Efficacy and Safety of Donut-Shaped Circumferential Spine CyberKnife Stereotactic Body Radiotherapy for Metastatic Spine Disease

BACKGROUND AND OBJECTIVES: Spinal metastases (SM) with epidural spinal cord compression (ESCC) present a significant challenge because of the high risk of radiation-induced injury to critical structures such as the spinal cord and nerve roots. Traditional treatment approaches often avoid circumferential stereotactic body radiotherapy (SBRT) to reduce these risks. The efficacy and safety of donut-shaped circumferential SBRT, designed to target the spinal column while sparing the spinal cord, remains underexplored. The aim of this study was to evaluate the safety and efficacy of donut-shaped circumferential CyberKnife SBRT for SM, particularly in preventing radiation-induced myelopathy and achieving local tumor control (LTC). METHODS: We retrospectively analyzed data from patients treated with donut-shaped circumferential SBRT between 2014 and 2023. Key parameters examined included patient demographics, ESCC grade (Bilsky), prior treatments, clinical symptoms, and treatment parameters. We focused on SBRT dosimetric data, radiation exposure to the spinal cord and cauda equina, adherence to dose-volume constraints, and post-SBRT outcomes, including myelopathy and LTC. RESULTS: Forty-eight lesions in 43 patients (median age: 65; range: 20-78) were reviewed. One patient required separation surgery for severe ESCC (Bilsky grade 3). The median clinical target volume was 63.77 cm 3 , and the median margin dose was 24 Gy. Over a median follow-up of 8 months, LTC was 91.1% at 6 months, 87.1% at 1 year, 82.8% at 3 years, and 62.1% at 5 years. The median overall survival was 17 months. Of the 21 lesions exceeding dose constraints, only one patient exhibited clinical myelopathy, which correlated with local tumor recurrence. No radiographic myelopathy or other radiation-induced complications were observed. CONCLUSION: Donut-shaped circumferential CyberKnife SBRT is a safe and effective treatment of SM, achieving high LTC with minimal radiation-induced complications, including myelopathy.