December 14, 2009
CT Scans Boost Cancer Rate

Think twice before getting a CT scan.

Doses of radiation from commonly performed computed tomography (CT) scans vary widely, appear higher than generally believed and may contribute to an estimated tens of thousands of future cancer cases, according to two reports in the December 14/28 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

CT scans have become increasingly common in the United States—about 70 million were performed in 2007, up from 3 million in 1980, according to background information in one of the articles. "While CT scans can provide great medical benefits, there is concern about potential future cancer risks because they involve much higher radiation doses than conventional diagnostic X-rays," the authors of one report write. For example, a chest CT scan exposes the patient to more than 100 times the radiation dose of a routine chest X-ray. "The risks to individuals are likely to be small, but because of the large number of persons exposed annually, even small risks could translate into a considerable number of future cancers."

I've come across marketing literature promoting CT scans as valuable for early detection screening for cancer and other diseases. For the vast majority of the population CT scans for seemingly healthy people seem like an unnecessary risk.

Here are some odds of cancer from CT scans.

The estimated number of CT scans that would lead to the development of one cancer case also varied by type of CT scan and also by each patient's age and sex. For instance, an estimated one in 270 women and one in 600 men who undergo CT coronary angiography (a heart scan) at age 40 will develop cancer as a result. One cancer case will likely occur among every 8,100 women and 11,080 men who had a routine head CT scan at the same age. "For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50 percent lower," the authors write.

When you are older you have fewer years to live due to other reasons. So radiation can zap some cell and kick it on the long road toward cancer and yet you might die from a heart attack or stroke before abnormal cells can accumulate enough additional mutations to become malignant.

Those 70 million CT scans per year in the United States might cause 29,000 future cancers per year. That's a very high number.

"Overall, we estimated that approximately 29,000 future cancers could be related to CT scans performed in the U.S. in 2007," the authors write. This includes an estimated 14,000 cases resulting from scans of the abdomen and pelvis; 4,100 from chest scans; 4,000 from head scans; and 2,700 from CT angiography. One-third of these projected cancer cases would occur following scans performed on individuals age 35 to 54 years, compared with 15 percent due to scans performed in children and teens. Two-thirds of the cancers would be in women.

To put that in perspective, about 1.4 million people get diagnosed with cancer per year in the United States and about 564 thousand die from cancer. So if this estimate about CT scans causing cancer is correct then CT scans are increasing the rate of cancer by slightly more than 2%.

Share |      Randall Parker, 2009 December 14 08:06 PM  Aging Cancer Studies

John Moore said at December 14, 2009 8:32 PM:

The cancer risk models are based on the pretty well debunked linear-dose/no-threshold theory. This holds that the cancer risk from radiation is linearly related to the level of radiation, from very high doses (100REM/year) to very low doses (50 mREM/year).

This is the formula that gave us the bogus forecasts of huge excess deaths from Chernobyl, which haven't materialized.

The formula is a result of few examples, almost all with high (but not well known) radiation doses.

It is now well known that cells have the ability to repair genetic damage, and also have aptosis mechanisms that often come into play if the damage is too much.

Examination of genetic material from animals living right next to the Chernobyl plant show much lower than expected effects, with most animals having no detectable effect. The area around the plant is now a wildlife mecca.

Statistical evidence for radiation risks from low doses is, AFAIK, nonexistent.

Note, btw, that a lot of the damage predicted from coal emissions is a result of the radioactivity released in them. If the linear theory is wrong, then those risks are much lower.

PacRim Jim said at December 16, 2009 12:38 AM:

The scans undoubtedly save more than this number, by detecting hidden cancers.

Randall Parker said at December 16, 2009 9:33 PM:

PacRim Jim,

People who are 20, 30, 40, 50 are very unlikely to have hidden cancers that are growing.

Your body contains many small cancers that haven't mutated the ability to induce angiogenesis (new blood vesel growth). But I doubt the CT scans can find them.

Charla said at February 24, 2010 10:37 PM:

I was recently diagnosed with Chronic Myelogenous Leukemia, AKA, Chronic Myeloid Leukemia, with a WBC of 381,000. It is estimated by the oncologist-hematologist who is working with me that it had been progressing for 2-3 years at the time of diagnosis in early Feb. 2010. In studying the causes of this rare leukemia, I was at a loss to explain any high level of radiation exposure, toxic chemical exposure or aflatoxin consumption (I don't eat peanuts). Then I remembered an auto accident in June 2007 where I got glass in my eye. The attending MD at the hospital insisted that I have a CAT scan that night rather than just letting an ophthalmologist look at my eyes the next morning. I will never be able to prove that this was the cause of this leukemia, but it is certainly a possibility.

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