A European multicenter cohort study of patients with oligometastatic prostate cancer receiving stereotactic body radiotherapy for non-spinal bone metastases

Purpose Stereotactic body radiotherapy (SBRT) is increasingly used for the treatment of bone metastases (BoM) of oligometastatic prostate cancer. This study aims to provide new information on SBRT for non-spinal BoM of oligometastatic prostate cancer in a large multicenter cohort. Methods Retrospective data from 20 European centers on patients with oligometastatic prostate cancer who received SBRT for BoM between 2010 and 2024 were analyzed to assess patterns of practice, efficacy, safety, and prognosis. Results A total of 317 patients with 401 BoM were analyzed. The SBRT was delivered in 1–10 fractions, with a median fractional dose of 8 Gy (range 4.0–22.0 Gy) and a corresponding total prescribed dose of 18.0–50.0 Gy. Median follow-up was 25.4 months. Local control at 1 and 3 years was 98.0% (95% confidence interval [CI]: 95.2%–99.1%) and 93.3% (95% CI: 88.1%–96.2%). Progression-free survival (PFS) rates after 1 and 3 years were 74.2% (95% CI: 67.5%–79.6%) and 44.1% (95% CI: 36.0%–51.9%). Overall survival (OS) at 1 and 3 years was 98.4% (95% CI: 95.7%–99.4%) and 86.3% (95% CI: 79.4%–91.1%). In multivariable analysis, improved PFS and biochemical recurrence-free survival (BRFS) were observed for higher biologically effective doses with an α/β = 4 Gy (BED 4 ) to the gross tumor volume (GTV) mean (hazard ratio [HR] 0.99; p < 0.01; HR 0.98; p < 0.001) and use of a simultaneous integrated boost (SIB; HR 0.41; p = 0.04; HR 0.40; p < 0.01; respectively). Grade 3 acute and late adverse events were rarely reported (1.0% and 0.5%, respectively). Conclusion Stereotactic body radiotherapy of non-spinal BoM from oligometastatic prostate cancer was an effective and well-tolerated treatment. Higher GTV-BED and the use of an SIB concept were associated with more favorable PFS and BRFS, warranting confirmation in prospective studies and further standardization of target volume and dose prescription concepts.