Somatic effects that result from substantial doses of radiation have been well documented and the causal relationship of early effects to the fact of exposure has been fairly clearly established. The present knowledge regarding the late effects on humans which occur months and years after the exposure is based on meager data from acute exposures, from epidemiologic investigations, and from occupational and medical exposures.’76 These late effects are nonspecific and cannot be differentiated from naturally occurring disease; only the incidence of the disease is increased.’ The general pattern of somatic effects following irradiation varies with sev- eral factors which include the quality of radiation, absorbed dose, and rate and homogeneity of exposure (spatial distribution). Acute effects. The median acute lethal dose (LD;,) in man for short-term. total body radiation is not precisely known butis estimated to be somewhere between 300 and 500 rads.17 18 Doses over 2,000 rads are fatal within a few hours, producing rapid clinical deterioration in which neurological symp- toms are striking. Between 500 and 2,000 rads, effects are characterized by severe gastrointestinal disturbances; death occurs within a week. After an exposure to 100 to 500 rads, less serious gastrointestinal symptoms predominate in the early clinical pattern. Following subsidence of the gastro- intestinal symptoms, the effects of injury to the hematopoietic tissue (infections, anemia, bleeding) may become evident in about 3 weeks.'* Clinical syndromes of acute radia- tion injury have been described in detail in a number of publications.19*! The relative sensitivity of children com- pared with adults to high doses of radiation is not precisely known. “In assessing sus- ceptibilities various end points can be used; the apparent radio-sensitivity of a tissue or organ depends on the methodof observation. Sensitivity depends on age at the time of exposure, children being more susceptible than adults.“'? Marshallese children irradi- 659 ated with 175 rads of whole body gamma rays showed a slightly greater degree of nausea and vomiting and greater depression of leukocytes than did the adults.**7? However, the dose may have been greater in these children due to their shorter stature (nearer the ground source) and smaller bodies. The skin of children is known to be moresensitive to radiation than that of adults.2> The Marshallese children exposed to fallout also developed more widespread “beta burns” of the skin and epilation than did the adults. This greater sensitivity may be related to the thinner skin of the children.*¢ Late effects. In considering the possible late effects of radiation, it should be borne in mind that children have a greater chance of developing some of the late effects since their longer life span would permit effects with prolonged latent periods to become manifest. Leukemia. The occurrence of leukemia as the result of exposure to ionizing radiation has been established in studies of atomic bomb survivors in Japan® * 27 8 °° and of therapeutically irradiated ankylosing spondylitis patients in England.*®*! In the Atomic Bomb Casualty Commission (AB CC) study, calculations based on 82 cases of confirmed leukemia of all types occurring from 1947 through 1958 among the proximaliy exposed (within 1,500 meters of the hypocenter) survivors demonstrated that the highest calculated annual rate of 673 per million was in the age group 0 through 9 years; the calculated over-all incidence was 455 per million for all age groups combined. During the same period of time, the leukemia rates among the distally exposed (1,500 to 10,000 meters from the hypocenter) survivors, calculated on the basis of 67 confirmed cases, were 26 per million in the 0 through 9 year age group and 35 per million for all ages combined.®: ® The expected incidence of leukemia of all types for all ages in Japan was 20 to 30 per million per year.2 When acute lymphocytic leukemia was considered separately, the calculated annualrates in the O through 9 age group were 269 per million pene ee ae ee SOMATIC EFFECTS OF HIGH DOSES wri Effects of ionizing radiation Number + ee > ot Volumess7 TEN RE pal GTOR ARA ol erNIE LNYEmete we ee ed nae ee :