provide the basis for determining the extent and method of distribution of KI.

In summary, a review of experience with thyroid cancer in populations exposed to the consequences of nuclear events shows that:

  • Exposure to external radiation or internal radiation from radioactive iodine is linked to a dose-dependent increase in thyroid-cancer incidence.

  • Young children are by far the most sensitive to the carcinogenic effect of radiation on the thyroid, especially after exposure to radioactive iodine in fallout.

  • The risk of thyroid carcinoma in adults exposed to radioactive iodine in fallout is very low, and can be assumed to be absent for adults over 40 years old although at very high doses there is a risk of hypothyroidism.

  • The probability of a large release of radioactive iodine from the type of reactor used in the United States is much lower than the chance of a large release in countries that use reactors of the type used at Chornobyl. Therefore, the risk of thyroid carcinoma in the US population in the event of a nuclear accident is likely to be considerably less than the risk after Chornobyl both because of the level of dietary iodine and because of the use of precautionary measures.

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