In 1998 Congress mandated a study of the health consequences for Americans exposed to radioactive fallout from above-ground nuclear weapons tests conducted around the world. The feasibility study, conducted by the Centers for Disease Control and Prevention and the National Cancer Institute, was designed to examine 19 radionuclides present in fallout from weapons testing conducted between 1951 and 1962.
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"Implicit in the feasibility study is the question of whether it is worthwhile to perform a substantially expanded study of all radionuclides," the report stated. "The committee believes that although a more detailed study is technically possible, neither the data nor the consequences appear to justify it."
In particular, the committee recommended further studies of exposure to iodine-131 (I-131), a radionuclide that can cause thyroid cancer, now that more information is available from the Chernobyl accident on the consequences of such exposure.
"Prior to Chernobyl, most of the data seemed to suggest that I-131 gave much less risk per unit dose to the thyroid than external radiation," said Roy Shore, Ph.D., Dr.P.H., director of the Epidemiology Program at New York Universitys School of Medicine and a member of the review committee.
Inherent in the challenge NCI and CDC faced in this study was estimating exposures using extremely limited original data. There were fewer than 100 monitoring stations throughout the United States taking fallout readings when the weapons tests were conducted. "You cant make a silk purse out of a sows ear," Shore said. "You have really limited data. Theres no way that you can finesse that to come up with very precise estimates. We felt that they had, within the limits of the data, pretty much captured the variation."
The lifetime risk of dying of cancer is 20%, and the feasibility study estimated that exposure to radioactive fallout would increase that risk to 20.03%. This risk translates into what may have been 11,000 cancer deaths among Americans exposed to fallout from tests conducted between 1951 and 1962 in addition to the approximately 40 million cancer deaths among the same population.
Now, information about the health effects of exposure to I-131 learned from the Chernobyl accident could be used to create more precise population-level risk estimates. "Thyroid cancer incidence among children appears to be more serious than it was thought before the accident," said Andre Bouville, Ph.D., a senior investigator in NCIs Radiation Epidemiology Branch and the lead NCI researcher on the study. Bouville specializes in research on the effects of the Chernobyl accident in Belarus and Ukraine. "Before the accident, a majority of radiobiologists thought that internal radiation resulting from intake of iodine-131 couldnt cause [thyroid cancer]."
Other Recommendations
The National Research Council review committee recommended that, before the feasibility study is finalized, the CDCNCI study group add context to dose estimates, clarify risk parameters, continue to retrieve and archive all historical fallout data, and use NCIs I-131 communication campaign as a model to develop a communications component.
By adding context to dose estimates, the study would make more clear the assumptions, methods, and uncertainties inherent in estimating radiation doses. This clarity will be especially crucial when communicating the results of the feasibility studyin particular the recommendation that only I-131 be studied furtherto the public, the committee concluded.
Also, risk parameters should be clarified. As it stands, the draft report discusses population-based exposure and risk because the limited data set does not allow for individuals to take the information and estimate their own personal risk. The committee favors "placing more emphasis on levels of individual risk and the associated uncertainty."
"In effect, were saying wed like the most realistic, most precise estimates for I-131 and thyroid cancer risk we can get given the database thats available," said Shore. To respond to this recommendation, researchers would need to include individual-level risk in the final report or include a full discussion of the reasons for retaining population-based risk estimates.
Continuing to retrieve and archive all historical fallout data will allow ongoing research using the most current models and methods. Although retrieving all fallout data may not be possible, the committee recommended that the study group gather information from the most likely sites, re-evaluate what they find, and attempt to ensure that other fallout informationespecially that held by the Department of Defensewill also be retained.
The committee also suggested that the authors of the study gather information directly from scientists who were involved with the testing. "The ability to collect, document, extract, archive, and effectively use fallout records depends on the knowledge possessed by the diminishing number of scientists from that era who are still available and who can help to identify and interpret the data," the review committees report noted. "It is not that the type of data available cannot be analyzed now, but that the scientists of that era have knowledge unobtainable except through the experience of the instruments and methods used at that time."
There is a plan in place at NCI to communicate information related to I-131. Focusing on working with the various stakeholders and publishing findings as soon as they are ready will allow CDC and NCI to effectively communicate results to people who may have been exposed to radioactive fallout who might otherwise be reluctant to accept the results of the feasibility study. To do this, the committee recommended that the two organizations develop a comprehensive and understandable summary of the findings designed for release with the final report. CDC has already taken responsibility for preparing a summary of the findings of the feasibility study for the public.
Next Steps
Representatives from CDC and NCI met on April 1 to discuss the National Research Councils report and recommendations. Charles Miller, Ph.D., chair of the Radiation Studies Branch and lead CDC researcher on the study, thought that the review committees overall reaction was positive. "I found that good and heartwarmingthat we were addressing the goals that Congress had intended," he said.
Although the next official step is for CDC and NCI to release the final study report, the groups will first respond to the committees recommendations. "We will prepare a response to all the comments and make a number of changes to the documentwhich I believe are improvements," said Miller. "We cant do everything because we dont have funding." Although researchers are nearly finished with the work Congress mandated in 1998, Miller noted that there is no funding earmarked for major work on this topic in the future.
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