The latest generation of hospital scanners could be far more dangerous than previously believed, according to a study showing that as many as one in 80 people could be at risk of developing cancer as a result of being scanned.

Computed tomography (CT) scanners produce a much higher dose of radiation than conventional x-rays and research suggests the extra exposure could result in a 10-fold greater risk of cancer than is usually cited, scientists said.

Two studies into the growing use of CT scanners in the United States have identified wide variations in the radiation dose patients receive, with some people getting 13 times the level of radiation received by other CT patients, depending on their medical condition and where they were treated.

Scientists believe the additional risks posed by CT scanners, used to diagnose a range of conditions, could result in thousands of extra cases of cancer caused by exposure to x-rays used in the scanners.

"The risk associated with obtaining a CT is routinely quoted as around one in 1000 patients who undergo CT will get cancer. In our study, the risk of getting cancer in certain groups of patients for certain kinds of scans was as high as one in 80," said Rebecca Smith-Bindman, professor of radiology at the University of California San Francisco.