Hanford Thyroid Disease Study (HTDS)Final Report

Michael A. McGeehin, Ph.D., M.S.P.H.

Director

Division of Environmental Hazards and Health Effects

National Center for Environmental Health

Centers for Disease Control and Prevention

June 21, 2002

HTDS Overview

• A study of thyroid disease among people exposed to iodine-131 from Hanford.

• The question: “Did this exposure result in increased incidence of thyroid disease?”

Why study thyroid disease?

• Iodine-131 was a primary source of radiation from Hanford.

• Iodine-131 concentrates in the thyroid gland.

About the thyroid

• Located at base of neck.

• Affects energy, temperature, weight and mood.

• Thyroid disease includes abnormal functions and abnormal growth.

What happened at Hanford

• Built to produce plutonium for nuclear weapons.

• Large amounts of radioactive iodine-131 released into the air from 1944 through 1957.

• Drinking contaminated milk was a major way people were exposed.

How the study came about

• Public concern led to release of Hanford data.

• Scientific panel reviewed what happened.

• Panel recommendations led to:

– Hanford Environmental Dose Reconstruction Project

– HTDS

Type of study: Dose Response

Dose

Disease

Does greater radiation dose result in increased incidence of thyroid disease?

Example of strong dose response

Dose

Disease

Example of weak dose response

Dose

Disease

Example of no dose response

Dose

Disease

Study Design

• Universally accepted approach.

• One study group with similar characteristics but different levels of exposure.

• Similar characteristics:

– All were young children at time of highest releases.

– All are from Hanford region.

Participant Selection

• Scientists identified a sampling of 5,199 birth certificates from seven counties.

• 3,440 people were able to participate.

• Participants represent a wide range of radiation doses.

Study Implementation

• All participants examined for thyroid disease.

• Detailed information collected for estimating participants’ radiation dose.

• Scientists analyzed the data.

• All dose estimates and data analyses recalculated and checked after release of draft report.

Findings

• The percentages of people with each kind of thyroid disease were about the same regardless of participants’ radiation dose.

• No increase in risk observed with increasing dose.

• The occurrence of thyroid disease was about the same as has been reported in other populations.

Meaning of the findings

• Hanford radiation may have had an effect on health but no increase in risk of thyroid disease was observed.

• If there is an increased risk of thyroid disease from exposure to Hanford’s iodine-131, it is probably too small to observe using the best scientific methods available.

Comparison to other radiation studies

• No other study is directly comparable.

• Drawing comparisons is difficult because many factors affect thyroid health:

– General health, age, gender, family health history.

– Type of radiation, dose, dose rate, age at time of exposure, amount of iodine in diet.

• Hanford has a unique profile of exposure.

How reliable are the data?

• HTDS used most advanced methods available to reconstruct what happened 50 years ago.

• Dose estimation is inherently uncertain.

• Several alternative approaches used to account for uncertainty. No change in results.

Public involvement and scientific review

• Entire process open to public input and scientific review.

• HTDS Advisory Committee met regularly.

• Public meetings and written comments to CDC.

• National Academy of Sciences peer reviewed the pilot study, analysis plan and draft report.

• Independent scientists’ reviews throughout.

Work conducted since release of HTDS Draft Report

• Revised the software used for estimating doses.

• Recalculated all dose estimates.

• Re-did all data analyses.

• Researched audiences and developed communications plan

Closing thoughts

• For more information: http://www.cdc.gov/nceh/radiation

• If you are concerned about exposure to iodine-131 or experience thyroid disease symptoms, you are encouraged to see your doctor for a thyroid evaluation.

Thank you for coming.