Predictors for post-treatment biopsy outcomes after prostate stereotactic body radiotherapy

PURPOSE: To investigate predictors associated with post-treatment biopsy outcomes after stereotactic body radiotherapy (SBRT) for localized prostate cancer. MATERIALS AND METHODS: 257 patients treated with prostate SBRT to dose levels of 32.5 Gy to ≥40 Gy in 5–6 fractions underwent a post-treatment biopsy performed approximately two years after treatment to evaluate local control status. 73 had% intermediate-risk disease (n=187) and the remaining 17% (n=43) and 10% (n=27) had low-risk and high-risk disease, respectively. RESULTS: The incidence of positive, negative, and treatment-effect post-treatment biopsies were 15.6%, 57.6%, and 26.8%, respectively. The incidence of a positive biopsy according to dose was 37.5% (n=9/24), 21.4% (n=6/28), 19.4% (n=6/31), and 10.9% (n=19/174) for 32.5 Gy, 35 Gy, 37.5 Gy, and ≥40 Gy, respectively. In a multivariable model, patients treated with SBRT doses of