Surgical resection of epidural disease improves local control following postoperative spine stereotactic body radiotherapy

Abstract

Background: Spine stereotactic body radiotherapy (SBRT) is increasingly being applied to the postoperative spine metastases patient. Our aim was to identify clinical and dosimetric predictors of local control (LC) and survival.

Methods: Eighty patients treated between October 2008 and February 2012 with postoperative SBRT were identified from our prospective database and retrospectively reviewed.

Results: The median follow-up was 8.3 months. Thirty-five patients (44%) were treated with 18-26 Gy in 1 or 2 fractions, and 45 patients (56%) with 18-40 Gy in 3-5 fractions. Twenty-one local failures (26%) were observed, and the 1-year LC and overall survival (OS) rates were 84% and 64%, respectively. The most common site of failure was within the epidural space (15/21, 71%). Multivariate proportional hazards analysis identified systemic therapy post-SBRT as the only significant predictor of OS (P = .02) and treatment with 18-26 Gy/1 or 2 fractions (P = .02) and a postoperative epidural disease grade of 0 or 1 (0, no epidural disease; 1, epidural disease that compresses dura only, P = .003) as significant predictors of LC. Subset analysis for only those patients (n = 48/80) with high-grade preoperative epidural disease (cord deformed) indicated significantly greater LC rates when surgically downgraded to 0/1 vs 2 (P = .0009).

Conclusions: Postoperative SBRT with high total doses ranging from 18 to 26 Gy delivered in 1-2 fractions predicted superior LC, as did postoperative epidural grade.

Keywords: postoperative radiation; spinal cord compression; spine metastases; spine radiosurgery; spine stereotactic body radiotherapy.

Fig. 1.

This patient with metastatic breast cancer involving T8 (vertebral body, posterior elements, and paraspinal tissue), with near circumferential epidural disease (Bilsky grade 3), presented with pain and no neurologic deficit. (A) The preoperative axial T2-weighted MRI. (B) The postoperative sagittal T2-weighted MRI following circumferential decompression, epidural resection, and instrumentation. This image clearly illustrates the artifact induced by the surgical hardware that prevents accurate delineation of the spinal cord. (C) The axial CT myelogram that allowed the spinal cord to be delineated despite the surgical hardware. (D) The “donut” type of dose distribution where radiation conforms around the circumference of the spinal cord/thecal sac and encompasses the entire spinal segment and postoperative bed. The patient was treated with 24 Gy in 2 fractions with the thecal sac limited to a maximum dose of 17 Gy.

Fig. 2.

LC according to SBRT dose.

Fig. 3.

LC for the entire cohort according to postoperative epidural disease Bilsky grade.

Fig. 4.

LC probability for those 48 patients presenting with preoperative Bilsky grade 2 or 3 epidural disease according to their postoperative epidural grade.