Answer to Question #5351 Submitted to "Ask the Experts"

In the Radiology article "Estimated Radiation Risks Potentially Associated with Full-Body CT Screening," David Brenner found that a full-body CT scan results in a mean effective dose of 12 mSv of radiation, which translated into a lifetime mortality risk from cancer (for a 45-year-old) of about one in 1,250. This raises the lifetime cancer mortality risk for a 45-year-old adult who undergoes 30 annual full-body exams to 1.9 percent (about one in 50).

Why does the Health Physics Society maintain that there are no observable effects to humans for a lifetime radiation dose of less than 100 mSv?

There are several issues associated with your question.

First, as noted in the Brenner paper, the values are estimates of both exposure values and risks. Over the years, diagnostic radiation exposure values have changed as techniques and equipment have improved. Over 30 years ago, CT technology was very primitive, and who knows what technology will look like in five years, let alone in 30 years. In addition, it is important to consider what the authors say in the next-to-last paragraph of this article.

"It is important to note that the doses and risk estimates used here are based on a particular full-body CT protocol (Brenner and Elliston 2004). Even with the same CT settings, different scanners will produce different doses and therefore different risks—we estimate by up to 35% . . ."

Second, self-referral CT scanning, which is the situation that Dr. Brenner is referring to, is not recommended by many groups, including the Food and Drug Administration and the Health Physics Society.

Third, the increased estimated increase cancer risk for 30 CT scans is 1.9 percent. As noted in "Cancer Facts and Figures," the current cancer death rate in the U.S. population is 1 in 4, or 25 percent.

Finally, it should be pointed out the HPS Position Statement is based on actual epidemiological data, not estimations.

John Jacobus, MS
Certified Health Physicist

Reference
Brenner DJ, Elliston CD. Estimated radiation risks potentially associated with full-body CT screening. Radiology 232:735-738; 2004.