Millions of Americans, especially children, needlessly get
dangerous radiation from "super X-rays" that raise the risk of cancer and are
increasingly used to diagnose medical problems, a new report warns.
In a few decades, as many as 2 percent of all cancers in the U.S. might be due
to radiation from CT scans given now, according to the authors of the report.
Some experts say that estimate is overly alarming. But they agree with the need
to curb these tests particularly in children, who are more susceptible to
radiation and more likely to develop cancer from it.
"There are some serious concerns about the methodology used," but the authors
"have brought to attention some real serious potential public health issues,"
said Dr. Arl Van Moore, head of the American College of Radiology's board of
chancellors.
The risk from a single CT, or computed tomography, scan to an individual is
small. But "we are very concerned about the built-up public health risk over a
long period of time," said Eric J. Hall, who wrote the report with fellow
Columbia University medical physicist David J. Brenner.
It was published in Thursday's New England Journal of Medicine and paid for by
federal grants.
The average American's total radiation exposure has nearly doubled since 1980,
largely because of CT scans. Medical radiation now accounts for more than half
of the population's total exposure; it used to be just one-sixth, and the top
source was the normal background rate in the environment, from things like radon
in soil and cosmic energy from the sun.
A previous study by the same scientists in 2001 led the federal Food and Drug
Administration to recommend ways to limit scans and risks in children.
But CT use continued to soar. About 62 million scans were done in the U.S. last
year, up from 3 million in 1980. More than 4 million were in children.
Since previous studies suggest that one-third of all diagnostic tests are
unnecessary, that could mean that 20 million adults and more than 1 million
children getting CT scans are needlessly being put at risk, Brenner and Hall
wrote.
Ultrasound and MRI, or magnetic resonance imaging, scans often are safer options
that do not expose people to radiation, they contend.
CT scans became popular because they offer a quick, relatively cheap and
painless way to get 3D pictures so detailed they give an almost surgical view
into the body. Doctors use them to evaluate trauma, belly pain, seizures,
chronic headaches, kidney stones and other woes, especially in busy emergency
rooms. In kids, they are used to diagnose or rule out appendicitis.
But they put out a lot of radiation. A CT scan of the chest involves 10 to 15
millisieverts (a measure of dose) versus 0.01 to 0.15 for a regular chest X-ray,
3 for a mammogram and a mere 0.005 for a dental X-ray.
The dose depends on the type of machine and the person -- obese people require
more radiation than slim ones -- and the risk accumulates over a lifetime.
"Medical care in this country is naturally so fragmented. Any one doctor is not
going to be aware of the fact that a particular patient has had three or four CT
scans at some point in the past," said Dr. Michael Lauer, prevention chief at
the National Heart, Lung and Blood Institute.
People with chronic problems like kidney stones are likely to get too many
scans, said Dr. Fred Mettler, radiology chief in the New Mexico Veterans
Administration health care system.
"I've seen people who are 30 years old who have had at least 18 scans done," he
said.
That puts them at risk of developing radiation-induced cancer, Brenner and Hall
said. They base this on studies of thousands of Japanese atomic bomb survivors
who had excess cancer risk after exposures of 50 to 150 millisieverts -- the
equivalent of several big CT scans.
"That's very controversial. There's a large portion of the medical physics
community that would disagree with that" comparison, said Richard Morin, a
medical physicist at the Mayo Clinic in Jacksonville, Fla.
However, others defended the data, which has been widely cited in other
radiation studies.
"It's the best evidence we've got" on cancer risks, Lauer said.
Dr. Robert Smith, the American Cancer Society's director of screening, said the
authors' estimate that 2 percent of future cancers may be due to CT scans "seems
high." But since cancers take 10 to 20 years to develop, "the ability to even
observe that kind of an increase is going to be very difficult," he said.
The authors stressed that they were not trying to scare people who need CT scans
away from having them. In most cases, the benefits exceed the risks, especially
for diagnostic scans.
However, using the scans to screen people with no symptoms of illness -- like
screening smokers for signs of lung cancer -- has not been shown to save lives
and is not currently recommended.
Many groups also condemn whole-body scans, often peddled by private
practitioners in shopping centers as peace of mind to the worried well. Many of
these centers are not accredited by the College of Radiology; only one-third of
all places that do CT scans in the U.S. are, although insurers are starting to
require it for reimbursement, Moore said.
Many CT centers also are set up for adults and rarely image children, who need
adjustments to limit dose and radiation risk, said Dr. Alan Brody, a radiologist
at Cincinnati Children's Hospital Medical Center who wrote a report on the
topic. He said parents should seek a center that often handles children.
Both doctors and patients need to be more aware of radiation risks and discuss
them openly, Brenner and Hall said.
"We were astonished to find, when we were researching materials for this paper,
how many doctors, particularly emergency room physicians, really had no idea of
the magnitude of the doses or the potential risks that were involved," Hall
said.
Other studies found the opposite problem: Three out of 10 parents in one study
insisted on CT scans instead of observing the child's condition for awhile even
after they were told of the radiation risk, Brody said.
"This is what our patients want," and they expect fast answers from doctors, he
said.
The pressure is greatest for ER doctors who "are in a bind ... they have all
these patients stacked up" and need to make quick decisions, Mettler said.
Future generations of devices using less radiation should help alleviate the
concern, but these mostly are directed at the emerging field of heart scans,
Lauer said.
"When we order a CT scan it just doesn't seem like such a big deal" but it
should be, he said. "The threshold for ordering these tests is low and it's
getting lower and lower over time, which means that the risks become potentially
all that more important."
