CT scans and radiation exposure: Exactly how much is too much?
CT scans and radiation exposure: Exactly how much is too much?
Controversial findings prompt new debate and calls for safeguards
There is no denying that the use of CT scans has increased dramatically since CT was first introduced in the 1970s. According to some estimates, the number of CT scans performed in the United States has grown from 3 million per year in 1980 to more than 62 million per year today, as the technology has become increasingly available and easy to use.1
However, with new concerns being raised about the risks associated with radiation from CT scans, debate is brewing among imaging professionals and other clinicians about whether CT scans are being used appropriately in all settings and whether there are times when safer imaging alternatives, such as ultrasound, would be a better option.
Much of the current discussion regarding radiation exposure from CT scans stems from a review article by David Brenner, PhD, DSc, and Eric Hall, DPhil, DSc, both from the Center for Radiological Research at Columbia University Medical Center in New York City, published in The New England Journal of Medicine.1 Relying largely on studies of survivors of the atomic bombs that were dropped on Japan in 1945, Brenner and Hall note that there was a significant increase in the overall risk of cancer in a subgroup of survivors who received low doses of radiation that are comparable to the doses of radiation associated with a typical CT study, involving two or three scans in an adult patient (about 40 mSv).
Brenner and Hall acknowledge that while the risk of developing cancer from a single CT scan is small, they nonetheless argue that clinicians need to consider the risks associated with repeated scans over a lifetime, and they are particularly concerned about the growing use of CT scans in asymptomatic patients and in children. Children are at greater risk because they are more sensitive to radiation and because they have more years ahead of them in which radiation-induced cancer could develop, they say.
Many organizations, such as the American College of Radiology (ACR), question the validity of comparing the radiation exposure received by atomic bomb survivors to that received by people undergoing CT scans of particular organs under controlled circumstances. Nonetheless, there is wide agreement that clinicians and imaging centers should be careful to only use CT scans when medically necessary and to always use the lowest recommended dose of radiation.
Consider the safest imaging procedure
Image Gently Alliance American Academy of Pediatrics |
Further, given that the issue is of particular concern with respect to young adults and children, the Alliance for Radiation Safety in Pediatric Imaging has unveiled a new campaign, dubbed Image Gently, designed to ensure that clinicians are aware of the enhanced risks posed by radiation exposure to children and that they follow established guidelines when ordering CT studies. (See members of campaign, left.)
The alliance points out that there were four million CT scans conducted on children in the United States in 2006 and that the number of pediatric CT scans has tripled in the last five years. Consequently, through its web site, the alliance is making available guidelines and protocols pertaining to CT scanning in children, and it is publishing recommended dosing-reduction formulas to ensure that imaging centers appropriately "child size" the amount of radiation used when a CT scan is deemed medically necessary.
Donald Frush, MD, chair of the ACR Pediatric Imaging Commission, says, "I don't think we have a firm grasp on whether CT scans are overused or abused in a way that everybody would agree on." Consequently, he stresses that the campaign is an effort to disseminate best-practice information so that clinicians and imaging programs will, at least, begin to use appropriate techniques. "Any time a study is expected or anticipated, one should think about the safest way to [carry it out], and that would probably be ultrasound in a pediatric population," says Frush, noting that radiation is not an issue with MR either. "But if it is not a situation where those [modalities] are likely going to give adequate information, and CT is the indicated examination, then people need to go to CT."
Frush acknowledges that there are several factors that are driving the use of CT scanning devices.
"It is an easy study to get. There are a lot of scanners around. And it is a very fast examination," says Frush, noting that children don't have to be sedated. Further, he points out that it is much easier to get a CT through an emergency department than it is to get an MRI examination.
Nonetheless, safety needs to be a primary concern, and Frush emphasizes that radiologists should serve as expert consultants to clinicians in recommending what is going to be the best examination in a particular circumstance.
"That communication needs to be encouraged and cultivated," he says. "The radiologist needs to talk with clinicians about how specific examinations are done, and what they are good for too, and that comes from individual discussions with referring pediatricians, internists, and ER physicians."
In response to concerns about radiation exposure, the American Society of Radiologic Technologists (ASRT) sent an email message to all members who are involved with CT that informed them of the Image Gently campaign and asked them to visit the campaign's web site. In addition, the CT division of ASRT is considering development of a pediatric CT practice position statement for deliberation by the organization's house of delegates in June 2008.
Consider the risks and benefits
While radiologists are in wide agreement that CT scans should be used only when indicated, they point out that there are other pressures in the medical environment encouraging them to order tests.
Kieran Murphy, a professor of radiology at Johns Hopkins Medical School in Baltimore, MD, says, "We are pushed on all sides." In the current medical-legal environment, physicians are getting sued, so they order studies, Murphy says. "There is a huge demand to diagnose what is wrong with the patient at the time of entry to the ER, and Medicare is going to make that the point that determines how the patient is billed from then on, so the patient is going to be studied with more CT."
Despite these pressures, there is anecdotal evidence that the concerns about radiation exposure, raised most recently by Brenner and Hall, are having the effect of prompting at least some clinicians to put more thought into the overall risks and benefits of ordering CT scans, according to John Boone, PhD, chairman of the American Association of Physicists in Medicine (AAPM) and a radiology professor of biomedical engineering at the University of California Davis Medical School in Sacramento.
"It has provoked a healthy and useful discussion that has brought the CT utilization issue to the attention of referring physicians and their patients," says Boone. However, he emphasizes that the article focused almost solely on the risks associated with CT scans, and he echoes the sentiments of many in the radiologist community by pointing out that the benefits of undergoing a CT exam need to be considered as well.
"Referring physicians and radiologists need to consider the benefit/risk trade-off when a CT study is being ordered or performed, and as with all medical tests, a CT exam has risks and benefits, and both need to be considered before the exam is performed."
Reference
- Brenner D, Hall E. Computed tomography — An increasing source of radiation exposure. N Eng J Med 2007; 357:2,277-2,284.
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