rate brachytherapy as monotherapy compared to dose-escalated external beam radiation therapy for localized prostate cancer

BACKGROUND Using a prospectively collected institutional database, we compared rectal toxicity following high dose rate (HDR) brachytherapy as monotherapy relative to dose-escalated external beam radiotherapy (EBRT) for patients with localized prostate cancer. METHODS 2683 patients treated with HDR or EBRT between 1994 and 2017 were included. HDR fractionation was 38 Gy/4 fractions (n = 321), 24 Gy/2 (n = 96), or 27 Gy/2 (n = 128). EBRT patients received a median dose of 75.6 Gy in 1.8 Gy fractions [range 70.2-82.8 Gy], using either 3D conformal or intensity modulated radiotherapy (IMRT). EBRT patients underwent 3D image guidance via an off-line adaptive process. RESULTS Median follow-up was 7.5 years (7.4 years for EBRT and 7.9 years for HDR). 545 patients (20.3%) received HDR brachytherapy and 2138 (79.7%) EBRT. 69.1% of EBRT patients received IMRT. Compared to EBRT, HDR was associated with decreased rates of acute grade ≥2 diarrhea (0.7% vs. 4.5%, p