C
thyroid size.* These children should then be classified
into graded dose categories. The high-dose children will
probably be those who drank local milk as infants from
19 May-19 June 1953 (and to a lesser extent, from
17 March-17 April 1953, and from 31 August-30 Sep-
ternber 1957). Low-dose children should be those whose
infant years occurred after these times (or long before),
plus those who drank powdered milk or uncontaminated
fresh milk during these incidents.
If non-radiation factors predispose the children of
this region to a high incidence of thyroid abnormalities,
these abnormalities should occur throughout the dose
categories.
the state to be materially higher than calculated for
the early tests. Rainfall is greater in northern Utah,
and rain brings down fallout from the air. Also, the
studies of Pendleton have shown that plant uptake
is higher from wet pastures than from dry.’ In the
1962 incident, the highest levels of iodine 131 observed in Utah milk were not in the south-west and
central farmsfirst traversed by the fallout; the highest observed levels were in the north-east portion of
the state, over 400 miles from the Nevada test site.
b) From feeding practices, the transfer of iodine 131
to milk should be estimated for each milkshed. Very
little iodine 131 appears in milk when the cattle are
However, if the incidence is significantly greater in
the higher-dose groups, radiation would be implicated
on aged stored feed,' as, for example, during the
tremely important to have low-dose subjects from the
which supplied large populations.
c) The populations served by the major dairies
should be identified and recorded. Dose estimates to
these populations should be made, and the populations classified into graded dose-levels.
as a causative factor. In a study of this nature it is exsame region and culture to serve as controls.
In the thirteen years which have elapsed since the
incident of 1953, perhaps half of the total cumulative
radiation-induced cancers should have appeared among
the St. George children; or one—four cases under assumption {A), 0.1-0.4 cases under assumption (B), and
no cases under assumption (C). The fact that no
thyroid cancers have yet been observed* in these children™ suggests that assumption (A) overestimates the
true effect and therefore constitutes an upper limit.
Establishment of an upper limit is of real value, but
establishment of the true dose-response relationship
would be of even greater importance. To establish the
true dose-response relationship, the study needs to be
winter. Special efforts should be made to estimate
the iodine 131 levels in the milk of those dairies
d) Procedures should be established to have all thy-
roid abnormalities reported to a central file where
periodically the effects would be correlated with
dose-level. Detailed dosimetric reconstructions should
be made for those individuals developing thyroid abnormalities, with particular emphasis given to evaluation of prior X-ray therapy. In fact, a retrospective
survey should be made to document the prevalence
of medical irradiation of Utah infants to determine
whateffect this might have on the iodine 131 studies.
expanded. Note that under assumption (B), less than
Also, new techniques should be explored for improved estimates of iodine 131 dose (see Appendix).
curred before now
children.
e) If the Utah study is to yield maximum information, it must receive long-term support. Many years
may elapse before the appearance of delayed effects
of irradiation. If no effects appear, it will be even
more imperative to document the study extremely
one radiation-induced cancer is predicted to have oc(1966)
among the St. George
2) For the entire state of Utah, the estimated number of
radiation-induced
cancers
is ftve—ten
times
larger than for the hmited St. George area, assuming a
linear dose-response relationship (compare Tables 3
and 4).
How might the present study be expanded to obtain
additional information? The following plan is suggested:
a) The fallout deposition should be established for
each one of the Nevadatest shots. The actual deposi-
tion of fallout should be evaluated by recordsof field
gamma-ray intensities and fallout tray beta-activities,
when available. When measurements are lacking, the
deposition on the ground should be estimated from
meteorological considerations. Ecological factors
could have caused the doses to the northern part of
*The approximate size of a child's thyroid at iodine 131 intake can be
calculated from his age at intake.
*°*The children who moved from this area before the recent survey have
not been examined.
thoroughly, because it is much more difficult to
prove that a given dose is safe than to verify that a
higher dose is dangerous. However, the establishment
of a safe dose is of much greater importance.
3) While thyroid cancer has been of major concern
in this paper, other conditions should be considered,
such as the more frequent benign thyroid tumors. In a
study (Starr et. al.) of 73 children and adolescents
treated with iodine 131 for hyperthyroidism (an overactive thyroid) and followed for two—fourteen years,
there were five thyroid tumors of which only one (a
papillary adenocarcinoma) was malignant.'> In a different study, out of eighteen children treated with iodine
131 for hyperthyroidism, six thyroid tumors were observed five—fourteen years later..°. More cases may yet
appear after longer follow-up times.
POE ARCHIVES
August, 1966
Qf