DM: How much radiation exposure do we get from the sun?

MH: Total background radiation gives everybody about 3 mSv per year from the Earth, the Sun, and man-made sources. The biggest contributor is radon gas (2 mSv/year).


During a 7 hour airline flight, we are exposed to more cosmic radiation because there is less protective atmosphere. This is about the same as a chest x-ray.

DM: That brings to mind the risk to pilots and crews.

MH: They are exposed to more radiation than the average person. They are not
regulated by any government oversight board or protection agency like radiologists are even though pilots are exposed to more radiation. Domestic airline pilots are exposed roughly an additional 2 mSv a year, but studies haven't shown that pilots get cancer any more than people who are not pilots.

DM: Of course radiation is also used to kill cancer.

MH: Yes, really high doses of radiation kill cells. The way that radiation
causes cancer in low doses is by damaging the DNA. Usually, cells repair DNA damage and all goes back to normal. But sometimes the DNA repair is faulty and that is how you can get cancer. The doses to treat cancer are very high doses. Unfortunately, one of the reasons we know that radiation does cause cancer is that people who were treated as children with high doses of radiation have a higher risk of other cancers later on.

In terms of medical imaging, we have no studies of people that just got CT scans and X-rays to say they have more cancer than those who don't have CT scans and X-rays. We can't do that study because the risks are so small it would take millions of people to study.

DM: What can the average patient take away from all this?

MH: Unfortunately, the lifetime risk of developing cancer is about 45% for men and 38% for women, which is scary in itself.

The increased risk from the average imaging studies is very small and theoretical at best. People argue about what it all means. In the end it is all about weighing the risks and benefits. My advice would be don't get a whole body CT without good reason, although the risk is low, because the potential benefit is also low. Versus someone who comes in to the ER after a car accident--their potential benefit is very high and the risk very low. In that case the risks of radiation exposure should not even be discussed.

You have to weigh the risks and benefits. The same way that if your doctor tells you to take an aspirin for general heart health. Aspirin has a laundry list of side effects yet we know aspirin prevents heart attacks and strokes and the benefits outweigh the risks. That approach to a CT or chest X-ray should be the same: If the potential benefit is greater than the potential risk, it is worth doing. The www.xrayrisk.com website allow users to quantify this risk.

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