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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
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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
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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.
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Overview of the HTDS Draft Final Report
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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
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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
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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.
.
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Review of the HTDS Draft Final Report
Statistical power and interpretation.
Communication of results.
Representative terms from entire chapter:
htds draft
