Stereotactic Ablative Radiotherapy Achieves Local Control on Bone Metastases

Results from a phase 2 trial showed a 1-year local control rate of 93.1% with SABR in patients with solid tumors who have uncomplicated bone metastases: © rdkcho - stock.adobe.com

Stereotactic ablative radiotherapy (SABR) of uncomplicated bone metastases achieved an encouraging 1-year local control rate with an acceptable toxicity profile in patients with oligometastatic disease when treated at a dose of 37.5 or 30 Gy in 3 fractions, according to results from the single-arm phase 2 BONY-M trial (NCT05101824) shared in The International Journal of Radiation Oncology, Biology, and Physics.

With a median follow-up of 12.5 months (95% CI, 12.3-12.9), the 1-year local control rate was 93.1% (95% CI, 87.3%-99.2%) at a lesion-per-lesion analysis, thus exceeding the 75% threshold set in the study. When analyzed as patient-per-patient, the 1-year local control rate was 91.8% (95% CI, 85.0%-99.0%).

At the 1-year follow-up, a competing risk analysis of local failure and death showed the cumulative incidence was 8.1% (95% CI, 1.2%-14.9%) for local failures and 4.6% (95% CI, 0.0%-9.6%) for death.

The overall 1-year fracture incidence inside or bordering the planning target volume was 9.9% (95% CI, 2.6%-16.7%); of that, 13.6% (95% CI, 0.3%-25.2%) and 7.7% (95% CI, 0.0%-15.9%) were for spinal and non-spine targets. The 1-year incidence of G3 fractures was 3.3% (95% CI, 0.0%-7.8%), and the 1-year symptomatic skeletal events rate was 6.0% (95% CI, 0.0%-11.6%).

The 6- and 12-month overall survival (OS) rates were 96% (95% CI, 91%-100%) and 92% (95% CI, 86%-99%), respectively. The median progression-free survival (PFS) was 13.6 months (95% CI, 10.4-not reached), with 6- and 12-month PFS rates of 71% (95% CI, 61%-83%) and 57% (95% CI, 46%-71%).

A subgroup analysis revealed that the PFS of oligoprogressive disease and induced oligometastatic disease combined was significantly lower for de novo and recurrent oligometastatic disease (P = .04), with a 12-month PFS rate of 44% (95% CI, 27%-69%) vs 65% (95% CI, 52%-81%). Notably, OS and PFS were higher for prostate and breast cancer compared with other primary tumor types, but not for renal cell carcinoma.

“These results confirm the clinical practice of SABR of bone metastases and the true potential in specific tumor types needs to be further investigated,” wrote lead study author Nicklas Juel Spindler, PhD, of the Department of Oncology at Copenhagen University Hospital in Herlev, Denmark, and coauthors, in the manuscript. “The [BONY-M] trial successfully reached its objective of implementing safe and effective SABR for bone metastases in patients with [oligometastatic disease], but longer follow-up is needed.”

From December 2019 to January 2022, 75 patients were enrolled in the trial, and 67 were included. Of the 67 patients included, there were 79 bone metastases, of which 31 were spinal and 48 were non-spinal. Treatment consisted of either 37.5 Gy or 30 Gy in 3 fractions; the recommended dose level was 37.5 Gy, though if the gross tumor volume or planning target volume was less than 80% of the dose prescribed to either structure, the 30 Gy in 3 fractions was prescribed.

Eligible patients were adults with solid tumors, one or more bone metastases eligible for SABR regardless of anatomical region, and a life expectancy of 6 or more months.

Bone metastases had to be deemed mechanically stable, with a diameter less than 5 cm. Assessment of bone stability in non-spine targets was done at the discretion of the treating radiation oncologist, and for spinal metastases, the modified Spinal Instability Neoplastic Score should be less than 6.

Those with a spinal tumor with a Bilsky Score greater than or equal to 1b, 3 or more continuous spine metastases within neighboring vertebrates, uncontrolled brain metastases, and prior radiotherapy that hindered compliance with constraints to organs at risk were excluded from participating in the trial.

The trial’s primary end point was the 1-year per-lesion local control rate measured from the time of enrollment. Secondary end points included OS, PFS, symptomatic skeletal events, and the rate of adverse effects (AEs). Pain-response and quality of life end points will be published separately.

Overall, 61% of patients experienced a treatment-related AE (TRAE) of any grade; 38% experienced a grade 1 event, 18% experienced a grade 2 event, and 4% experienced a grade 4 event. No grade 4 TRAEs or treatment-related deaths were observed.

Grade 1 and grade 2 pain related to treatment was reported in 42% during the 1-year follow-up, and 9% had any treatment-related pain from 12 to 52 weeks of follow-up.

References

Spindler NJ, Overseem Felter MB, Hansen O, et al. Stereotactic ablative radiotherapy of bone metastases in an oligometastatic setting: one-year follow-up of the BONY-M phase II trial. Int J Radiat Oncol Biol Phys. Published online July 24, 2025. doi:10.1016/j.ijrobp.2025.07.1419