THE NCI STUDIES ON RADIATION DOSES AND CANCER RISKS IN THE MARSHALL ISLANDS ASSOCIATED WITH EXPOSURE TO RADIOACTIVE FALLOUT

The U.S. National Cancer Institute (NCI, National Institutes of Health) was requested by the U.S. Congress in 2004 to assess the number of radiation-related illnesses to be expected among the people of the Marshall Islands from nuclear tests conducted there during 1946-1958. A thorough analysis conducted by the NCI concluded that 20 of the 66 nuclear devices tested in or near the Marshall Islands resulted in measurable fallout deposition on one or more of the inhabited atolls of the Marshall Islands; all other tests deposited their fallout on the test site atolls and in the open ocean. In this work, the deposition densities (kBq m-2) of the 63 radionuclides that are responsible for 98% of the doses received were estimated at each of the 32 atolls and separate reef islands of the Marshall Islands for each test. Those data along with reported measurements of exposure rates and bioassay results were used to estimate radiation absorbed doses to the red bone marrow, thyroid gland, stomach wall, and colon wall of atoll residents from both external and internal exposure. Annual doses were estimated for six age groups ranging from newborns to adults. The geographic pattern for total deposition of 137Cs, external doses, internal organ doses, and cancer risks were similar with the large population of the southern atolls receiving the lowest doses and populations of atolls nearest the test sites that had not be relocated prior to testing receiving the highest doses. The annual doses and the population sizes at each atoll in each year were used to develop estimates of cancer risks for the permanent residents of all atolls that were inhabited during the testing period as well as for the Marshallese population groups that were relocated prior. About 170 excess cancers (radiation-related cases) are projected to occur among more than 25,000 Marshallese, half of whom were born before 1948. All but about 65 of those cancers are estimated to have already been expressed.
The 170 excess cancers are in comparison to about 10,600 cancers that would spontaneously arise, unrelated to radioactive fallout, among the same cohort of Marshallese people. This paper summarizes the methods and results that are presented in a series of papers published in Health Physics in 2010 [1].