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Ask the doctor: Should I worry about x-rays?

Anthony L. Komaroff, M.D.

Q. I always worry about cancer risks when I have -x-rays or airport screenings. Am I overreacting?

A. We use a lot of x-rays in medicine and in other places (like airports). Too much radiation exposure over time definitely can have adverse effects on health. So you’re right to be careful, and to ask if you really need a test that involves radiation when your doctor orders one. How can you assess how much radiation you’re getting, and how much is too much?

The biological effects of radiation on the body are described by a measurement called a millisievert (mSv). We are all exposed to some amount of natural radiation from the sun, from the earth, and even from some natural chemicals in our bodies. The average natural background radiation in the United States is 3.7 mSv per year.

So that’s the context. That’s the radiation that you can’t avoid. Now let’s look at how much radiation you get from different types of scans. There is so little radiation with airport scanners that you would have to get over 25,000 scans in one year to equal the amount of radiation that you are naturally exposed to. (That would be a lot of frequent flyer miles.)

A simple chest x-ray (two views) exposes a person to an average of 0.01 mSv, or roughly the amount of radiation you get in a day from the natural background. Dental x-rays are even less.

On the other hand, radiation from CT scans is much greater—4 to 7 mSv for chest CT scans, somewhat higher for abdominal scans. The more scans you have, the higher your lifetime exposure and therefore the higher your risk. The American College of Radiology recommends limiting lifetime diagnostic radiation exposure to 100 mSv. That is equal to 10,000 chest x-rays or up to 25 chest CTs. I’ve known patients who have had 25 or more CT scans in their lives. But I’ve never met anyone who’s had 10,000 chest x-rays.

So the bottom line for me—as a doctor or a patient—is to make very sure to use CT scans only when they are absolutely necessary. And not to worry about standard x-rays or airport scanners.

—Anthony L. Komaroff, M.D.
Editor in Chief
Harvard Health Letter

Posted by: Dr.Health

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