Time dependent repair of radiation damage in the rat spinal cord after X-rays and neutrons

Abstract

The increases in total dose required to cause paralysis after irradiation of the cervical cord or lumbar cord by two equal doses of X-rays or neutrons separated by times from 1 to 120 days have been measured. No increase was needed until the doses were separated by times in excess of 15 days. The timing was the same for irradiation of the lumbar and cervical cord in the same rat strain and was different from that observed in a different rat strain. The time course of repair was the same after X rays or neutrons. The data show that for irradiation induced myelopathy the exponent of T in the Ellis formula is zero until 15 days and is then, between 15 and 120 days, 0.08 for both X-rays and neutrons. Comparison with results of Van der Kogel indicate that the time for which the exponent of T is zero varies with rat strain. It is suggested that the time dependent repair in the spinal cord, which is the same after X-rays or neutrons, is due to repopulation and not slow repair. The recovery from sublethal damage after neutrons is about half that observed after X-rays.