HANFORD DOWNWINDERS INFORMATION SITE

Perspectives on the Hanford Thyroid Disease Study

CONTENTS

K. F. Baverstock

Summary: HTDS Draft Final Report (CDC)

This information sheet provides the viewpoints of scientists and citizens on the Draft Final Report of the Hanford Thyroid Disease Study (HTDS). The Centers for Disease Control and Prevention (CDC) made the draft report public in January 1999. CDC invited public comment and requested the National Academy of Sciences (NAS) to provide scientific peer review. The NAS is expected to provide a report of its scientific peer review in the fall of 1999.

For a summary of the HTDS preliminary results and background information on the study, see the information sheet provided by the CDC.

Many Downwinders had questions about the HTDS draft report, what the results might mean and what questions have been raised about the report. To respond to these questions, the Network asked nine people with different areas of expertise or interests for a brief statement of their views on the draft HTDS report. To spur their thinking, the Network suggested four questions:

1. What issues, if any do you see that are raised by the draft HTDS report?

2. What, if anything, do you think should be done to follow up on this study?

3. The HTDS report was released in draft form to make the results available to the public as soon as possible and to provide opportunity for comment. What comments do you have on the release of the study in draft form and/or on the process of announcing the draft report?

4. What do you see as the significance of this study? (Or, how would you place the study in context for our readers?)

Those who contributed to this information sheet had the option of responding to these questions or focusing on their area of expertise or their concerns. Each contributor was asked to write for the general public. Network staff edited the statements for ease of understanding and added a glossary of key scientific terms. Each contributor approved the final edited version of his or her statement.

K.F. Baverstock

First I want to stress that the comments below represent my views as a scientist and should under no circumstances be taken to represent the views of the World Health Organisation.

I have read the introduction and executive summary of the draft HTDS report. Full details of the results and methodology (in particular how doses were calculated and distributed and how confounding due to exposure to the Nevada Test Site [NTS] fallout was dealt with) are not given there, so I cannot provide a final view on the implications of the report's negative findings. However, I am surprised that the investigators thought that a study on the scale reported (3,441 study participants) would provide the information they claimed to seek, namely evidence of a dose-response relationship.

However, in my view, a case could be made that HTDS found an excess of thyroid cancer cases in the study population. There are certainly more cases detected than would be expected on the basis of the national rates for invasive thyroid cancer. This excess is not necessarily the result of the exposure to radioiodine (there are other possible explanations), but I am surprised that the investigators do not address this issue in the executive summary before concluding that there is no excess of disease.

The criterion adopted by HTDS for detecting excess thyroid cancer due to iodine-131, namely that a "dose response" is evident, is much more demanding than detecting an excess of thyroid cancer in the population. This will be especially the case where individual doses are uncertain and where there have been other exposures, such as from the NTS, which may also induce the disease. These are both factors relevant to the HTDS. Detecting an excess is not absolute proof of causation by iodine-131 (for example, national rates may not be appropriate due to the design of the study). However, it is at least a potential indicator of effect and should be addressed before an excess of thyroid cancer is discounted.

I am, therefore, surprised that the report concludes so firmly that there is no increase in thyroid cancer. It may indeed be that there is no evidence of an increase. But, on the basis of this study, that is not, in my view, evidence for no increase.

K. F. Baverstock, Ph.D., has led the Radiation Protection Programme at the World Health Organisation European Centre for Environment and Health in Rome, Italy, since its founding in 1991. This program was instrumental in bringing to world attention the increase in thyroid cancer in Belarus, now attributed to the Chernobyl accident. Prior to 1991, Dr. Baverstock was at the UK Medical Research Council Radiobiology Unit where he pursued a wide range of scientific research interests related to the public and occupational health aspects of exposure to ionizing radiation. He has served on the oversight committee for a Nationwide Radiological Survey of the Marshall Islands and on the Committee on Exposure of the American People to Iodine-131 from Nevada Atomic-Bomb Tests. Ph.D., has led the Radiation Protection Programme at the World Health Organisation European Centre for Environment and Health in Rome, Italy, since its founding in 1991. This program was instrumental in bringing to world attention the increase in thyroid cancer in Belarus, now attributed to the Chernobyl accident. Prior to 1991, Dr. Baverstock was at the UK Medical Research Council Radiobiology Unit where he pursued a wide range of scientific research interests related to the public and occupational health aspects of exposure to ionizing radiation. He has served on the oversight committee for a Nationwide Radiological Survey of the Marshall Islands and on the Committee on Exposure of the American People to Iodine-131 from Nevada Atomic-Bomb Tests.

Betty Bergdahl

Impressions of the HTDS Findings

I am impressed with the thoroughness of the findings. This study has taken nine years, covered an area of 7,500 square miles, which includes Benton, Franklin and Adams Counties. A total of 4,875 individuals were interviewed including those born during 1940-1946. The majority of these people went to thyroid clinics, had thorough thyroid examinations, and were questioned about their past history of thyroid disease.

Two recognized groups were involved in the study-CDC and the Fred Hutchinson Cancer Research Center. To me, this makes the study legitimate and objective.

Issues Raised or Addressed by the Study

We have had articles in the Tri-City Herald and "Letters to the Editor," one right after another, about the people in this area who were concerned about the radionuclide emissions of iodine. I am sure that it must have been a decided relief to them to read the results of this study and to know there was not this concern.

