Sequelae after Application of High-Intensity X-Radiation to the Head of Rabbits

Abstract

In 1943, Warren (1) published an excellent review of the literature, suggesting that the central nervous system is not as insensitive to ionizing radiation as has been widely believed. This suggestion is strongly supported by experimental findings of the last decade as shown by the following survey of reported functional disorders. Russell et al. (2) administered 2.85 kr to the left side of the rabbit's skull. After a latent period of approximately 100 days, the animals developed neurological signs including transitory attacks of head retraction accompanied by salivation, circling movements which were usually toward the right, and episodes of nystagmus. Quastler et al. (3) observed motor in mice irradiated with doses higher than 12 kr. This effect occurred after both total-body exposure and exposure of the head alone; it disappeared when the brain was shielded. Andrews and Brace (4) saw in irradiated guinea pigs a picture which, at doses above 10 kr, was characterized by cycles of convulsions and periods of extensor rigidity. Ross et al. (5) administered to the head of monkeys either 6 kr or 3 kr of X-radiation. After exposure a general depression of activity developed which rapidly progressed to preterminal coma. Epileptic seizures of the grand mal type and corresponding changes of EEG pattern were observed. The survival time was 2 to 3 days for the 6-kr dose and 2 to 3 weeks for the 3-kr dose. Although a distinct sensitivity to ionizing radiation thus was established for the adult animal's brain, an even higher susceptibility was found for the fetal organ. Hicks (6) produced malformations of the nervous system in rat embryos and fetuses with doses as low as 100 r. The findings of the animal experiments were corroborated by clinical observations made by other authors on human patients. Severe functional and structural lesions of the brain could be demonstrated (1, 7) in several cases which received therapeutic X-radiation to the head. After a latent period of months or years, clinical symptoms became evident which were characterized by epileptic seizures in some of the cases and by hemiparesis or deviation of the head in others. Under these conditions the causal connection between irradiation and pathologic process was not absolutely certain because of possible intercurrent diseases developing during the time of