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Pioneering work at the University of Arizona led to the introduction of spinal radiosurgery in 1995.1 Initially, spinal radiosurgery advanced slowly as a frame-based procedure, but a rapid expansion in imaging technology has enabled widespread clinical implementation of the “frameless” image-guided approach used today. Many of the technical challenges facing spinal radiosurgery have been resolved, but an understanding of the response of normal human tissues in close proximity to the spine lags behind. The potential for toxicity from excessive irradiation of the spinal cord and spinal nerves has compelled clinicians to exercise caution when prescribing doses for spinal neoplasms. The extreme impact of radiation toxicity to the central and peripheral nervous systems on patient quality of life makes clinicians reluctant to investigate such toxicity in human clinical trials. A better understanding of toxicity is critical to avoid both underestimation, with the prescribing of radiation doses that will lead to catastrophic injury to normal tissue, and overestimation, which results in the prescribing of lower doses that are less likely to ablate tumors. For this reason, animal models have been used widely to investigate radiation toxicity to these structures, and they have provided the overwhelming majority of data. 2 Animal studies applicable to spine radiosurgery have been ongoing since the 1970s. 2, 3 In the early years, the spinal cord was recognized to be a good model to study the effects of X-ray and neutron irradiation in the central nervous system because it allowed analysis of both neurons and supporting cells over a relatively long period, and functional …