Abstract
Emerging data suggests that post-operative SBRT for malignant spinal tumors may improve local control compared to conventional radiation therapy. However, few guidelines exist. The purpose of this study was to develop consensus guidelines to guide safe, effective treatment. Twenty spine specialists representing 19 centers in 4 countries with a collective experience of >1300 cases completed survey. Responses were defined as follows: 1) consensus: selected by ≥75%, 2) predominant: selected by ≥50%, 3) controversial: no single response selected by a majority of respondents. Consensus indications include: radio-resistant primary, 1-2 levels of adjacent disease and/or prior RT to same site. Contra-indications include: >3 contiguous vertebral bodies involved, ASIA score A (complete spinal cord injury without preservation of motor or sensory function), post-operative Bilsky grade 3 residual (cord compression without any CSF around the cord). For treatment planning, predominance of physicians co-register pre-operative MRI and post-operative T1 post-gadolinium MRI and delineate cord on T2 variant MRI or CT myelogram in cases of significant hardware artifact. Consensus GTV is post-operative residual tumor based on MRI. CTV is predominantly post-operative bed defined as entire extent of pre-operative tumor & anatomic compartment plus residual disease. Consensus is that hardware and scar do not need to be included. PTV expansion is controversial (range: 0-2 mm). Predominant prescription dose for initial treatment is 18 Gy x 1 with max point to cord <12-14 Gy (prescription range: 16-48.5 Gy in 1-10 fractions). For re-treatment, physicians predominantly account for repair and time interval between prior RT and spinal SBRT in calculating cord constraints. Acceptable PTV coverage is controversial, but physicians predominantly compromise coverage to meet cord constraint and/or fractionate to improve coverage while meeting cord constraint. Future investigation will be critical in better understanding areas of controversy including circumferential treatment of epidural space, margin for paraspinal extension and optimal dose/fractionation.