Uncertainty over possible health effects seems to be less of an issue when the findings are examined. I am sure that many people had built up in their mind things that maybe were happening or were going to happen. From that standpoint, the findings have done a good job.

However, there is uncertainty for individuals born between 1940-1950 who now have thyroid disease. Was this caused by Hanford iodine released during 1944-1957? There are questions concerning infant mortality, fetal death and pre-term birth which may be answered when this study is completed later.

What, if anything, should be done to follow-up on the study?

CDC should continue to study the development of thyroid disease and implement public education outreach programs. The public can be alerted to signs of thyroid disease by public health agencies and health care providers. The results of the data on infant mortality, fetal death, and pre-term birth should be fully explained. Those are very important things to mothers and mothers-to-be. This should be settled so that there is an understanding of what the studies have proved on these issues.

The results of this study were released to the public before they were finalized. What are some positives and negatives of releasing the findings of a study early?

On the positive side, early release gives the highly interested public an opportunity to learn the results of the study at an early stage. This emphasizes the policy of complete openness and the intensity of the study. It shows that they want to keep the public current with what is going on at CDC.

What do the results of this study mean for you and your family?

As to us personally, I feel happy to know that there is no one in our family who has any concern about the thyroid. Our family grew up here and played in the river because we lived on the riverfront. This study was worthwhile because it has been a real concern for many families, while it wasn't a direct concern to us. I am sure that there are other parents who were worried about what might happen. For this reason, it is excellent that the study is completed and is being made public.

Betty Bergdahl has resided in Richland, Washington, since June 1943. She grew up in southeastern Washington state. She came to Richland when her husband began working at Hanford. Their first child was born in Dayton, Washington, in April 1943, two months before they moved to Richland. Between 1944 and 1948, the Bergdahls had three other children. The childhood and high school years of all four children were spent in Richland. The Bergdahls' home is on the riverfront of the Columbia. From May to October, the family and their friends lived on the dock, played on the river bank, camped on the islands, and sailed, water skied, and swam in the river. has resided in Richland, Washington, since June 1943. She grew up in southeastern Washington state. She came to Richland when her husband began working at Hanford. Their first child was born in Dayton, Washington, in April 1943, two months before they moved to Richland. Between 1944 and 1948, the Bergdahls had three other children. The childhood and high school years of all four children were spent in Richland. The Bergdahls' home is on the riverfront of the Columbia. From May to October, the family and their friends lived on the dock, played on the river bank, camped on the islands, and sailed, water skied, and swam in the river.

Bill Burke

There is a lot of thyroid disease reported on the Umatilla Indian Reservation. When I learned about the HTDS and iodine-131, I was immediately concerned. I was born in 1930. Many in my generation have thyroid disease. My children's mother had thyroid disease and was of an age to be affected by iodine-131.

Indians live close to the land and the river, and have traditionally eaten natural foods. This gives us unique exposures to the radionuclides released from Hanford.

We talked a lot about HTDS in the Native American Working Group. (The Native American Working Group coordinated Hanford-related Tribal research and recommended research activities to the Technical Steering Panel that directed the work of the Hanford Environmental Dose Reconstruction Project.) We thought that the Thyroid Disease Study would provide specific results about affected Indian Tribes. But in the end, we learned that our Tribal population was too small for epidemiologic study methods to give us a true picture of how our health was affected by the radionuclides.

There needs to be a study of thyroid disease in Tribal people. I am really interested seeing if ANOVA, or "analysis of variance" (a statistical method for detecting differences in the average of a factor such as dose or estimated risk, between groups), could be used to calculate ranges of risk with uncertainty for Tribal populations. Why not look at health risks to Tribal people using this or another alternative method?

The U.S. government has a real responsibility to understand Hanford-related health issues, including risks to the health of Tribal people. Under pressure from westward expansion, the Columbia Basin Tribes and Bands ceded many millions of acres in present-day Washington, Oregon and Idaho to the United States. Reservations were formed. Treaties established special legal responsibilities or trust relationships between the U.S. government and Indian nations. For example, Tribal leaders reserved rights to pursue their traditional lifestyles on ceded lands. Agreements between the United States and the Tribes are government-to-government commitments. But the trust relationships and the Tribes very often are overlooked. This seems to be the case here, too. It's very troubling.

I think a lot about the post-colonization trauma (PCT) that Native American people have experienced. Like post-traumatic stress syndrome, it describes the shock and confusion that follow an overwhelming event outside the range of human experience, such as combat or a natural disaster. It makes protecting our culture and the trust issue more meaningful to me as a Tribal leader. I don't understand-or maybe I do understand-the continuing attempt to take Indian lands. Understanding the effects of PCT made me feel more strongly about trust relations.

Today we still don't have any definite answers about the effects of the radionuclides released from Hanford into the air and into the Columbia River. All we know about radionuclides is, you can't see them, hear them or taste them-but they can affect us.

Bill Burke is one of four chiefs of the Confederated Tribes and Bands of the Umatilla Indian Reservation and one of two Walla Walla Chiefs. He is a past member of the Native American Working Group and the Hanford Health Information Network Tribal Advisory Board. Mr. Burke has served on the Future of the Hanford Site Lands Committee and the States and Tribes Government Working Group. is one of four chiefs of the Confederated Tribes and Bands of the Umatilla Indian Reservation and one of two Walla Walla Chiefs. He is a past member of the Native American Working Group and the Hanford Health Information Network Tribal Advisory Board. Mr. Burke has served on the Future of the Hanford Site Lands Committee and the States and Tribes Government Working Group.

