RSNA, ACR respond to NEJM study: CT could cause 2% of U.S cancers

CT heart scan. Source: Toshiba

CT scans could be responsible for as much as 2 percent of all cancers in the United States in the next 20 to 30 years due the radiation exposure, according to a study conducted at the Columbia University Medical Center in New York City and published in the New England Journal of Medicine (NEJM). The news was the “buzz” yesterday at the 93rd annual meeting of the Radiological Society of North America (RSNA) in Chicago, as well as on national and local TV news programs, and in newsletters and blogs. A response from the American College of Cardiology was unavailable prior to deadline.

Authors David Brenner, PhD, DSc, and Eric J. Hall, DPhil, DSc, discussed the growth in the use of CT and the increase in patient radiation exposure as a result. “It is estimated that more than 62 million CT scans are currently obtained each year in the United States, as compared with about 3 million in 1980,” they wrote.

RSNA responded to the article, saying it “is important that one of the salient points from the authors is not overlooked, that ‘from an individual standpoint, when a CT scan is justified by medical need, the associated risk is small relative to the diagnostic information obtained.’” The article was released amidst RSNA’s annual meeting in Chicago, and the organization emphasized that there “is overwhelming agreement in the radiology community that there is risk with CT, but that the potential benefits far outweigh this small risk.”

Brenner and Hall also compare the effects of CT scans with the effects of the atomic bomb survivors in Japan, which the ACR believes is an inappropriate comparison. According the ACR, “CT exams are performed in a controlled setting. They result in limited radiation exposure to a small portion of the body. Atomic bomb survivors experienced instantaneous radiation exposure to the whole body.” 

“Patients need accurate information on which to base their healthcare decisions,” said Arl Van Moore Jr., MD, FACR, chair of the ACR Board of Chancellors. “They may be terribly confused and unduly distressed by some of the statements in this study,”

In summary, the authors said that “there is direct evidence from epidemiologic studies that the organ doses corresponding to a common CT study (two or three scans, resulting in a dose in the range of 30 to 90 mSv) result in an increased risk of cancer. The evidence is reasonably convincing for adults and very convincing for children.”

Brenner and Hall also said that the greatest risks are pediatric cases: “The situation is even clearer for children, who are at greater risk than adults from a given dose of radiation, both because they are inherently more radiosensitive and because they have more remaining years of life during which a radiation-induced cancer could develop.” They also estimated that the “the proportion of CT studies that are currently performed in children range between 6 percent and 11 percent.”

In their response, the ACR acknowledged the potential risks associated with the radiation exposure in CT, but stressed that there are currently preventative precautions in place. For example Moore said the organization “has long opposed full body CT scans for asymptomatic patients, one of the exams that the NEJM article authors put forth as a driver of future CT growth. We also support the as low as reasonably achievable concept which urges providers to use the minimum level of radiation needed in such exams to achieve the necessary results.” 

In their final summary, Brenner and Hall suggest three steps to reduce the radiation risk to the overall population:

• Reduce the CT-related dose in individual patients. “The automatic exposure-control option on the latest generation of scanners is helping to address this concern,” according to the Brenner and Hall.
• Replace CT, “when practical,” with other options, such as MRI.
• Decrease the number of CT studies that are prescribed, which they describe as the “most effective” method of reducing risk.

Brenner and Hall concluded that “when a CT scan is justified by medical need, the associated risk is small relative to the diagnostic information obtained. However, if it is true that about one third of all CT scans are not justified by medical need, and it appears to be likely, perhaps 20 million adults and, crucially, more than one million children per year in the United States are being irradiated unnecessarily.”

The study was funded by the National Cancer Institute, the National Institute of Allergy and Infectious Diseases, and the Department of Energy Low Dose Radiation Research Program.