61
T
30 —
TTT
im Rongelap
16
_
r
T
4
S83 Ailingnae
[J Utirik
/
Varee cust Pe tengats cot teeta besrenzes
Cc] Unexposed
Thyroid dose (rads)
i00
T
of
1000 eee
T
T
1
TTT
e Benign
4 Malignant
se
a
ro
!
t
'
{
.
500
{
i
e
1
e
4&4
@
!
1
I
e
a
10
e
e
»
°
ya 8
6-200
30 40
4
!
50
|
OS
Age at developmentoflesions
Figure 47. Relationship of thyroid dose to age whenlesions develop in Marshallese. e, Benign; a, malignant.
10
=.
WSL70
30
40
50
60
Ageat developmentoflesions
8,
12
Figure 46.
hypothyroidism develops, the cases of thyroid cancer are fewer than expected.120,121, 128,129 The devel-
opment, in the two stunted Marshallese boys, of
thyroid atrophy with hypothyroidism but without
the development of tumors is in line with this reasoning. Offsetting, somewhat, the greater incidence
of thyroid cancerin childrenis the findingthat children survive longer than older people, even with
the well differentiated types.15°
The possible effects of the stress of puberty in
the developmentofthyroid lesions have been previously noted.?3 The stress of frequent pregnan-
cies, which had occurred before the development
of malignant lesions in the three Rongelap women,
mayhave been a factor in development of neoplasia. Both these correlations, however, may be
fortuitous.
2. Comparison of Thyroid Neoplasias From
X-Ray Radiation and Radiciodine Irradiation
The data in Tables 33 and 34 show thatthe risk
per rad for the developmentof thyroid neoplasms
in the Marshallese was quite similar to that in
populations exposed to x-irradiation. The data in
Figure 44 indicate a linear relationship between
nodularity in the Marshallese children, who re-
ceived their dose largely from radiotodines, and
the groups receiving x-irradiation. These data are
not extensive enoughto show possible threshold
effects. Since in animal experiments 1411 is only
about Mo to Ks as effective as x-irradiation in producing thyroid tumors,85-120,129,130 why do the
Marshallese data indicate near equality of effect?
It is estimated that thousands of children havereceived diagnostic 1411 (20 to 50 pCi) in the past resulting in thyroid doses up to hundredsof rads,
yet only 1 case with thyroid tumors has been reported.131.132 U.S. Public Health Service workers
recently reviewed a large numberofcase histories
of people who had received radioiodines for treatment of hyperthyroidism.!22 They were unable to
show anyclear-cut increase in incidenceof thyroid
tumors in this group compared with a group
treated by surgical thyroidectomy. Increasing
numbers of the patients treated with 431] developed varying degrees of hypothyroidism in later
years. The low incidence of tumors following such
treatment may be related to the high doses of
radiation given to the thyroid,sufficient to destroy
its regenerative capacity.
It should be noted, however, that in the past
few years a numberof thyroid malignancies have
been reported following radioiodine therapy for
hyperthyroidism.?14-146 The numberof cases reported is lower than expected on the basis ofdosage to the thyroid. The increased tumorigenesis in
the Marshallese maybe related to the natureof the
radiation, more thanhalf the dose being due to
short-lived isotopes of iodine (particularly 1971,
133, and 135]), which are more energetic (see Ap-
pendix 9C). Vasilenko and Klassovskii!5? have
demonstrated that when these shorter-lived isotopes of iodine are combined with 151] the tumori-