1059 Stereotactic Radiosurgery for Spinal Metastases: A Comparative Analysis by Number of Affected Vertebral Segments and Lesion Volume

INTRODUCTION: Stereotactic radiosurgery (SRS) for metastatic spinal disease has high rates of local control. However, there is a paucity of data evaluating how radiation to multiple spinal levels or the pre-treatment volume of spinal metastases impact treatment effect and patient outcomes. METHODS: All patients with metastatic spinal disease treated with SRS at a single-institution over a seven-year interval were retrospectively reviewed. Baseline demographics, primary tumor histology, anatomic distribution of metastases/epidural extension, and radiation dosing parameters were recorded. TTR (recurrent disease at a previously treated segment), TTP (progressive disease at a new segment), and OS were measured. Cox proportional hazard models were used to identify patient and lesion characteristics associated with TTR, TTP and OS. RESULTS: 375 patients with metastatic spinal disease were treated with SRS (465 isocenters). Median minimum and maximum target doses were 9.98 and 17.73 Gy respectively. Overall, 10.6% of patients developed disease progression, while 11.2% developed recurrence. OS was significantly better in younger patients (p=0.047), and those with high baseline KPS (p=<0.001), and was significantly worse with lesion volume >50 cc (HR: 1.37, p=0.011) and treatment at >2 vertebral levels (HR: 1.42, p=0.012). Multivariate regression revealed TTP was significantly worse with lesion volume >50 cc (HR: 2.14, p=0.0229), but was unaffected by number of vertebral segments treated. TTR was not significantly associated with high lesion volume or the number of vertebral body segments affected. CONCLUSIONS: In patients undergoing SRS for spinal metastases, no significant association was found between the number of index vertebral segments treated or lesion volume with TTR. High index lesion volume was associated with both shorter TTP and worse OS.