CT Scans Can Cut Lung Cancer Deaths by 20 Percent, Study Shows
Heavy and former smokers who get annual CT scans rather than chest X-rays have a lower risk of dying from lung cancer, according to a large study released Thursday. National Cancer Institute researchers examined 53,500 men and women between the ages of 55 and 74 who smoked for at least 30 "pack years"—such as a pack a day for 30 years or two packs a day for 15 years, the Washington Post reports. Participants either received three annual CT scans—which may detect cancer at an earlier stage—or three standard X-rays. By Oct. 20, 2010, 442 people who received X-rays died of lung cancer versus 354 people in the CT group, a difference of roughly 20 percent. Officials halted the $250 million study earlier than planned, given such clear results. "Lung cancer is the leading cause of cancer mortality in the U.S. and throughout the world, so a validated approach that can reduce lung cancer mortality by even 20 percent has the potential to spare very significant numbers of people from the ravages of this disease," Harold Varmus, NCI's director, told the Post. The findings were published in the journal Radiology.
The verdict is still out, though, on whether the benefits of CT scans trump the risks that come with the much-increased radiation they deliver compared to X-rays, researchers say.
In November 2007, U.S. News spoke with Fred Mettler, chief of radiology and nuclear medicine at New Mexico Veterans Health Care System, on whether opting for a CT scan is a wise move.
Q: How is a CT scan different from a traditional X-ray?
A: With a traditional X-ray—a chest X-ray, for example—radiation goes through you from one side to the other, with 3-D information ultimately projected onto a two-dimensional picture. With a CT scan, an X-ray tube rotates around the patient and presents the results to you as a three-dimensional picture. The advantage is that it's much more sensitive, is high resolution, and offers much more anatomically specific information with great detail.
But a typical chest CT means around a 175-times-greater dose of radiation than a similar chest X-ray—that's like 20 sets of mammograms. That range can be between 20 and 200 times higher depending on which part of the body is being scanned.
Q: What are the risks involved in CT scanning?
A: Certainly a CT scan won't make your hair fall out or anything so drastic. But the risk of cancer is there, and it depends on a few things. There's the dose of the radiation, which depends substantially on the age of the patient. We know that kids are more sensitive and their risk of getting cancer is higher [when they are given] an adult dose. But these cancers tend not to occur for years or decades at least. For children, the risk of developing a fatal cancer is somewhere around 1 in 500 or 1 in 1,000—the older you get, the lower the risk becomes. So if someone is 90, for instance, there is virtually no cancer risk. For an adult, the risk is around 1 in 2,000.
At this point, people believe there is [a] linear relationship between the dose and the risk of cancer. So if you cut the dose in half, you also cut the risk in half. The question should be, can you optimize the dose by using a lower amount of radiation or can the scan be done only once instead of three times?
Q: What are some alternatives to CT scanning that patients should know about or ask their doctors?
A: I would ask if there are ways we can find out the answer without using radiation. Using ultrasound, for example, or doing an MRI scan. Those don't use ionizing radiation, so there is virtually no risk. And if the scan is definitely going to be done, ask about the dose you will be getting.
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