Single-Fraction Stereotactic Body Radiotherapy for Localized Prostate Cancer

Importance: Stereotactic body radiotherapy (SBRT), most commonly delivered in 5 fractions, is an established treatment option for patients with localized prostate cancer. While efforts to further reduce treatment to fewer than 5 fractions are ongoing, the efficacy and tolerability of single high-dose SBRT remain to be established. Objective: To determine in men with localized prostate cancer whether a single-fraction SBRT can be a valid treatment option in terms of biochemical disease control and safety. Design, Setting, and Participants: This multicenter, single-arm, prospective, phase 1/2 nonrandomized clinical trial included men with localized prostate cancer at low or intermediate risk, with International Society of Urological Pathology grade group 1 or 2, and without significant tumor in the transitional zone. Participants were recruited between 2017 and 2022 in 5 academic centers in Europe and the US. Data were analyzed between February and May 2026. Intervention: Participants were treated with a 19-Gy single-fraction prostate SBRT with urethra-sparing and intrafraction motion control. Main Outcomes and Measures: The primary end point was biochemical relapse-free survival (bRFS) at 3 years (expected value of 96% included in the 95% CI). Secondary end points included occurrence of genitourinary (GU), gastrointestinal (GI), and sexual adverse events (AEs) and quality of life (QOL) assessment. Results: Among the 45 patients recruited (median age, 72 [range, 60-82] years), 43 were treated per protocol. After a median follow-up of 55.3 (IQR, 49.9-60.7) months, the estimated 3-year bRFS was 92.9% (95% CI, 85.4%-100%), meeting the primary end point. At 3 years, grade 2 GU and GI AEs were observed in 4 (9.8%) and 2 (4.9%) participants, respectively, with only a grade-3 proctitis observed in 1 patient at month 12. Grade 2 or higher erectile dysfunction increased from 9 of 42 patients (21.4%) at baseline to 15 of 39 (38.4%) at 3 years. A significant minimally clinically important change in Expanded 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. Conclusions and Relevance: In this multicenter phase 1/2 trial, a single-fraction 19-Gy urethra-sparing SBRT met the primary end point, achieving a 3-year bRFS 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. Trial Registration: ClinicalTrials.gov Identifier: NCT03294889.