Answer to Question #2080 Submitted to "Ask the Experts"

Q

I am concerned about the amount of radiation I have received so far in my life. Recently I had a heart scan for calcium scoring due to symptoms and family risk of heart disease, and I was told the dose I received was 1 rad. I'm only 31 years old, female, and weigh about 110. The CT machine used was a Siemens spiral CT. My question is, did I actually receive 10 mSv or is my real dose lower? Five days prior to the scan I had a chest x ray, and about three months prior to that I also had a chest x ray.

A

Good question. From your use of various units, it sounds like you have a little background in radiation terminology, so I won't give a lot of general information as an introduction.

Doses from heart scanning for calcium scoring where I work, i.e., a health-care organization, have an absorbed dose of about 2 rad where the x-ray beam enters the skin. The "real" dose or effective whole-body dose from our scans is about 0.2 rem. Effective whole-body dose means that the biological effectiveness of the 2 rad to the skin around the heart is roughly equivalent to having your whole body exposed to 0.2 rem.

The effective dose from a chest x ray is about 0.005 rem for a posterior/anterior chest, where you have the front of your chest up against the chest plate, and about 0.010 rem for the lateral or side view. For purposes of comparison, natural background radiation from cosmic rays, and other natural and man-made sources, is close to 0.36 rem/year.

Primary individual risks of radiation exposure include cataracts if the eye is exposed to large (i.e., several hundred rads) amounts of radiation and an increased risk of cancer. In general, the population in the United States has about a one in three chance of having some form of cancer—this is without additional radiation exposure—and a one in seven lifetime chance of dying from cancer. The increased risk, if any, from medical radiation exposures is negligible.

Essentially, there is no direct evidence that the small doses of radiation, similar to those in your question, cause harmful effects in persons exposed. If you are concerned about undergoing medical exams involving radiation, I would strongly suggest you discuss the need for the exams with your physician. Perhaps an exam without radiation will give the needed information.

Kelly Classic
Certified Medical Health Physicist