Is that CT scan worth the risk?

A few years back, I was offered the exciting prospect of a free, full-body CT (computed tomography) scan, courtesy of a company that was launching this as a private service in the UK.

The invitation came with full-color images, demonstrating how my internal organs might look in 3D, sliced one way then another. It would be the ultimate medical check-up, identifying anything that might cause me health problems in future.

The public relations lady was surprised when I turned it down. I've never been a fan of going looking for trouble, preferring to wait until my body tells me something's wrong. And, I thought, what if it does show something that could cause a problem in future? What would I do about it?

Boy, am I glad I said ‘no thanks'. Research out this week shows that CT scans, far from being the risk-free diagnostic check-up that I was encouraged to get, may have caused 29,000 cancers among approximately 70 million Americans who had a scan in 2007.

The average dose of radiation from a CT scan is the equivalent of 442 chest x-rays, or 74 mammography scans. And sure, for most people, it won't cause any harm. But for an unlucky 1 in 270 women aged 40 who have a CT angiography (a scan of the arteries of the heart), it'll cause a cancer. Radiation to the chest, abdomen, and pelvis is more risky for women than men, because of the chance of breast or gynecological cancers.

OK, so few people choose to pay for full-body CT scans when they're perfectly healthy. But the numbers of diagnostic CT scans has risen rapidly in the past decade, sometimes for relatively minor symptoms. And repeat scans mean that you could clock up plenty of radiation exposure over a lifetime.

No one's saying you don't need proper diagnostic scanning for potentially serious problems, such as to confirm a suspected stroke or a blood clot in the lungs. But if your doctor tends to run scans ‘just to be on the safe side,' it may be worth asking how necessary they really are. This is one area where you really can be too careful.

What you need to know. CT scans are very useful diagnostic tools. But they do involve a dose of radiation, and it's best to be sure that the risk is outweighed by the benefit of the scan. 

—Anna Sayburn, patient editor, BMJ Group

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