Stereotactic Ablative Radiation Therapy of Bone Metastases in an Oligometastatic Setting: One-Year Follow-Up of the BONY-M Phase 2 Trial

Purpose: SABR is increasingly applied to treat oligometastatic disease (OMD). As patients may be asymptomatic, severe toxicity must be carefully balanced with effect in this setting. The BONY-M trial aimed to determine the efficacy and toxicity after SABR of uncomplicated bone metastases in patients with OMD. Methods and Materials: The BONY-M trial is a single-arm phase 2 multicenter trial (clinicaltrials.gov ID: ClinicalTrials.gov ID NCT05101824) investigating SABR of uncomplicated bone oligometastases with 30 or 37.5 Gy in 3 fractions. Patients with OMD and ≥1 mechanical stable bone metastasis without epidural invasion were eligible for inclusion. Up to 5 active metastatic lesions were allowed if all received ablative therapy. The primary endpoint was 1-year local control rate (LCR). Secondary endpoints included toxicity (CTCAE) and survival. Results: The BONY-M trial included 67 patients with 79 bone metastases (31 spine, 48 nonspine) in Norway and Denmark. The 1-year centrally assessed LCR rate was 93.1% (95% confidence interval [CI], 87.3-99.2). Two patients had grade 3 fractures within 1 year, 3.3% (95% CI, 0%-7.8%) and 4 patients had a symptomatic skeletal event, 6.0% (95% CI, 0.0%-11.6%). The 1-year overall centrally assessed fracture rate was 9.9% (95% CI, 2.6%-16.7%; n = 7). The 1-year overall and progression-free survival were 92% and 62% after a median follow-up of 12.1 months. Conclusion: SABR of uncomplicated bone metastases with 37.5 or 30 Gy in 3 fractions showed a promising 1-year LCR with an acceptable toxicity profile in patients with OMD.