Dose effect relationship for epilation and late effects on spinal cord in rats exposed to gamma rays

The response of rat spinal cords exposed to single and multifractionated gamma-ray exposures revealed no significant differences between the threshold doses for 2 fractions given with a 24-hr interval and 2 fractions given with a 15-day interval. The latent period for spinal cord damage was about 190 days when the incidence of paralysis was high; it was less than this in animals with a lower probability of paralysis. There was a marked sparing effect from dose fractionation: the initial part of a Strandqvist type of isoeffect curve had a slope of 0.44 for doses causing paralysis in 50 percent of the animals, and 0.36 for threshold doses. The level of epilation was not useful for predicting spinal cord damage