Receiving CT scan radiation to the head for diagnostic purposes during childhood triples the small risk of developing brain cancer and leukemia later in life, say doctors who recommend keeping doses as low as possible.

CT imaging is an important diagnostic tool and its use has increased rapidly. Doctors take care to limit the amount of CT radiation that children are exposed to and, when possible, look for alternatives that don't use ionizing radiation that can cause cancer.

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CT scans deliver more radiation than tradiational X-rays. (Charles Rex Arbogast/Associated Press)

In Thursday's online issue of the medical journal The Lancet, British, American and Canadian pediatricians and radiologists looked back at the doses received by 178,000 people in Great Britain who were younger than 22 between 1985 and 2002.

"CT scans deliver appreciably more radiation than X-rays and there is a measurable risk associated with the use of CT scans especially for those who might get multiple CT scans," said study author Dr. Louise Parker, a professor of medicine and pediatrics at Dalhousie University in Halifax.

The amount of radiation in CT scans for young children has fallen about 80 per cent since the machines were first introduced. The equipment and techniques are now more sophisticated at delivering doses adjusted to a child's size.

"Our view is that we need to make further reductions in CT doses and this should be a priority for both the clinical community and the manufacturers," study author Mark Pearce of Newcastle University told reporters.

Justify CT use

The researchers concluded the risk of brain tumours tripled if children under age 10 had two to three scans, and the risk of leukemia was tripled with five to 10 scans in the decade after the first radiation exposure.

The researchers emphasized these were rare diseases and that the higher risk was still small. The risk of leukemia in children is about 1 in 2,000, so having several CT scans would raise that to about 1 in 600, still "exceedingly rare."

The scans do save lives when used as needed, such as assessing head injuries and imaging chest diseases, the researchers said.

In a journal commentary accompanying the research, Dr. Andrew Einstein of Columbia University Medical  Center in New York said the study confirms that CT scans "almost certainly produce a small cancer risk."

"Use of CT scans continues to rise, generally with good clinical reasons, so we must redouble our efforts to justify and optimize every CT scan," Einstein said.

Parker suggested that if parents have concerns about use of CT scans in children, they should discuss it with the doctor, understand why it may be the best diagnostic for their child at the time and whether alternative could be used such as regular X-rays, ultrasounds or MRIs.

The study was paid for by the U.S. National Cancer Institute and the U.K. Department of Health.

With files from CBC's Amina Zafar