Widespread overuse of CT scans and variations in radiation doses caused by different machines and different operators are subjecting patients to high radiation doses that will lead to tens of thousands of new cancer cases and as many as 15,000 deaths for each year that the scanners are used, researchers reported this week.
Several recent studies have suggested that patients have been unnecessarily exposed to radiation from CTs or have received excessive amounts, but two studies reported in the Archives of Internal Medicine are the first to quantify the extent of exposure and the related risks.
In one study, researchers from the University of California-San Francisco found that the same imaging procedure performed at different institutions — or even on different machines at the same hospital — can yield a 13-fold difference in radiation dose, potentially exposing some patients to inordinately high risk.
While a normal CT scan of the chest is the equivalent of about 100 chest X-rays, the team found that some scanners were giving the equivalent of 440 conventional X-rays. The absolute risk may be small for any single patient, but the sheer number of CT scans — more than 70 million per year, 23 times the number in 1980 — will produce a sharp increase in cancers and deaths, experts said.
“The articles in this issue make clear that there is far more radiation from medical CT scans than has been recognized previously,” wrote Dr. Rita Redberg of UCSF, editor of the journal, in an editorial accompanying the reports.
Even many otherwise healthy patients are being subjected to the radiation, she said, because emergency rooms are often sending patients to the CT scanner before they see a doctor.
Whole-body scans of healthy patients looking for hidden tumors or other illnesses are also becoming more common, even though they rarely find anything wrong. The irony is that, by exposing healthy people to radiation, they may be creating more problems than they solve.
CT scans, short for “computed tomography,” provide exceptionally clear views of internal organs by combining data from multiple X-ray images. But the price for that clarity is increasing exposure to X-rays, which cause mutations in DNA that can lead to cancer.
Scanner manufacturers are designing new instruments that use lower doses of radiation, but many older machines rely on higher doses. Machine settings for particular procedures, furthermore, are not standardized, and individual radiologists use the technology differently in different patients, leading to variance in doses delivered to the subjects.
The highest doses of radiation are routinely used for coronary angiography, in which cardiologists image the heart and its major blood vessels to look for blockages or other abnormalities.
Using normal dosages of radiation for the procedure, about 1 in 270 women who receive it at age 40 and 1 in 600 men of the same age will develop cancer down the line as a result, reported Dr. Rebecca Smith-Bindman, a professor of radiology and epidemiology at UCSF, and her colleagues.
For a routine head scan, 1 in 8,100 women and 1 in 11,080 men will develop a tumor.
“For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50 percent lower,” according to the report.
“This study is being taken very seriously by radiologists,” said Dr. Alex Megibow, a professor of radiology at New York University’s Langone Medical Center, in a statement.
He cautioned that careless use of scanners can lead to high doses of radiation but argued that, with proper use, “the benefits of a CT scan far outweigh the risks.”
In a separate paper, epidemiologist Amy Berrington de Gonzales and her colleagues at the National Cancer Institute constructed a computer program to estimate the risks associated with CT scans.
They concluded that about 29,000 future cancers could be related to CT scans performed in the United States in 2007 alone.
That includes 14,000 cases resulting from scans of the abdomen and pelvis, 4,100 from chest scans and 2,700 from heart scans.
