Elective full-body computed tomography (CT) scans in healthy individuals have long been controversial because of uncertainties surrounding their ability to detect hidden disease. Now, researchers report that radiation from a single full-body CT examination corresponds to a dose comparable with a level of radiation linked to increased cancer mortality in low-dose atomic bomb survivors from Hiroshima and Nagasaki, in Japan (Radiology. 2004;232:735-738).
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Full-body CT scans deliver a radiation dose nearly 100 times that of a typical mammogram.
The authors question the use of such an expensive procedure of disputed value in asymptomatic people in light of such risk. Full-body CT scans deliver a dose of radiation nearly 100 times that of a typical mammogram.
“There is direct epidemiological evidence that the sorts of doses of relevance for a single full-body CT scan do increase an individual's cancer risk,” said lead investigator David Brenner, PhD, DSc, from Columbia University in New York City. “Thus our goal was to contribute the assessment of the risks vs benefits of full-body CT scans.”
Brenner and coauthors found that undergoing a single full-body CT scan at age 45 years would confer an estimated risk of 0.08% of developing a fatal radiation-induced cancer, about 1 death in 1200 individuals (with a 95% chance that the true risk is between 1 death in 400 and 1 in 4000). For individuals undergoing an annual full-body CT scan from age 45 to 75 years, the estimated risk would increase to 1.9% (with a 95% chance that the true risk is between 1 in 25 and 1 in 100 individuals).
Different CT scanners produce different radiation doses and therefore different risks. But machine-to-machine variations in doses were included in the overall uncertainty estimates.
The study considered risks only for asymptomatic adults—the so-called worried well—who chose to undergo elective scans to screen for a variety of diseases, including colon and lung cancer and coronary artery disease.
On the other hand, patients who are referred for CT scans for medical diagnoses should not view the study as a reason to avoid the procedure, said Brenner. “When there is a diagnostic rationale for a CT scan, then the risk-benefit equation is very different,” he explained. “The benefits of an accurate diagnosis of a disease or injury will generally far outweigh the risks.”
The controversy over elective full-body CT scans has focused primarily on disease detection vs risk of false-positive findings. False-positive results can lead to more extensive, costly, and unnecessary testing. No studies have reported life-prolonging benefits from the procedure.
“In general, if one subscribes to the application of evidence-based medicine, then routine full-body CT screening may be premature, until some estimate of the benefits can be made,” said Brenner. In terms of the value of having a single full-body CT scan, Brenner said, “it is not clear that a single CT scan would be of significant benefit. The analogy would be having just a single mammogram or PSA test in one's life.”
More research will be needed to bolster the study’s conclusions. If individuals continue to undergo elective full-body CT scans, the true cancer mortality risks may become clear. “Because of the latency period between radiation exposure and a solid cancer appearing, which averages 15 to 25 years, it is too early to do direct epidemiological studies on individuals who have had full-body CT scans,” said Brenner.
The authors conclude that their risk estimates should be used to assess the utility of full-body CT examinations from both an individual and a public health perspective.
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