Preliminary results of RTOG 0831, a randomized, double-blinded, placebo-controlled trial of tadalafil in the prevention of erectile dysfunction in patients treated with radiotherapy for prostate cancer.

9525 Background: Determine if prophylactic tadalafil maintains spontaneous (off-drug) erectile function (EF) compared to placebo in patients (pts) treated with radiotherapy (RT) for prostate cancer. Methods: Double-blind 1:1 randomization to tadalafil 5mg daily for 6 mos vs placebo starting with RT. Primary outcomes measured by International Index of Erectile Function (IIEF). Eligibility included pre-RT IIEF Question [Q] 1 response “sometimes/most times/always” able to get an erection. Ps treated with hormones were excluded. Primary outcome was response to IIEF Q1 at 30 wks (6 wks off drug). Pts were stratified by RT modality (external vs. brachytherapy) and age (≤65 vs. >65 years). 182 pts were needed in an intent-to-treat analysis to show a difference from 20% responders with placebo to 40% with tadalafil based on a 2-sided Fishers exact test with α=0.05 and 80% power. Results: We report on 155/222 analyzable/eligible pts. Median age was 63 years, white (73%), and external RT (63%). Mean total dose for ...