National Cancer Institute issues warning on pediatric CTs
Scans conducted at adult settings expose children to unnecessary
cancer risk, the NCI says.
By
John Dudley Miller, AMNews correspondent. Oct. 7, 2002.
Additional information
Dial it down is the message the National Cancer Institute is sending to
doctors who order or perform computed tomography scans on children.
In a guide sent to 158,000 physicians, the NCI notes that CT settings
frequently are not lowered from adult levels when scans are performed on
children. Failure to adjust scanners exposes children to more radiation
than necessary and increases their risk of future cancer, according to the
guide, which was co-sponsored by the Society of Pediatric Radiologists.
For instance, adult CT settings give four times as much radiation as is
necessary to image a newborn's abdomen, and they give twice as much as is
needed to scan its head, the guide indicates.
The NCI and SPR expect that those higher doses could double to
quadruple the tiny added chance of dying from cancer later in life that a
properly adjusted CT scan gives to a baby.
"Minimizing radiation exposure from pediatric CT, whenever possible,
will reduce the projected number of CT-related cancer deaths," the
document states.
The guide cites the latest data from research on Japanese A-bomb
survivors, which suggests that of every 2,500 newborns who receive a head
scan at adult settings, one can be expected to die prematurely from cancer
because of the scan. But the older and larger a child is when scanned, the
lower the danger. So a 15-year-old getting the same scan would incur only
half that risk. And some experts believe that even these numbers
exaggerate the risk.
2 million to 3 million CT exams are performed on U.S. children
every year.
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The federal government does not regulate the radiation dose of CT
scanners.
But an advisory panel to the Food and Drug Administration recommended
in May that the agency require all new CT machines to automatically adjust
the dose to a practical minimum by measuring, as they scan, how much of
the x-ray beam a person's body attenuates, child or adult. The FDA has not
yet acted on that proposal.
CT manufacturers are already responding. Siemens Medical Solutions,
Toshiba America Medical Systems and General Electric Medical Systems have
just started offering the automatic dose-minimizing feature recommended by
the FDA advisory panel. Philips Medical Systems plans to follow suit next
spring.
The number of CT scans performed on adults and children has risen
sevenfold in the last decade.
Each year 2 million to 3 million CT exams are performed on children in
the United States.
"It's increasing, particularly in emergency rooms, because there's such
huge pressure to move patients through," said Fred Mettler, MD, chair of
the radiology department at the University of New Mexico Health Sciences
Center in Albuquerque.
A single CT scan gives roughly as much radiation as 100 x-rays.
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The NCI/SPR guide, mailed to members of several medical societies,
stresses that the benefit of a properly performed CT almost always
outweighs its risk for a child.
"CT is clearly a terrific test. We just want it to be used properly,"
said Thomas Slovis, MD, a pediatric radiologist at the Children's Hospital
of Michigan, Detroit, and the prime mover behind the brochure project.
But there are risks.
The NCI and SPR note that major radiation standard-setting
organizations here and abroad agree that there is probably no low-dose
radiation threshold for inducing cancers. So no amount of radiation should
be considered absolutely safe, they say.
Many physicians don't realize that a single CT scan gives roughly as
much radiation as 100 x-rays, according to many radiologists.
Dialing down CT scans for kids is especially important because
radiation impacts them much more than it affects adults.
The NCI/SPR guide and the research it cites point out that:
- Children who are scanned will usually live much longer than adults
who are scanned, giving them longer to develop any cancer a scan might
cause.
- A newborn is 10 times as radiosensitive as a 50-year-old adult, and
girls are twice as sensitive as boys.
- Even when children and adults are exposed to exactly the same
strength CT beams, kids get substantially larger doses because their
thinner bodies allow the beam to penetrate them with higher average
intensity.
It's easy to habitually overexpose kids and not know it, according to
an FDA public health notification issued in November 2001. If adult
settings are used, the CT scan of a child will simply produce a
higher-quality image than usual. This might offer a temptation to use
adult doses on kids. Instead, the NCI/SPR guide urges doctors to aim for
the lowest dose that gives acceptable image quality.
The guide also raises concern about multiple scans. Among children who
have undergone CT scans, about one-third have had at least three. This
would be expected to triple the cancer risk of a single CT, the document
notes.
Call for action
The NCI and SPR call on physicians, CT technologists, CT manufacturers,
and medical and government organizations to take steps to reduce the
amount of radiation that children receive from CT scans. The two groups
encourage the development of pediatric CT protocols, along with new
research to determine the lowest doses that will give diagnostically
adequate image quality.
The guide recommends that physicians not even order CT scans if
ultrasound or magnetic resonance imaging will suffice, because neither of
those techniques gives off radiation. But MRIs are much less useful in
emergencies, pediatric radiologists say, because they take a total of 45
minutes or more, compared with 15 minutes or less for a CT.
In actual practice, experts say, the faster speeds of the latest
multidetector CT scanners are making CT the image of choice for increasing
numbers of physicians.
"Where before it might take you 20 minutes to get a CT of the belly,
now it takes you 40 seconds," Dr. Mettler said. So unstable patients can
now be scanned, and fewer fidgety kids must be sedated beforehand.
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ADDITIONAL INFORMATION:
CT discussion tips
The guide recommends that physicians discuss the following issues with
parents:
- Is computed tomography the best examination to diagnose conditions
in the child?
- Will the CT examination be adjusted based on the child's size?
- Will a radiologist be responsible for performing and interpreting
the child's CT exam?
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Weblink
Article, "Radiation Risks and Pediatric Computed Tomography (CT): A
Guide for Health Care Providers," National Cancer Institute
(http://www.cancer.gov/cancerinfo/causes/radiation-risks-pediatric-ct)
Johns Hopkins University
spiral CT protocols (http://www.ctisus.com/ctprotocols/)
American College of Radiology
appropriateness criteria
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Copyright 2002 American Medical Association. All
rights reserved.
