Erectile Function after High-Dose-Rate Brachytherapy-like Stereotactic Body Radiation Therapy for Organ-Confined Prostate Cancer

Abstract

Given the higher dose of radiation per fraction using stereotactic body radiation therapy (SBRT) there is concern about erectile function after prostate SBRT. This endpoint was measured in a prospective multi-institutional study of high-dose-rate brachytherapy-like (HDR-like) SBRT for prostate cancer. Between 2007 and 2012, 259 men with clinically localized prostate cancer were treated with SBRT monotherapy using a heterogeneous, HDR-like approach. Patients were treated with robotic SBRT to a total dose of 38 Gy in 4 fractions. Patients did not receive androgen deprivation therapy (ADT). Potency was defined as a score of 4 or 5 on question 8.a of the patient-reported quality of life (PR-QOL) survey EPIC-26. In addition, the Sexual Health Inventory for Men (SHIM) was collected. PR-QOL was assessed at baseline and 6, 12, 24, 36, 48, and 60 months after treatment. Erectile function was correlated with multiple patient and dosimetric variables. There were 107 men potent at baseline, including 46 low- and 61 intermediate-risk patients, with a median age of 65 years (range, 45-80 years). The proportion of patients reporting potency decreased with time post-treatment. The median time post-treatment to the first report of “non-potent” was 12 months. The 24- and 60-month proportion potent was 43% and 36%, respectively. None of the dosimetric variables (dose to prostate, penile bulb, and neurovascular bundles) were found to correlate with potency at any time point. Likewise, neither baseline testosterone levels nor age at treatment predicted potency. Baseline SHIM score was correlated with higher potency rates at 6 and 60 months post-treatment (median baseline SHIM 21.6 for potent versus 16.2 for not potent at 60 months, p=0.004). Smaller prostate volume was correlated with a higher potency rate at 60 months (median prostate volume 33.8 cc for potent versus 46.1 cc for not potent at 60 months, P=0.008). Only higher baseline sexual QOL and a smaller pre-SBRT prostate volume were correlated with improved long-term post-treatment erectile function post-SBRT, while no other prostate, penile bulb or neurovascular bundle dosimetry variable had any significant measurable potency outcome correlation. This suggests that “patient factors” are more significant than dosimetry factors in predicting sexual QOL domain outcome post-SBRT.