Review of the Hanford Thyroid Disease Study Draft Final Report

Epidemiological studies involving radiation have the ability to cause a fuss. This is usually because a positive statistical association between some adverse health outcome and exposure to radiation is reported. Perhaps the most notorious example occurred 10 years ago when Martin Gardner and his colleagues found an association between the dose of radiation received occupationally by fathers before the conception of their children and the level of leukaemia in these children. Ironically, this book deals with a report that found no evidence for the radiation-induced effect that was expected.
The Hanford Thyroid Disease Study (HTDS) was mandated by the US Congress in 1988 after the US Department of Energy (DOE) released documents showing that large quantities of radioactive materials, in particular radioactive iodine-131, were released from the Hanford nuclear site in Washington State during its early years of operations in the 1940s and 1950s. The release of these documents raised public concerns about the possible health effects of exposure to I-131, especially an increased risk of thyroid disease. The HTDS, a 9 year, $18 billion investigation, was funded by the Centers for Disease Control and Prevention (CDC) and carried out by researchers from the Fred Hutchinson Cancer Research Center in Seattle. The research team enrolled almost 3500 individuals in the study, who had been born near Hanford in 1940-46 and who were medically examined during the 1990s for thyroid disease. The I-131 was released during the reprocessing of `short-cooled' irradiated nuclear fuel rods for the production of plutonium during the early US nuclear weapons programme, particularly during 1945 and, to a lesser extent, 1946. Individual thyroid doses were reconstructed through the Hanford Environmental Dose Reconstruction (HEDR) project.
The expectation, certainly among members of the public after the dramatic increase in childhood thyroid cancer found in the areas of the former Soviet Union most heavily contaminated with radioiodine, was that the releases of I-131 from Hanford in its early years of operations would be shown to have increased the risk of thyroid disease, particularly thyroid cancer. However, when a Draft Final Report of the HTDS was released in January 1999, somewhat earlier than anticipated for a number of complex and intertwining reasons, the primary finding was that there was no evidence linking radiation exposure from Hanford to the rate of thyroid disease found in the study population. This finding and the way it was communicated to the public caused considerable controversy and the CDC asked the National Academy of Sciences - National Research Council (NAS - NRC) to give an independent appraisal of the study methodology, results and interpretation, and the communication of the findings to the public. This report presents the results of this appraisal. Apart from presenting the background and setting out how the Subcommittee went about its task, the report is structured into sections dealing with the main issues considered by the review group: epidemiological and clinical methods, dosimetry, statistical analysis, statistical power and interpretation of the study, comparison with other studies, and the communication of the study results to the public. Also provided is a comprehensive Executive Summary and a useful Public Summary which attempts (largely successfully) to summarise the Subcommittee's conclusions in non-technical language.