Cancer risk low with annual CT for cystic fibrosis

NEW YORK (Reuters Health) - In patients with the lung disease cystic fibrosis, the cumulative risk of radiation-induced cancer resulting from routine annual lung computed tomography (CT) is "quite small" -- less than 0.5 percent, a study shows. However, the lack of documented benefit of routine CT scans makes its use questionable, the researchers say.

CT is now being considered as a tool for routine monitoring of lung damage in patients with CF, but concerns have been raised about radiation-induced cancer from repeated CT scans, Dr. Amy Berrington de Gonzalez, of Johns Hopkins Bloomberg School of Public Health in Baltimore, and colleagues note in the American Journal of Respiratory and Critical Care Medicine.

Using radiation risk models derived largely from a study of Japanese atomic bomb survivors, they estimated the excess risk of radiation-induced cancer for organs receiving measurable doses from lung CT.

Assuming current median survival of CF patients to age 36 years, the estimated risk of radiation-induced cancer from annual lung CT is 0.02 percent for males and 0.07 percent for females.

If the median survival of CF patients improves to about age 50 years, as has been suggested, the estimated risk will increase to 0.8 percent for males and 0.46 percent for females, which is still relatively low, the report indicates.

"The risks are higher for females because of the risk of radiation-induced breast cancer (50 percent of total risk) and higher risk of thyroid cancer," note the researchers.

Nonetheless, Berrington de Gonzalez and her associates conclude that routine CT monitoring "should not be recommended until there is a demonstrated benefit that will outweigh these risks."

SOURCE: American Journal of Respiratory and Critical Care Medicine, November 15, 2007.