847 POSTER Difference in rectal dosimetry between pre-plan and post-implant analysis in transperineal interstitial brachytherapy for prostate cancer

Abstract

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.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.Median follow-up was 12 months. Patients with planning target volume V100 volumes > 120 cm3 had the worst reduction in urinary QOL. Urinary QOL was also decreased significantly in patients with bladder V100 volumes > 5.5 cm3. Bowel QOL was decreased significantly in patients with rectal V90 and V100 volumes > 4.2 and > 1.5 cm3, respectively.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.