Answer to Question #8964 Submitted to "Ask the Experts"

Category: Nuclear Power, Devices, and Accidents — Nuclear Accidents

The following question was answered by an expert in the appropriate field:


I am a 31-year-old female. When I was almost one year old in 1979, I lived a half mile from the Three Mile Island nuclear power plant, which had the accident. More recently I had surgery for papillary thyroid cancer. My sister and mother have thyroid problems too. They say that less than 1 millisievert was the dose from that accident. I wonder if that much radiation dose can be the reason for my thyroid cancer. I did some research and found that after the accident there were reports of plagues of cancer, leukemia, birth defects, and so on including birds that were found scattered on the ground and stillborns in animals. I understand that thyroid cancer is a slow-growing cancer, so I must have had mine for a long time. I heard that Pennsylvania has the highest rate of thyroid cancer, but I thought it takes a lot of radiation to cause your thyroid to be damaged. Please help me to understand.


I’m sorry about your thyroid problems. Your question is about the link between radiation exposure and thyroid cancer. There is certainly a link between the two. However, there is no way to know if an individual cancer was due to radiation or some other cause.

We know from accidents at Chernobyl and elsewhere that exposure to radioactive iodine will lead to a radiation “dose" to the thyroid and potentially lead to cancer. In your case, you may have been exposed to radioactive iodine released during the accident at Three Mile Island in 1979. This release was measured and studied. One study by the University of California1 found that the highest dose to the thyroid would occur about 1½ miles from the plant. If you were located there, your estimated radiation dose was only 0.07 millisieverts. This is a very low dose and unlikely to be enough to cause a cancer.

The 1 millisievert dose that you quote is a good estimate of the highest, total dose to residents on the north side of the plant. This dose was caused by the release of other radioactive gases. Looking only at the thyroid, the addition of this radiation exposure would increase the dose to the thyroid to about 0.02 millisieverts,2 still a very low dose.

Finally, you state, “. . . it takes a lot of radiation to cause your thyroid to be damaged." That is correct. It was the conclusion of a federal study group3, among others, that the radiation from the accident might cause, at most, one cancer among nearby residents. Follow-up studies by the Pennsylvania Department of Health4 have been unable to detect any increase in cancer rates. Stories of “plagues" and high cancer rates have, fortunately, proven to be unfounded.

Joel I. Cehn, CHP

1Lawrence Livermore National Laboratory; Report UCRL-JC-104077 by Paul Gudiksen and Marvin Dickerson; September 1990.

2Radiation and Health Effects, GPU Nuclear Corporation, Middletown, PA; August 1986.

3NUREG-0558 "Population Exposure and Health Impact of the Accident at the Three Mile Island Nuclear Station," 1979.

4"Cancer Mortality and Morbidity (Incidence) Around TMI," Pennsylvania Department of Health; 1985.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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