"We needed to get a grip on how much radiation the U.S. was getting and where it was coming from," Mettler said.
In the intervening years, the number of procedures performed has risen "by leaps and bounds," he said. "The biggest chunk of that is CT scanning, which has been growing at better than 10 percent a year while the U.S. population is growing at less than 1 percent."
Widely used as a diagnostic tool, CT scans provide detailed images of organs, allowing more accurate diagnoses of conditions such as cancer. But CT involves a higher radiation dose than most other imaging tests. According to this paper, CT provides half of the country's total radiation dose, even though it represents only 17 percent of total procedures.
Emergency room physicians may be at the epicenter of the surge in scan use, Mettler said. "Twenty-five to 40 percent of CT scans are ordered out of the ER," he noted. "The emergency physicians are in a tough box because they're worried about getting sued. And they tend to get patients who they haven't seen before. This is a one-time walk-in and their mantra is, 'We can't afford to miss anything.'"
Of course, the trend is not limited to the U.S., although it may be more extreme here. Globally, the per-capita annual dose from medicine has doubled in the past decade or so.
Still the U.S. leads the pack, with 12 percent of all radiologic procedures and half of nuclear medicine procedures performed here.
"We have a little under 5 percent of the world's population and 25 percent of X-ray studies in the world and double and triple that of other developed countries," Mettler said. "Nobody thought about how much radiation goes with this."
But not all of uptick in scans has been unnecessary, said Dr. Robert Zimmerman, executive vice chair of r
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