Long-term cerebral effects of small doses of x-irradiation in childhood as manifested in adult visual evoked responses.

In Israel between the years 1949 and 1960, approximately 20,000 children ranging from 1 to 15 years of age were irradiated for eradication of tinea capitis. Radiation to the cerebral hemipheres ranged up to 140 rads. Of those treated, now adults, 44 subjects were elected by stratified sampling for recording and analysis of visual evoked responses (VERs). A control group of 57 subjects similar in age and ethnic origin was chosen. Two occipital leads, a right and a left, were recorded by the international 10-20 system. Fifty responses to diffuse white-flash stimulation were averaged in each case. The first 256 msec (data points) of each VER were reduced to 77 variables by repeated averaging over three adjacent data points; these variables were then analyzed by several statistical methods. The analyses detected significant differences between the VER averages in study subjects compared with controls. These differences may reflect delayed, probably permanent functional damage to the central nervous system caused by small doses of x-radiation (XR) to immature normal human brain. The left hemispheres appeared to be more involved, consistent with the fact that these children received, on the average, more XR to the left side of the brain, as shown in simulated phantom models. This disparity is reflected in a greater degree of difference between the left VERs of the irradiated versus control group. The major differences between the VERs occurred in the first part of the secondary response and suggest possible subcortical involvement. The results strengthen previous evidence of potential hazards of XR in children.