RADT-21. EFFICACY AND SAFETY OF DONUT-SHAPED CIRCUMFERENTIAL SPINE CYBERKNIFE STEREOTACTIC BODY RADIOTHERAPY FOR METASTATIC SPINE DISEASE

Abstract BACKGROUND Spinal metastases (SM) with epidural spinal cord compression (ESCC) are challenging to manage due to the risk of radiation-induced injury. Traditional approaches often avoid circumferential stereotactic body radiotherapy (SBRT) because of these risks. The efficacy and safety of donut-shaped circumferential SBRT, which envelops the spinal column while sparing the cord, remains underexplored. OBJECTIVE This study evaluates the safety and efficacy of donut-shaped circumferential spine CyberKnife SBRT in treating spinal metastases, focusing on preventing radiation-induced myelopathy and achieving local tumor control. METHOD We retrospectively analyzed patients treated with donut-shaped circumferential spine SBRT from 2014 to 2023. We evaluated demographics, grade of ESCC (Bilsky), prior treatments, symptoms, treatment parameters, and outcomes. Key measures included SBRT dosimetric data, radiation exposure to the spinal cord or cauda equina, adherence to dose-volume constraints, occurrence of post-SBRT myelopathy, other radiation-induced complications, and local tumor control. RESULTS Forty-eight lesions from 43 patients (median age: 65 years; range: 20-78) were analyzed. Only one patient underwent separation surgery for severe ESCC (Bilsky grade 3). The median clinical target volume (CTV) was 63.77 cc (range: 20.31-270.05), and the median margin dose was 24 Gy (range: 18-30). Over a median follow-up of 8 months (range: 1-91), local tumor control rates were 91.1% at 6 months, 87.1% at 1 year, 82.8% at 3 years, and 62.1% at 5 years. Median overall survival was 17 months. Of 20 lesions exceeding dose constraints, only one patient displayed clinical myelopathy symptoms, correlating with local tumor recurrence. There was no radiographic myelopathy or other radiation-induced complications during follow-up. CONCLUSION Donut-shaped circumferential spine CyberKnife SBRT provides effective and safe treatment for spinal metastases with or without epidural involvement. It achieves substantial local tumor control and has a minimal incidence of radiation-induced myelopathy, offering a viable non-surgical option for managing this complex condition.