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Are CT Scans Raising Our Cancer Risk?

By Heather Millar

Scan

I know a young med student who’s a thyroid cancer survivor.

When we first talked about it, she said, “I had some CT scans when I was a kid. That’s probably what caused it.”

As I outlined in my previous post, there will always be pro and con arguments about medical procedures, the causes of disease, and so on. But there seems to be growing evidence that we should use caution when it comes to this particular type of x-ray scan.

A CT scan is essentially a batch of x-rays taken from many different angles. It gives doctors a much more detailed picture of both the soft and hard tissues in your body than a single x-ray would. CT scans absolutely save lives. They diagnose cancer. They detect bleeds in the brain. They provide a quick picture without the need for anesthesia or exploratory surgery. Yet all these good things come at a price: a much higher dose of radiation than a single x-ray image delivers.

Two recent studies suggest that we should at least consider this downside before rushing to the CT machine.

• An English team published a paper in The Lancet that looked back over the medical histories of 176,000 patients. The team found that brain tumors in later life were three times as common among those who had had two to three head CT scans in childhood. If a person had five to 10 scans in childhood, their risk of leukemia tripled. In absolute numbers, the risk remains small: two extra cases of cancer per 10,000 children. Still, it’s what scientists call “statistically significant.”

• A special paper in the Archives of Internal Medicine concludes that avoiding unnecessary medical scans may be one of the most important things a woman can do to protect herself from breast cancer.

The paper points out that the use of CT scans has grown five-fold in the last two decades, and that a large and varied scientific literature shows that radiation, in the wavelength range that CT machines use, can cause cancer. At the same time, “thought leaders” in radiology—that is, the heavyweights at medical conferences—have been quoted as saying 30 percent or more of these scans may be unnecessary.

The paper is responding to an Institute of Medicine report concluding that a year’s worth of medical radiation exposure in the United States would result in 2,800 breast cancers. Two-thirds of those cancers can be linked to CT scans. While these represent a small fraction of total breast cancers (about 230,000 a year), they’re important because simply dialing back the use of scans might prevent them. Many other risk factors for breast cancer—age of puberty or number of pregnancies—simply can’t be controlled.

When you’re a cancer patient, most things come down to a “cost-benefit” analysis: Are the costs of a proposed test or treatment more, or less, than the benefits?

Think about all this the next time your doctor recommends a CT scan.  Here are some questions you might ask:

• Why is this CT scan necessary?

• Why does the scan need to be done right now?

• How will this scan change how my disease is managed?

This isn’t to say you should never get a CT scan. Just remember that the decision to get one shouldn’t be a reflex, but a measured decision.

Photo: Photodisc

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