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|