New research highlights the risk of ionising radiation to children

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Radiation exposure from 2 to 3 CT scans of the head in childhood (aged under 15 years)—giving a cumulative dose of around 60 mGy—could increase the risk of developing brain cancer; around 5 to 10 scans (cumulative dose around 50 mGy) could increase the risk of leukaemia.

The use of CT scans for children to evaluate head, neck or spine injuries or neurological disorders has increased dramatically since they were introduced 30 years ago.   CT, or computed tomography, scans take X-rays from various angles and combine them to create cross-sectional images, and they involve much more radiation than traditional X-ray techniques. 

An x-ray is lower than a CT scan because it is just a one direction CT scan. X-rays don’t give you near the detail a CT could or image organs or anything other than bones. CT’s are 360 degree x-rays, of course they are going to have lots more radiation, but they also give you a lot more picture/clarity and gives you the ability to image everything.

Every year in the U.S., more than 70 million children and adults receive CT scans, a number that has grown six-fold over the last few decades.

International researchers studied nearly 180,000 patients under age 22 who had a CT scan in British hospitals between 1985 and 2002. They followed those patients until 2008. They found 74 of them were diagnosed with leukemia while 135 had brain tumors.

The first author of that study, David Brenner, director of the Center for Radiological Research at the Columbia University College of Physicians and Surgeons, said that young people were often given CT scans to diagnose kidney stones, appendicitis and dental problems, and that some of those scans could have been avoided by using other methods, like ultrasound or conventional X-rays.

Lead study author Amy Berrington de Gonzalez, from the U.S. National Cancer Institute, said this study is the first to look at the actual cancer risk of radiation from CT scans.

“All the previous studies about the potential risk of CT scans have been theoretical studies using models from other radiation-exposed populations,” she said. Specifically, they studied the results of radiation exposure after atom bombs were dropped on Japan during World War II.

“It’s well known that radiation can cause cancer but there is an ongoing scientific debate about whether relatively low doses of radiation, like those received from CT scans, do increase cancer risks, and if so the magnitude of those risks,” she added.

Pearce and colleagues concluded the risk of brain tumors was tripled if children had two to three scans and the risk of leukemia was tripled with five to 10 scans.

The risk of leukemia in children is about 1 in 2,000, so having several CT scans would bump that up to about 1 in 600.

The researchers noted that modern CT scanners give off about 80 percent less radiation than the older machines (1989-2003) used in the study. Even at low doses, the radiation can damage genes that may increase the patient’s risk of developing cancer later.

In the U.K., laws already require radiation from medical scans be kept as low as possible. In the United States, the government is pushing manufacturers to design new scanners to minimize radiation exposure for the youngest patients.

“CT scans are very useful, but they also have relatively high doses of radiation, when compared to X-rays,” said Mark Pearce of Newcastle University, the study’s lead author, at a press briefing Wednesday, adding CT scans were warranted in most situations but more needed to be done to reduce the amount of radiation.

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