Answer to Question #2146 Submitted to "Ask the Experts"

Q

While pregnant and working in a nuclear medicine department I received roughly 300 mrem of exposure (over nine months). Most studies refer to the risk of malformations, death, or childhood leukemia. What is the increased risk of young-adult to middle-aged cancers for an individual with this level of exposure?

A

The only available data dealing with adult-onset cancer following radiation exposure in utero comes from the Japanese atomic-bomb survivors. Their doses were many times greater than yours. It is extremely difficult to document risk of cancer following low-dose radiation (such as occupational, environmental, or diagnostic medical). The overall probability of getting cancer in the United States is about 16%. A small radiation exposure such as yours would increase this to about 16.000001%. There is no way to determine which case or cases were caused by radiation and which arose spontaneously. Therefore, unless one studies a sample of many millions of subjects, all receiving exposures under conditions like yours, plus many millions more as controls, one is unlikely to find any increase in cancer that could not be explained by random variations. Further, these studies would follow all these individuals throughout life—at least 80 years. I think you can understand why it is impossible to perform such studies. Now to your situation. There are data that suggest a correlation between diagnostic exposure in utero and childhood cancer. There are equally good data showing no such correlation. Specifically, a study years ago at the University of Chicago followed firstborn children born there in a given year in which all firstborns received x-ray pelvimetry. This was somebody's research project. The children have been compared with firstborns born the year before and the year after. No difference in childhood cancer was found. In this study, the radiation exposure was routine; everybody in the year in question got it. In all other studies, the radiation exposure was presumably rational. That is, the attending physician identified a problem that required the x-ray study. Maybe that problem was related to the childhood cancer. The best we can say is that the jury is still out on this issue. However, if there is a risk, it must be very small. Otherwise, we would have clear data; there have been so many studies.

Conclusion: You should not be concerned about such effects on your unborn child. There is certainly no justification for radical treatment such as therapeutic abortion.

S. Julian Gibbs, DDS