Answer to Question #4730 Submitted to "Ask the Experts"

Q

I'm 35 years old and have never had any major health problems. Last year, however, I experienced some heart palpitations and visited a local emergency room. Among the tests ordered by the doctor who treated me were chest x rays, the procedure of which seemed routine. All the tests were essentially normal and I sought no medical treatment afterwards.

About two weeks after my visit, however, I became quite ill with fever and a painfully swollen thyroid gland. I was in bed for a week, but felt weak and generally poorly for a solid month. In the weeks and months that followed, my hair—head, body, pubic—began thinning and falling out, and while I feel healthy today, my hair remains quite thin, having never recovered after this period of thinning and loss.

My question is whether the x rays I received may have damaged my thyroid gland, thus causing the illness that followed my hospital visit and the hair problems I'm now experiencing. I've read elsewhere on your site that chest x rays are among the least irradiating of all standard medical x rays, but is there a chance perhaps that an overdose was administered or that the machine was improperly configured, resulting in a higher and dangerous dose of radiation?

A

You are correct that chest x rays expose patients to very low levels of radiation. The thyroid can be in the field of view during a chest x ray. The thyroid also receives some scatter radiation from the x rays that interact in the body. Estimates of the dose to the thyroid is 2 mrad with the whole-body dose being 4 mrad from a single chest x ray, according to a Web site by Vanderbilt University. It is one of the lowest-exposure exams that patients are given. It is a measurable dose, but not much more than natural background radiation. For comparison, I am exposed to approximately 1 mrad every day of my life from radiation in the air, food, water, and the earth. And a flight from San Francisco to New York exposes the passengers to approximately 5 mrad.

If the radiation exposure was too high, there would not be an image for the doctor to look at. A comparison would be you taking the film out of your camera and exposing it to daylight and then having it developed. There would be no picture since the film was overexposed. So, even multiple chest x rays would not expose the thyroid to an excessive amount of radiation. Reports of the doses needed to cause hypothyroidism from external radiation that is given in fractions, such as when people have radiation therapy to treat cancer, ranges between 2,600,000 and 5,000,000 mrad (Mettler 2001). Of course, every individual is different, but you can see that it takes a lot of radiation to cause significant clinical effects to the thyroid.

There is a simple blood test for thyroid function. You should talk to your physician if you feel that you are having thyroid problems. But it is unlikely that it was a result of your chest x rays.

Marcia Hartman, MS

Reference:
Mettler FA. In: Gusev IA, Guskova AK, Mettler FA, eds. Medical management of radiation accidents (2nd Ed). Boca Raton: CRC Press; 2001:79.