CT Radiation Dose on the Table

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Long a point of concern in Europe, radiation dose has emerged as a key point of consideration for pediatric radiologists in the United States, particularly with the development of multidetector CT. Recent headlines, however, have broadened the issue. Patients, referrers, hospital and radiology-department administrators, and CT equipment vendors are all looking for ways to minimize the radiation delivered during one or a series of CT exams.

imageE. Stephen Amis Jr., MD, FACR

“You can’t pick up a journal, whether for radiology or not, without an article about the radiation dose of CT,” according to E. Stephen Amis Jr, MD, FACR. “It’s the topic du jour.” Amis knows the landscape. He is the former chair of an ACR® Blue Ribbon Panel on Radiation Dose in Medicine and the current cochair of the Task Force on Adult Radiation Protection sponsored by the ACR and the RSNA. He also deals with CT radiation exposure on the day-to-day level.

Amis is professor and chair of the radiology department at the Albert Einstein College of Medicine and its teaching hospital, Montefiore Medical Center (MMC), in the Bronx, New York. As department chair, Amis is accountable if CT radiation-exposure levels aren’t monitored. He routinely counsels MMC’s medical staff on limiting exposure, he says.

The current consternation over CT radiation began in 2007, when the New England Journal of Medicine published a study 1 concluding that patients were being exposed to excessive and unnecessary radiation through CT scanning. Cedars–Sinai Medical Center in Los Angeles, California, sent fresh shock waves through the medical imaging community in October 2009, when it admitted that over a period of 18 months, 206 patients undergoing brain-perfusion scans had received eight times the normal dose of radiation from mistakenly programmed CT units. The excessive radiation doses resulted in a class-action lawsuit.

“When I saw that suit at Cedars–Sinai,” Amis says, “the first thing I did was say, ‘Check all our machines,’ although we rarely do that study. We did, and everything was fine.” MMC was more careful than some. Since the Cedars–Sinai exposures, at least three other hospitals—two in California and one in Alabama—have initiated investigations into apparent overexposures involving CT radiation, according to a report 2 in the Los Angeles Times. Moreover, a pair of studies 3,4 published in December 2009 in the Archives of Internal Medicine estimate that as many as 29,000 patients nationwide could develop cancers from CT-scan radiation, and that 14,500 of them could die as a result.

Amis says that the 14,500 figure could be accurate. He notes that several research teams have come up with estimates of CT-induced cancer cases in the 29,000 range, and it’s not unreasonable to estimate that half of those patients could die. “The problem with that,” he notes, “is there’s absolutely no way to prove, for any given cancer, whether it is radiation induced or it just arose by itself. If you look under the microscope, there are no markers that say one way or the other, so the whole thing is based on projections, on models, and on guesses based on data from the atomic bombings back in 1945.”

A Public Health Issue

Because individual cancers can’t be blamed on CT, Amis says, the problem of overexposure demands widespread attention. “I think the risk is real, but if you take the individual patient who is having a CT scan, ionizing radiation is an incredibly low-risk carcinogen. The benefit is almost always going to outweigh the risk in the individual patient,” Amis says, “but when you’re looking at a 300-million population base and 72 million CT scans a year, then you do have to worry about 28,000 or 29,000 new cancers. It becomes a public health issue.”

The recent overexposure cases reported in California and Alabama all involved CT brain-perfusion scans. Even at the proper setting, Amis notes, a CT brain-perfusion scan requires a significant radiation dose. “A lot of people don’t use that exam much because of the high exposure. We almost never use it. We almost always use MRI,” he says.

There is significant variation in how different institutions and physicians use CT. As Amis says, “There is a lack of uniformity—a lack of standardization—in the whole enterprise, across the United States.”

On the positive side, he adds, the recent headlines have caught the attention of the CT community. “All the manufacturers are working hard to produce significantly reduced doses