To the Editor: In his Editorial, Dr Boice1 draws what we believe to be unsupportable conclusions about the relation between iodine 131 and thyroid disease. He states that the evidence for iodine 131 and thyroid cancer from the Chernobyl nuclear disaster is not straightforward due to the presence of other iodine isotopes that could have contributed to excess risk, yet there is strong evidence that isotopes other than iodine 131 delivered at most only a few percent of the total dose to the thyroid of exposed persons.2 Boice alludes to possible interactions between radioiodine exposure and iodine deficiency but notes no evidence that iodine deficiency and potassium iodide act independently in modifying iodine 131–related thyroid cancer risk.2
Of the Hanford Thyroid Disease Study (HTDS),3 Boice states that HTDS results indicate that childhood exposures to prolonged releases of pure iodine 131 are associated with a risk of radiation-induced thyroid cancer that is an order of magnitude lower than that reported for exposures to iodine 131 mixed with other short-lived radioiodines or for exposures to external sources of radiation. He also notes that the dose-response relationship reported for iodine 131 exposures from the Hanford nuclear site is 11-fold lower than that reported for children exposed to an acute dose of high-energy gamma radiation or to multiple (fractionated) treatments using x-rays. We believe there are more plausible explanations for the HTDS findings.
The absence of statistically significant dose-response relationships and the low estimates of excess risk reported for the HTDS can be explained by the high uncertainty associated with the use of mathematical models to reconstruct iodine 131 releases, environmental transport, and thyroid doses for individual cohort members. This uncertainty arises from unknown degrees of systematic overestimation of dose, as well as random measurement errors. Although there have been published attempts to account for some of these uncertainties,4 - 5 we regard these attempts as inadequate, in part because they addressed only certain error components and not others (eg, Berksonian but not classical or systematic errors). Incomplete accounting for the full effect of these problems would result in an overestimation of statistical power and inappropriately narrow interval estimates for the excess risk of disease.6 It is our expectation that increasing the width of the uncertainty interval will demonstrate that the HTDS results are consistent with recent conclusions of the National Research Council BEIR VII Committee regarding radiation exposures and risk of thyroid cancer.7
Financial Disclosure: Drs Hoffman, Ruttenber, Greenland, and Carroll report having served as expert witnesses on behalf of plaintiffs in the Hanford litigation. They report that they have not received funding or compensation for submitting this letter.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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