Outcomes of a third course of salvage spine stereotactic radiosurgery for spinal metastases: a single-institution case series.

OBJECTIVE: Re-irradiation with salvage spine stereotactic radiosurgery (sSRS) has emerged as a viable strategy for spinal metastases with progressive disease. We report the characteristics and clinical outcomes of spinal segments that received at least three courses of sSRS. METHODS: 10 spinal segments in 6 patients who received at least three courses of sSRS were evaluated from an Institutional Review Board-approved retrospective single-institution database. Overall survival (OS) and radiographic progression-free survival (rPFS) were calculated by Kaplan-Meier analysis. Radiographic failure was defined as progression on imaging at the treated segment. RESULTS: Median follow-up was 8.9 months (range, 0.2–46.3). Three patients had died at the time of analysis. Median age at treatment was 63.2 years (range, 36.9–77.2), and median Karnofsky Performance Status (KPS) was 80 (range, 70–90). The 1-year overall survival (OS) rate was 50.0%. The median cumulative thecal sac EQD22.5 Dmax after the third course of sSRS was 137.9 Gy (range, 97–227.5). The median third course re-irradiation sSRS thecal sac EQD22.5 Dmax was 37.15 Gy (range, 21.8–57.8). 30% (3/10) of treated segments had radiographic progression, with a 6-month rPFS rate of 85.7%. 28.6% (2/7) of treatment courses resulted in pain flare. No cases of vertebral compression fracture (VCF), radiation myelopathy, or neuritis were reported. CONCLUSIONS: Three courses of sSRS may be considered for salvage treatment of progressive spinal metastases. Given that cumulative neural structure doses exceed established thresholds, careful multidisciplinary review of all treatment options including surgery and other ablative treatments is essential before proceeding.