Tim Connor

The Hanford Thyroid Disease Study Has Done More Harm Than Good for Hanford Downwinders

A decade ago, I was one of the people who worked very hard to gain Congressional support for a health study of people exposed to radioactive iodine emissions from Hanford. At the time, we believed such a study could provide a valuable public service for Hanford downwinders.

Regrettably, given the way in which the draft results of the study were communicated, the HTDS actually inflicted a good deal of harm on those whom the study was intended to serve.

The cause of this harm is not the fact that the HTDS investigators found no link between Hanford radiation and thyroid disease. The fact is, it is rare for individual epidemiologic studies to provide strong evidence for connections between low-dose exposures and diseases like cancer. More often than not, the results are inconclusive.

The problem with the January 1999 release of the HTDS is that the draft results of the study were presented as if they were conclusive. The message from the researchers was that if you are among those who suspected (or believed) that Hanford emissions are responsible for an increase in thyroid disease among downwinders, you should be "reassured" that there is no such connection.

Such statements by scientists are practically unheard of in connection with environmental epidemiologic studies. The simple reason for this is that scientists understand that the results of any such study (whether it finds a link, or doesn't) have to be viewed as a piece in a larger puzzle. This is because environmental epidemiology is not laboratory science where researchers conduct carefully controlled experiments that can be repeated by other scientists. It is an observational science, where a given hypothesis must be tested via repeated observations and evaluated within the context of animal studies, cellular and molecular research, etc.

In the case of the HTDS, there is considerable evidence from previous studies that exposure to radioactive iodine does cause increases in thyroid diseases. Why the HTDS team would offer "reassurance" in light of this other evidence is puzzling. The mildest criticism one can offer is that their statements do not reflect the circumspection and caution that is the hallmark of the science.

This basic problem with the way the HTDS results were reported is compounded by the several technical criticisms of the study. The most important technical criticism is that the HTDS was a "low power" study rather than the "powerful" study asserted by its authors.

What does this mean? In simplest terms, statistical power is a measure of confidence. The higher the power of a study, the less likely it is that a true cause/effect relationship will be missed. Conversely, a low-power study is one where the lack of an observed link between cause and effect has little, if any, meaning.

If the scientific critics of the HTDS are found to be correct, it will come as little, if any, consolation for Hanford downwinders. Not only has the HTDS left them more confused than ever. It has also left them feeling more betrayed than ever.

Tim Connor is the founder and Editorial Director of the Northwest Environmental Education Foundation. Previously, he was Associate Director and staff researcher for the Energy Research Foundation, a public interest foundation based in Columbia, S.C., where his work focused on health and environmental research. Before joining this organization, Mr. Connor was research director for the Hanford Education Action League, a public interest organization that was based in Spokane, Wash. Prior to his public interest work, Mr. Connor was an investigative reporter. He is the author of Burdens of Proof: Science and Public Accountability in the Field of Environmental Epidemiology, with a Focus on Low Dose Radiation and Community Health Studies (Energy Research Foundation, 1997).

William Farris

The HTDS relies on radiation dose estimates that were produced through a six-year study called the Hanford Environmental Dose Reconstruction (HEDR) Project. The HEDR Project, which was completed in 1994, developed detailed models and computer codes that could be used to calculate iodine-131 thyroid dose estimates for individuals, including HTDS study participants.

The HEDR Project was initiated because of public interest in the historical radioactive releases from the Hanford Site. Over 38,000 pages of documentation from the early years of Hanford operations were released to the public during 1985 and 1986. This information indicated that substantial quantities of radioactive materials had been released from Hanford. This information alone could not be used to reconstruct the actual radiation doses received by the population surrounding the Hanford Site. To accomplish that, a methodical reconstruction of the releases, environmental conditions and human activities was necessary. However, due to limitations in available data, it is important to note that the actual radiation dose received by any single individual will never be known with complete certainty. The radiation doses were not directly measured during the early years of site operations, so the use of predictive models was deemed necessary.

The primary purpose of the HEDR Project was to estimate the radiation dose using all existing information about the operations of the site, the knowledge about how radioactive materials are transported in the environment and the way in which people might be exposed to those materials. A system of computer models was developed to estimate radiation doses from atmospheric releases throughout the study area (eastern Washington, northern Oregon, and western Idaho). This system consisted of four separate but interrelated models and associated computer codes: source term (the amount and type of radioactive material released), atmospheric transport, environmental accumulation and individual dose.

The ability of scientists to recreate key events and conditions that existed 40 years in the past is limited by the lack of detailed data. Therefore, uncertainty estimates (that is, the range of possible estimates along with a most likely estimate) were included as a key component of the HEDR effort. For the first time on any dose reconstruction project, the individual radiation dose estimates included information about the uncertainty in those estimates. This was a major advance in the science of dose reconstruction. Uncertainties in the actual amounts released are addressed through use of multiple recreations (called realizations), each of which represents an alternative interpretation of the conditions that existed in the past and are consistent with existing knowledge. Together, these alternative conditions represent the range of conditions that could have existed.

One hundred separate realizations of the complete release history, environmental transport and human exposure assessment were performed to estimate the uncertainty in the model predictions. The reliability of the models was tested by reviewing the concepts underlying the models, testing the implementation of the models in the computer codes, analyzing the uncertainty and sensitivity, and validating the model output.

