HARRY E. WALBURG, JR. 
941 
qualitative generalizations outlined above has 
resulted in the best estimates of risks to man 
I from radiation. Turning to the specific problem 
of estimating the risk to man of radiation ema- 
nating from implanted nuclear-powered medi- 
cal devices, several points must be emphasized. 
1. There is no evidence that data for late 
somatic effects of radiation from any 
single animal model system, not even the 
nonhuman primates, can be extra- 
polated quantitatively to man. 
2. Since v^e are dealing with low levels of 
radiation, which result in small (but 
not necessarily unimportant) risks of 
induction of neoplastic diseases, large 
numbers of animals are required to 
validate statistically the level of risk 
involved. 
3. Induction of neoplasia occurs charac- 
teristically late in life, requiring studies 
throughout the entire life-span of the 
population at risk. 
SUMMARY 
It seems clear that the risk of inducing or 
accelerating neoplasms by radiation emanating 
from implanted nuclear-powered medical de- 
vices cannot be determined by implanting these 
devices (or "radiation-equivalent sources") in 
a few nonhuman primates and examining them 
for pathology within two to five years. While 
these studies may be valuable for determining 
the amount of "acute" pathology, such as tissue 
necrosis, aneurism, etc., it is the risk of induc- 
tion of neoplasms that must be estimated. A 
reasonable estimate of risk can be made by 
determining the quality of the radiation, its 
dose-rate, and the dose to the susceptible tissue 
and then applying to these data the entire body 
of knowledge on radiation carcinogenesis in 
man and animals. 
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DISCUSSION 
McClellan G. Blair, ARCO Nuclear Co. : I 
note that your studies have all been of full body 
radiation. Have you noted the effect of small 
size or local radiation? 
Dr. Walburg: Yes, there is quite a bit of 
data. Dr. Goldman and others have data on 
internally deposited radionuclides. I avoided 
discussing that case because one gets into the 
