The effects of single and multifraction radiation courses on the mouse spinal cord.

Thoraco-lumbar spinal cord segments of C3H mice were irradiated with 250 kVp x rays and the acute and late effects of several variables were compared: single and multifraction radiation courses; changes in the length of irradiated spinal cord; and multifraction studies in which three-week and three-month splits were compared to a continuous radiation course. A scoring system for assessing the degree of radiation-induced myelopathy was devised, using a scale ranging from 1.0 (loss of rear limb reflex extension) to 4.0 (paraplegia). A significant increase in severity of spinal cord radiation injury was noted when single doses were compared to equal doses given in 10 consecutive fractions. Increasing the irradiated segment from 6 to 12 mm was also associated with more severe and earlier radiation cord injury.