People who undergo a lot of CT scans over a lifetime may have an elevated risk of developing cancer, suggests a new study, though the risk is still small.
Unlike conventional X-rays, CT scans -- short for computed tomography -- provides a detailed, three-dimensional image of internal organs, which helps physicians diagnose and track disease. The use of the scans has increased substantially in recent years, along with the use of MRIs.
But CT scans expose people to a higher dose of radiation compared to X-rays, and there have been concerns about their long-term effects.
For this study, researchers at Brigham and Women's Hospital in Boston looked at the cumulative CT radiation exposure of more than 31,400 patients who'd had at least one scan over the previous 22 years. One in three patients had undergone five or more CT examinations and one in 20 had more than 22 CT scans.
Fifteen percent had been exposed to a radiation equivalent of 1,000 traditional chest X-rays, according to the researchers.
Overall, seven percent of the patients had had enough radiation exposure to raise their cancer risk by one per cent over the U.S. norm, according to the findings.
The researchers say that while the increase in cancer risk associated with multiple CT scans is modest, it is clinically significant.
But for most people, the benefits of CT imaging outweigh the risks of radiation exposure, lead researcher Dr. Aaron Sodickson writes in the journal Radiology.
"CT is an excellent diagnostic tool of tremendous clinical value in many situations," Sodickson said in a news release from the journal.
"Individual decisions about its use should balance the expected clinical benefits against the potential cumulative risks of recurrent imaging."
Doctors may want to be more cautious about using the technology in people who've already had multiple CT scans in the past, according to Sodickson, especially if those previous scans had turned up nothing.
"This scenario," he noted, "may result in a combination of high cumulative risk with low clinical benefit."
There are a number of potential ways to help protect patients from the radiation exposure of multiple CT scans. Alternative types of imaging, such as MRI, could be used for some patients, while technical advance should be able to lower the radiation dose delivered with each scan.
