Over the past quarter century, exposure to ionizing radiation from medical procedures in the U.S. has grown sevenfold, according to the National Council on Radiation Protection and Measurements. CT is a major source.

Managing x-ray dose is the subject of a morning session on opening day, May 19, of the International Symposium on Multidetector-Row CT in San Franciso. There is good reason to be concerned. In 2006, CT accounted for 24% of all radiation exposure in the U.S., twice that of nuclear medicine, three times that of interventional fluoroscopy, and nearly five times more than radiography and diagnostic fluoroscopy, according to a report issued in March by the NCRP.

"CT and nuclear medicine alone contributed three-quarters of the medical radiation exposure of the U.S. population," said Dr. Kenneth R. Kase, senior vice president of NCRP and chair of the scientific committee that produced the report.

In 2006, 67 million CT scans and 18 million nuclear medicine procedures were performed in the U.S., according to the report, Ionizing Radiation Exposure of the Population of the United States.
 

About half of radiation exposure comes from natural sources found in soil and rocks, radon gas that seeps into homes and other buildings, and radiation from space. A very small amount comes from radiation sources that occur naturally in the human body, according to the NCRP report. Other small contributors of exposure to the U.S. population included consumer products and activities, industrial and research uses, and occupational tasks.