Outcomes of a Third Course of Salvage Spine Stereotactic Radiosurgery for Spinal Metastases

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 IRB-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. Toxicity outcomes were collected. Results Median follow-up was 8.9 months (range, 0.2–46.3). Three patients had died at the time of analysis. Half the patients were female, median age at treatment was 63.2 years (range, 36.9–77.2), and median consult KPS was 80 (range, 70–90). The median cumulative thecal sac EQD2 ₂ D _max after the third course of sSRS was 137.9 Gy (range, 97–227.5). The median third course re-irradiation sSRS thecal sac EQD2 ₂ D _max was 37.15 Gy (range, 21.8–57.8). 30% (3/10) of treated spinal segments had radiographic progression (range of time to radiographic progression, 0.98–14.3 months), with a 1-year radiographic progression-free survival rate of 87.5%. 42.9% (3/7) of treatments resulted in pain flare, which were all adequately treated with steroids. No cases of VCF or radiation myelopathy were reported. Conclusions Three courses of sSRS may be considered for salvage treatment for spinal metastases demonstrating progression. Though it appears to be safe and effective, more investigation is warranted. Since the cumulative doses to the neural structures exceed those established by other studies, great care and review of all treatment options including surgery and other ablative treatments like radiofrequency or cryoablation should be considered in a multidisciplinary setting prior to proceeding with salvage spine SRS.