a
LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT
development of thyroid carcinoma has been
shown experimentally in rats (30).
The one carcinoma in the Marshallese
adult is quite different from the type of
disease about which we have thus far been
concerned, since there was no hyperplasia
1239
plasms in a significant number of exposed
individuals. It would also seem likely that
lesser amounts of radiation, every direct hit
on a gene beingeffective, might also lead
to cancer formation. This, however,
be-
comes a problem in disease statistics and
is one that is currently engaging the inter-
of the surrounding thyroid gland. This was
est of many, thus far with no clear-cut
answers, The experience in the Marshall
population. On the other hand, there is
one portion of the spectrum of thyroid
radiation effects in man.
typical, then, of the usual case of thyroid
carcinoma occurring in a nomirradiated
considerable evidence that thyroid carctnoma in young adults, and especially in
children, is frequently caused by radiation
of the cervical area in childhood. Lindsay
and Chaikoff (20) have reviewed the various clinical reports on this subject, and
Winship and Rosvoll (31) reported that as
many as 80% of children with thyroid car-
cinoma, in a series of 562 -cases, have a
history of prior cervical irradiation, The
amount of radiation, which 1s usually given
in the form of X-ray therapy for thymic
hypertrophy or tonsillitis, can be even
smaller than that in the Marshallese population, being in the range of 90 to 1,500
rads. This was the dose range in a prospec:
tive study of over 4,500 patients in whom
thyroid carcinoma developed, on the av-
erage, 1] years later in approximately 0.5%
of persons exposed to such radiation (24,
32, 33). Although adults may not be immune to radiation-induced tumors——as sug-
gested by the apparent increased preva-
Islands has, at least, served to illuminate
I would now like to call for questions.
Dr. WoLtFF: What fraction of the radia-
tion was from 1]?
Dr. Conarn: Probably less than half.
Dr. WotrF: In connection with that, was
there any 17°I? Have you gotten any counts
on the material that was removed surgically?
Dr. RALL: °I has a half-life of approximately 17 million years, so that essentially
it is unradioactive. For any such molecules
in the lifetime we are talking about, they
do not decay but are still there to be measured by neutron activation. The question
is, would there be any there? Well. we do
not know. Maybe we should have mea-
sured it. Maybe there is still tissue left. I
am afraid that 10 years of biological turnover in the affected individuals would leave
almost none of the origtnal iodine around
for measurement.
Dr. JESSE RoTH: With hyperthyroid pa-
sumably require cell diviston for their expression.
It appears clear that the sizable amounts
of irradiation that we have been discussing
about 10,000 rads, and these children got
have the potential to produce thyroid neo-
the early uptake of iodineis high, but then
a large portion of this todine is not organi-
e
tients who have been treated with radioiodine it is common to see a defect where
There is a difference in the radiation delivered: The hyperthyroid patients get
EO
lence of thyroid cancer in adults exposed
to the atomic bomb in Hiroshima (34) and
other types of radiation (35, 36)—the propensity for this sequela in children is almost surely related to the fact that in the
celis of the growing thyroid gland there
must be numerous mitoses, whereas mitoses
in the adult gland are rare. The gene al-
terations leading to cancer formation pre-
oe eeee
of such TSH suppression to prevent the
|
e ee
June 1967
fied. I was curious as to why it did not
seem to show up in these radiated groups.
Dr. Rossins: I have no real answer.
about 1,000 rads. Also, these were children
who did not have so much damage that
they could not grow nodular goiters. The
hyperthyroid patients are probably dam-
—itae,
re
Volume 66, No. 6