Answer to Question #4238 Submitted to "Ask the Experts"

My question is regarding my eight-month-old child who received a CT head scan. I was told he received about 3.5 rem. I tried converting that to chest x rays but was confused. Could you tell me how many chest x rays that would be and compare it to regular environment radiation? I am especially concerned about the possibility of a brain tumor or cancer because of his young age. Does the body completely repair if he doesn't have any more x rays for many years? Is there a certain time that a tumor or cancer hasn't happened, e.g., by five years, it probably won't? What is the possibility of a tumor for his lifetime? I also read an article about a study that said infants who received radiation doses to treat birth marks in the amount similar to CT head scan were less intelligent and less likely to succeed in school or graduate. How accurate is this study?

The ability of radiation exposure to have an impact on IQ scores appears to be limited to that period of time in which the brain is developing while the fetus is growing within the mother, i.e., between the 8th and 15th week of gestation. And, there does not appear to be any effect for radiation doses received during that critical period that are below 10 rem. The dose that you mention, 3.5 rem, would not be expected to pose any significant risk to your child. We are not sure there is a risk for such levels of radiation doses and, if there is a risk, it is minuscule compared to the normal risk faced by each child even in the absence of any radiation exposure. Risk estimates are based on information obtained from individuals who received radiation exposure to the whole body. If the radiation received for the head CT scan were averaged over the entire body, it would amount to about the same radiation dose that is received from natural background radiation each year. Background radiation doses are received each year from continuous exposure to cosmic rays, radioactive materials present in the earth and building materials and radioactive materials normally present within the human body.

Kenneth L. Miller, CHP, CMHP

Editor's Note:
Comparisons between different types of radiation examinations can be found in "Ask the Experts" Q-708.