Outcomes of a Dose-Escalated Stereotactic Body Radiation Phase 1 Trial for Patients With Low- and Intermediate-Risk Prostate Cancer.

PURPOSE: This study presents a prospective phase 1, institutional review board-approved dose-escalated stereotactic body radiation therapy trial for prostate cancer (CaP) to assess the impact of dose level on quality of life, toxicity, and clinical outcomes.

METHODS AND MATERIALS: From 2011 to 2016, 26 patients with low- and intermediate-risk CaP received 40, 45, and 50 Gy in 5 fractions to the prostate in cohorts of 9, 10, and 7 patients. Self-reported quality of life was prospectively measured from the Expanded Prostate Cancer Index Composite and American Urological Association. Common Terminology Criteria for Adverse Events (version 4.03) data were collected to observe acute and late toxicities. The Phoenix definition was used to calculate outcome. No patients received androgen deprivation therapy.

RESULTS: Median follow-up was 67.2 months (range, 71-230 months). There was an increase in Expanded Prostate Cancer Index Composite and American Urological Association scores followed by a return to baseline over 2 years for all cohorts. There were no grade 3 or higher toxicities or significant differences in toxicity between treatment arms. The prostate-specific antigen (PSA) nadir was significantly lower in the 45-Gy and 50-Gy cohorts when compared with the 40-Gy cohort (P < .05). Two biochemical failures were observed in the 40-Gy arm after 43 and 62 months, resulting in a freedom from biochemical failure rate of 92%. PSA survival was 100%, and actuarial overall survival was 96%. PSA nadir was 0.6, 0.1, and 0.1 ng/mL, in the 40-Gy, 45-Gy, and 50-Gy cohorts, respectively.

CONCLUSIONS: This prospective, phase 1 dose-escalation study of stereotactic body radiation therapy for CaP identified acceptable genitourinary and gastrointestinal toxicity for each dose level of 40, 45, and 50 Gy. Although there was no difference in biochemical failure between the groups, we showed that higher doses of 45 and 50 Gy are associated with improved PSA nadir. The results of this study will be used to develop a larger prospective study to confirm the findings.