EFFECTS OF IONIZING RADIATION 100 conditions a realistic statistical prognosis could be made. However, the problems involved with estimation of dose received by the individual present real practical difficulties. It is probable that does estimates will be available from dosimetry devices or from dose contour lines and the position of the individual during exposure. Some of the difficulties of relying heavily on dose estimates are obvious. The exact position of the individual and the degree of shielding will not be known precisely. The dosimetry device records the dose or a dose rate which may not reflect accurately because of shielding, energy dependence of the device,etc., the deposition of energy within the individuals at the site of interest, namely bone marrow and gastrointestinal tract. More important, be- cause of individual differences in sensitivity, individuals exposed to the same measured dose may differ widely in their responses. Thus, estimates. of dose calculated from dose rates or derived from an integrating dosimeter or from position of an individual during exposure cannot be accepted as the best index of the probable fate of an individual, or as the final index to therapy, triage or prognosis. Since the syndromesof radiation injury have varying symptoms and are dose dependent, the symptomology is In sense, a personal indicator of one’s fate. Experience with human radiation injury at Hiroshima, Nagasaki, with reactor andcritical assembly accidents and the fallout accident described herein strongly suggest that the best method for estimating the seriousness of exposure at the individual level is the symptomatic approach. As with any disease, an accurate appraisal of the patient’s condition results only from a thorough evaluation of the history, physical and laboratory examination (see Section 6.53 below). 6.42 Influence of Geometry of Exposure on the Effective Dose; LD; for Man Theinfluence of the geometry of exposure on the effective dose is discussed in Chapter I, and the minimal lethal dose for man in Chapter IV. Dose rates from which the total dose received by the Marshallese was calculated were measured free in air in a plane 3 feet above the ground sur- face. Because of the planar geometry of exposure and the energy of the beam, for this measured dose rate, the dose rate at the center of the body would be greater than for the same dose rate from a high energy X-ray source, measured in air at the proximal skin surface. The effects of fallout gammaradiation would thus be expected to be greater, for the same dose measured in air, than would laboratory radiations. Thehighinitial incidence of nausea, vomiting and diarrhea in the high-exposure Marshallese group, and the profound neutrophile and platelet count depression indicated a greater effect than might have been expected from 175 r in the laboratory, in keeping with the above. As indicated in Chapter IV, from this value for the dose received, and from the degree of leukocyte depression it is possible to estimate the dose at which a small incidence of mortality would have resulted without treatment. These considerations would place the threshold for mortality at approximately 225 r, and the LDs. at approximately 350 r for fallout gammaradiation. It is also clear from the above considerations, that a figure for an LD, for man, independent of the condition of exposure is essentially meaningless. The LD,, figure of 350 r is belowthe value of 400 or 450 r commonly quoted (7). A recent re-evaluation of the Japanese Nagasaki and Hiroshima bombing data has resulted in a figure well above the 400 or 450 r value for the immediate radiation from the bomb. The error in this figure, as well as that obtained from the Marshallese data, is very great. However, the profound hematological effects seen in the Marshallese would argue strongly for lowering, or at least not raising, the current LD, esti- mates for civil defense and other planning,this particularly under circumstances where fallout radiations may be expected to be the chief radiological hazard.