Extensive scientific peer review was conducted throughout the HEDR Project. Scientists and other stakeholders reviewed, critiqued and commented on the HEDR computer models as they were being developed.

Based on limitations in data, no model can ever hope to estimate perfectly the radiation impacts from Hanford. However, the science and models developed by the HEDR Project have proven highly reliable and provide for a sound technical base for Hanford-related individual dose assessments, including the HTDS.

William T. Farris is Program Manager, Environmental Technology Division, of Pacific Northwest National William T. Farris is Program Manager, Environmental Technology Division, of Pacific Northwest National Laboratory. Mr. Farris is an environmental health physicist specializing in the assessment of impacts of radioactive and hazardous waste disposal and restoration. He has degrees in geological sciences, radiological sciences and technology management. His experience includes public, worker and environmental health assessments that pertain to radioactive, hazardous chemical and mixed wastes. Past work includes the retrospective assessment of radiation doses from releases from the Hanford site. He served as Deputy Project Manager and authored the two final dosimetry reports for the HEDR Project.

F. Owen Hoffman

Issues in the Draft Report

The HTDS aimed to find a statistically significant relationship between increasing dose and the frequency of thyroid disease. Its failure to do so has been interpreted by the authors as being evidence of no effect (i.e., the negative findings are conclusive). I disagree. Because there could be a true underlying effect that cannot be detected by the study, I believe that the results of HTDS are, at present, inconclusive.

HTDS appears to be very well-designed, but the weakest link is the dosimetry (the method of estimating individual exposure and radiation dose). The individual estimates of thyroid dose are afflicted with relatively large uncertainty and the potential for bias. These dose estimates, which depend on the methods developed in HEDR, are calculated entirely using mathematical models. Few environmental measurements were available to permit calibration of the model against real-world conditions.

I believe it is likely that the individuals with high doses may have been overestimated, but those with the lowest doses may have been underestimated. The amounts of iodine-131 Hanford released after mid-1951 also appear to have been underestimated (raising the total curies released from about 750,000 to more than 900,000). Revision of the amount released would have a significant effect on the dose estimates for those who received low exposures to the high releases that occurred in 1945-46. Furthermore, an important confounder (a factor that could interfere with detecting a true effect) is the additional exposure to iodine-131 from the Nevada Test Site (NTS) and global fallout. These confounding exposures to iodine-131 were not given detailed consideration by HTDS.

The apparent negative findings of HTDS are at odds with other epidemiological studies, especially for people exposed in childhood. Studies of the Chernobyl accident, the nuclear tests at the Marshall Islands, and medical diagnostic uses of radiation show a strong dose-response effect for irradiation of a child's thyroid gland.

Why is HTDS inconsistent with other studies? I think the answer is a combination of the factors I have just mentioned: (1) the high degree of uncertainty in the dose model, (2) the confounding effects from NTS and global nuclear tests, and (3) HEDR's underestimation of Hanford's iodine-131 releases after mid-1951.

Release of the Study Results in Draft Form

In my view, the release of the HTDS draft report was not premature. I have always supported full disclosure of results, even when the results are in draft. However, the manner in which the draft report was released to the public (the formality of the release, the emphasis on pre-release secrecy) was certainly inappropriate. The preliminary nature of the HTDS findings should have been stressed more strongly and the possibility of the negative findings being inconclusive should have been discussed in detail. In retrospect, I believe that public representatives on the Hanford Health Effects Subcommittee and HTDS oversight committees should also have been briefed on the draft results prior to the U.S. Department of Energy (USDOE), Congress and the press.

Significance and Follow-up

The HTDS results show the need to look at exposures in a larger population, and at higher dose levels. It also shows the need for follow-up on the Chernobyl and Marshall Islands studies, since dosimetry for individuals in these cohorts is known with greater accuracy. In particular, the Chernobyl dosimetry is contemporary, and the exposed population is much better known and much larger than at Hanford.

HTDS is only one study; other studies show a dose-response relationship and have found risk for radiation-induced thyroid disease. The weight of evidence suggests that there is a risk for thyroid disease from exposure to iodine-131. In fact, I know of no compelling reason why the effect of exposure of the thyroid gland to iodine-131 should be substantially different from exposure of the thyroid to other types of ionizing radiation. Factors such as gender and age at the time of exposure should be more important than differences between exposure to iodine-131 and to external X- and gamma radiation.

The next step is to determine how much risk there is. Much of this determination will depend on epidemiological evidence obtained from careful study of other exposed populations.

F. Owen Hoffman, Ph.D., president of SENES Oak Ridge, Inc., is an expert in dose reconstruction and risk analysis. He has led the tasks to reconstruct thyroid doses to area residents from historic releases of iodine-131 from federal government facilities at Oak Ridge, Tennessee. Dr. Hoffman has advised dose reconstruction projects for the states of Tennessee and Colorado. He is a member of the National Council on Radiation Protection and Measurements and a corresponding member of the International Commission on Radiological Protection.

Larry Jecha

What issues, if any, do you see that are raised by the draft HTDS report?

I believe the HTDS report puts some issues to rest. This community (Benton and Franklin counties, which are the closest to Hanford) has not seen any increase in thyroid disease. We have the lowest rates of thyroid cancer in the state, and yet we had the highest exposures. The study results are consistent with what our medical community has observed.

