With the above digression, we can uow ceturn to Fig. 3. from the figure that it is incomplete and misleading to present the data terms of a “linear-no-threshold” Fig. 2 It is clear relationship. Rather, as shown also in the data should be presented as distributions of hit cells, the area of the distribution representing the total amount of exposure. It then becomes clear that what ts needed that will respond quantally is response curve, to evaluate the number of hit cells the cell equivalent of an organ-dose 1.,¢@., a relationship that will provide the probability of a cell quantal response, as a function of iucreasing cell dose. function, - termed a hit-size effectiveness developed (11-14). curve In Fig. 2, in One such curve function (HSEF), Such a has heen is shown schematically as the S-shaped An actual curve for chromosome abnormalities, derived From the data in Fig. 1, is shown in Fig. 5.(3). The use of these curves is now discussed, following which thetr derivation is summarized. . &3 ca 2 1.0 T T oF ot ae: PROBABILITY OF QUANTAL EFFECT CH26, CELLS chromosome abnomalities 0.8} (Skarsgard} 4 abnormal metaphases 0.6 o 8215p m* 4 O4F 4 0.2 5+ 4 chromatid exchange F = 10.4 pm? oO 10 20 L 30 ai. id 50 70 100 iiiJ y/ kev m' Fig. 5 Ref. 3}. 1 200 300 An HSEF derived from the data shown in Fig. 1 (from The two curves are for different chromosome aberrations. Use of the HSEF The use of the liSEF is shown schematically in Fig. 2. For any one or combination of cell hit size distributions shown, one simply multiplies theja distribution by the HSEF, ise., the number of hit cells at each hit size 1s multiplied by the corresponding point on the HSEF. -216- 20129 16 The resulting products egy r ai ne af,