Overexposed?

Considering the risks and benefits of radiation

A recent study in the New England Journal of Medicine (NEJM) suggests that millions of Americans may be exposed to moderate or higher levels of radiation each year through diagnostic medical imaging procedures. But there is at least some concern that people might forego necessary scans because they misinterpret the study’s findings.

Based on insurance claims data, the NEJM study found about 2 percent of test subjects received at least 20 milliSieverts (mSvs) of radiation from diagnostic medical imaging procedures every year.

“Even though that’s a small proportion, when you generalize it to the U.S. population, it translates to about 4 million people,” says lead author Reza Fazel, MD, MSc, assistant professor in the department of cardiology at Atlanta’s Emory University School of Medicine. “When you start talking about millions of people, those small risks start adding up over the population.” He adds that another point to note is that the study looked at “just a small slice in the life of these patients. This is just per-year. So many of those patients, over their lifetime, may be exposed to much higher doses.”

Fazel says the risk to individuals from procedures such as CTs or nuclear medicine is very small and outweighed by the benefits. “It’s really those situations where the tests are used without a clear reason or with a good indication, where this radiation becomes a concern, and it becomes one more reason that the study should not be done,” he adds. But the claims data relied on in the NEJM study do not contain information to tell whether procedures are being used appropriately. Fazel says, “That’s one of the limitations of the study.”

While not questioning the study’s findings, Shawn Farley, director of public affairs at the American College of Radiology in Reston, Va., cautions against drawing the wrong conclusions from them. “Our general outlook on it was not necessarily that there was something wrong with the study,” Farley says. But, he adds, the way the data was presented could create the impression that people might be exposed to high levels of radiation while undergoing imaging procedures under ordinary circumstances.

An Ongoing Issue

The study by Fazel and colleagues, “Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures,” in the Aug. 27 issue of NEJM, is the latest in a number of published reports over the last few years to look at Americans’ risk of radiation exposure from medical imaging procedures.

For instance, in November 2007, the NEJM published an article looking at the potential impact in increased CT usage. A report issued earlier this year by the National Council on Radiation Protection and Measurements (NCRP) in Bethesda, Md., identified medical imaging examinations as the primary cause of a nearly sevenfold increase in radiation exposure between the 1980s and 2006.

“There have been a lot of articles looking at the sort of rapidly increased utilization, rates of utilization of medical imaging over the past few decades in the U.S. across different modalities. And that’s actually one of the main reasons why radiation exposure has become sort of more of a concern over recent years, this increased use of imaging,” says Fazel.

He adds that the recent NEJM study confirms the findings published by the NCRP. “But we also looked at exposure within demographic subgroups by age and gender,” Fazel says. The study also examines what specific imaging procedures contribute the most radiation exposure in the U.S.
Among other things, the study found that 68.8 percent of the subjects underwent a procedure involving radiation over a three-year period. A sizable majority of individuals received at least moderate “effective doses” of radiation.

“Our finding that in some patients worrisome radiation doses from imaging procedures can accumulate over time underscores the need to improve their use,” the authors wrote.

Explaining the Study Method

The recent study in NEJM looked at UnitedHealthcare claims data for more than 950,000 nonelderly adults – ranging from 18 to 64 years in age – from the beginning of 2005 to the end of 2007. Women made up 52.4 percent of the subjects.

UnitedHealthcare administers medical benefits for 26 million people in the U.S. Whenever a procedure is done for a patient, a claim is submitted to the company. The claims in the study were from five markets: Arizona; Dallas; Orlando, Fla.; southern Florida; and Wisconsin. Fazel says the markets were selected based on size and geographic variation.

The study excluded procedures in which radiation was used for therapeutic purposes. During the study period, 655,613 subjects – 68.8 percent of the total – underwent a total of more than 3.4 million imaging procedures involving radiation exposure.

Fazel says, “So any claims that were submitted for individuals in that age group in those five markets were screened for procedures that involved exposure to radiation, and that let us basically get a sense of exactly how many of these procedures were done for each of these patients for that three-year period. Then, we used published estimates for the radiation doses for each one of these procedures to calculate what dose each one of those individuals got over that three-year period, and from what procedures. And so that allowed us basically to calculate what the average exposure to radiation was, and again, within different subgroups, by age and gender, and also which procedures contributed the most to radiation.”

The imaging procedures were divided into mutually exclusive categories according to the type of modality used and the anatomical focus. To approximate the radiation exposure from each procedure, the researchers relied on their typical effective doses. Fazel explains that the effect of a given amount of radiation on body organs depends on their sensitivity. The concept of effective dose is a measure of the biological harm based on how much energy is delivered to each individual organ.

