Safety and efficacy of salvage conventional re-irradiation following stereotactic radiosurgery for spine metastases

Purpose: There has been limited work assessing the use of re-irradiation (re-RT) for local failure fol-lowing stereotactic spinal radiosurgery (SSRS). We reviewed our institutional experience of conven-tionally-fractionated external beam radiation (cEBRT) for salvage therapy following SSRS local failure. Materials and Methods: We performed a retrospective review of 54 patients that underwent salvage conventional re-RT at previously SSRS-treated sites. Local control following re-RT was defined as the absence of progression at the treated site as determined by magnetic resonance imaging. Results: Competing risk analysis for local failure was performed using a Fine-Gray model. The median follow-up time was 25 months and median overall survival (OS) was 16 months (95% confidence in-terval [CI], 10.8-24.9 months) following cEBRT re-RT. Multivariable Cox proportional-hazards analysis revealed Karnofsky performance score prior to re-RT (hazard ratio [HR] = 0.95; 95% CI, 0.93- 0.98; p = 0.003) and time to local failure (HR = 0.97; 95% CI, 0.94-1.00; p = 0.04) were associated with lon-ger OS, while male sex (HR = 3.92; 95% CI, 1.64-9.33; p = 0.002) was associated with shorter OS. Local control at 12 months was 81% (95% CI, 69.3-94.0). Competing risk multivariable regression revealed radioresistant tumors (subhazard ratio [subHR] = 0.36; 95% CI, 0.15-0.90; p = 0.028) and epidural disease (subHR = 0.31; 95% CI, 0.12-0.78; p =0.013) were associated with increased risk of local failure. At 12 months, 91% of patients maintained ambulatory function. Conclusion: Our data suggest that cEBRT following SSRS local failure can be used safely and effec-tively. Further investigation is needed into optimal patient selection for cEBRT in the retreatment set-ting.