Imagers question New England Journal CT dose critique

November 11, 2009
Rebekah Moan

Imaging advocates, including the American College of Cardiology, cautioned against giving too much credence to a study in the New England Journal of Medicine concluding that adults are exposed to excessive doses of radiation from medical imaging procedures that are not supported by the clinical data.

Imaging advocates, including the American College of Cardiology, cautioned against giving too much credence to a study in the New England Journal of Medicine concluding that adults are exposed to excessive doses of radiation from medical imaging procedures that are not supported by the clinical data.

"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," the ACR said.

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

The journal's retrospective cohort study covered more than 655,000 patients younger than 65 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 (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.

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

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."