Multicenter phase 1-2 trial of single-fraction stereotactic body radiotherapy for localized prostate cancer

Stereotactic body radiotherapy (SBRT), most commonly delivered in 5 fractions, is an established treatment option for patients with localized prostate cancer. The phase 1-2 ONE-SHOT trial at 5 centers in Europe and the US evaluated single-fraction high-dose SBRT for men with localized prostate cancer at low or intermediate risk, with ISUP grade group 1 or 2, and without significant tumor in the transitional zone. Patients were treated with a 19-Gy single-fraction prostate SBRT with urethra-sparing and intrafraction motion control. The primary endpoint was biochemical relapse-free survival (bRFS) rate at 3 years (expected value of 96% included in the 95% CI). Among the 45 patients recruited (median age 72 years; range 60-82), 43 were treated per protocol. The median follow-up was 55.3 months (IQR 49.9-60.7). The estimated 3-years bRFS rate was 92.9% (95% CI 85.4-100), meeting the primary endpoint. At 3 years, grade 2 GU and GI adverse events were observed in 4 (9.8%) and 2 (4.9%) participants, respectively, with only one grade-3 proctitis observed at month 12. Grade 2 or higher erectile dysfunction increased for 9 of 42 patients (21.4%) at baseline to 15 of 39 patients (38.4%) at 3 years. A significant minimally clinically important change in Expended Prostate Cancer Index Composite scores was observed in 6 (14%) and 12 (28%) participants for GU and sexual scores, respectively. The impact in GI bother scores was minimal. The authors conclude that a single-fraction 19-Gy urertha-sparing SBRT achieved a 3-year bRFS rate of 92.9%, with grade 2 GU and GI AEs remaining below 10% and 5%, respectively, at 3 years. Longer follow-up is warranted to assess long-term disease control.