Risk of vertebral compression fracture specific to osteolytic renal cell carcinoma spinal metastases after stereotactic body radiotherapy: A multi-institutional study.

PURPOSE:Determine the risk of vertebral compression fracture (VCF) following stereotactic body radiotherapy (SBRT), specific to osteolytic renal cell carcinoma (RCC) spinal metastases, and associated predictive factors. METHODS:187 RCC osteolytic spinal tumor segments in 116 patients obtained from a multi-institutional pooled database were reviewed. Each segment was evaluated according to the Spinal Instability Neoplastic Score (SINS). RESULTS:The median follow-up was 8.0 months. 34 VCF (34/187, 18%) were observed and median time to VCF was 2.4 months. VCF was observed in 43% (10/23), 24% (4/17) and 14% (20/147) of segments treated with 24Gy/fraction (fx), 20-23Gy/fx and ≤19Gy/fx, respectively. Multivariate analysis identified dose per fx (p=0.005), baseline VCF (p<0.001) and spinal misalignment (p=0.002) as predictors of VCF. Prior conventional radiotherapy (p=0.029) was found to be protective. CONCLUSIONS:18% of osteolytic RCC spinal metastases fractured post-SBRT. The presence of a baseline fracture, spinal mal-alignment and treatment with ≥20Gy/fx predicted for VCF.