Residual injury in the spinal cord after treatment with X rays or neutrons.

Residual injury in the spinal cord 100 days after X rays or neutrons was measured by the reduction in dose of a second radiation required to produce nerve damage assessed by the development of ataxia within the first post-irradiation year. Between 5-10% residual damage was observed after X-ray doses of 25% or 50% of the single X-ray dose which produced ataxia in 50% of animals (ED50), but 30% residual injury was observed if the X-ray dose was 75% of the ED50 dose. Neutron doses of 25% and 50% of the ED50 neutron dose gave the same level of residual injury as observed after equivalent X-ray doses, indicating that for this type of damage the shedding of residual damage was similar after X rays or neutrons. More residual damage is observed after a dose of X rays for vascular related damage than for damage associated with glial cell loss. However, if residual damage is expressed in terms of the relevant vascular or glial cell damage caused by the priming dose the same relationship between primary damage and residual damage is seen for both glial and vascular related damage.