National Cancer Institute

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Estimating Your Exposure to I-131

How can people reach a sound decision about their risk of thyroid cancer? When is it time to visit a doctor?

Scientists estimate that about 25 percent of the radioactive materials released during atomic bomb testing in Nevada reached the ground somewhere in the United States. But information about where the wind carried these materials is not precise. In addition, most adults cannot remember exact details of their milk-drinking habits in childhood.

Still, scientists and doctors think that I-131 exposure is a potential risk factor for thyroid cancer, and that some Americans have a higher risk than others. A "personal risk profile" includes four key points that may influence a person's decision to visit a doctor or other health professional for evaluation:

• Age—People who are now 40 years of age or older, particularly those born between 1936 and 1963 and who were children at the time of testing, are at higher risk.
• Milk drinking—Childhood milk drinkers, particularly those who drank large quantities of milk or those who drank unprocessed milk from farm or backyard cows and goats, have increased risk.
• Childhood residence—The Mountain West, Midwest, East, and Northeast areas of the United States generally were more affected by I-131 fallout from nuclear testing.
• Medical signs—A lump or nodule that an individual can see or feel in the area of the thyroid gland requires attention. If you can see or feel a lump or nodule, it is important that you see a doctor.