Researchers at Columbia based their estimates on a single study showing an excess risk of cancer death among survivors from Hiroshima and Nagasaki. They say that people several miles away from where the atomic bombs were dropped received radiation doses similar to those patients receive from CT scans.
However, experts do not think the actual risk of cancer can be estimated from the Japanese data because atomic bomb radiation and medical radiation are significantly different.
"This article makes the same mistakes as every other article on the subject to date -- they extrapolate atomic bomb data to medical radiation," says Schultz. "This is like comparing apples with oranges.
"The radiation from atomic bomb blasts is essentially gamma radiation and is received in a single exposure. Medical radiation is closer to beta radiation, as it can be completely attenuated with shielding and has lower energy."
But aside from the debate about how much CT scans increase the risk of cancer, researchers and radiologists alike agree that too many are being performed.
Because of its numerous applications and relative ease of use, the number of CT scans being performed in the United States today has increased dramatically from 3 million in 1980 to more than 68 million today.
Dr. Devra Davis, director of the Center for Environmental Oncology at the University of Pittsburgh Cancer Institute, explains there are two main reasons for this large increase.
"First, we are tempted to use technology simply because it is available even when it's not necessary," she says. "We tend to use this kind of technology without thinking about negative health impacts down the road.
"Second are issues of defensive medicine. The growth in lawsuits has put doctors on high alert to use all technologies at their availability to diagnosis patients."
And while CT scans have certainly made diagnosis easier, researchers say that about one-third of the scans could be replaced by alternative approaches or not done at all.
"If it is true that about one-third of all CT scans are not justified ... perhaps 20 million adults and, crucially, more than 1 million children per year in the United States are being irradiated unnecessarily," write the authors in the study.
Performing CT scans only in emergencies and using other imaging techniques, such as MRIs, may be the solution.
"The number of scans could possibly be reduced by using more ultrasound and MRI," says Davis. "CT is an important and valuable tool for true emergencies, but it is used excessively for nonemergency situations when other technologies could be used instead."
Schultz agrees. "Many times doctors order CT scans because it's protocol instead of carefully assessing the patient."
And while this study shouldn't deter anyone who needs a CT scan from getting one, it does highlight the need for more education among both medical professionals and the patients themselves.
"The bottom line for both practitioners and the public should be essentially the same -- use diagnostic tools that have some potential for harm on a very judicious basis," says Dr. Tim Byers, professor in epidemiology and program leader for the Clinical Cancer Prevention and Control at the University of Colorado Cancer Center.
"Providers need to ask themselves if the test is really needed, or if an alternative test might be just as good. The public also needs to be prepared to ask the same questions as informed consumers."
Consumers may also be relieved to hear that CT technology itself is evolving in ways that allow technicians to garner the same images with less radiation.
"The [radiation] dose for CT exams has fallen by factors of two or three in the last two decades," McCollough says. "We in the radiology field have been working to reduce doses for a long time."