HUMAN RADIATION INJURY 6.5 Radiation Syndromes as a Function of Type of Exposure, Dose and Time After Exposure 6.51 Effects of Superficial, Penetrating and Internal Radiations Radiation injuries can be divided into three general classes: a. The syndromes of whole body radiation injury which are produced by penetrating ionizing radiation, and which are dose dependent. b. Superficial radiation burns produced by soft radiations (beta and low energy X- or gammaradiations). ec. Radiation injury produced by the deposition of radionuclides within the body. The clinical picture varies with the site and amount of deposition. Eachof the aboveis associated with an early phase in which acute symptoms and signs may be observed, and a late phase in which chronic changes or manifestations such as cancer may be observed. Also, the degree of injury is proportioned to dose. Particularly in Class a, total-body irradiation, the disease entity seen is highly dependent on dose. 6.52 The Syndromes From Total Body Penetrating Radiations The dose-dependent syndromes resulting from total-body exposure in the mammal have been described in detail (10-13) and need only be summarized here. After large doses (approximately 6,000 r or more*) the central nerv- ous system syndrome (CNS) is produced (10). Death may occur under the beam after some hours, and is preceded by hyperexcitability, ataxia, respiratory distress, and intermittent stupor. Doses capable of producing this syndrome are always uniformly fatal. If an occasional animal survives this CNS he has yet to experience the gastrointestinal syndrome (GIS), (10, 12) which when produced by doses *Species variation. 101 in excess of 1500 r is always fatal within 3-9 days.** The GIS is so named because of the marked nausea, vomiting, diarrhea, and denudation of the small bowel mucosa. The GIS is a uniformly fatal syndrome in most laboratory animals, If the short duration GIS of a few hours does not produce the 3-4 day death, the survivors of this syndrome have yet to experience the sequelae of bone marrow depression which has been termed the Aemopoietic syndrome (HS). The HSis not necessarily fatal. It is the clinical picture that is seen in the lethal range for all mammals and in general the LD,. values reported represent the LD, for the sequela of hemopoietic depression——granulocytopenia and depressed defenses against infection, thrombopenia, and anemia withthe possible resulting infections, diffuse purpura, and hypoxia due to anemia, any of which may be fatal. More detailed descriptions of the pathogenesis of these phenomena have been pub- lished (10-16). The above picture of radiation syndromesis based on animal experimentation; however, humanexperience (6, 17-22) has indicated that man probably corresponds quite closely to the general mammalian response outlined above with the exception of some differences in time of occurrence. The CNS apparently was not observed by the Japanese at Hiroshima and Nagasaki (21, 22) nor would one expect it to be observed since doses to produce this syndrome were well within the area of total destruction. The GIS with deaths in the Ist week are well documentedclinically and patho- logically as are deaths from the HS (6, 18, 21, 22). However, in the case of man, deaths from infection were most prevalent in the 2d to 4th weeks (maximum incidence during 3d week) and from hemorrhagic phenomenain the 3d to 6th weeks (maximum incidence in 4th week). In the Japanese, after the bombing of Hiroshima and Nagasaki, deaths from radiation injury were occurring as late as the 7th **There are species and Strain variations. The 3-4 day deaths are most prevalent in dogs, rats and mice, but deaths on 5-6th days are seen. Guinea pigs and hamsters survive 6-8 days.