-7feel that cancer induction is not proportional to dose, but that a certain
"threshold" level must be exceeded before cancers can be induced.
If such
a threshold exists and if the doses fall below this level, no induced cancers
Will appear.
It is possible that no cancers will result from the Utah
exposures.
The number of radiation-induced thyroid cancers will now be predicted
for each of the following 3 assumptions:
(A) a linear dose response with
175? irradiation equally as effective as x-irradiation, (B) a linear dose
response, but 3?
irradiation only 1/10 as effective as x-irradiation, and
(C) a@ high threshald.
is unlikely that I'3?
Assumption (A) probably sets an upper limit, for it
is more effective than x-rays.
sets the Lower limit:
Assumption
Assumption (C) certainly
the number of induced cancers cannot be less than zero!
(B), while between the upper and lower limits is not necessardly
the best estimate, but it yields reasonable values for planning the experimental search for thyroid cancer.
Predicted thyroid cancers in the 250,800
irradiated Utah children are shown in Table 3.
Table 3
PREDICTED THYROID CANCERS
IN THE 250,000 IRRADIATED UTAH CHILDREN
AVERAGE DOSE
(1.3 rad - 10 rad)
ASSUMPTION
A) [35 Thyroid Cancers
L1O® Infants given 1 rad.
(Effect of x-rays; Beach & Dolphin)
B) 1/10 of x-ray effect
(I'?? “x-ray RBE in rats; Doniach)
C) High Threshold
—_—
wee
ee
ee
eee
11
-
88
1
-
9
0
eee
eee
eee
"NATURAL" INCIDENCE BY 15 YEARS AGE
(from Mustacchi & Cutler)
6
Similarly, it is instructive to predict the expected number of thyroid
cancers in the 565 infants in Washington county, Utah, exposed to higher
thyroid doses estimated at 120-440 rads 3) following the "Harry" shot of
19 May, 1953.
These predictions are shown in Table 4.