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Semin Radiat Oncol. 2016 Apr;26(2):165-71. doi: 10.1016/j.semradonc.2015.11.010. Epub 2016 Jan 4.

Estimated Risk Level of Unified Stereotactic Body Radiation Therapy Dose Tolerance Limits for Spinal Cord.

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Bott Cancer Center, Holy Redeemer Hospital, Meadowbrook, PA. Electronic address:
Sunnybrook Health Sciences Center, University of Toronto, Toronto, Ontario, Canada.
Department of Radiation Oncology, Stanford University, Stanford, CA.
Department of Radiation Oncology, MD Anderson Cancer Center at Cooper University Hospital, Camden, NJ.
Division of Radiation Oncology, Abington Memorial Hospital, Abington, PA.
Department of Radiation Oncology, University of California at San Francisco, San Francisco, CA.
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY.
Department of Neurosurgery, Stanford University, Stanford, CA.


A literature review of more than 200 stereotactic body radiation therapy spine articles from the past 20 years found only a single article that provided dose-volume data and outcomes for each spinal cord of a clinical dataset: the Gibbs 2007 article (Gibbs et al, 2007(1)), which essentially contains the first 100 stereotactic body radiation therapy (SBRT) spine treatments from Stanford University Medical Center. The dataset is modeled and compared in detail to the rest of the literature review, which found 59 dose tolerance limits for the spinal cord in 1-5 fractions. We partitioned these limits into a unified format of high-risk and low-risk dose tolerance limits. To estimate the corresponding risk level of each limit we used the Gibbs 2007 clinical spinal cord dose-volume data for 102 spinal metastases in 74 patients treated by spinal radiosurgery. In all, 50 of the patients were previously irradiated to a median dose of 40Gy in 2-3Gy fractions and 3 patients developed treatment-related myelopathy. These dose-volume data were digitized into the dose-volume histogram (DVH) Evaluator software tool where parameters of the probit dose-response model were fitted using the maximum likelihood approach (Jackson et al, 1995(3)). Based on this limited dataset, for de novo cases the unified low-risk dose tolerance limits yielded an estimated risk of spinal cord injury of ≤1% in 1-5 fractions, and the high-risk limits yielded an estimated risk of ≤3%. The QUANTEC Dmax limits of 13Gy in a single fraction and 20Gy in 3 fractions had less than 1% risk estimated from this dataset, so we consider these among the low-risk limits. In the previously irradiated cohort, the estimated risk levels for 10 and 14Gy maximum cord dose limits in 5 fractions are 0.4% and 0.6%, respectively. Longer follow-up and more patients are required to improve the risk estimates and provide more complete validation.

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Conflict of interest statement

Conflict of Interests Notification: None of the authors has received any funding for this research. Dr. Grimm developed and holds intellectual property rights to the DVH Evaluator software tool which is an FDA-cleared product in commercial use, which has been used for this analysis.

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