Dosimetric parameters predict short-term quality-of-life outcomes for patients receiving stereotactic body radiation therapy for prostate cancer

Purpose: Stereotactic body radiation therapy (SBRT) is a treatment option for patients with localized prostate cancer, with reported clinical and health-related quality-of-life (QOL) outcomes comparable to standard fractionation radiation therapy. The goal of this study was to evaluate correlations between short-term QOL outcomes and dosimetric parameters to guide future prostate SBRT planning. Methods and materials: From 2010 to 2013, QOL data were prospectively collected from 75 patients enrolled in a prostate SBRT clinical trial. A comparison was made between Expanded Prostate Cancer Index Composite scores for patients with the top 25th percentile versus the bottom 75th percentile of the following dose-volume histogram parameters: planning target volume V100; bladder V50 and V100; and rectum V50, V80, V90, and V100. A linear mixed-effect model was used to estimate the difference between the 2 strata for each parameter. Results: Median follow-up was 12 months. Patients with planning target volume V100 volumes >120 cm(3) had the worst reduction in urinary QOL. Urinary QOL was also decreased significantly in patients with bladder V100 volumes >5.5 cm(.)(3) Bowel QOL was decreased significantly in patients with rectal V90 and V100 volumes >4.2 and >1.5 cm(3), respectively. Conclusions: Patients with large prostate size or large volumes of rectum and bladder that receive >= 90% of the prescribed radiation dose are more susceptible to short-term QOL decrements after prostate SBRT. These volumes should be minimized to maximize recovery to baseline QOL after prostate SBRT. (C) 2015 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.