Full-Body CT Screening Found to be Risky
This pitch, found on one Internet site aimed at attracting people to have full body CT (computed tomography) scans, doesn't talk about the possible risks that go along with the procedure.Now, CUMC research suggests that even one full-body CT scan exposes an individual to enough radiation to increase the risk of dying from cancer.
Full-body CT scans are marketed on the radio, TV, and the Internet as an effective early detection method for heart disease and cancer, despite the fact that there's no evidence that the scans can reduce deaths from either disease.
Most criticism levied on the use of full-body CT scans in healthy patients has focused on their questionable benefit and the number of false positives they produce. Less attention has been paid to the technique's radiation risks.
"A CT scan is hundreds of X-ray beams coming from many different directions that are put together by a computer to produce a high-definition 3-dimensional image" says the study's lead author, David J. Brenner, Ph.D., D.Sc., professor of radiation oncology and public health at Columbia University Medical Center. "The risk will not be zero, simply because of the nature of the X-rays used by the scan."
The new research, the first time cancer risk from full-body CT scans has been estimated, shows that the risk from one scan is modest, but not negligible. One scan for a 45-year-old creates a 1 in 1,200 chance of dying from a CT-induced cancer later in life.
"The issue really arises if you think of scans as surrogates for yearly physicals and have them on a regular basis," Dr. Brenner says. "Then the risk builds up."
"We calculated that a 45-year-old who has yearly scans for 30 years has a huge risk of dying from cancer, about 1 in 50," he says. "There would have to be an enormous benefit gained from yearly scans to balance out that significant risk. Because the risk is well-known and the benefits of full-body scans are unclear, I wouldn't recommend getting one every year, or even every few years."
Dr. Brenner and Carl Elliston, a staff associate in the Center for Radiological Research, calculated the risk from CT scans based on cancer mortality data collected from survivors of the Hiroshima and Nagasaki atomic bombs. A subset of survivors was exposed to low doses of radiation comparable to a single full-body CT scan (typically around 12 mSv). In the latest report on this group, survivors who were exposed to between 5 and 50 mSv from the bombs had experienced more cancer deaths than the unexposed population. Dr. Brenner's data are published in the September issue of Radiology.
Extrapolating from the low-dose survivors to an American population introduced some uncertainty in the final risk estimate, Dr. Brenner says. "It could be two to three times greater, or two to three times lower. But for someone getting multiple scans, even the lower estimate confers a high risk of cancer."
In a related paper, published in the same journal in May, Dr. Brenner also found a cancer risk from a more limited lung CT scan currently being evaluated as a screening tool for smoking-induced lung cancers.
Using similar methods to the full-body CT scan study, Dr. Brenner established that annual CT screening for smokers would increase the number of lung cancers in the United States by 2 percent assuming 50 percent of smokers were scanned.
While full-body CT scans of healthy people are generally frowned upon by the medical community, many believe yearly CT screening of smokers will be able to detect tobacco-induced lung cancers early when they may be more amenable to treatment. A national clinical trial, testing the ability of chest CT scans to reduce lung cancer mortality in smokers, is now under way at CUMC and other centers.
"There's clearly going to be a risk involved for the smokers from the radiation," Dr. Brenner says. "The question is whether this risk will be offset by the benefit of annual screening. We've shown there's a 2 percent increase in number of lung cancer cases if this population got screened, so to be beneficial, screening should decrease mortality in smokers by about 5 percent or more."