What, if anything, do you think should be done to follow up on this study?

If anything, it might be useful to follow up on study participants, in terms of their ultrasound and fine needle aspiration tests, to see what happens to them over time. This follow-up could provide information on what the results of these tests really mean-which are normal findings and which are abnormal. At this time, there's no standard for interpreting these test results. This would not be follow-up related to radiation exposure but to the testing procedures that the study did.

What comments do you have on the release of the study in draft form and/or on the process of announcing the draft report?

I think the release of the results was premature, but it was a decision based on requests from interest groups. The plan, as discussed and approved by the HTDS Advisory Committee, had been to release the study results after peer review.

What do you see as the significance of this study?

The study verified what the medical community in our area has thought based on what they see in practice-that there is no increase in thyroid morbidity/mortality. Of all communities in Washington state, you would have thought our area would have been affected. Also significant is that this study has had more involvement by and with the public than any other study I have seen.

Larry Jecha, M.D., MPH, is the Health Officer for the Benton-Franklin County and Klickitat County Health Departments in Washington state. He served as chair of the Hanford Thyroid Disease Study Advisory Committee for all eight years of its existence. Dr. Jecha also chairs the Tri-Cities Health Care Task Force, is President-elect of the Benton-Franklin Medical Society and chair of the Washington State Public Health Executive Leadership Forum.

Judith Jurji

Birth of a Cynic

In retrospect it seems astonishing that there was so little early critique by health and science experts regarding the HTDS design. Certainly the public had its concerns. I remember the meetings where the study protocol was presented, and recall numerous people expressing dismay that the "control group" was in an exposed (albeit lesser) area, that the number of test subjects chosen seemed too small, and that attempting meaningful radiation doses was sure to be near impossible. All of this plain common sense fell, of course, on deaf ears.

In spite of their concerns, most of the affected population was supportive of the study, yet felt it was merely one item of many that needed doing. People wanted the government to deal with this health crisis in other ways. There was clearly a need for a system to medically monitor exposed people for radiogenic diseases and there was a need to provide health care if necessary.

But what did we get? One expensive flawed study that took over a decade while everything else was put on hold. Unfortunately down-winders were not frozen in time. Diseases progressed, health deteriorated, and unnecessary deaths piled up. Public health officials looked the other way. Politicians saw no advantage in helping a scattered population that formed no identifiable voting block. Health physicists, with a few notable exceptions (such as John Gofman and Alice Stewart) busily defended the practices of the past. Denial was rampant and still is.

During this decade the USDOE was positioned legally and financially with enormous power to do the right thing. They did not. After years of serious citizen and scientific effort on the part of the Hanford Health Effects Subcommittee and federal health agencies to launch a medical monitoring and disease registry project, the USDOE snuffed it out like a tank crushing a flowerbed.

After 13 years of intense activism, I remain bewildered as to how the USDOE got so powerful and can remain so arrogant and irresponsible in a 20th century democracy. Although I believe the Thyroid Study was scientifically flawed as well as badly presented to the public with unwarranted certitude, yet I think the study team was, in fact, sincere in their efforts to answer an important scientific and health question. On the other hand, the USDOE has earned its place in history as the entity that used every opportunity to prohibit, curtail and block understanding of the toll to human health of the nuclear age. It might be added that the recent USDOE publicity about proposed programs in response to additional undisclosed worker exposures is clearly too late to help the many now-deceased workers. It appears to be all for show.

Judith Jurji is President of the Hanford Downwinders Coalition and a member of the Hanford Health Effects Subcommittee. She is also a founding member of the Advisory Board for the Hanford Health Information Archives. Ms. Jurji grew up in Kennewick, Wash., where her family moved in 1949. Her father worked at Hanford from that time until his retirement. She has been actively involved in Hanford-related health issues since the mid-1980s.

Duncan Thomas

My activities in the field of radiation and health include the Utah study of school children exposed to radioactive fallout from the Nevada Test Site (NTS). That study found associations between NTS exposures and leukemia and various thyroid diseases, mainly thyroid nodules. In the early days of this study, many of our peer reviewers wondered whether the findings were real or whether they were due to some methodological error or chance. It took hard work to convince people that the study was conducted correctly. The question of chance remains, but, in the end, even many critics came to believe that what we were seeing was real.

The HTDS results are different from those of the Utah study. The HTDS results are considered negative in that the study found no significant associations between increased dose and increased risk for any thyroid disease. But the question is similar. Are the HTDS results a convincing negative or are they due to a problem with methodology or with low statistical power?

Control Group

I believe that the HTDS researchers made a sensible decision to depend on internal comparisons. (In this case, study participants in Eastern Washington counties who were likely to have received the highest doses from Hanford were compared to participants in Eastern Washington counties who would have little or no dose from Hanford.) Most epidemiologists feel that using an internal control group within the study population is stronger basis for reaching a causal conclusion than an external control group methodology. It is very difficult to find an external control group that is comparable in all ways. With an external control group, you can't tell whether differences between the groups are due to real differences in exposure or to some other factor. Internal comparisons are a stronger basis for inferences about what a study's findings might imply for other similarly exposed populations.

