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Making Choices: Screening for Thyroid Disease

  • Posted: 08/01/2003

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What was your dose of I-131

What was your I-131 dose from the Nevada tests?

The dose of I-131 people likely got from the Nevada tests depends on:

  • How old they were at the time
  • How much milk they drank at the time and whether that milk was processed
  • Where they lived at the time

I-131 doses are measured in radiation absorbed doses (called rad). The National Cancer Institute estimates that the average dose to the adult population living in the United States at the time (between 1951 and 1963) was about 2 rad. Because children likely absorb more I-131, people younger than 15 at the time of testing may have absorbed higher doses of radiation. Their thyroid glands were still developing during the testing period. An children were more likely to have consumed milk contaminated with I-131.

You can roughly estimate your I-131 dose using the following chart. Find the year in which you were born in the column on the left. Next, locate the column for the kind and amount of milk you drank during the nuclear tests (between 1951 and 1963). Then read your estimated dose in rad.

What Is Your Estimated I-131 Dose?

Year of birthDoses in rad by amount and type of milk
No milkProcessed milkFarm cowFarm goat
0 cups/day1-3 cups/day4+ cups/dayAny amountAny amount
Before 1933Less than 124630
1933-1937Less than 136945
1938-1942Less than 15101575
1943-1947Less than 171421105
1948-1957Less than 1102030150
1958-1963Less than 112315
After 1963Less than 1Less than 1Less than 1Less than 1Less than 1

Example: If you were born between 1948 and 1957, and drank 1-3 cups of milk a day of store-bought milk, your estimated dose of I-131 is about 10 rad.

Example: If you were born between 1958 and 1962, and drank 4 or more cups of milk a day of store-bought milk, your estimated dose of I-131 is about 2 rad.

Where did you live?

Depending on where you lived, your likely dose could be much higher or lower than the doses provided on the chart.

High-dose areas

Some counties in these states received higher doses: Montana, Idaho, Utah, Colorado, Wyoming, North Dakota, South Dakota, Nebraska, Kansas, Missouri, Nevada, and Arkansas.

If you lived in one of these states, your likely dose may be 2 to 3 times greater than the dose shown for you on the chart.

Low-dose areas

Some counties in these states received much lower doses: Oregon, California, Arizona, and New Mexico.

If you lived in one of these states, you may have received a dose 10 times smaller than that shown on the chart.

Dose calculator

If you want to calculate your exposure more accurately based on your county of residence, see the dose calculator on the NCI Web site (ntsi131.nci.nih.gov).

How accurate are these doses?

Given the amount of time that has passed since the tests were conducted, scientists cannot be certain about how much exposure each person received. Because few data were collected at the time of the tests, scientists have used available information to make their best estimates. As a result of this uncertainty, these dose figures are very rough estimates. The uncertainty in the dose estimate may be up to 5 times lower or 5 times higher. For example, if you estimate your dose was 5 rad, your real dose was likely in the range of 1 to 25 rad.

What is your risk of thyroid cancer?

Now, you can use your dose estimate to roughly work out whether exposure to I-131 has affected your chance of developing thyroid cancer.

The figures that follow are for people who are 50 years old and cancer-free.

Look to find your dose in rad and read your chance in 1,000 of eventually developing thyroid cancer in your remaining lifetime.

Men

Example: A 50-year-old cancer-free man who was exposed to about 10 rad has about 3 to 4 chances in 1,000 of eventually developing thyroid cancer. He has about 996 to 997 chances in 1,000 of not developing thyroid cancer.

Women

Example: A 50-year-old cancer-free woman who was exposed to about 10 rad has about 6 to 8 chances in 1,000 of eventually developing thyroid cancer. She has about 992 to 994 chances in 1,000 of not developing thyroid cancer.