61
|
16
14}
MB Rongelap
a Ailingnae
{_] Utirik
4
@ Benign
q
4 Malignant
10.20
30 40
50
Age at developmentof lesions
&
&
(_"] Unexposed
T
Figure 47. Relationship of thyroid dose to age whenlesions develop in Marshallese. , Benign: 1, malignant.
ceived their dose largely from radioiodines, and
the groups receiving x-irradiation. These data are
not extensive enoughto show possible threshold
effects. Since in animal experiments !31I ts only
about “io to is as effective as. x-irradiation in pro-
oS
bo
-
Percent lesions oftotal lesions
80 |
T
Thyroid dose (rads)
J
Loo
ml
10
20
30
40
30
60
Age at developmentoflesions
70
Figure 46.
hypothyroidism develops, the cases of thyroid cancer are fewer than expected.120.121, 128,129 The development, in the two stunted Marshallese boys, of
thyroid atrophy with hypothyroidism but without
the developmentof tumorsis in line with this rea-
soning. Offsetting, somewhat, the greater incidence
of thyroid cancerin childrenis the finding that children survive longer than older people, even with
the well differentiated types.13°
Thepossible effects of the stress of puberty in
the developmentof thyroid lesions have been previously noted.23 The stress of frequent pregnan-
cies, which had occurred before the development
of malignantlesions in the three Rongelap women,
may have been a factor in developmentof neoplasia. Both these correlations, however, may be
fortuitous.
2. Comparison of Thyroid Neoplasias From
X-Ray Radiation and Radioiodine Irradiation
The data in Tables 33 and 34 show thatthe risk
per rad for the development of 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, whore-
ducing thyroid tumors,85.120.129,130 why do the
Marshallese data indicate near equality of effect?
It is estimated that thousands of children have received diagnostic 141I (20 to 50 Ci) in the past resulting in thyroid doses up to hundredsof rads,
yet only | case with thyroid tumors has been re-
ported.!31.132 U.S. Public Health Service workers
recently reviewed a large number ofcase histories
of people whohad received radioiodines for treatment of hyperthyroidism.!22 They were unable to
show any clear-cut increase in incidenceof thyroid
tumors in this group compared with a group
treated by surgical thyroidectomy. Increasing
numbersof the patients treated with !31] 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 therapyfor
hyperthyroidism.!!4-116 The numberof cases reported is lower than expected on the basis of dosage to the thyroid. The increased tumorigenesisin
the Marshallese mayberelated to the natureof the
radiation, more than half the dose being due to
short-lived isotopes of iodine (particularly 1421,
1337, and 1357), which are more energetic (see Ap-
pendix 9C). Vasilenko and Klassovskiil33 have
demonstrated that when these shorter-lived isotopes of iodine are combined with 1411 the tumori-