If a study using both an internal and an external control group reached different findings for each method, I would tend to believe the internal control group. Exceptions to this are situations when there is not enough variation in the doses and when there is a lot of measurement error. For example, there is abundant evidence for an association between dietary fat and breast cancer from comparisons between countries, but this finding has been difficult to replicate in comparisons within a single population. While the international comparisons could be biased by confounding, it is also possible that some of the failure of the within-population comparisons could be due to insufficient variation of diet within populations or the difficulty of measuring long-term diets accurately. In this circumstance, some have argued in favor of external comparisons.

Uncertainty and Statistical Power

All estimates contain uncertainty. Uncertainty analysis is a statistical method for accounting for the lack of precise knowledge of a given estimate based on the amount and quality of the data. Uncertainty analysis is key to understanding whether or not the study's negative results could be due to random or systematic measurement error. Generally, random uncertainties will lower a study's statistical power and bias risk estimates downwards, but that bias can be removed if the uncertainties are correctly allowed for.

Statistical power measures the probability that a study can distinguish a true exposure-to-disease relationship from a coincidence. I have not studied HTDS's statistical power. I understand that HTDS researchers are still working on the uncertainty analysis for the dose estimates. This is important. The dose estimates were constructed with care but they are still estimates. However, I would be surprised if accounting for uncertainties in the dose estimates changed the negative result of the study to a positive result.

Measurement error tends to reduce the magnitude of association between dose and disease rates when there is a real relationship to begin with. I would expect that including the uncertainty analysis on the dose estimates will make the upper confidence limits higher, and the lower limits lower. In other words, it will broaden the range of risk estimates that are compatible with the data, but will not substantially increase the probability that they are significantly positive.

Duncan C. Thomas, Ph.D., is a professor in the Department of Preventive Medicine at the University of Southern California. He was an investigator for the Utah study of children exposed to radiation from the Nevada Test Site. Dr. Thomas served as a member of the National Research Council's Committee on the Biological Effects of Ionizing Radiation (BEIR V) which conducted a comprehensive review of the biological effects of ionizing radiation. He was also a member of the President's Advisory Committee on Human Radiation Experiments, whose report includes a chapter on the "Green Run" at Hanford.

For further information, contact HTDS in writing or by phone:

Hanford Thyroid Disease Study
Fred Hutchinson Cancer Research Center
1100 Fairview Avenue N., MP-425
PO Box 19024
Seattle, WA 98109-1024

Call toll-free: 1-800-638-4837

Summary of the Preliminary Results

THE HANFORD THYROID DISEASE STUDY DRAFT FINAL REPORT September 1999

Preliminary Results

On January 28, 1999, the Centers for Disease Control and Prevention (CDC) released the Draft Final Report from the Hanford Thyroid Disease Study (HTDS) which was conducted by the Fred Hutchinson Cancer Research Center in Seattle, WA, and funded by the CDC. This nine-year study evaluated whether or not the occurrence of thyroid disease was related to different levels of estimated radiation dose in a group of 3,441 people who were exposed as children to radioactive iodine (I-131) from the Hanford Nuclear Site during the 1940s and 1950s. This study was designed to investigate possible health effects of exposures to I-131 though other radionuclides were also released from the Hanford Facility. I-131 was the main radionuclide released from the facility and concentrates in the thyroid gland when inhaled or ingested. Therefore thyroid disease was the most likely health effect to occur in the population.

VISIT THE HTDS AND CDC WEB SITES

The complete text of the HTDS Draft Final Report and summary public information materials are available on the web at: www.fhcrc.org/science/phs/htds (The Fred Hutchinson Cancer Research Center's web site) .
During the 5 month comment period (January 28 - July 1, 1999), CDC received 31 written comments on the Hanford Thyroid Disease. These comments have been posted on CDC's website. In order to maintain the privacy of individuals submitting comments we transcribed their letters verbatim, deleting only personal identifying information.

While thyroid diseases were observed among the HTDS participants, the initial study results did not show a link between the estimated dose to the thyroid from I-131 and the amount of thyroid disease in the study population.

Based on initial study results provided in the Draft Final Report, those who had higher estimated radiation doses appear to be no more likely to have thyroid diseases than those who had very low doses. (If study participants with higher estimated doses showed higher risk of thyroid disease, then that would provide evidence of a link between exposure and thyroid disease.)

These preliminary results do not mean that people living in the Hanford area during the 1940s and 1950s were not exposed to I-131 and other radionuclides, or that these exposures had no effect on the health of people living in the Hanford area. Although no link between estimated I-131 radiation dose and the amount of thyroid disease was identified by the HTDS in the study population, the study results do not prove that a link between I-131 and thyroid disease does not exist. There may be individuals in the overall population who were exposed to Hanford radiation and did develop thyroid disease because of their exposure.

Epidemiological studies are designed to examine large populations, and through analysis of levels of exposure and rates of disease, establish an association between exposure and the risk of disease in a general population. It is not possible in any epidemiological study to determine whether an individual person's thyroid disease is or is not caused by Hanford radiation exposure.

