• Raphael Jakubovic, Mark Ruschin, Chia-Lin Tseng, Ana Pejović-Milić, Arjun Sahgal, and Yang Victor X D VXD Division of Neurosurgery, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada. .
• Division of Neurosurgery, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
• Neurosurgery. 2019 Jun 1; 84 (6): 1242-1250.

BackgroundThe clinical paradigm for spinal tumors with epidural involvement is challenging considering the rigid dose tolerance of the spinal cord. One effective approach involves open surgery for tumor resection, followed by stereotactic body radiotherapy (SBRT). Resection extent is often determined by the neurosurgeon's clinical expertise, without considering optimal subsequent post-operative SBRT treatment.ObjectiveTo quantify the effect of incremental epidural disease resection on tumor coverage for spine SBRT in an effort to working towards integrating radiotherapy planning within the operating room.MethodsTen patients having undergone spinal separation surgery with postoperative SBRT were retrospectively reviewed. Preoperative magnetic resonance imaging was coregistered to postoperative planning computed tomography to delineate the preoperative epidural disease gross tumor volume (GTV). The GTV was digitally shrunk by a series of fixed amounts away from the cord (up to 6 mm) simulating incremental tumor resection and reflecting an optimal dosimetric endpoint. The dosimetric effect on simulated GTVs was analyzed using metrics such as minimum biologically effective dose (BED) to 95% of the simulated GTV (D95) and compared to the unresected epidural GTV.ResultsEpidural GTV D95 increased at an average rate of 0.88 ± 0.09 Gy10 per mm of resected disease up to the simulated 6 mm limit. Mean BED to D95 was 5.3 Gy10 (31.2%) greater than unresected cases. All metrics showed strong positive correlations with increasing tumor resection margins (R2: 0.989-0.999, P < .01).ConclusionSpine separation surgery provides division between the spinal cord and epidural disease, facilitating better disease coverage for subsequent post-operative SBRT. By quantifying the dosimetric advantage prior to surgery on actual clinical cases, targeted surgical planning can be implemented.Copyright © 2018 by the Congress of Neurological Surgeons.

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