oe t sr or me 1, alah. atthe 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 dose-responserelationship. (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 Project. 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 atolls. 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 629 ee Thomas E. Hamilton, MD, PhD: Gerald van Belle, PhD; James P. LoGerfo, MD, MPH ee mn cee Thyroid Neoplasia in Marshall Islanders Exposed to NuclearFallout eeeg EY ES EE Tee et AOL a7