PUBLIC INVOLVEMENT AND EXPERT REVIEW

Since the beginning of the study, scientists at the FHCRC and the CDC have actively included other scientists and the public at every step in the study. This began with a series of public meetings in 1990 to inform the public and interested scientists on the study design. Copies of the study protocol, which outlined the plans for conducting the study were distributed to a number of experts and were made available to the public in area libraries. Many of the recommendations made during that process became part of the final study protocol.
The first meeting of the federally chartered Hanford Thyroid Disease Study Advisory Committee was held in March 1991. This committee consisted of eight members representing areas of scientific expertise, environmental groups, the public, and Native American tribes. A consultant from the Hanford Downwinders Coalition was added a short time later. The study did not begin until this HTDS Advisory Committee, another committee at the FHCRC in charge of protecting the rights of research study participants, and the federal Office of Management and Budget approved the study protocol.
The HTDS Advisory Committee met on a regular basis throughout the study, making recommendations to the CDC regarding the research plan and conduct of the study. In 1997, the HTDS Advisory Committee reviewed and approved the written HTDS Analysis Plan, a detailed document describing how the study would be analyzed. In February 1998, the HTDS Advisory Committee reviewed and approved a written HTDS Communications Plan, which described how the first available results from the study would be made public. Due to the high level of public interest in the results, the CDC and the FHCRC decided jointly to make the Draft Final Report available to the public while the peer review process was still underway, and before CDC or others made any revisions.
The National Academy of Sciences' Committee on Assessment of CDC Radiation Studies also reviewed the HTDS Pilot Study Report and the HTDS Analysis Plan. Currently, the NAS is conducting a scientific peer review of the HTDS Draft Final Report. The results of their review are expected by late summer 1999. Suggested revisions and clarifications from all reviews will be incorporated into the HTDS Final Report.
Background

The HTDS was mandated by Congress in 1988, after the U.S. Department of Energy released documents showing that large amounts of I-131 were released into the air from Hanford, primarily during the late 1940s and early 1950s. Many area residents were concerned that their health might have been affected by the radiation from Hanford. Diseases of the thyroid (a small gland at the base of the neck that helps regulate growth and metabolism) were of particular concern because radioactive iodine inhaled or ingested by an individual concentrates in the thyroid.

How the Study Was Conducted

The Hanford Thyroid Disease Study was based on a group or cohort of 5,199 people born during 1940-46 to women who lived in any of seven counties of Washington State: Benton, Franklin, Adams, Walla Walla, Okanogan, Ferry, and Stevens. Starting with the birth certificates for this group, the research team tried to locate as many people as possible. A total of 4,875 (94%) were located. Those who could be contacted were invited to participate in the study. Because of these efforts, 3,441 people attended special HTDS clinics between 1992 and 1997, and provided information that could be used to determine their estimated thyroid radiation dose. At the study clinics, participants received thorough thyroid examinations by physicians experienced in the diagnosis of thyroid disease. They were also asked if they had any past history of thyroid disease. Pertinent medical records were obtained whenever possible to document and clarify past diagnoses.

Radiation dose to the thyroid was estimated for study participants based on information about residential history and factors such as milk consumption. Using this information, the study estimated thyroid doses using mathematical models that were developed by the Hanford Environmental Dose Reconstruction (HEDR) Project. This was a separate research project that investigated the releases of radioactive materials from Hanford, and estimated the radiation doses that people may have received as a result of exposure. Doses were estimated for the time period between December 1944 through the end of 1957 for individuals residing inside a region called the HEDR Study Area during any part of that time period. The HEDR study area consists of an approximately 75,000 square mile area surrounding Hanford. Results of the HEDR project indicated that people living in Benton, Franklin, and Adams Counties during 1944 (the year that the largest amounts of radioactive iodine were released from Hanford) most likely received the highest thyroid doses.

Of the 3,441 HTDS participants, 3,193 or (93%) had dose estimates calculated. Their estimated thyroid doses ranged from essentially zero to a maximum of more than 2,800 mGy (280 rad). (A mGy and a rad are units of radiation dose.) The average (mean) estimated dose among HTDS participants was 186 mGy (18.6 rad). About half of these 3,193 participants had doses over 100 mGy (10 rad), and only about 1% had doses over 1000 mGy (100 rad). The remaining 248 HTDS participants whose doses were not estimated never lived inside the HEDR Study Area between December 1944 and the end of 1957. Therefore, researchers could not estimate a thyroid dose for them. While this does not mean that they were completely unexposed to Hanford's radioactive iodine, their doses are believed to be very low.

Nine categories of thyroid disease were studied in the HTDS. Some individuals were diagnosed with more than one disease (for example, goiter and thyroid nodules) and are included in multiple disease categories. Nineteen confirmed cases of thyroid cancer (0.6%) were found among the 3,441 study participants. Five of the nineteen participants with thyroid cancer were among the 248 who never lived inside the HEDR Study Area between December 1944 and the end of 1957. Two hundred forty-nine participants (7.2%) had confirmed diagnoses of benign (noncancerous) thyroid nodules. Confirmed diagnoses of hypothyroidism and autoimmune thyroiditis were recorded for 267 (7.8%) and 648 (18.8%) participants, respectively. Thirty-four (1.0%) had confirmed diagnoses of Graves' disease. However, none of these diseases appeared to be significantly more common among study participants with higher estimated radiation doses than among those with lower doses. If there were a link between radiation dose and thyroid disease, we would expect thyroid diseases to occur more frequently in study participants with higher radiation doses.

In addition to thyroid diseases, the study evaluated whether three other outcome measures were related to radiation dose from Hanford's I-131: hyperparathyroidism; results of an ultrasound examination of the thyroid; and results of the blood tests related to thyroid and parathyroid function.

