Purpose-This study was performed to determine the spinal cord tolerance to single-fraction, partial-volume irradiation in swine.Methods/Materials-A 5 cm long cervical segment was irradiated in 38-47 week old Yucatan minipigs using a dedicated, image-guided radiosurgery linear accelerator. Radiation was delivered to a cylindrical volume approximately 5 cm in length and 2 cm in diameter that was positioned lateral to the cervical spinal cord resulting in a dose distribution with the 90%, 50% and 10% isodose lines traversing the ipsilateral, central and contralateral spinal cord, respectively. Dose was prescribed to the 90% isodose line. Twenty-six pigs were stratified into 8 dose groups from 12-47 Gy. The mean maximum spinal cord doses were 16.9±0.1, 18.9±0.1, 21.0±0.1, 23.0±0.2, and 25.3±0.3 Gy in the 16, 18, 20, 22 and 24 Gy dose groups, respectively. The mean percentage spinal cord volumes receiving >= 10 Gy for the same groups were 43%±3, 48%±4, 51%±2, 57% Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Author ManuscriptInt J Radiat Oncol Biol Phys. Author manuscript; available in PMC 2012 January 1.
NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript ±2 and 59%±4. The study endpoint was motor neurologic deficit determined by a change in gait during a one year follow-up period.Results-A steep dose response curve was observed with an ED 50 (95% CI) for the maximum dose point of 20.0 Gy (18.3-21.7). Excellent agreement was observed between the occurrence of neurologic change and the presence of histological change. All animals with motor deficits showed some degree of demyelination and focal white matter necrosis on the irradiated side with relative sparing of the gray matter while histology was unremarkable in animals with normal neurologic status.
Conclusions-Resultsindicate that for a dose distribution with a steep lateral gradient, pigs have a lower ED 50 for paralysis than has been observed in rats and more closely resembles that for rats, mice and guinea pigs receiving uniform spinal cord irradiation.