The use of pediatric CT, a valuable imaging tool, has been increasing rapidly. Because of the growing use of CT and the potential for increased radiation exposure to children undergoing these scans, pediatric CT has become a public health concern. This brochure 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: a public health issue

• Immediate strategies to minimize CT radiation exposure to children

CT as a Diagnostic Tool

CT is an extremely valuable tool for diagnosing illness and injury in children. For an individual child, the risks of CT are small and the individual risk-benefit balance almost always favors the benefit. Approximately 2-3 million CT examinations are performed annually on children in the U.S. The use of CT in adults and children has increased about 7-fold in the past 10 years. Much of this increase is due to increased availability, technical improvements and utility for common diseases. The newest technology, multidetector (or multislice) CT, provides even greater imaging opportunities in both adults and children. Despite the many benefits of CT, a disadvantage is the inevitable radiation exposure. Although CT scans comprise about 10% of diagnostic radiological procedures in large U.S. hospitals, it is estimated that CT scans contribute approximately 65% of the effective radiation dose from all medical x-ray examinations to the population.

Unique Considerations for Radiation Exposure in Children

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

• Children are considerably more sensitive to radiation than adults, as demonstrated in epidemiologic studies of exposed populations.

• Children also have a longer life expectancy, resulting in a larger window of opportunity for expressing radiation damage.

As an example, compared with a 40-year old, the same radiation dose given to a neonate is several times more likely to produce a cancer over the child's lifetime.

Moreover, the same exposure parameters used for a child and an adult will result in larger doses to the child. There is no need for these larger doses to children, and CT settings can be reduced significantly while maintaining diagnostic image quality. Therefore, children should not be scanned using adult CT exposure parameters. Currently, adjustments are not frequently made in the exposure parameters that determine the amount of radiation children receive from CT, resulting in a greater radiation dose than necessary.

Radiation Risks from CT in Children: A Public Health Issue

Major national and international organizations responsible for evaluating radiation risks agree there probably is no low-dose radiation "threshold" for inducing cancers, i.e., no amount of radiation should be considered absolutely safe. Recent data from the atomic bomb survivors and medically irradiated populations demonstrate small, but significant, increases in cancer risk even at the low levels of radiation that are relevant to pediatric CT scans. Doses from a single pediatric CT scan can range from about 5 mSv to 60 mSv (see box). Among children who have undergone CT scans, approximately one-third have had at least three scans. Multiple scans present a particular concern. For example, three scans would be expected to triple the cancer risk of a single scan.

Although the benefits of properly performed CT examinations almost 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 cancer deaths.

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. Although there are standard indications for CT in children, radiologists should review reasons prior to every pediatric scan and be available for consultation when indications are uncertain. Consider other modalities such as ultrasound or magnetic resonance imaging, which do not use ionizing radiation.

• 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 settings should be considered for skeletal and lung imaging.

  • 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.

• Minimize the CT examinations that use multiple scans obtained during different phases of contrast enhancement (multiphase examinations). These multiphase examinations are rarely necessary, especially in body (chest and abdomen) imaging, and result in a considerable increase in dose.

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 development and adoption of pediatric CT protocols.

• 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 and the American Academy of Family Physicians. Provide readily available information sources on the World Wide Web.

• Conduct further research to determine the relationship between CT quality and dose, to customize CT scanning for individual children and to clarify the relationship between CT radiation and cancer risk.

Conclusion

While 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 must continually think about reducing exposure as low as reasonably achievable (ALARA), 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 our most valuable imaging modalities for both children and adults.

References

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Donnelly LF, Emery KH, Brody AS, et al. Minimizing radiation dose for pediatric body applications of single-detector helical CT. AJR 2001; 176:303-6.

Frush DP, Donnelly LF. Helical CT in children: technical considerations and body applications. Radiology 1998; 209:37-48.

Mettler FA Jr, Wiest PW, Locken JA, et al. CT scanning: patterns of use and dose. J Radiol Prot 2000; 20:353-9.

Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR 2001; 176:297-301.

Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res 2000; 154:178-6.

Robinson AE, Hill EP, Harpen MD. Radiation dose reduction in pediatric CT. Pediatr Radiol 1986; 16:53-4.

Rogers LF. Taking care of children: check out the parameters used for helical CT. AJR 2001; 176:287.

Slovis TL, editor. ALARA Conference Proceedings. The ALARA concept in pediatric CT-intelligent dose reduction. Pediatr Radiol 2002;32:217-317.

Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, Volume II: Effects. New York: United Nations, 2000.

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