Multi-fraction stereotactic body radiotherapy for spinal metastases.

INTRODUCTION: Single-fraction stereotactic body radiotherapy (SBRT) has demonstrated efficacy in the management of spinal metastases. This study sought to investigate the role of multi-fraction spine SBRT in managing metastatic spinal tumors, particularly for tumors large in volume, compressing the spinal cord, or previously irradiated with conventional external beam radiotherapy (EBRT). METHODS: Overall, 146 treatments were analyzed from a prospectively maintained spine SBRT database from 2002 to 2024. Treatments were excluded for missing baseline imaging or less than 1 month of follow-up. The most prescribed fractionation schemes were 24 Gy/2 fractions, 24 Gy/3 fractions, and 30 Gy/5 fractions. The median tumor volume was 40 cc (IQR: 18–79). Tumors were previously irradiated with EBRT (108 tumors, 74%), and most had epidural tumor extension (109 tumors, 75%). RESULTS: The median follow-up was 9 months (IQR: 2–17). Eighteen (12%) tumors exhibited local tumor progression with local tumor control (LTC) rates of 89%, 84%, and 78% at 6-, 12-, and 24- months following SBRT. Lytic lesions (HR: 8.63, 95%CI: 1.11–67.3, p = 0.040) and tumors spanning > 1 vertebral level (HR: 2.76, 95%CI: 1.02–7.46, p = 0.046) were significantly associated with worsened LTC. Pain improvement or stability was noted for 93%, 89%, and 87% of treated cases at 1-, 3-, and 6-months post-SBRT. The median overall survival (OS) was 13 months with KPS ≤ 80 (HR: 0.41, 95%CI: 0.26–0.64, p < 0.001) and radioresistant primary tumor histology (HR: 0.50, 95%CI: 0.31–0.80, p = 0.004) being associated with worsened OS. The crude vertebral compression fracture development rate was 9%. CONCLUSION: Multi-fraction spine SBRT is safe and effective for large spinal metastatic tumors, including those previously irradiated with EBRT.