Experts Call for Closer Scrutiny of Radiation Exposure From CT Scans
Biologic effects from medical imaging tests are not entirely understood (Nov. 28)Amid increasing fear of overexposure to radiation from computed tomography (CT) scans, a panel of experts has recommended more research on the health effects of medical imaging and on ways to reduce unnecessary CT tests, as well as industry standardization of CT machines. The recommendations, published in the November 2012 issue of Radiology, were developed at the Radiation Dose Summit, organized by the National Institute of Biomedical Imaging and Bioengineering (NIBIB). The summit included more than 100 medical physicists, radiologists, cardiologists, engineers, industry representatives, and patient advocates. The proceedings, held in Bethesda, Md., in early 2011, covered currently understood risks of radiation exposure from CT scans, set priorities for future research, and called for changes to industry practices.
“The number of CT exams in the U.S. has increased by about 10% each year over the past decade,” said lead author Dr. John Boone. “This trend underscores the importance of developing a better understanding of the health risks of radiation exposure versus the benefits of enhanced diagnosis.”
The experts conceded that despite widespread public concern about radiation risks, the biologic effects from medical imaging tests are not entirely understood. Most direct evidence comes from the effects of instantaneous, high-dose, whole-body exposures due to industrial accidents and from survivors of the atomic bombs in Hiroshima and Nagasaki, Japan. Whether these findings can be extrapolated to people exposed to occasional and much smaller dosages applied to only parts of the body is uncertain. Even accurately recording patient exposures of radiation from medical imaging is extremely difficult, according to the authors. Although it is easy to ascertain how much radiation a machine administers during an imaging study, the amount actually received by a patient depends on various factors, including body size. Federally sponsored research is needed to develop methods to more accurately measure patient exposures from different types of CT scans, the authors suggested.
The summit participants also discussed the role of human error in CT scanning, which has resulted in widely publicized instances of radiation overexposure. They point out that CT operators often are responsible for several machines made by different manufacturers, each of which may use dissimilar nomenclature and control consoles, thereby increasing the chance for error.
“For some scanners, you turn a dial to the right to get a larger dose, and for others, turning it the same way gives a smaller dose,” said Boone. “There are so many differences in current CT scanners, it can be like driving a car with the brake pedal on the left in the morning, then with the brake on the right in the afternoon.”
The experts also considered “wasteful imaging” ? tests that have little impact on patient diagnoses or outcomes ? resulting in unnecessary radiation exposures. Wasteful imaging can arise if physicians are unaware of a patient's prior tests or don't know whether a scan will benefit a patient with certain signs and symptoms. In addition, physicians may order tests they know are only marginally useful to avoid accusations of negligence in a possible future lawsuit.
The experts recommend the use of information technology to develop national imaging and radiation exposure registries, as well as standardized protocols that guide physicians on the use of optimal imaging modalities for different clinical problems.
Source: University of California – Davis; November 28, 2012.