Spine stereotactic body radiotherapy for renal cell cancer spinal metastases: analysis of outcomes and risk of vertebral compression fracture

Object. The aim of this study was to evaluate local control (LC) and the risk of vertebral compression fracture (VCF) after stereotactic body radiotherapy (SBRT) in patients with renal cell cancer spinal metastases. Methods. Prospectively collected data on 71 spinal segments treated with SBRT in 37 patients were reviewed. The median follow-up was 12.3 months (range 1.2-55.4 months). The LC rate was assessed based on each spinal segment treated and overall survival (OS) according to each patient treated. Sixty of 71 segments (85%) were radiation naive, 11 of 71 (15%) were previously irradiated, and 10 of 71 (14%) were treated with postoperative SBRT. The median SBRT total dose and number of fractions were 24 Gy and 2, respectively. The VCF analysis also included evaluation of the Spinal Instability Neoplastic Score criteria. Results. The 1-year OS and LC rates were 64% and 83%, respectively. Multivariate analysis identified oligometastatic disease (13 of 37 patients) as a positive prognostic factor (p = 0.018) for OS. Of 61 non-postoperative spinal segments treated, 10 (16%) developed VCFs; 3 of 10 were de novo VCFs and 7 of 10 occurred as progression of an existing VCF. The 1-year VCF-free probability rate was 82%. Multivariate analysis identified single-fraction SBRT and baseline VCF as significant predictors of SBRT-induced VCF (p = 0.028 and p = 0.012, respectively). Conclusions. Spine SBRT yields high rates of local tumor control in patients with renal cell cancer. Baseline VCF and 18-24 Gy delivered in a single fraction were predictive of further collapse. Patients with oligometastatic disease may benefit most from such aggressive local therapy, given the prolonged survival observed.