CT-Related Cancer Risk Among Children Can Be Lowered

June 11, 2013

Children’s risk from radiation exposure from CT scans drops significantly when dose from the highest-dose exams is lowered and unnecessary exams eliminated.

CT dose-reduction strategies in children can result in as much as a 62 percent decrease in radiation-induced cancers later in life, according to a study published in JAMA Pediatrics.

As physicians try to lower the radiation exposure among their pediatric patients by cutting unnecessary exams, they are also looking at lowering the amount of radiation used in these exams without compromising image quality. This issue is important in the pediatric population because children, with their smaller body size, tend to absorb more radiation from imaging than do adults.

"The radiation children absorb will lead to greater harm, because they are more likely than adults to develop cancer from radiation exposure," Diana L. Miglioretti, PhD, said in a release.

Miglioretti, senior investigator at Group Health Research Institute and a professor of biostatistics at the UC Davis School of Medicine and one of the HMORN Cancer Research Network study's lead authors,   also pointed out that the children's small size means they do not need as much radiation exposure during CT scans as do adults. Projected risks of resulting solid cancers are higher for younger children and girls than for older children and boys. They are also higher for patients who undergo CT scans of the abdomen/pelvis or spine rather than other sites.

"We estimated that the number of cancers caused by CT scans performed on children could fall dramatically - by 62 percent - if dose-reduction strategies like that instituted by the Image Gently initiative were targeted to exams with the highest quarter of doses and if CT scans were used only when medically necessary," Miglioretti explained. Higher dose exams include those done of the abdomen and chest. Image Gently is a campaign that was initiated by the Alliance for Radiation Safety in Pediatric Imaging. Since 2008, the program aims to educate providers on how to reduce radiation exposure among children.

Forty-three percent of the decrease could result “simply by lowering the radiation from the highest-dose exams,” Miglioretti said. “We found the biggest gains would come from targeting the highest quarter of doses.” Lowering the doses plus reducing the number of total exams performed resulted in the overall 62 percent reduction in cancers.

In response to the study, The American College of Radiology (ACR) noted that the “absolute potential lifetime cancer risks reported in the study are very small compared with the lifetime risk of developing cancer in the general population.” The group also stressed that medical imaging, when used appropriately, are safer and less expensive than invasive procedures and can lead to greater life expectancy.

The study authors said that use of CT doubled from 1996 to 2005 for children younger than 5 , and nearly tripled for children age 5 to 14, at six U.S. health care systems: Group Health, Marshfield Clinic, and Kaiser Permanente Colorado, Georgia, Hawaii, and Northwest. However, CT use was stable between 2006 and 2007, and it started to decline from 2008 to 2010, particularly among younger children.

This finding was backed up by the ACR’s response statement, which further clarified that not only have imaging rates stabilized, but modern CT scanners use radiation doses that are up to 90 percent lower than those that were used even 10 years ago.

In their study, the research team calculated radiation doses absorbed by each organ and the effective (overall) dose from 744 CT scans in children conducted between 2001 and 2011 at four of their hospital systems and at the Henry Ford Health System. Those doses per scan varied widely, and many scans delivered an effective dose of 20 mSv or higher, which is the yearly limit set for people who work with radiation in Europe. There, if the dose for an exam exceeds the 75th percentile for that exam type, the high dose must be justified.

The researchers used a new approach to estimating both organ and effective doses in children, recently developed by the National Cancer Institute. Models used were developed by the Biological Effects of Ionizing Radiation (BEIR) committee, based on sources including the Life Span Study of survivors of the atomic bombing of Hiroshima and Nagasaki, Japan, to estimate how the radiation doses they observed translated into increased risk of developing cancer during the children's remaining lifetimes.

The authors pointed out that they do not suggest that CT scans should not be performed, but that in some cases, alternatives to CT scans may include MRI and ultrasound, which involve no ionizing radiation, and may be preferable.

The ACR, however, advised parents not to make decisions regarding imaging tests for their children based solely on these study findings and conclusions: “Medical imaging exams are directly linked to greater life expectancy, declines in mortality rates, and are generally safer and less expensive than the invasive procedures that they replace, such as exploratory surgery. Diagnostic scans reduce the number of invasive surgeries, unnecessary hospital admissions, and the length of hospital stays. However, they must be used judiciously, when indicated, and when the needed information cannot be obtained in other ways, in order to minimize radiation exposure to all Americans, particularly children.”

The ACR encouraged parents to discuss the risks and benefits of any procedure, including CT scans, with their child’s physician to allow for informed decisions.

“If an imaging scan is warranted, the immediate benefits outweigh a potential and very serious long-term risk,” Marta Hernanz-Schulman, MD, FACR, FAAP, chair of the ACR Pediatric Imaging Commission, said in a statement. “Parents should certainly discuss such potential risk with their physician, but this appropriate concern should not translate into refusal of necessary and potentially life-saving care.”