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Thyroid Neoplasia in Marshall Islanders
Exposed to Nuclear Fallout
Thomas E. Hamilton, MD, PhD: Gerald van Belle, PhD; James P. LoGerfo, MD, MPH

We studied the risk of thyroid neoplasia in Marshall Islanders exposed to
radioiodines in nuclearfallout from the 1954 BRAVO thermonuclear test. We
screened 7266 Marshall Islanders for thyroid nodules;the islanders were from 14

atolls, including several southern atolls, which were the source of the best
available unexposed comparison group. Using a retrospective cohort design, we

determined the prevalenceof thyroid nodularity in a subgroup of 2273 persons
who were alive in 1954 and whotherefore were potentially exposed to fallout from
the BRAVOtest. For those 12 atolls previously thought to be unexposed to fallout,

the prevalence of thyroid nodules ranged from 0.9%to 10.6%. Using the distance

of each atoll from the test site as a proxy for the radiation dose to the thyroid
gland, a weighted linear regression showed an inverse linear relationship

betweendistance and the age-adjusted prevalenceof thyroid nodules. Distance

was the strongestsingle predictor in logistic regression analysis. Anew absolute
risk estimate was calculated to be 1100 excess cases/Gy/y/1 x 10* persons (11.0
excess Cases/rad/y/1 million persons), 33%higher than previous estimates. We
conclude that an excess of thyroid nodules was not limited only to the two

IT HASbeen 21 years since the publication of an early case series of thyroid
neoplasia (including thyroid cancer and

From the Departments of Medicine (Drs. Hamilton

and LoGerfo) and Biostatistics (Or van Belle}, University
of Washington, Seattle.

The opinions, conclusions, and proposais in this

article are those of the authors and do not necessarily
representthe views of the Robert Wood Johnson Foundation or tha Marshall Islands Atornic Testing Litigation

Reprint requests to Occupational Medicine Program,

Harbormew Medicat Center, 325 Ninth Ave, Seattie, WA
98104 (Dr Hamilton).

JAMA, Aug 7, 1987—Vol 258, No. 5 _

commonlate effect from this exposure
has been the development of thyroid

nodules. Between 1954 and 1985, thyroid nodules developed in approximately 33% of the Rongelap population,
including 63% of children less than 10
years old at the time of exposure, and

10% of the Utrik population.*”* Previous
investigators have assumed that Rongelap and Utrik were the only two northern atolls exposed to fallout radiation; in
their studies they used as unexposed
controls those living on other northern

atolls during the 1954 BRAVOtest and

benign nodules) developing in children
of Marshall Islanders as a late effect of
exposure to radioactive fallout.’ This
exposure resulted from the detonation
of a 15-megaton thermonuclear device
on March 1, 1954, on Bikini Atoll in the
northern Marshall Islands (Fig 1). This
atmospheric nuclear test, code-named

found the prevalence of thyroid nodules
in this comparison group to be 6.3%.”*
Although the estimates of thyroid dose
for islanders from Rongelap and Utrik
have been widely published, almost no
information exists about the possible
contamination of other northern atolls
by radioiodines in 1954.*"*"" There is no
verification that exposure to radioiodine
did not occur on the other northern
Radiation exposure to the thyroid
gland in the Marshallese people resulted primarily from beta radiation
from a mixture of radioiodines (I, “I,
™1, I) and, to some extent, gamma

lands of Rongelap Atoll (86 inhabitants),
and to a lesser extent, Utrik Atoll (167
inhabitants), The acute radiation sickness that developed in mostof the people from Rongelap has been well de-

tion-induced thyroid neoplasia comes
largely from two sources: (1) studies of
children exposed to gamma radiation
for benign diseases*™ and(2) studies of
survivors exposed to gammaradiation

northern atolls but extended throughout the northernatolls; this suggestsa linear

dose-response relationship.

scribed in previous reports.*" The most

(JAMA 1987;258:629-636)

BRAVO, heavily contaminated the is-

radiation.*"” Knowledge about radia-

Thyroid Neoplasia—Hamilton et al


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