We studied the risk of thyroid neoplasia in Marshall Islanders exposed to
radioiodines in nuclearfallout from the 1954 BRAVO thermonucleartest. We
screened 7266 Marshall Islandersfor 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 prevalence of thyroid nodularity in a subgroup of 2273 persons
whowere alive in 1954 and whotherefore were potentially exposed to fallout from
the BRAVOtest. For those 12 atolls previously thought to be unexposedto fallout,
the prevalenceof 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
between distance and the age-adjusted prevalence of thyroid nodules. Distance
wasthe strongestsingle predictorin logistic regression analysis. A new absolute
tisk 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
northern atolls but extended throughoutthe northernatolls; this suggestsa linear
(JAMA 1987;258:629-636)
IT HASbeen21 years since the publication of an early case series of thyroid
neoplasia (including thyroid cancer 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

From the Departments of Medicine (Drs Harilton
and LoGero) and Biostatistics (Dr van Belle), University
of Washington, Seattle
The opinions, conclusions, and proposals in this

northern Marshall Islands (Fig 1). This

article are those of the authors and do not necessarily
represent the viewsof the Robert Wood Johnson Foun-

dation of the Marshall tsiands Atomic Testing Litigation
Reprint requests to Occupational Medicine Program,
Harborview Medical Center, 325 Ninth Ave, Seattle, WA
98104 (Or Hamilton).

JAMA, Aug 7, 1987—Vol 258, No. 5

on March 1, 1954, on Bikini Atoll in the

atmospheric nuclear test, code-named

BRAVO, heavily contaminated the islands 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-

scribed in previous reports.** The most
common late effect from this exposure
has been the development of thyroid
nodules. Between 1954 and 1985, thy-

roid 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 assumedthat Rongelap and Utrik were the only two northern atolls exposedtofallout radiation; in

their studies they used as unexposed
controls those living on other northern
atolls during the 1954 BRAVOtest and
found the prevalence of thyroid nodules
in this comparison group to be 6.38%.*"*
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,

7, I) and, to some extent, gamma
radiation.’ Knowledge about radiation-induced thyroid neoplasia comes
largely from two sources:(1) studies of
children exposed to gammaradiation
for benign diseases*™ and (2) studies of
survivors exposed to gamma radiation
Thyroid Neoplasia—Hamilton et al



Thomas E. Hamilton, MD, PhD: Gerald van Belle, PhD; James P. LoGerfo, MD, MPH

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Thyroid Neoplasia in Marshall Islanders
Exposed to NuclearFallout

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