Review of the Hanford Thyroid Disease Study Draft Final Report (2000) / Chapter Skim
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Executive Summary
Executive Summary
Pages 17-39
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From page 17... ...
Releases of 13~{ began in December 1944 as a consequence of the chemical removal of plutonium from the fuel rods irradiated at the Hanford nuclear site. The main study objective of the HTDS is described in the Draft Final Report as a "determination of whether thyroid morbidity is increased among persons exposed to releases of radioactive iodine from the Hanford nuclear site." l:n the study, 3,441 subjects who had been born near Hanford in 1940-1946 were contacted in the 1990s and taken to several locations for medical examination for thyroid disease.
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From page 18... ...
To respond to the charge, the NRC subcommittee felt that it needed to go beyond the specific questions addressed to it by CDC and develop a broad understanding and critique of the HTDS and the Draft Final Report. As part of those activities, the subcommittee solicited comments from outside experts and members of the public primarily in a public meeting held in Spokane, Washington, in June 1999, where 14 scientists and members of the public made formal presentations to the subcommittee about various aspects of
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From page 19... ...
in addition, efforts were made to evaluate all information materials prepared for the public and additional CDC communication plans. Information was gathered through interviews with journalists, members of concerned citizen groups in the Hanford region, members of the CDC scientific and media staff in Atlanta, and the HTDS investigators.
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From page 20... ...
The HTDS investigators provided the subcommittee with additional tabulations for examining deaths in the group studied. Although there was a small increase in mortality, mostly
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From page 21... ...
An adequate review of the cytopathology results is · The HTDS investigators should indicate for how many potential past thyroid diagnoses they were unable to obtain any medical confirmation, with a breakdown by reported type of thyroid disease and dose. detail.
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From page 22... ...
if the doses were underestimated across the board, the study would have greater statistical power than was projected, in which case negative results of the study would be more persuasive. However, if there was variation by subject in the degree of dose underestimation, or in the degree to which subjects vary in sensitivity (because of age differences, and so on)
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From page 23... ...
The HTDS team performed some analysis of the impact of NTS fallout, but not of global fallout. A rough assessment of the thyroid doses arising Dom global fallout was performed as part of our review.
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From page 24... ...
The HTDS used the HEDR thyroid doses as its only, or at least primary, tool to describe patterns of likely exposure. The subcommittee believes that the HEDR dosimetry should not have been the sole method for evaluating the association between AT exposure and thyroid disease, and it suggests that supplemental
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From page 25... ...
Other potential risk factors were evaluated as possible confounding or effect-modifying variables, but no tables were presented to show the results of those evaluations. The HTDS investigators assigned thyroid doses only for periods when subjects lived as children in the geographic area for which exposures were estimated.
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From page 26... ...
Persons living in various geographic areas often vary in their baseline risk of thyroid diseases because of differences in dietary iodine intake and other unknown factors. The rates of detected disease in the HTDS are based on thyroid examinations and depend on the methods and criteria of those examinations.
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From page 27... ...
(See chapter 5.) A number of key tables were absent from the report, for example, tables of frequency distribution of doses; of observed and expected frequencies of each thyroid disease by, say, quartiles of dose; of thyroid disease rates by milk-drinking habits and other risk factors in disease; and of average doses by year of birth, amount of milk consumption in childhood, and the like.
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From page 28... ...
· The HTDS investigators should report on those who were out of the dosimetry area for part of the exposure period and examine the impact of the assumption of zero dose received during such periods. · Analyses designed to control for possible confounding by geographic area should be conducted.
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From page 29... ...
for detecting plausible nonzero dose-response relationships. Nevertheless, the HTDS investigators' discussion of statistical power did not present how small the expected excess of thyroid cancers was.
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From page 30... ...
Conclusions: · The HTDS investigators were successful in achieving the sample size and dose distnbution that they projected as necessary if the study were to have adequate statistical power. · However, the HTDS assumptions regarding statistical power did not include the possibility that dose uncertainty would weaken the associations.
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From page 31... ...
· The compatibility of the HTDS study with other studies of radiation and thyroid disease should be re-examined, taking into account the impact of dose uncertainties. COMMUNICATION OF THE STUDY RESULTS TO THE PUBLIC Compared with the history of a less-than-open publicinformation policy of the Department of Energy and its predecessor agencies, the early plans by CDC and the HTDS investigators for open communication about the study were enlightened and promising.
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From page 32... ...
The main message of the report was problematic. The written materials and oral presentations made by HTDS investigators overstated the certainty (the statistical power)
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From page 33... ...
Conclusions: · The early enlightened plans by CDC and the HTDS investigators for open communication about the study and for a citizen advisory group for the study should have helped to build trust and credibility. · Early release of the Draft Final Report and public concerns about CDC changes in that draft led to many of the communication problems that resulted from the draft report's release.
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From page 34... ...
of the study and the conclusiveness of the negative findings and failed to discuss the uncertainties. CDC officials should have expressed their own interpretations in addition to those of the HTDS investigators about the draft report in the briefings and public documents.
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From page 35... ...
has been found, on the whole, to be reasonably sound for the estimation of thyroid doses, but several questionable assumptions have been identified that would have some impact on the estimated individual doses. The estimated-dose uncertainties that the HEDR project produced and the HTDS study used are underestimates of the total dose uncertainty because some significant sources of uncertainty were overlooked.
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From page 36... ...
Most important, there was no adequate discussion of how dosimetric uncertainties might have affected the confidence intervals and the statistical power of the study.
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From page 37... ...
Its members believe that the high certainty with which the HTDS investigators presented the negative findings of the draft report was overoptimistic. Still, the main finding of the final HTDS report might indeed be that no radiation effect could be observed: the lack of evidence of a dose-response relationship for any type of morbidity suggests that overall risks were unaffected by Hanford releases.
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From page 38... ...
The small numbers of thyroid-cancer cases and the lack of precision in estimating individual exposures mean that one can have little confidence in the risk estimates found in the HTDS. At the various publiccomment meetings, people who lived in down-wind areas stated that they and their families experienced more thyroid disease than would have been expected in the population at large.
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From page 39... ...
Executive Summary 39 show concern and sensitivity for the thyroid-health issues that people perceive affect them. The full picture of the study results should be given, including all the uncertainties and other problems.
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