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.

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.

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.

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?

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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