Two studies in the United States have found that radiation from computed tomographic (CT) scanners may cause cancer long after patient exposure.
CT scanning combines special X-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor or printed.
The images are three-dimensional, but good imaging has led to a higher risk of damage decades later.
Researchers from the University of California, San Francisco, found that CT scans emit higher levels of radiation than was thought at first.
A separate study done by the National Cancer Institute estimated that radiation from more than 70 million CT scans performed in the United States in 2007 will ultimately cause about 29,000 cases of cancer, and a possible 15,000 deaths.
Ray Navarro, director of imaging for Mercy Medical Center Merced, said the CT scanners that are under scrutiny are at least 16-slice scanners. The scanner used at Mercy is a four-slice scanner.
But when the new hospital opens in May, those CT scanners will be 64-slice and 32-slice scanners.
"What has been proposed is a software package that shows us how to lower the dosage to the patient," Navarro said.
Navarro said CT scans are used on patients' heads when a cerebral accident is feared.
"A CT scan shows slices of the brain," Navarro said. "X-rays don't show any tissue or anything other than bone."
He said CT scans will show tissue, blood and fluid.
Although most CT scans are deemed a necessity, Dr. Rebecca Smith-Bindman, a radiology professor at UCSF, said some are not.
"Nobody knows how many CTs are too many," Smith-Bindman said. "But I would estimate about 20 to 30 percent of the scans are not necessary."
The number of CT scans performed each year has risen from about 3 million in 1980 to more than 70 million today, according to UCSF. A standard CT scan of the chest exposes patients to more than 100 times the radiation of a typical chest X-ray.
Navarro believes that in the future, CT scans will be monitored very closely.
"We are going to take a very close look at how calibration of the scanner is done," Navarro said. "We've all been given a heads up."
Reporter Carol Reiter can be reached at (209) 385-2486 or firstname.lastname@example.org