By Janet Raloff
Tuesday, May 5th, 2009
Collectively, Americans now receive more than twice as much radiation each year as in the 1980s. That's according to a new tally by the National Council on Radiation Protection and Measurements.
Of course, the operant word here is collectively. NCRP isn't saying every individual is getting twice as big an annual radiation dose, only that if you sum up doses to the entire population each year, that big figure has doubled and more over the past two decades or so.
A burgeoning population accounts for 30 percent of the increase, notes Ken Kase, who chaired the NCRP panel that prepared the report. The rest of the increase stems largely from an increase in medical procedures that rely on radiation - from conventional diagnostic X-rays and CT scans to radiotherapy for cancer. Kase, a semi-retired health physicist and senior vice president of NCRP, describes his team's findings in a Q&A appearing in the May Health Physics News.
The medical component to U.S. exposures has grown disproportionately, his team's new analysis found. Whereas medical procedures accounted for 15 percent of the nation's cumulative annual dose each year in the early 1980s, it now accounts for a whopping 48 percent. Kase attributes much of the increase to a boom in CT scanning - largely to image the chest, abdomen and pelvis. CT's use in diagnosis of disease, he notes, "has increased from a few million procedures per year in the 1980s to over 60 million procedures in 2006." Another big contributor: nuclear medicine procedures targeted at diagnosing problems affecting the heart.
The medical component is now just two percentage points smaller than the contribution of background sources (50 percent) - which includes the inhalation of radon naturally emitted by water, rocks and soil.
One interesting stat: Airline crews receive the highest average occupational exposures to radiation - a little more than 3 millisieverts annually. (The source:cosmic rays - mainly protons, alpha particles and atomic nuclei - encountered flying high above the atmosphere.) What about nuclear-plant workers? They sustain annual radiation doses about one-third smaller. And a conventional chest X-ray: It would typically deliver an effective dose of about 0.06 millisieverts (or, in the old terminology, 6 millirem).