Radiation and the young mind

A study raises concerns over the effect of CT scans on young children


A small child's fall or head injury can be alarming, especially if the child loses consciousness. Sometimes a CT scan is needed to rule out a skull fracture or bleeding inside the brain.

But as reassuring as the high-tech answer may be, it could do harm in the long run. Researchers have found that low-dose radiation to the head before the age of 18 months can impair a child's intellect — and a CT scan uses high-dose radiation.

In a study of 3,094 men, Swedish scientists found that the greater their exposure to radiation as babies, the more impaired their eventual learning ability and logical reasoning. The researchers studied men who received low-dose radiation therapy to the head as children, and then looked at their schooling and test performance. Their findings suggest that radiation may damage children's developing brains and should be weighed by doctors considering CT scans for minor trauma.

Dr. Marvin D. Nelson Jr., a neuroradiologist and chief of radiology at Childrens Hospital Los Angeles, said the study raises important questions about the long-term effects of radiation.

But he pointed out it should be followed up with a study that assesses the effects of CT radiation instead of the types of radiation — beta rays, gamma rays, X-rays and radium-226 — with which the Swedish youngsters were treated.

In the study, which appeared in a recent issue of the British Medical Journal, researchers at the Karolinska Institute in Stockholm assessed the intellectual capacity of men who as babies received low-dose radiation therapy. Because 95 per cent of Swedish men ages 18 and 19 are tested before military service, researchers were able to track information about the education and cognitive test results of these former pediatric patients.

The researchers found that the proportion of boys who attended high school decreased in relation to increasing doses of ionising radiation to the front and back of the brain. The more radiation they were exposed to, the more impaired their learning ability and logical reasoning. Because the dosages overlap those of CT scans, the findings raise questions about the long-term developmental effects of CT scans, which increasingly are used to assess minor head injuries.

But Nelson said the types of radiation used then are different from today's CT. CT is the preferred test when a doctor suspects that a child has sustained a brain injury. But it's not always required. If a child is knocked out briefly, he or she should be observed and usually won't need a CT scan, Nelson said.

If a CT is recommended, Nelson suggests that parents ask "whether the CT facility is using the proper reduced-dose protocols for children based on the size of the child." Many hospitals use radiation guidelines for adults, which "deliver two to three times more radiation than is needed for a pediatric CT."

When evaluating possible skull fractures and bleeding inside the skull, Nelson said no test provides as much information as a CT scan.

An MRI, which lasts 30 to 60 minutes and uses magnetic fields instead of radiation, is three to four times more expensive and requires that the child's condition be stable. It's better-suited to evaluating long-term brain injury. CT scanning, he said, takes only minutes and is better at evaluating the situation early.

© Los Angeles Times-Washington Post News Service