ulting in a larger window of opportunity for expressing radiation damage.
- Children may receive a higher radiation dose than necessary if CT settings are not adjusted for their smaller body size.
As a result, the risk for developing a radiation-related cancer can be several times higher for a young child compared with an adult exposed to an identical CT scan.
In the last decade improvements in CT equipment have allowed for better images at lower doses. The use of appropriate settings has also become much more widespread, resulting in reductions in doses for children. There is no need for higher doses in children, and appropriate settings should always be used.
Regardless of the lower doses, multiple scans to an individual patient present a particular concern. In addition, the use of more than one scan (that is, more than one contrast "phase") during a single examination will further increase the radiation dose. In the vast majority of cases, a single scan should be sufficient during pediatric CT.
Radiation Risks from CT in Children
Major national and international organizations responsible for evaluating radiation risks agree that there probably is no low-dose radiation "threshold" for inducing cancers. In other words, no amount of radiation should be considered absolutely safe.
The first study to assess directly the risk of cancer after CT scans in childhood found a clear dose-response relationship for both leukemia and brain tumors: risk increased with increasing cumulative radiation dose. For a cumulative dose of between 50 and 60 milligray or mGy (mGy is a unit of estimated absorbed dose of ionizing radiation) to the head, the investigators reported a threefold increase in the risk of brain tumors; the same dose to bone marrow (the part of the body responsible for generating blood cells) resulted in a threefold increase in the risk of leukemia. For both findings, the comparison group consisted of individuals who had cumulative doses of less than 5 mGy to the relevant regions of the body.
The number of CT scans required to give a cumulative dose of 50-60mGy depends on the type of CT scan, the age of the patient, and the scanner settings. If typical current scanner settings are used for head CT in children, then two to three head CT scans would result in a dose of 50-60mGy to the brain. The same dose to red bone marrow would be produced by five to 10 head CT scans, using current scanner settings for children under age 15.
Previously, the potential cancer risk from CT use has been estimated using risk projection models derived primarily from studies of survivors of the atomic bomb explosions in Japan. The risks observed in the study described above were consistent with those previous estimates.
It is important to stress that the absolute cancer risks associated with CT scans are small. The lifetime risks of cancer due to CT scans, which have been estimated in the literature using projection models based on atomic bomb survivors, are about 1 case of cancer for every 1,000 people who are scanned, with a maximum incidence of about 1 case of cancer for every 500 people who are scanned.
The benefits of properly performed and clinically justified CT examinations should always outweigh the risks for an individual child; unnecessary exposure is associated with unnecessary risk. Minimizing radiation exposure from pediatric CT, whenever possible, will reduce the projected number of CT-related cancers.
Immediate Measures to Minimize CT Radiation Exposure in Children
Physicians, other pediatric health care providers, CT technologists, CT manufacturers, and various medical and governmental organizations share the responsibility to minimize CT radiation doses to children. Several immediate steps can be taken to reduce the amount of radiation that children receive from CT examinations:
- Perform only necessary CT examinations. Communication between pediatric health care providers and radiologists can determine the need for CT and the technique to be used. There are standard indications for CT in children, and radiologists should revi