time, since the pathological response is saturated in this experiment, it is inappropriate to draw any inference about the magnitude of the response at smalier burdens. burden (at death) The smallest in a dog showing lung cancer was 0.2 uCi. Presumably this would correspond to a particle burden of about 107 particles. Burdens which are smaller by orders cf magnitude may still induce a substantial incidence of cancer. Indeed, the cancers risk may, as for skin and soft tissues, , correspond to a risk per particle in the neighborhood of 1/1000 Critical Particle Activity Be i: te le 14 ete he ee 24 st ek - 4 VI to 1/10,000. icles would be expected to result in these re hich cancer probabilities. As the particle size or specific activity per particle is reduced so is the dosage to the Surrounding tissue. Indeed, at sufficientiy smail carticle Size or specific activity, one would expect the radiation insult to behave similar to uniform irradiation. The study of Albert on induction of cancer in rat skin indicates a precipitous change in the dose response curve as the dosage exceeds 1,000 rem”. (See Figure 2). This suggests that a particular level of tissue damage must occur before this unique carcinogenic response occurs. 95/ Albert, R.E., et al, The experiments of Radiation Res. 30, Op. cit., pp. 515-5 Figure 7; reproduced in Geesaman, UCRL-50387 Addendum, Op. cit., p. 2. Oe MOB ae 2 7 lg tte :. oy . at rr ww 7s 5 . 7 we . a a é . om sony SOF, fe teerey ral, Sige tyr ‘i ts ry mbafers &1, Loe aN . be ne ae ty aaa . ae, AE oom on” Lot Eo é . 2h fF gt OO a bp og . ad “gt . le The be areWt? a Logit) . rs * aes ee Te 1 , ww vege: uh . hey ' . - “age . 4 +. a - ‘ei ‘ : . 4 4