There was some indication that the proportion of individuals with small focal (individual) thyroid abnormalities detectable only by ultrasound increased slightly at higher doses. However, this increase was not statistically significant, meaning that it could have been due to chance. Small growth abnormalities of this type, which can be detected by sensitive ultrasound equipment but not by a physician during an examination, are very common in the general population. It is generally believed that most of these do not indicate thyroid disease.

The preliminary results of the study indicate that hyperparathyroidism was no more common in people with higher radiation doses from Hanford than those with very low doses. Hyperparathyroidism was evaluated using a measurement of calcium in the blood. Higher levels of serum calcium are associated with hyperparathyroidism. There was evidence from the study that the level of calcium in the blood (serum calcium) was slightly lower in people who received higher radiation doses from Hanford, but there was no increase in the proportion of persons with below-normal calcium levels in relation to thyroid radiation dose. Even among study participants with the highest doses, the levels of serum calcium were well within normal limits.

Evaluation of Mortality in the HTDS Study Population

Of the 5,199 people originally identified for inclusion in the study, it was determined that 541 were deceased. In an effort to see whether exclusion of these individuals from the study might in some way bias or influence the results, an investigation was undertaken to determine whether these deaths might be related in some way to thyroid cancer or other thyroid disease. Information from the death certificates was obtained for 502 of the 541 deceased individuals. An analysis of the causes of death revealed no indication that thyroid disease or thyroid cancer was responsible for any of these deaths.

However, some individuals may have had thyroid disease when they died. These cases of thyroid disease would not have been identified by the examination of death certificates. Overall mortality (death) rates in the HTDS study group were somewhat higher than what would be predicted based on mortality rates in the State of Washington for the same time period. In addition, there was an elevation in deaths related to birth defects, complications of pregnancy and delivery, and premature birth. Preliminary results from the HTDS indicate that the increase in mortality was evident before releases from Hanford began and continued after the Hanford facility started operation. The reasons for this higher death rate are not known. The HTDS was not designed to evaluate mortality in the population around the Hanford facility. Consequently, the amount of information that can be gained from this study about mortality is limited.

However, a study of infant and fetal deaths in eight Washington counties during the years 1940 to 1952 is currently being conducted by the Agency for Toxic Substances and Disease Registry with the results expected by late spring. Though the counties in the ATSDR study are different from those included in the HTDS, the study will provide additional information on rates of infant mortality, fetal death, and pre-term birth by geographic area.

FREQUENTLY ASKED QUESTIONS ABOUT THE HTDS RESULTS

Q: Why was the study done?

The HTDS was conducted to find out whether there has been an increase in thyroid or parathyroid disease related to exposures from releases of radioactive iodine-131 into the air from the Hanford Nuclear Site in the 1940s and 1950s.

Q: What did the study find?

The initial study results provided in the Draft Final Report do not show a link between the estimated dose to the thyroid from I-131 and the amount of thyroid disease in the HTDS study population. While thyroid diseases were observed among the HTDS participants, those who had higher estimated radiation doses appeared to be no more likely to have thyroid diseases than those who had lower doses. Although no link between estimated I-131 radiation dose and the amount of thyroid disease was identified within the HTDS study population, the study results do not prove that a link does not exist.

In addition, these results do not mean that people living in the Hanford area during the 1940s and 1950s were not exposed to I-131. Nor do these results prove that these exposures had no effect on the health of people living in the Hanford area. There may be individuals in the overall population who were exposed to Hanford radiation and did develop thyroid disease because of their exposure. However, it is not possible in an epidemiological study like HTDS to determine whether an individual person's thyroid disease is or is not caused by Hanford radiation exposure.

While conducting the HTDS, researchers found that the death rates in the study population were slightly higher than predicted, based on death rates in the state of Washington for the same period, particularly due to birth defects, complications of pregnancy and delivery, and premature birth. Preliminary results from the HTDS indicate that the excess in mortality was evident before releases from Hanford began and continued after the Hanford facility started operation. The reasons for this apparent elevated rate in overall mortality are currently not known. However, a study of infant and fetal deaths in eight Washington counties during the years 1940-52 is currently being conducted by the ATSDR with the results expected by late spring.

Q: What if my dose was high?

The results of the study cannot rule out the possibility that an individual exposed to Iodine-131 from Hanford might have suffered some type of health effect as a result. No epidemiologic study is capable of doing so. If you are concerned about your health or the radiation dose you may have received, you should discuss your concerns with your health care provider.

Q: Were there other health effects from Hanford radiation releases?

The results of this study are limited to the effects of I-131 exposure and thyroid disease, associated laboratory tests and ultrasound results, and hyperparathyroidism in persons who were infants and children at the time of exposure. They do not answer questions about effects from other types of radiation released from Hanford, or other types of diseases in relation to Hanford exposures.

Q: Why were the study results released early?

CDC's commitment to conduct the study in complete openness, together with the intense interest about the study results on the part of the affected citizens, led to the release the Draft Final Report at this stage. The same public process has been used to release CDC reports at other nuclear weapon production sites.

The original HTDS Communications Plan, approved by the federally chartered HTDS Advisory Committee in February 1998, called for a report of the study results after the peer review process was complete. The purpose of this type of independent, expert peer review is to help ensure that the final results are accurate and complete. However, due to the high level of public interest in the results, the CDC and FHCRC decided jointly to make the Draft Final Report available to the public while the peer review process was still underway, and before CDC or others made any revisions. By doing so, all interested parties were given the opportunity to review the unedited findings at the earliest possible time.

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