Editor's Note: Reducing Dose

First do no harm. Although often believed to be the words of Hippocrates and a phrase in the Hippocratic Oath taken by physicians in various forms, they are not. Hippocrates phraseology reads like this: “Declare the past, diagnose the present, foretell the future; practice these acts. As to diseases, make a habit of two things—to help, or at least to do no harm.” (Epidemics, Bk. I, Sect. XI )

How prognostic these words are of modern medicine, and imaging in particular—especially in the debate on CT and radiation control. This is the focus of this month’s cover story “Cracking Down: CT Radiation Dose Control.”

Concerns over radiation dose go back over a century. But a New England Journal of Medicine article—“Computed Tomography—An Increasing Source of Radiation Exposure”—published last fall stirred the debate once again.

As David J. Brenner, PhD, DSc, and Eric J. Hall, DPhil, DSc, point out, the widespread use of CT brings concerns over radiation exposure. In 2006, approximately 62 million CT scans were performed in the U.S.—a significant jump since the 1970s.

CT uses a higher dose than most other imaging methods but the modality keeps growing including: CT cardiac risk assessment, CT colonography (just endorsed by the American College of Radiology as an effective risk assessment tool), CT lung risk assessment for current and former smokers and CT whole-body risk assessment (even though it is not recommended by professional societies). Brenner and Hall site a study in which 75 percent of pediatric radiologists underestimated the radiation dose from a CT scan. Clearly, awareness can be raised.

But, new dose reduction software across all vendor’s systems is cutting dose significantly, particularly in cardiac CT. A combination of software, careful analysis of patient characteristics and some technologist tweaks, has cut radiation dose in 64-slice CT studies 75 to 83 percent to the range of <1 to 6 mSv, depending on the multidetector scanner used. Other methods are in the works to reduce dose in other studies as well.

Hippocrates’ words “diagnose the present, foretell the future” are the objective of modern day cardiac CT scanning. When there is a strong indication for a CT scan, there is no doubt that the benefits outweigh the risks. What must be clear is a valid indication for the study.