The use of pediatric CT, a valuable imaging tool, has been increasing rapidly. Because of current and growing use of CT and the potential for increased radiation exposure to children undergoing these scans, pediatric CT is 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 extremely valuable, and 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 4-7 million CT examinations are performed annually on children in the U.S. The use of CT in adults and children has increased about 8-fold since 1980, with annual growth estimated at about 10% per year. Much of this increase is due to its utility in common diseases as well as technical improvements. Despite the many benefits of CT, a disadvantage is the inevitable radiation exposure. Although CT scans comprise up to about 12% of diagnostic radiological procedures in large U.S. hospitals, it is estimated that CT scans contribute approximately 45% of the U.S. population's collective radiation dose from all medical x-ray examinations. CT is the largest contributor to medical exposure to 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 also have a longer life expectancy than adults, resulting in a larger window of opportunity for expressing radiation damage.
  
  
• Children receive a higher dose than necessary when adult CT settings are used for children.

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.

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. Adjustments are frequently not made in the CT 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 other irradiated populations demonstrate small, but significant, increases in cancer risk even at the low levels of radiation that are relevant to pediatric CT scans. Effective doses from a single pediatric CT scan can range from about < 1 to 30 mSv (see table below). 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. In addition, more than one scan (more than one "phase") may be done during a single examination, further increasing the radiation dose. A single scan during pediatric CT should be sufficient in the vast majority of cases.

It is important to stress that the individual cancer risks associated with CT scans are small. The highest lifetime risks estimated in the literature are less than 1 in 1000, and most estimates are substantially lower than that. The public health issue is the increasingly large pediatric population being exposed to these small risks.

The benefits of properly performed 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 cancer deaths.

# Effective dose using the 2008 ICRP tissue weighting factors. Effective dose is used in radiation protection to express detriment to the whole body when only a part of the body is exposed. It takes into account the type of radiation and the sensitivity of the exposed organs / tissues (tissue weighting factor).

* "Unadjusted" refers to using the same settings as for adults. "Adjusted" refers to settings adjusted for body weight.

** Dose estimates for two views for each breast combined.

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, 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 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. Be familiar with the dose descriptors available on CT scanners.¹ 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.
  
  
• 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 and the American Academy of Family Physicians. Provide readily available information sources on the World Wide Web (e.g. www.imagegently.org)
  
  
• 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 should 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.

¹ The most commonly shown dose-related parameters are CT dose index (CTDIw or CTDIvol) and the dose length product (DLP). The CTDIw is based on dosimetry readings for a 10 cm thick region from either a 16 cm or 32 cm diameter acrylic phantom; the CTDIvol takes account any gaps or overlaps from consecutive rotations of the x-ray source related to pitch; the dose length product is the CTDIvol × the length of the scan. Using conversion factors (for neonatal, 1, 5, 10, and 15 yr old), the DLP can provide a rough estimate of the age-dependent effective dose for the protocol.

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