Late effects of spinal cord irradiation with 300 kV X rays and 15 MeV neutrons

Abstract

Dose-effect relationships were determined for late damage caused by local irradiations of the spinal cord of rats with single and fractionated doses of 300 kV X rays and 15 MeV neutrons. After latent periods of 4–12 months, symptoms of myelopathy develop. The latent period decreases with increasing dose, but rapidly reaches a minimum of four months with both X rays and neutrons. The relative biological effectiveness of 15 MeV neutrons is 1·1 for single irradiation and 1·7 for irradiation in five fractions. For X rays, the total dose required increases with the number of daily fractions. The main histological changes consist of degeneration of the nerve roots if the lumbar region was irradiated. Irradiation of the cervical region resulted in focal necrosis of the white matter. An analysis of the data with respect to an hypothesis about the mechanism through which damage to the spinal cord may develop, is given.