Postoperative Stereotactic Body Radiation Therapy (sbrt) for Patients with Spinal Metastasis: Predictive and Prognostic Factors Analysis

Spine SBRT is increasingly being applied to the post-operative patient, as an alternative to conventional palliative radiation therapy, with the aim to improve upon existing rates of local control. As an emerging indication, our aim was to identify clinical and dosimetric predictors of local control and survival. Eighty patients treated between October 2008 and February 2012 with post-operative SBRT (within 8 weeks of surgery), were identified from our prospective database and retrospectively reviewed. The pre- and post-operative MR images were reviewed to characterize the disease extent within the spinal segment, and to grade epidural disease such that grade 0 is no epidural disease, grade 1 is dural compression without spinal cord displacement, grade 2 is cord compression with visible CSF and grade 3 is cord compression obliterating CSF. Other factors analyzed included type of surgery, use of systemic therapy post-SBRT, prior radiation exposure, total dose, dose per fraction and various dosimetric factors. The median follow-up was 8.3 months. The most common primary histology was non-small cell lung cancer (16%), and 56% of tumors were in the thoracic spine. Sixty-nine (86%) patients underwent a decompressive surgery while 11 (14%) underwent a stabilization procedure alone. Thirty-five (44%) patients were treated with 1 or 2 fractions (total dose ranging from 18-26 Gy), and 45 (56%) with 3 to 5 fractions (total dose ranging from 18-40 Gy). Pre- and post-operative epidural grade 0, 1, 2, and 3 were observed in 5%/8%, 35%/82%, 35%/10%, and 25%/0% of patients, respectively. 21 local failures (26%) were observed, and the 1-year local control (LC) and overall survival (OS) rates were 84% and 64%, respectively. The median time to local failure was 6.9 months (range, 0.1 - 37.4 months). The most common site of failure was within the epidural space (15/21, 71%). We identified systemic therapy post-SBRT as the only significant predictor of OS (p = 0.03). Multivariate proportional hazards analysis identified treatment with1 or 2 fraction SBRT, and a post-operative epidural disease grade of 0/1 as significant predictors of LC. Subset analysis for only those patients with a pre-operative epidural disease grade of 2 or 3 (n = 48/80) indicated significantly greater LC rates when down-graded to 0/1 vs 2 (p = 0.0009). We observed favorable local control 1 year following post-operative spine SBRT. We observed total doses ranging from 18-26 Gy delivered in 1-2 fractions, and epidural disease debulking predicted for superior local control.