Outcomes of Stereotactic Body Radiation Therapy (SBRT) for Femur Oligometastases

Abstract

Stereotactic body radiation therapy (SBRT) is increasingly used for oligometastatic bone disease, but there is limited data regarding the clinical outcomes of utilizing SBRT in treatment for femur metastases, which was excluded from SABR-COMET. We aimed to identify patient or treatment factors associated with clinical outcomes among patients treated with SBRT to femur metastases for oligometastatic disease control or re-irradiation. We identified 50 patients with 56 femur lesions consecutively treated with SBRT at a single institution May 2017-June 2022. The Kaplan-Meier method was used to characterize time-to-event endpoints and Cox proportional hazards models were performed to evaluate the associations between baseline factors and clinical outcomes. Local control was defined as the absence of regional tumor progression at treated area or need for surgical fixation post radiation. Most patients had ECOG 0-1 (90%), prostate (50%) or breast/lung (16%) cancer, and 1-3 lesions (100%), including 30 proximal and 5 distal. 55% of lesions received concurrent systemic therapy, including ADT (n = 18) or immunotherapy (n = 6). Median PTV volume was 54.7cc (range, 6.6 to 387cc). PTV V100(%) was 99% (range 71.5-100). Fractionation included 18-20 Gy/1F, 27-30 Gy/3F, 25-40 Gy/5F, and 50 Gy/10F. 43% of lesions had Mirel's score ≥ 7 and 91% of lesions did not have extraosseous bone extension on diagnostic CT and/or MRI. Acute toxicities included grade 1 fatigue (14.3%), pain flare (7.1%), and decreased blood counts (1.8%). Late toxicities included fracture (1.8%) at 1.5 years and 2 patients with radiation-induced osteonecrosis (3.6%) from dose of 40 Gy in 5F and 30 Gy in 5F (after prior 30 Gy/10F). One patient (n = 2%) required fixation post-radiation due to progression of disease or symptoms. With median follow up 19.4 months, 1 and 2-year rates of local control were 84% and 69%, progression-free survival were 55% and 27%, and overall survival were 91% and 74%. There was no significant association between patient or treatment characteristics and local control outcomes. Femur SBRT for oligometastatic disease control in well-selected patients was associated with good outcomes with minimal rates of acute and late toxicity. Further prospective study is warranted.