CT Radiation Dose on the Table
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.
E. 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 study1 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 report2 in the Los Angeles Times. Moreover, a pair of studies3,4 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 with high-quality pictures,” he says. “There is software available you can add on for dose reductions in some protocols,” even using existing scanners. He notes that the new low-dose CT scanners are expensive (costing as much as $700,000 more than a standard system, bringing the total outlay to around $2 million), making it too expensive for many providers to install new scanners. What’s needed, he says, is a broad-based educational push accompanied by usage guidelines to hold down overexposure using existing technology. Overutilization According to the Los Angeles Times article,2 the number of CT scans done in the United States has grown from about 3 million in 1983 to more than 70 million now. Few people dispute that there is overutilization of CT today, but there is less agreement when it comes to identifying the causes. Some think that self-referral by nonradiologist physicians who own CT scanners is the major culprit. Others blame defensive medicine occasioned by the threat of lawsuits. Still others blame emergency-department physicians for a knee-jerk reliance on CT scans to get patients processed and out the door. Amis sees all three factors at work. He is a member of the National Council on Radiation Protection & Measurements (NCRP), which is working with the ACR and the American College of Emergency Physicians to develop consensus guidelines for the use of CT in emergency departments. The NCRP was chartered by Congress in 1964 to monitor radiation exposure, but its focus on CT in the emergency department is new, Amis says. He reports that at a 2009 meeting, emergency-department physicians argued that, with a legal requirement to diagnose each patient, they were under pressure to rely on CT exams, which are fast and accurate. “We said, ‘We understand, but why not develop consensus CT guidelines for common conditions where CT is used frequently?’ They’ve agreed to do this. Whether anybody will adhere to them or not, I haven’t a clue,” Amis says. Amis says that self-referral by nonradiologists with CT scanners in their offices does contribute to overutilization directly through the profit motive, but he says that self-referral is only one factor in the growth of CT. As for tort reform—designed to control lawsuits against physicians, who may defend themselves from liability by relying excessively on CT studies—action is unlikely with Democrats controlling congress. “Tort reform has always been a Republican initiative,” Amis adds. Limiting Exposure What can be done to limit excessive radiation exposure from CT exams? Many things could help, beginning with radiology departments or clinics getting their own houses in order, Amis says. At MMC, he adds, reducing CT radiation exposure has become “a mantra” for technologists, radiologists, and medical physicists (who are involved to ensure that CT scanners are properly programmed and emitting the called-for amounts of radiation). The radiology staff also works with referrers and emergency physicians to hold down patient exposure. Amis uses the example of diagnosing a pulmonary embolism. He says, “A patient comes in; she’s a 20–year-old woman with pleuritic chest pain. She’s on the birth control pill, and you want to make sure she’s not having a pulmonary embolism. We do a plain chest radiograph first, which uses a hundredth of the dose of CT. If that’s normal, we do a nuclear-medicine ventilation-perfusion scan, which uses much less radiation than going straight to a CT pulmonary arteriogram. That’s the understanding we have with our emergency-department physicians here: If the chest radiograph is abnormal, we go ahead with the CT pulmonary angiogram. It’s an algorithm that puts patients in a different pathway.” Amis says that patients who suffer from recurrent kidney stones also have to be watched so that they don’t undergo successive CT exams. One of MMC’s endeavors, which other hospitals are also pursuing, involves creating a database that tracks the radiation exposure of patients as they undergo various imaging studies. “I think that’s the best way we can go,” Amis says. He cautions, however, that such automated tracking (with a pop-up warning for overexposure) is difficult to implement. MMC is still years away from marrying its clinical database with a physician order entry system that will display the exposure warnings. “It sounds easy,” he says. “It’s not.” In the meantime, Amis says that referring physicians should have the dangers of CT radiation overexposure explained to them to the point that they automatically make risk–benefit calculations before ordering CT exams. Radiologists can also help by defining adequate CT studies that use less radiation but get the job done—even if they are “less pretty,” Amis adds. Technologists should be trained to adjust CT radiation exposure based on patient weight, as is already done routinely for pediatric CT studies. Image Wisely In January 2008, the ACR, the American Society of Radiologic Technologists, the Society for Pediatric Radiology, and other founding members launched the Alliance for Radiation Safety in Pediatric Imaging. The goal of the alliance is to hold down radiation exposure in children. Through its Image Gently program, the alliance has been credited with educating referrers on the use of pediatric CT. Now, Amis says, the ACR and RSNA have launched a task force to get the same message out with regard to CT imaging for adults. Called the ACR/RSNA Task Force on Adult Radiation Protection, it will institute an Image Wisely campaign to educate radiologists, technologists, referrers, and patients on the risks of radiation exposure from CT scans. Amis is cochair of the task force, which is still in the formative stages; he says that the campaign will begin with radiology providers and work outward to referrers and patients. “Patients often expect a CT,” he says. “We need to get beyond that and the opposite extreme. There has to be a happy medium somewhere in the middle.” Amis also recommends that CT providers have their systems accredited by the ACR, ensuring that the scanners are properly calibrated and decreasing the risk of overexposure because of faulty settings. “It’s like a Good Housekeeping stamp of approval on your machine,” he says. George Wiley is a contributing writer for ImagingBiz.com.