Click for next page ( 43


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 42
2 Overview of the HTDS Draft Final Report and Organization of the Committee's Report The HTDS was conducted as an epidemiologic followup study of the prevalence of thyroid disease among those born in 1940-1946 in seven counties in the state of Washington. The counties were chosen for the likelihood of having residents who received high (Franklin, Adams, and Benton counties), intermediate (WalIa WalIa county), or low (Okanogan, Stevens, and Ferry counties) radiation doses to their thyroids from iodine- 13~ (13~:) released from the Hanford facilities. The research was conducted in two phases: a pilot study that was completed in 1994 and the full study, which is the subject of the Draft Final Report. It is well recognized that ~3~] is particularly important with respect to human exposure to radionuclides. That is because of the existence of the pasture-cow-milk-thyroid pathway: IT deposited on grass can be eaten by cows, be secreted into the cows' milk, be consumed by people, and result in substantial doses to the thyroid as it is efficiently taken up by this gland. On the basis of data from the atomic-bomb survivors and other studies of radiation exposure, as described in the background section of the HTDS Draft Final Report, young children are considered to be more sensitive to thyroid disease as a consequence of exposure to ~ The NRC committee uses the term "prevalence" loosely as a convenient way to refer to "cumulative incidence", which is what was actually assessed by the HTDS. 42

OCR for page 42
Overview of the HTDS Draft Final Report 43 radiation than are older children or adults. Therefore, the HTDS focused on people who were young children at the time of the releases.The HTDS Draft Final Report comprises 10 sections and an executive summary, references, and several appendixes. Section ~ introduces the HTDS, which began in 1989 and was conducted by investigators at the FHCRC and the University of Washington under contract with CDC. Section IT provides background information on the Hanford nuclear site and activities that led to the establishment of this epidemiologic study. Of particular importance was the Hanford Environmental Dose Reconstruction (HEDR) project, which was started in 1987 to develop estimates of radiation doses that people might have received from Hanford operations. Radiation doses to the thyroid from IT have been the main ones. The HEDR results were critical for the dose-response analyses conducted in the HTDS. Section TI also includes descriptions of the various thyroid diseases and other conditions that were studied as possible outcomes of irradiation from internally deposited inlet. Section Ill discusses several objectives of the HTDS. The primary objective was to determine whether thyroid morbidity was increased among persons exposed to ~3~} released Tom the Hanford nuclear site in 1944-1957. Section {V provides information on the study design. it discusses why the eligibility criteria were related to place and time of birth. An evaluable participant was defined as one who could be located and for whom sufficient information on thyroid disease and for determining radiation dose could be obtained. Outcome criteria, which define diagnostic criteria for various thyroid and parathyroid diseases and other changes, are also provided. Section V summarizes the field procedures and methods and the results of data collection, including detailed information on how the cohort was defined and its members were identified, how study subjects were traced and recruited, how telephone interviews were conducted, and how doses were estimated. Attempts were made to determine vital status and to

OCR for page 42
44 Review of the HTDS Draft Final Report trace and contact all the living among the 5,199 eligible potential participants. The section also provides information on scheduling, clinical investigations, interviews, medical reviews, determination of final diagnoses, and management of medical records. Section VT discusses three special considerations related to the conduct of the HTDS. The first was an assessment of the feasibility of conducting a similar health study in the nine American Indian tribes and nations near the Hanford site; it discusses the steps taken to determine the feasibility and the decision that such a study would have insufficient statistical power to detect an increase in thyroid disease caused by Hanford releases. The second was a CDC-appointed advisory committee; it discusses the role of this committee in the design and conduct of the study, the schedule and locations of committee meetings, and the openness of the meetings to the public. The third was provision of information to the public throughout the whole HTDS process; it describes the approaches used such as newsletters, fact sheets, and a telephone line to keep the public informed of the activities and results ofthe HTDS. Section VIT describes the statistical methods used in the HTDS analyses. The information provided is related generally to the tests of the statistical significance of exposure-response relationships for various thyroid diseases, including an examination of possible confounding or effect-modifying factors. The data collected were in three categories: process information, characteristics of living evaluable participants, and analyses of exposures and outcomes. The analytic methods used to summarize the data are described in detail, as are the calculations made to examine uncertainties in dose. The possible confounding or effect- modifying factors included sex, age at first exposure to ill, ethnicity, smoking, and other radiation exposures. With respect to the last factor, exposure to 13~} in fallout from weapons tests conducted at the Nevada Test Site (NTS) is given particular attention.

