30 GY IN 4 STEREOTACTIC BODY RADIOTHERAPY (SBRT) FRACTIONS FOR COMPLEX SPINAL METASTASES: MATURE OUTCOMES SUPPORTING THIS NOVEL REGIMEN

Abstract We designed a 30 Gy in 4 fractions stereotactic body radiotherapy (SBRT) protocol, as an alternative option to our standard 2-fraction approach, for primarily large volume, multilevel, or previously radiated spinal metastases. report imaging-based outcomes of this novel fractionation scheme. MATERIALS AND METHODS: Retrospective analysis all patients who underwent Gy/4 from 2010-2021 identified institutional database. Primary were magnetic resonance-based vertebral compression fracture (VCF) and local failure (LF). RESULTS: reviewed 245 treated segments 116 patients. The median number consecutive within the treatment volume was 2 (range, 1-6) clinical target (CTV) 126.2 cc 10.4-863.5). Fifty-four percent had received at least one prior course radiotherapy. cumulative incidence LF 10.7% (95% CI 7.1-15.2) 1 year 16% 11.5-21.2) years. VCF 7.3% 4.4-11.2) 11.2% 7.5-15.8) On multivariable analysis, age ≥68 years (p=0.038), CTV ≥72 (p=0.021), no surgery (p=0.021) predicted VCF. risk volumes <72 cc/≥72 1.8%/14.6% No case radiation-induced myelopathy observed. CONCLUSION: safe efficacious despite population increased toxicity. lower stabilized highlights potential multi-modal approach complex metastases, especially those with cc.