Stereotactic body radiation therapy for prostate cancer: systematic review and meta-analysis of prospective trials

Background: Despite the increasing worldwide utilization of stereotactic body radiation therapy (SBRT) for prostate cancer, there are no known summative data regarding its safety and efficacy. To address this knowledge gap, we conducted a PRISMA-guided systematic review and meta-analysis of prospective prostate SBRT trials. Results: Fourteen trials with a total of 2,038 patients were included. Median follow-up was 37 months (range 6-55 months). Most patients had cT1-T2a, Gleason ≤7 disease with median pre-treatment PSAs of 5-10; 1,042 (51%) were low-risk, 744 (37%) were intermediate-risk, 158 (8%) were high-risk, and the remainder were unreported. Doses ranged from 33.5-50.0 Gy, most typically in 5 fractions, with nearly all studies delivering nondaily fractionation with some type of daily image guidance. Outcomes were converted into counts at the end of one year. The pooled rate of FFBF was 98% [95% confidence interval, 97-98%]. The pooled rate of late grade ≥3 gastrointestinal and genitourinary toxicities were 1% [0-5%] and 2% [1-3%], respectively. Methods: PubMed and Google Scholar were queried for prospective studies evaluating survival and/or toxicity outcomes in SBRT (≤5 fractions) for localized prostate cancer. Pooled rates of freedom from biochemical failure (FFBF) and late grades ≥3 gastrointestinal (GI) and genitourinary (GU) toxicities were assessed. Meta-analysis of proportions was logit transformed and pooled using generalized linear mixed models (both fixed and random effects) and subsequently back transformed to standard proportions. Conclusions: Despite the lack of long-term follow-up and heterogeneity of the available evidence, prostate SBRT affords appropriate biochemical control with few high-grade toxicities. These data have implications for ongoing worldwide utilization of prostate SBRT as well as ongoing prospective investigations.