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Data on SBRT for long bone metastases are scarce and limited to a few cases series. The purpose of this multicenter retrospective study is to report efficacy and safety of SBRT for long bone metastases, with fracture after SBRT being the primary endpoint.    

An international multicenter retrospective cohort of 120 patients with 123 long bone metastases from seven centers in Australia, Canada, Netherlands, Switzerland and the USA has been established for this analysis. All patients were treated with SBRT techniques in ≤10 fractions of total radiation doses higher than conventional radiation doses of 8 Gy/1, 20 Gy/5 or 30 Gy/10. 

The median follow-up was 22 months (range 6-91 months). The majority of patients (68%) were male, with a median age of 64 (range 34-90 years). All but one patient had a Karnofsky performance status of ≥70. There were 86 femur (68.1%), 26 humerus (21.3%), 9 clavicle (7.3%) and 4 tibia (3.3%) metastases from prostate (49 [40%]), breast (23 [19%]), lung (17 [14%]), kidney (12 [10%]) and other (22 [17%]) malignancies. Twenty-nine percent of metastases were lytic. Eleven impending fractures were diagnosed before SBRT, of which 4 were surgically stabilized and 1 irradiated prior to SBRT. Oligometastases alone or in combination with pain or preserving function/skeletal integrity were the indication for treatment in 89 (74%) patients. The most common SBRT dose prescriptions were 30-50 Gy/5 (50%) and 18-24 Gy/1 (30%). Local metastasis control was 96.9%, 92.3% and 83.7% at 12, 24 and 36 months, respectively. With a median time to fracture of 10 months (range 1-28 months), 9 pathological fractures (7.3%) were diagnosed. Of the 9 pathological fractures, 3 developed at a site of impending fracture. Seven pathological fractures were in lytic metastases. During follow-up, 8 stabilization surgeries (6.5%) and 2 additional SBRT treatments (1.6%) were performed. Cumulative incidence of pathological fracture was 4.3%, 5.6% and 9.9% at 12, 24 and 36 months, respectively (Fig.1). On multivariate analysis, none of studied variables (gender, primary tumor site, metastasis location, metastasis type, and impending fracture status) was significantly associated with pathological fracture.

SBRT appears to be an effective treatment for long bone metastases with an acceptable risk of pathological fracture, which does not appear to be increased in historical comparison with conventional low-dose radiotherapy.