By David Gutierrez
Although the use of computed tomography (CT) scans has become increasingly common, there is no reliable evidence that such scans are safe, according to a paper recently published in the journal Radiology.
“The number of CT exams in the U.S. has increased by about 10 percent each year over the past decade,” said lead author John Boone, of the University of California-Davis. “This trend underscores the importance of developing a better understanding of the health risks of radiation exposure versus the benefits of enhanced diagnosis.”
The article summarized the recommendations of the 20111 Radiation Dose Summit, which was organized in response to growing concern from medical professionals and the public about overexposure to radiation from CT scans. The summit’s participants, including more than 100 radiologists, cardiologists, medical physicists, engineers, patient advocates and industry representatives, called for more safety research and issued recommendations on ways to reduce patients’ radiation exposure.
Too much radiation, not enough data
The experts noted that few, if any, studies have directly examined the cumulative, lifelong effects of small, occasional doses of radiation delivered to specific areas of the body. Instead, safety standards for CT scans are based on studies of people exposed to single, large, whole-body doses of radiation – such as from industrial accidents or nuclear bombs.
“We don’t know whether the established thresholds are really meaningful for exposure from medical testing,” Boone said.
Unfortunately, collecting such data can be difficult. For one thing, even when CT devices deliver a standardized dose of radiation, the effective dose received by the patient can vary dramatically based on factors such as body size. And even if researchers can get an accurate picture of how much radiation a patient receives, cancer rates are so high that it can be difficult to pick out the influence of any one risk factor.
What is clear; however, is that some patients are getting too much radiation. A major cause of this is “wasteful imaging,” when a doctor orders a CT scan that will be of limited medical value. This can occur because a doctor is unaware that such a test has already been performed, or because doctors simply want to err on the side of caution – either for medical reasons, or to avoid the risk of a lawsuit for negligence. To reduce such problems, the experts recommend the development of a national radiation exposure registry and standardized testing protocols.
Another factor leading to overexposure is non-standard device construction, which dramatically increases the risk of accidents.
“For some scanners, you turn a dial to the right to get a larger dose, and for others, turning it the same way gives a smaller dose,” said Boone. “There are so many differences in current CT scanners, it can be like driving a car with the brake pedal on the left in the morning, then with the brake on the right in the afternoon.”
Like cars, the experts said, CT devices should all be built on a single, basic design.