Children are receiving radiation exposures from computed tomography (CT) that are five times higher than necessary, according to new data.

When researchers from the Children's Medical Center in Cincinnati, Ohio, compared radiation exposures of paediatric CTs performed at other centres with those at their institution, using a paediatric weight based sliding scale, they found that the tube current, a parameter directly proportional to radiation exposure, was often set too high at other centres.

There are several explanations for the high rates of radiation to which children are exposed. Several of the scans at outside centres took place in adult clinics, where lack of familiarity with the needs of children and poor knowledge of the research may be factors. Also, unlike regular x-rays, the more radiation used in a CT scan, the better the picture, so doctors may be tempted to crank up the dose for their own rather than the patients' benefit.

No increased cancer risk has yet been noted with paediatric CT scans. However, the technology is new and children undergoing scans now would probably need to be followed for 30 years for the risk to show up.

In the meantime, a child receiving a single chest CT scan will receive the same amount of radiation as for 20 mammograms roughly 2-3 rads. During World War II children exposed to 5 rads had four times the risk of developing breast cancer. So a child having two or three scans in the same area would receive well over the dose known to cause cancer (Am J Roentgenol, 2001; 2: 297- 301).

In a second report in the same journal, the research team outline a 'safe' sliding scale of exposure for children based on body size (Am J Roentgenol, 2001; 2: 303-6).