-- Mary Elizabeth Dallas
WEDNESDAY, May 22 (HealthDay News) -- Children and teens exposed
to radiation during CT scans are 24 percent more likely to develop
cancer, according to a large, long-term study.
The risks, however, are still low: Among a group of 10,000 young
people who each had one CT scan, only about six extra cancers would
be expected to occur within 10 years, according to researchers from
Australia and Europe.
The researchers said doctors should carefully weight the risks
to patients when making decisions about CT (computed tomography)
testing. The study was published online May 21 in the journal
The researchers used data from Australian Medicare records and
national cancer records to compare cancer rates among patients who
had a CT scan by age 19 to those who had never undergone the
The study involved nearly 11 million young people born between
1985 and 2005. The average length of follow-up for those who
underwent a CT scan was 9.5 years, and about 17 years for those who
did not have a CT scan.
Of the participants, about 680,000 had a CT scan at least one
year before they were diagnosed with cancer. Among those diagnosed
with cancer, 18 percent had more than one scan.
By the last follow-up in 2007, the researchers found that 3,150
of those who had a CT scan and about 57,500 of those who didn't had
been diagnosed with cancer.
After taking the participants' age, gender and year of birth
into account, the rate of cancer was 24 percent higher among those
who had a CT scan. That risk increased by 16 percent for each
Nearly 60 percent of CT scans involved the brain, according to a
BMJnews release. Although the prevalence of brain cancer
among those who had a CT scan decreased over time, the study
authors found that the incidence was still higher more than 15
years after they had their first scan.
Children exposed before age 5 had the greatest risk. The older a
patient is at first exposure to a CT scan, the lower their risk,
the researchers said. But even among the oldest participants --
between 15 and 19 -- the study revealed that risk for all cancers
combined was still higher.
For cancers involving tumors other than brain cancer, the
researchers found the proportional increase in risk was 23 percent
among females and 14 percent among males.
The researchers, led by John Mathews, a professor at the
University of Melbourne's School of Population and Global Health,
said that in some cases brain cancer may have resulted in a CT scan
and not the other way around. They added that participants may have
developed cancer beyond the final follow-up period in 2007. As a
result, they concluded that the "eventual lifetime risk from CT
scans cannot yet be determined."
Although the study found an association between having a CT scan
in childhood and a higher risk of developing cancer, it did not
prove a cause-and-effect relationship.
It's important to realize the incidence of cancer among children
is extremely small, said Dr. Aaron Sodickson, who wrote an
accompanying journal editorial. Sodickson is the section chief of
emergency radiology and medical director of computed tomography at
Brigham and Women's Hospital and Harvard Medical School in
"A 24 percent increase makes this risk just slightly less small," Sodickson wrote. He added that there are many ways to adjust radiation doses and that more accurate assessments of patients' risk can help doctors make more informed decisions about CT scans and other imaging tests.
The U.S. National Institutes of Health has more about
CT scans and the risks involved.
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