Imaging-Based Outcomes for 24 Gy in 2 Daily Fractions for Patients with de Novo Spinal Metastases Treated With Spine Stereotactic Body Radiation Therapy (SBRT)

Abstract

We report mature outcomes for a cohort of patients with no prior radiation (de novo) to the spine treated with 24Gy in 2 daily fractions for metastases, which represents the same stereotactic body radiation therapy (SBRT) regimen under evaluation in the current Symptom Control-24 phase 3 randomized trial (NCT02512965). The cohort consisted of 279 de novo spinal metastases in 145 consecutive patients treated with 24Gy in 2 SBRT fractions, identified from a prospective single-institution database. The endpoints were overall survival (OS), imaging-based local failure (LF), and cumulative risk of vertebral compression fractures (VCF). The median follow-up per treated metastasis was 15.0months (range, 0.1-71.6). The 1-year and 2-year OS rates were 73.1% and 60.7%, respectively. Presence of epidural disease (P<.0001), lung (P=.0415), and renal cell (P<.0001) primary histologies and baseline diffuse metastases (P=.0034) were significant prognostic factors for OS. The 1-year and 2-year LF rates were 9.7% and 17.6%, respectively, and the median time to LF was 9.2month (range, 0.4-31.3months). Only the presence of epidural disease predicted for LF (P<.0001). The cumulative risk of VCF at 1 and 2years was 8.5% and 13.8%, respectively. Lytic (P=.0143) or mixed lytic/blastic (P=.0214) lesions, spinal malalignment (P=.0121), and the dose to 90% of the planning target volume (P=.0085) were significant predictors for VCF. Twenty-four Gray in 2 daily fractions is safe and effective in achieving high tumor control rates for de novo spinal metastases. These outcomes will serve as a benchmark for the ongoing Symptom Control-24 randomized trial comparing 24Gy in 2 SBRT fractions to 20Gy delivered in 5 daily conventional fractions.