Answer to Question #5691 Submitted to "Ask the Experts"

I am a very concerned mother regarding radiation exposure to my children and the possiblity of their developing cancer later in life. I flew with each child across the country during my first trimester of pregnancy. Furthermore, my son had to have one chest x ray at three months, two head CT scans at six months, and five more chest x rays from one to four years. My daughter had to have an abdominal CT scan at one year four months and three arm x rays at 2.5 years. I am so scared that they might have received so much radiation that they are already at a high rish of cancer. Should I be extremely careful of future x-ray procedures (if not a life-or-death situation)? Should I take extra precautions to keep them out of the sun or away from natural environmental exposures? I am very scared now and if they ever need x rays in the future.

There is no conclusive proof that any of your or your children's radiation exposures pose any risk whatsoever. There is also no conclusive proof of complete safety. It is clear that larger doses do cause harmful effects, principally cancer (detected years to decades after exposure) and mutation (detected in future generations). These effects are probabilistic; none are certain to occur in any specific individual. They can be assessed only in large exposed populations, such as the Japanese atomic bomb survivors. The probability of effect is proportional to dose. As the dose is reduced to the level you mention, the probability becomes so small as to be undetectable in a population of finite size. The probability at low doses is extremely small. Otherwise it would have been detected.

All of this says that the risk to your children is at worst infinitesimally small and at best zero. No one knows where it really lies, between these two extremes.

Health benefits to your children from their medical exposures are real and apply specifically to them. They clearly outweigh any potential for hypothetical harm. Thus all responsible authorities recommend that medically justified x-ray procedures be carried out; radiation risk is not a primary concern.

There is essentially nothing anyone can do to avoid natural environmental exposure. It is everywhere. The US National Council on Radiation Protection & Measurements has concluded that the average American gets about 3 millisievert from natural environmental sources. About 2 millisievert comes from inhalation of radon and its products, which occurs everywhere, even in outside air. The remaining 1 millisievert comes from approximately equal parts of cosmic, terrestrial, and internal sources. Yes, there is natural radioactivity in our bodies.

Exposure to sun is a different story. It is well known that excessive sun exposure leads to skin cancer. It should be avoided.

Your air travel added less than 1 percent to your annual exposure from natural sources. Your children's chest and extremity x rays added about the same amount. The CT scans added more, each equivalent to about one to three years of environmental exposure.

Conclusion: You must not be unduly concerned about radiation exposure to yourself or your children from medically justified x-ray procedures. Experts agree that risks range from immeasurably small to zero.

S. Julian Gibbs, DDS, PhD