Small Increased Cancer Risk for Children Who Have CT Scans

May 22, 2013

CT scans performed on children and adolescents may contribute to a slightly elevated risk cancer over the following 10 years.

Radiation from CT scans performed on children and adolescents slightly increases their eventual lifetime risk of cancer, according to a study published in the journal BMJ.

As the use of imaging tests such as CT scans increases, so does the concern regarding irradiation that accompanies these exams, particularly among children and adolescents. While technology is improving, requiring lower doses, some exposure continues to occur.

To assess cancer risk from CT irradiation exposure, researchers from Australia and the United Kingdom identified patients who had undergone CT scans as children by looking through the records of 10.9 million people identified from the Australian Medicare records, who were aged 0 to 19 years on January 1985 or were born between January 1, 1985 and December 31, 2005. They then compared the cancer rate of those who had been exposed to CT scan more than a year before their diagnosis to those who had cancer but who did not have CT scans as children. The mean length of follow-up was 9.5 years for those who did have CT scans and 17.3 years for those who did not.

The researchers found 60,674 recorded cancers among the group, including 3,150 among the 680,211 who had been exposed to a CT scan at least one year before diagnosis.

“Overall cancer incidence was 24 percent greater for exposed than for unexposed people, after accounting for age, sex, and year of birth,” the authors wrote. This risk continued to increase by 16 percent for each additional CT scan.

The incidence of brain cancer was still significantly increased more than 15 years after first exposure, despite the decline in time since first exposure. Those at highest risk for brain cancer were patients who were exposed to CT scans before they were 5 years old. The risk did drop with age, but remained significantly increased in the oldest age at exposure, those children who were 15 to 19 years old.

For other solid cancers (digestive organs, melanoma, soft tissue, female genital, urinary tract, brain, and thyroid), the absolute excess cancer incidence increased significantly with time since first exposure. For all cancers combined, although the proportional increase declined with years since first CT scan, it was still increased at 15 years or more after first exposure.

For the solid cancers other than brain cancer, the proportional increase in risk was somewhat greater in females: 23 percent compared with 14 percent in males.

Speaking specifically about brain cancers, the authors did point out that while some brain cancers may be related to the radiation from the scans, it is also possible that the scans were needed because of the presence of brain cancer – that reverse causation is present for at least some patients.

Aaron Sodickson, section chief of emergency radiology and medical director of computed tomography at Brigham and Women’s Hospital and Harvard Medical School in Boston, wrote an accompanying editorial that stressed that the “baseline incidence of cancer in a general pediatric population is extremely small, so that a 24 percent increase makes this risk just slightly less small.”

Sodickson also noted physicians can continue to reduce risks in various ways, such as paying special attention to patients who are undergoing recurrent imaging, “because if frequently repeated scans are found to provide little clinical benefit, the cumulative risk-benefit balance may support a decision not to image again for the same clinical presentation.”

Newer technology also allows for reduced radiation doses and more accurate data capture.