58
not very reliable. From our surveys of the unex-
posed people of Rongelap and Likiep (a nearby
atoll not exposed to fallout), the incidence appears
to be about 5%, mostly present in older age groups
(see Figure 29 and Table 25). We haveseen a few
cases of hyperthyroidism and myxedema atthe
Majuro Hospital, but no statistics are available.
Two cases of thyroid cancer are reported from
hospital admissions for a 10-vear period (1952-
1962) for the Marshall Islands, the population
varving between 15,000 and 20,000 during that
period. This has been estimated by Trust Territory medical personnel to be about half the actual
number of cases (therefore 8 cases per 20,000
people per 20 years was used for statistical com-
parisons).
Data on iodine intake and excretion in the
Marshallese (tabulated below and presented in
detail in Appendix 9) indicate that iodine-deficlency goiter would not be expected in this
population.
Sample
28 Urines
19 Urines
7 Diets
(1965)
(1974)*
(1974)*
Todine, av. ug/day (range)
105 (19-279)
127 (25-266)
70 (48-152)
The urinary iodine excretion is somewhatlower
than the U.S. mean of 190 wg/day (18-483) in
1941.94 On the basis of the few diets analyzed, the
daily iodine intake seemsto be within the recommended range of 50 to 75 wg.These iodinelevels
are somewhatlower than would be expected in an
oceanic population but are much higherthan seen
in areas of endemic goiter.96 The Marshallese diet
contains no knowgoitrogens, and diffuse goiters
{typical of endemic goiter) have not been observed.
The high incidence of both benign and malignant thyroid nodules in the exposed Rongelap
people appears to be clearly related to radiation
exposure with a large component dueto radioiodine in the fallout. Numerous studies on animals
have shownthat thyroid neoplasia follows exposure both to x-irradiation and to radioiodines.9?-9?
Such tumors may be benign or malignant and appear to be dose-dependent to some degree. The
incidence of thyroid tumorsis increased in Japanese atom bomb survivors!09-103 (Figure 43).
Thereis a considerable amount of data showing
that children who were given radiation to the head
and neckregion for treatment of thymic hyper“The iodine analyses were done by M.T. Kinsley and DF.
Leahy at BNL.
1
60 +
= 530
=>
(| Hiroshima
Nagasaki
=
2g
e
x
T65 dose
Figure 43. Prevalence of diseases of the thyroid. fifth ex-
amination cycle, by radiation dose and city for females
age 0 to 19 at time of bomb. (From Belskyet ai.!°*)
trophy, acne, and fungus of the scalp have an tn-
creased incidence of both benign and malignant
thyroid lesions in later years.!95-112 Reports of
tumorigenic effects of radioiodine in man are more
limited. Shelineet al.,14 in their follow-up study
of 250 patients treated for hyperthyroidism, reported 8 having nodular goiter, of whom 6 had
been irradiated at age <20 and 4 at age <10.
Morerecently a number of cancersof the thyroid
have been reported in patients previously treated
with radioiodine for hyperthyroidism. !14-!16 The
numberof such cases reported is, however, lower
than might be expected on the basis of the widespread use of 1311, perhaps becausethe cells are
morelikely to undergo lethal damage.!17-122
In the more heavily exposed Rongelap group
the adult thyroids received a dose (335 rads) about
twice that to the whole body andthose of small .
children (700 to 1400 rads) about 8 timesthat to
the whole body. On the basis ofthe incidence of
benign nodules in the unexposed Marshall Islands
populations examined, about 3 to 4 cases would be
expected during the 20 years in the Rongelapexposed group, whereas 24 occurred. In the Utirik
group about 6 would be expected, and 6 occurred.
Regarding cancerof the thyroid, on the basis of
Marshall Islandsstatistics, about 0.033 cases would
be expected in the Rongelap group over the 20year period, whereas 3 occurred. In the Utirik
population about 0.06 cases would be expected,
and 1 occurred; in view of the low dose of radia-
tionit is unlikely thatthis case is radiation induced.
Tables 33 and 34 show the incidence and the
risk per rad in the Marshallese compared with
that in other populations for both benign and malignant thyroid neoplasms. Data on benign thyroid nodularity are scarce, but the incidencein