CT cancer risk small compared with underlying morbidity

By Lynda Williams, Senior medwireNews Reporter

The mortality risk associated with the underlying reason for computed tomography (CT) imaging in young adults outweighs the risk for radiation-induced cancer, reassure US researchers.

As reported in Radiology, over the average 5.5 years of follow-up after imaging, 7.1% of 8057 chest CT patients and 3.9% of 13,888 abdominal CT patients died.

This is a whole order of magnitude larger than the expected 0.1% predicted risk for death from CT-induced cancer in patients aged 18-35 years, say Robert Zondervan (Massachusetts General Hospital, Boston, USA) and co-authors.

"When advising on radiation concerns, the radiologist should inform patients that potential adverse outcomes are much more likely to occur from the underlying medical morbidity, rather than from CT-induced cancer for most common examination indications," the team emphasizes.

The study included data for 21,945 patients who received a total of 16,851 chest and 24,112 abdominopelvic CT scans between 2003 and 2007. Chest CT was indicated most commonly for cancer (31.6%) and trauma (14.8%), while abdominal CT was used most frequently for abdominal pain (19.8%), cancer (19.6%), and trauma (10.4%).

Patients without cancer who were very rarely scanned had the lowest mortality rates, the researchers explain.

Nevertheless, the risk for mortality due to underlying cause was 3.6% among the 5914 such patients without who received only one or two chest scans, and the corresponding figure for the 11,291 noncancer patients with one or two abdominopelvic scans was 1.9%.

"In this context, the added 0.1% death risk attributable to radiation from CT scanning, while not negligible, is tiny in comparison," Zondervan et al write.

Nevertheless, the researchers observe: "Over the population, most of the radiation-induced cancers are predicted to occur in the very rarely scanned; however, at the individual level, the greatest risk is predicted in the frequently scanned in whom the dose is additive over multiple examinations.

"These results emphasize that radiologists should also focus radiation reduction efforts on patients who are very rarely scanned and not just on those who are more frequently scanned," they say.

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