Imaging dose again comes under fire in New England Journal of Medicine

August 27, 2009

Nonelderly adults are exposed to excessive doses of radiation from medical imaging procedures for which clinical data are lacking, according to reports published today in the New England Journal of Medicine. Radiologists and others familiar with the reports, including the American College of Radiology, cautioned against giving them too much credence.

Nonelderly adults are exposed to excessive doses of radiation from medical imaging procedures for which clinical data are lacking, according to reports published today in the New England Journal of Medicine. Radiologists and others familiar with the reports, including the American College of Radiology, cautioned against giving them too much credence.

A retrospective cohort study covered more than 655,000 patients younger than 65 years and found a majority underwent at least one imaging procedure, some of them at doses exceeding 50 mSv per year.

An editorial accompanying the study took particular aim at cardiac and myocardial perfusion imaging.

No large-scale, randomized trials have shown imaging for patients with heart disease prolongs life, improves quality of life, prevents major clinical events, or reduces long-term medical costs, said Dr. Michael S. Lauer, director of the division of prevention and population science at the National Heart, Lung, and Blood Institute, which is a part of the National Institutes of Health.

Of 655,613 adults aged 18 to 64, nearly 70% underwent at least one imaging procedure, according to the researchers (NEJM 2009;361:841-843). Overall, moderate effective doses (between 3 mSv and 20 mSv per year) were incurred at an annual rate of 193.8 per 1000 patients. High (between 20 mSv and 50 mSv per year), and very high (greater than 50 mSv per year) effective doses were incurred at an annual rate of 18.6 and 1.9 per 1000 patients.

Cumulative effective doses were measured in five healthcare markets by examining claims data from UnitedHealthcare.

CT of the abdomen, pelvis, and chest accounted for nearly 38% of the total effective dose in the study. Myocardial perfusion imaging accounted for 22%.

The patients who experienced the higher doses of radiation were almost certainly cancer patients and others with chronic illnesses whose conditions necessitated repeat exams to gauge effectiveness of their treatment, according to the American College of Radiology.

For most patients, repeated exams and high levels of radiation are not a reality, the ACR said.

"It is important to understand this to provide context and avoid unnecessary hysteria that may lead to patients foregoing necessary imaging care and placing their health in jeopardy," according to the ACR.

The NEJM has raised serious concerns about imaging-related dose exposure before. In November 2007 a study published in the journal blamed 2% of cancers on imaging-related dose exposure. That figure was cited in Lauer's editorial.

The current study is a macro look at a problem radiologists already knew existed, according to Dr. Allen Taylor, codirector of noninvasive imaging at Washington Hospital Center in Washington, DC.

"The study provides some quantitative data on the exposure to medical radiation," he said. "Clearly there are already efforts in place to minimize and reduce medical radiation," he said.

Once such initiative is ACR's Appropriateness Criteria, which help physicians prescribe the most appropriate imaging exam for more than 210 clinical conditions, with radiation dose factored into the decision-making process.

"Physicians are referring their patients for so many imaging tests that as many as 2% of cancers may be attributable to radiation exposure during CT scanning," Lauer wrote in his editorial.

Linking medical imaging to cancer risk is not a proven fact, according to Dr. Joseph Schoepf, a professor of radiology and cardiology at the Medical University of South Carolina in Charleston.

"All estimates of cancer risk from radiation are extrapolations of data collected in WWII atomic bomb survivors," he said. "It is highly questionable whether these data can be applied to patients receiving the kind and level of radiation involved with medical imaging."

While the utilization of imaging tests is increasing, there has also been a decline in mortality from cardiovascular diseases and cancer, Schoepf said.

"It would be hard to argue that our increasing capabilities of applying noninvasive imaging for primary and secondary prevention and therapeutic monitoring are unrelated to this excitingly positive trend," he said. "Moreover, an increasing cancer incidence is not observed, which robs the argument of imaging's opponents of its base."

However, it's still important to use the as-low-as-reasonably-achievable approach when it comes to imaging patients, he said.