OCR for page 42
Overview of the HTDS Draft Final Report 45 Section VITI presents the results of the HTDS. Given first are the characteristics of the 3,441 living evaluable study participants, including year of birth, age at examination, race or ethnic origin, medical radiation exposure, occupational history, and smoking history. Radiation doses to the thyroid from Hanford AT are summarized on the basis of calculations derived with the CIDER computer program developed as part of the HEDR project; these calculations were based on a person living "in area" or "out of area" from December 1944 to the end of 1957. For each study participant, 100 dose estimates were calculated, and the median of the 100 estimates was used as the best estimate of the person's dose. The implications of the number of persons studied and their calculated thyroid doses relative to the statistical power of the HTDS results are discussed. These dose values were used with a large number of outcome variables to conduct dose-response analyses. The outcome variables consisted of 11 categories of thyroid disease, ultrasonographically detected abnormalities, hyperparathyroidism, and various thyroid-related laboratory tests. Definitions are provided for each outcome variable, as are the results of the dose-response analyses. Some of the diagnoses were rare (for example, there were only 20 thyroid cancers); others were common. For none was the dose-response trend statistically significantly positive; and for several, the estimate of the linear slope was negative. in addition to the basic analyses, results of alternative dose-response analyses and other factors are presented. Infonnation is also given on the patterns of mortality in the HTDS cohort. Section TX discusses the results of the HTDS. It first summarizes the study accomplishments, including the identification and location of members of the cohort. Other aspects discussed include telephone interviews, medical evaluations of the cohort, and the successful location of a large proportion of the related medical records. Results of the dose-response analyses are summarized: there was no relationship between thyroid radiation dose from Hanford and the cumulative incidence of any of the 13 primary outcomes even when alternative analytic approaches were

OCR for page 42
46 Review of the HTDS Draft Final Report used. The section discusses the possible influences exerted by such factors as the definition and selection of the cohort, the definition or misclassification of outcomes, the estimation of thyroid radiation dose, and uncertainty. It compares HTDS results with findings in other populations that were subject to irradiation of the thyroid, including the Japanese atomic-bomb survivors, Marshall island residents exposed to fallout from the Castle-Bravo test, residents of Utah exposed to ]3~{ from atmospheric releases from the NTS, and people who lived near the Chernobyl nuclear reactor at the time of its catastrophic release of radionuclides. Section X discusses communication of the HTDS results with the public. it summarizes ways that the HTDS staff used to maintain open and frequent communication, including public meetings, presentations at scientific meetings, interviews, fact sheets, and a toll-free 800 number. The remainder of this section is devoted to plans for communicating the study results to five targeted groups: study participants, the public and the mass media, the scientific community, the regional medical community. and government officials and agencies. To provide a thorough and balanced review of the Draft Final Report and its communication to the public, the subcommittee undertook a number of activities. We met on February 4-5, 1999, in Atlanta, Georgia, on March 29-30, 1999, in Augusta, Georgia, and on August 30-31, 1999 in Washington, DC, to review the report; during the same period, we requested additional information from the HTDS and HEDR investigators. We met in Spokane, Washington, on June 18-19, 1999, at an all-day open public meeting on June 19, attended by about 60 people. We heard from various experts and members of the public who wanted to present information regarding the HTDS Draft Final Report. During the clay, 14 experts and interested members of the public invited by the subcommittee some at the suggestion of citizen action groups presented their views in person and through conference calls. Many of them also provided written statements. In addition, four public-corrunent sessions allowed any member of

OCR for page 42
Overview of the HTDS Draft Final Report 47 the public to have his or her views heard on a variety of subjects in the HTDS Draft Final Report. (Appendix A contains the agenda and a list of speakers.) To gather additional information for the communication section of our report, we conducted telephone interviews with two journalists in the Pacific Northwest area, the HTDS principal investigator, members of the CDC scientific and media staff in Atlanta, and several members of citizen advisory groups in the Hanford region. We also examined various communication- planning materials that were made available by CDC. Because the HTDS was an epidemiologic study with substantial public-health implications and because there was intense public interest in the Draft Final Report, the subcommittee felt that the study and the draft report should be thoroughly reviewed both for its technical aspects and for its effectiveness and balance in communicating to the public. We therefore went beyond the six questions that were posed by CDC and considered additional issues pertaining to scientific quality. Consequently, the main body of our report is not organized around the six questions from CDC, although responses to them are given in chapter 9 and summarized in the executive summary. The executive summary also provides conclusions and recommendations regarding the HTDS Draft Final Report. The subcommittee's review of the HTDS Draft Final Report is organized around five main themes: Epidemiologic design and methods and clinical procedures. Dosimetry. Analysis of results. .

OCR for page 42
48 Review of the HTDS Draft Final Report Statistical power and interpretation. Communication of results.