Millions of Americans, especially children, are needlessly
getting 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
United States 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 a third of all diagnostic
tests are unnecessary, that means that 20 million adults and more
than 1 million children getting CT scans are needlessly being put
at risk, Brenner and Hall write.
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 a 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."
(Agencies via China Daily November 29, 2007)