Radiation Risks and Pediatric Computed Tomography (CT): A Guide for Health Care Providers

The use of pediatric CT, which is a valuable imaging tool, has been increasing rapidly. However, because of the potential for increased radiation exposure to children undergoing these scans, pediatric CT is a public health concern. This page discusses the value of CT and the importance of minimizing the radiation dose, especially in children. It will address the following issues:

• CT as a diagnostic tool
• Unique considerations for radiation exposure in children
• Radiation risks from CT in children
• Immediate strategies to minimize CT radiation exposure to children

CT as a Diagnostic Tool

CT can be a life saving tool for diagnosing illness and injury in children. For an individual child, the risks of CT are small and the individual risk-benefit balance favors the benefit when used appropriately.

Approximately 5 to 9 million CT examinations are performed annually on children in the United States. The use of CT in adults and children has increased about eightfold since 1980, with annual growth estimated at about 10 percent per year. Much of this increase is due to its utility in common diseases, as well as to technical improvements.

Despite the many benefits of CT, a disadvantage is the inevitable radiation exposure. Although CT scans comprise up to about 12 percent of diagnostic radiological procedures in large U.S. hospitals, it is estimated that they account for approximately 49 percent of the U.S. population's collective radiation dose from all medical x-ray examinations. CT is the largest contributor to medical radiation exposure among the U.S. population.

Unique Considerations for Radiation Exposure in Children

Radiation exposure is a concern in both adults and children. However, there are three unique considerations in children.

• Children are considerably more sensitive to radiation than adults, as demonstrated in epidemiologic studies of exposed populations.
• Children have a longer life expectancy than adults, resulting 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 review reasons prior to every pediatric scan and be available for consultation when indications are uncertain. When appropriate, other modalities such as ultrasound or magnetic resonance imaging (MRI), which do not use ionizing radiation, should be considered.
• Adjust exposure parameters for pediatric CT based on
  • Child size: guidelines based on individual size / weight parameters should be used.
  • Region scanned: the region of the body scanned should be limited to the smallest necessary area.
  • Organ systems scanned: lower mA and/or kVp settings should be considered for skeletal, lung imaging, and some CT angiographic and follow up examinations.
• Scan resolution: the highest quality images (i.e., those that require the most radiation) are not always required to make diagnoses. In many cases, lower-resolution scans are diagnostic. Providers should be familiar with the dose descriptors available on CT scanners and minimize the use of CT examinations that use multiple scans obtained during different phases of contrast enhancement (multiphase examinations). These multiphase examinations result in a considerable increase in dose and are rarely necessary, especially in body (chest and abdomen) imaging.

Long-Term Strategies to Minimize CT Radiation

In addition to the immediate measures to reduce CT radiation exposure in children, long-term strategies are also needed.

• Encourage the development and adoption of pediatric CT protocols.
• Encourage the use of selective strategies for pediatric imaging, such as for the pre-surgical evaluation of appendicitis.
• Educate through journal publications and conferences within and outside radiology specialties to optimize exposure settings and assess the need for CT in an individual patient. Disseminate information through associations, organizations, or societies involved in health care of children, including the American Academy of Pediatrics, the American Academy of Family Physicians, , and the American College of Emergency Physicians. Provide readily available information sources, such as the Alliance for Radiation Safety in Pediatric Imaging.
• Conduct further research to determine the relationship between CT quality and dose, to customize CT scanning for individual children, and to further clarify the relationship between CT radiation and cancer risk.

Conclusion

Although CT remains a crucial tool for pediatric diagnosis, it is important for the health care community to work together to minimize the radiation dose to children. Radiologists should continually think about reducing exposure as low as reasonably achievable by using exposure settings customized for children. All physicians who prescribe pediatric CT should continually assess its use on a case-by-case basis. Used prudently and optimally, CT is one of the most valuable imaging modalities for both children and adults.

Related Resources

Society for Pediatric Radiology
1891 Preston White Drive
Reston, Virginia 20191
http://www.pedrad.org

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