The authors of a report in the latest Radiology, a peer-reviewed medical journal, estimate that exposure to the radiation from one total-body CT scan -- often called a "CAT scan" -- may increase the risk of cancer by a small, but not negligible, amount. The researchers make this estimate by analogy to the measured radiation exposure of atomic bomb survivors in Hiroshima and Nagasaki, and the rate of cancer in those survivors.
The study authors assert that the increased risk of fatal cancer attributable to one total-body CAT scan at age forty-five approximates one in 1,250 people. For perspective and comparison, the risk of dying in a traffic accident in any given year are about one in 5,900.
The danger is cumulative: for an individual who has an annual CT scan from age 45 through age 75 -- that would be thirty scans -- the risk of radiation-induced, fatal cancer was estimated to be almost 2% (one in fifty)!
Interestingly, regarding some chemicals in the environment or consumer products, regulators have restricted or even banned substances that pose much lower risk to humans than these CT scans do. These include PCBs, DDT, arsenic, and the flame-retardant PCBE.
While the authors' conclusions and methodology can be criticized, there is a larger issue that cannot as easily be disputed: these whole-body "screening" CT scans, despite their increasing popularity, have never been shown to improve health or prevent illness by early detection, in large populations. Indeed, most physicians and medical societies agree that the procedure's "risk-benefit ratio," the paradigm decision-arbiter of medicine, does not support periodic CT scans for healthy, asymptomatic people. More harm than good is likely to be the result, due to insignificant abnormalities ("incidentalomas") requiring follow-up studies and even surgery. This downside is accompanied by two lesser problems: needless anxiety induced by findings requiring further testing, and the expense of tests, which is considerable (up to $1,500) and not covered by insurance.
Bear in mind that this decision analysis does not apply to CT scans ordered to diagnose specific symptoms or signs, or scans used to evaluate trauma patients. The dose of radiation in those cases is generally lower, but more importantly, the likelihood of such a test helping in the diagnosis and treatment of a condition is much greater than a "screening" test done for no particular reason other than to assuage a patient's groundless fears. The risk-benefit equation is weighted in favor of performing the test when specific symptoms call for it.
Some commentators, defending the practice of doing these unnecessary tests, note that the increased risk of cancer is "small." However, even a one in a thousand increase in the risk of death from cancer should not be cavalierly dismissed. Americans in particular are obsessed with hypothetical increases in cancer risk of one in one million and less, allegedly due to pesticides on nutritious fruits and vegetables and synthetic chemicals in the environment. This, despite the near-complete lack of scientific evidence supporting an increased risk from these substances, and despite the substances' known benefits. Yet, in order to keep groundless fears of cancer at bay, consumers will march to the radiologist (these "one-stop CAT scan" centers are proliferating), demanding a whole-body CAT scan, and actually increase their cancer risk! Some of these folks demand annual screenings, multiplying the risk of self-induced danger, while thinking they are wisely avoiding that very danger.
The quest for perfect health should not mislead Americans into getting these needless and possibly dangerous scans. Radiation itself is carcinogenic in humans, we know, so why expose oneself to it unnecessarily?
Gilbert Ross, M.D., is Executive and Medical Director of the American Council on Science and Health.