“The main issue with the effective dose is that it’s a population average measure. It’s something that is averaged over age, gender, and it’s not a patient-specific dose,” Fazel says. “It’s not appropriate to apply this to individual patients.” He adds that effective dose is not a perfect concept and has limitations and flaws. “But it’s sort of the best we have. It’s the only measure that you can use to compare radiation doses across different types of modalities,” Fazel says. “It’s the only concept that we could use to do this type of study.”

“I don’t know that there’s any better option at this point,” agrees Farley. “Is it perfect? No. But I’m not aware that there’s anything that’s greatly improved on that.”

Key Findings and Limitations

Fazel says that one of the findings that caught the research team’s attention was the fact that nearly seven in 10 people in the study had at least one imaging procedure involving radiation. Even in the youngest age group (18- to 34-year-olds), half had had at least one such study. “That kind of reflects how much we’re using imaging in the U.S.,” Fazel says.

But the fact that two-thirds of the population underwent a scanning procedure should not be seen as a bad thing, according to Farley. “If you can get the same information from a scan that takes only a couple of minutes and is cheaper for everyone all the way around – for the facility, the doctor, the patient – that you used to have to do an invasive surgery to get the same information, and you can avoid the anesthesia risk or infection or long hospital stays, why would you not want to have those patients get that scan, rather than the more invasive procedure?” he asks.

That is not to say that unnecessary utilization does not take place. “But certainly, [with] the majority of the imaging that’s going on out there, we have no reason to doubt that the doctors think that this is the best thing for their patient,” Farley says.

Fazel says that the researchers do not want patients to become wary and afraid of getting necessary tests. But Farley characterizes the study as “basically a collection of statistics that are put out there for everyone to make their own judgment.” He recounts receiving a number of phone calls from elderly patients who were scared about getting imaging procedures because of news coverage of the study.

In the NEJM study, effective doses were categorized according to whether they were low (less than 3 mSv per year), moderate (from 3 mSv to 20 mSv),  high (from 20 mSv to 50 mSv per year), and very high (more than 50 mSv per year).

One of the study’s key findings, Fazel says, was that about 2 percent of the population is receiving 20 mSv or more of radiation every year. “The study verifies, confirms some things that we either knew or suspected, which is that a small portion of the people who are exposed to repeated radiological diagnostic and/or therapeutic procedures do receive higher radiation dose than we would otherwise like, but it’s a very small portion of those people, and I think the article by Fazel confirms that it is a small proportion,” says Philip O. Alderson, MD, who chairs the Oak Brook, Ill.-based Radiological Society of North America’s public information committee.

Fazel says that, because the study relied on data from the insured population, there may be a question about whether its findings can be generalized to the elderly or uninsured. Also, improvements in imaging technology may supersede the effective dose information relied on in the study.

Farley says there is no reason to doubt the numbers contained in the NEJM article, but one problem is that it did not make clear that patients experiencing the higher levels or radiation – especially over 20 mSV – were almost certainly individuals with cancer or some other chronic disease requiring multiple imaging examinations.

“For those kinds of patients, you’re talking about people whose doctors have made the assessment, no doubt, that the benefit of having those exams far outweighed any theoretical risk of long-term cancer coming from the imaging they received,” says Farley. “If the priority’s getting this patient to their next birthday, having cancer theoretically develop three decades down the road is probably judged to be less of a risk than the immediate circumstance.”

Fazel responds that looking at the group receiving the highest doses of radiation will be one of the follow-up projects for the study. “You can’t include all of the study in one publication, because there are space limitations,” he adds.

The other issue, according to Fazel, is that the study found that “about 80 percent of the radiation exposure was in the outpatient setting, which argues that these are probably not critically ill patients.”

A press release from the ACR references the study’s finding about the percentage of administered dose occurring outside of hospitals. “Most of the scans explored in the study were performed by nonradiologist providers that self-referred patients to their own imaging equipment. Studies have shown that when providers can refer patients to their own scanners or those in which they have a financial interest, imaging is greatly increased. Many of the providers have little to no imaging or radiation safety training. Knowledge of the correct use of these technologies is not universal,” the release says.

Farley says that radiologists’ education and training are important factors in making sure imaging examinations are utilized properly and that radiation dosages are at appropriate levels. “That’s another factor that should really be discussed when talking about the New England Journal of Medicine article,” Farley says. “We’re not blaming [Fazel] for not necessarily explaining that, but it just goes back to the fact that this study was basically a snapshot, and there wasn’t much explanation or much context of the stuff therein, so that’s what we’re trying to provide.”

