Answer to Question #7748 Submitted to "Ask the Experts"

I am extremely worried about the radiation exposure to my two-year-old daughter from a head CT scan. Before the CT scan was taken, I was misinformed about the radiation level. After the scan, the radiologist told me that they do not do CT scans on children because of the risks. I then searched the Internet and I was shocked about the things I read. Thousands of articles talk about the dangers of radiation exposure of CT scans on children. The following are my questions:

1. I have read that girls are more sensitive to radiation and they are more susceptible to cancer from exposure to it. Additionally, it is said that radiation-related cancer deaths are seen more in female atomic bomb survivors. Is this true? Should I be worried more than the mothers of boys who received CT scans?
    
2. I am much more worried because of articles that say that damage of radiation can be seen after decades and the effects of radiation on children who received CT scans are not exactly known. How true is it to make estimations like "1 in 2,500 children who received a head CT scan will die because of radiation-related cancer?" Years later, is there the possibility that we will discover 1 in 10 children will get a radiation-related cancer? In the articles I read, it is said that radiation therapy done on children were found to cause certain cancers when they grow up. It is argued that the carcinogenic effects of radiation exposures from CT scans will be seen in the future. I wonder what you can tell me about this issue.
    
3. On the Web site www.radiationanswers.org, it is said, "When cells, organs, or tissues are developing, as they are in children, they are more likely to be affected if radiation interacts with them . . . When considering radiation exposure to children, it is important to weigh the benefits (diagnosing a broken arm or appendicitis) against the risks (is there enough radiation exposure to increase the cancer risk?)." Do the doctors measure the cancer risk by taking into account the estimations in the academic articles? How true is it to take these estimations in measuring the risks?

First of all, let me wish that no problems or complications were found with your daughter's exam, and that she is in good health.

A number of professional groups have considered recommendations regarding the reduction of dose in pediatric patients and small adults. See the Food and Drug Administration information. It should also be made clear that no researcher nor physician believes that CT exams should not be performed if it is in the best interest of the child or patient. See http://www.pedrad.org/associations/5364/ig/. It is also stated in http://pediatrics.aappublications.org/cgi/content/full/120/3/677#SEC7 that ". . . there is wide agreement that the benefits of an indicated CT scan far outweigh the risks." It should be quite clear that no effects have been observed in patients receiving CT examinations and that the risk ESTIMATES are based on extrapolation of data.

Regarding your specific questions, I will try to answer as best as I can. First, it is necessary to estimate what your daughter's exposure was, as risk is based on the exposure received. However, there is little information on doses to children receiving head CT exams. One reference (Lee et al. 2007) estimates the effective dose to a one-year-old male anatomical phantom to be 1.36 millisievert (mSv) and for a five-year-old female anatomical phantom to be 0.96 mSv. The effective dose is used to compare the risk between different types of radiation exams and exposure, e.g., chest x ray, whole-body CT exam, head CT exam, occupational radiation worker, etc. Without a specific number available, a reasonable value of exposure for your daughter's exam is about 2 mSv, or 2 milligray (mGy). The values for mGy and mSv are essentially the same when one considers the effective dose.

1. As noted in Table 12-13 at the National Academies Press, the increase in solid cancers in 100,000 women who each receive 100 mGy (0.1 Gy) of radiation is 1,300 or an increase of 1.3 percent.  Information on male exposure and cancer rates are also provided. It should be noted that the normal incident rate in women is 36,900 or 36.9 percent. Given the large natural incidence of cancer, one cannot determine if a specific individual's cancer is due to radiation exposure by itself. That is, if every woman in a population of 100,000 received 100 mGy, it can be estimated that 38,200 cancers may be observed. However, it would be impossible to determine which cancers would be due to the radiation dose. As your daughter's exposure of 2 mGy is significantly lower even than 100 mGy, the stochastic risks are even smaller than these values. I certainly would not worry about the risk of cancer from a CT head exam to any of my children.
    
2. I do not know what you read or in what context it was presented. Radiation effects are generally divided into two types—acute and stochastic. Acute effects are easy to identify as the response is based on the dose received. For example, it is easy to see decreases of white blood cells in radiation therapy patients over the course of their therapy, as total doses may involve treatments of thousands of mGy over several weeks. Even after recovery from the initial cancer, many patients develop secondary cancers years later.
   
   Stochastic or low-dose effects, such as those from CT exams not those associated with therapy, would be harder to detect as the radiation response is not observed in individuals undergoing a therapy, but in large populations, and occurs after many decades later. This is why stochastic radiation effects, which are the concerns associated with CT scans, are hard to identify. It should also be considered that in many cases risk estimates come from the studies of the atomic bomb survivors in Japan and of therapy patients. These populations received significant doses in short periods of time as opposed to diagnostic medical exposures where doses are much lower and the accumulated dose of 100 mGy may occur over weeks, months, or years.
   
   Because of the factors cited above, it is possible that the cited risk of 1 in 2,500 in children who all receive a head CT scan may be too high. It is based on risks associated at high doses and high-dose rates extrapolated to low doses and low-dose rates. It should also be kept in mind that advances in cancer detection and treatment may further reduce cancer incidents and deaths in the years ahead. I would also recommend our information sheet on the risks and benefits of medical radiation exposures.
    
3. I cannot comment on how individual physicians evaluate cancer risk in determining risk for any medical test or procedure. I believe that physicians will consider the immediate condition of the patient and order those tests that provide the information they need to help the patient at the time of exam, and there are guidelines to help physicians make the most appropriate choice. See the National Cancer Institute site.

In weighing risks, it is clear that CT and other radiological exams provide the best choice. See the HPS article on the Benefits of Medical Radiation Exposures. Again, the situation may involve using a CT scan to determine if a child has a hematoma that could lead, in a short time, to brain damage and extensive medical treatment or some future risk of cancer above the normal incident rate. Both choices have associated benefits and risks, and which will have the greatest impact on the child—possible brain damage or a speculated cancer in the distant future? Given the choice, I would allow the physician to do the CT on my child.

I hope this information helps.

John Jacobus, MS
Certified Health Physicist

Reference
Lee C, Lee C, Staton RJ, Hintenlang DE, Arreola MM, Williams JL, Bolch WE. Organ and effective doses in pediatric patients undergoing helical multislice computed tomography examination. Med Phys 34(5):1858-73; May 2007.