Taking Protective Steps

Alderson says the fundamental thing people need to keep in mind about studies like Fazel’s is risk-benefit ratios. “What is the risk of having that CT scan versus what’s the benefit of having that CT scan? And, I don’t think there’s any question in the literature that the ratio is much, much higher on benefit than it is on risk,” he says. “Is there a very small statistical risk associated with this exposure to radiation, especially if you are one of the very small group of people who get many, many of these? The answer is, ‘Yes, there is.’ And I think the article by Fazel attempts to point that out. But the fact is when you do the ratio of the benefit to that risk, there isn’t any question which side to come down on.”

Fazel says there are a number of things that can be done in light of the study’s findings.

Physicians need to take radiation into consideration when determining what tests should be used for patients. “When it’s clear that a patient does need a test, there are often options where the same result can be achieved with alternative tests that don’t involve radiation, like using ultrasonography or MRIs, and [we should] think about those possibilities, at least,” says Fazel. He also stresses the importance of promoting research to better clarify when tests can be helpful. Additionally, technological improvements can provide equal or better imaging with much smaller radiation doses.

“And then, finally, for patients, I think it’s important, whenever your physician is suggesting or recommending a test be done, just to have a frank discussion with your physician to make sure you understand why the test is being done and how it can help you,” Fazel says.

According to Farley, the ACR recommends that patients ask questions about why they need an examination, how the procedure will improve their healthcare, whether there are equally effective alternatives that do not use radiation, and if the facility is ACR-accredited.

Farley says the ACR has also been involved in a number of initiatives to address radiation exposure. It was one of the four founding members of the Image Gently program, which seeks to lower pediatric radiation dosage.

Farley says the ACR has also developed a White Paper on Radiation Dose in Medicine, identifying 33 steps for reducing the radiation dose from imaging. The ACR also promotes the ALARA (As Low As Reasonably Achievable) concept, to encourage radiologists and other providers to work with their medical physicists in making sure that the lowest amount of radiation is used in order to obtain optimal images. Appropriateness criteria developed by the ACR ranks the most appropriate imaging exam, if any, for more than 200 clinical conditions.

Farley says the ACR is also promoting the TRIAD™ program, currently undergoing testing in Texas and Wyoming, which would reduce radiation exposure by serving as a system through which scanning images and information could be shared between facilities regardless of the equipment or PACS they use. For instance, with such a system, Farley says, if someone is brought into an emergency room, the doctor would be able to bring up their imaging history and know whether it may be appropriate to order a CT scan.

“This isn’t a long-term outlook. We’re talking shorter-term, where you could see a big, big change in how radiology is done in the short term because of this,” Farley says.

Alderson says the RSNA plans to make educational materials and programs about radiation safety available to radiologists and people in the radiation sciences. Additionally, the organization will conduct public outreach, such as through radio spots. “So the RSNA is going to try to do its best to bring good information to patients and to the public about this issue,” Alderson says.

Part of the issue, he adds, is that radiologists do not see patients when they first present themselves. “The examination is ordered by usually a physician of another type – a general medical physician, a surgeon, an internist, and so on – and those doctors don’t necessarily have the same knowledge of the relative risk-benefit ratios as the radiologists do. They just know that they get an excellent answer that allows them to make a decision that changes patient management, and they want that help. And so they order them. So, systems have to be set up to keep track of the radiation exposures,” says Alderson.

Following up on the Study

Fazel says the study raised a number of issues that are worthy of further attention.

One such finding was that women on average received higher doses of radiation from imaging procedures than men. Mammography explained some, but not all, of the gap. “So one thing we’re looking into is what other procedures are leading to women getting more radiation exposure as compared to men,” Fazel says.

Another issue is to look at the temporal trend in exposure among different demographic groups and imaging modalities over the three-year period.

Also, Fazel says, the study steered clear of any extrapolations from how the radiation exposures from imaging would affect cancer risk. “It involves sort of a detailed analysis for each one of these procedures,” he says. “You have to figure out exactly what dose is delivered to every specific organ in the body and then translate that to a potential cancer risk and then add those up. So that’s something else we’re looking at right now, is trying to get a sense of what these exposures translate to in terms of cancer risk.”

– Mark D. Marotta is associate editor of rt image. Direct all questions and comments to editorial@rt-image.com.