CT scan risks in cystic fibrosis likely to rise
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The increased cancer risk from annual CT scanning of patients with cystic fibrosis is currently modest, but will become more substantial as patients with the disease live longer, an international team of researchers reports.
Cystic fibrosis is a genetic disorder that affects the glands that produce sweat and mucus, with the most significant damage occurring in the lungs and digestive system. Mucus in cystic fibrosis patients becomes thick and accumulates in the lungs and intestines, resulting in breathing problems, frequent respiratory infections and poor nutrition. Because most patients die of lung disease, the primary goal of cystic fibrosis therapy is to help keep the airways clear and avoid respiratory infections.
CT scanning is more sensitive than simple chest X-rays in detecting structural lung damage and may also be more effective for identifying disease progression than measuring lung function, Dr. Pim A. de Jong and colleagues report in the American Journal of Respiratory and Critical Care Medicine. For these reasons, routine CT scans are increasingly being used in cystic fibrosis patients, but the benefits for survival are not clear.
Because cystic fibrosis patients are living longer, the researchers note, the cancer mortality risks associated with CT radiation would be expected to increase, de Jong, of Erasmus Medical Center in Rotterdam, and his colleagues point out. They therefore estimated the excess mortality associated with radiation exposure from CT scans, based on atom-bomb survivor data.
Annual CT scanning beginning at age 2 years would reduce survival by 1 month for patients who lived to the age of 26. Survival time due to radiation exposure would be reduced by 2 years if a patient survives to age 50, the researchers estimate.
Cumulative cancer mortality would be 2 percent at age 40 and 13 percent at age 65.
Performing CT scans biannually reduced the associated mortality risk by half.
The average lifespan for cystic fibrosis patients is estimated to be 50 years by 2030, the researchers note. “Given the potential reduction in survival associated with radiation exposure from routine CT scans, it would be important to further demonstrate the clinical benefits related to this approach to justify the use of routine lifelong CT scanning in patients with cystic fibrosis,” they conclude.
In an editorial accompanying the study, Drs. Amy Berrington de Gonzalez and Jonathan Samet of Johns Hopkins School of Public Health in Baltimore call the estimated risks “surprisingly high.”
They note that another strategy de Jong and colleagues did not address that could help reduce radiation exposure would be to limit scanning in children, when risks associated with radiation exposure are believed to be greater.
This would be especially important for girls with cystic fibrosis, given that the breast is highly sensitive to radiation, and more so at a young age.
There is currently no evidence that CT scans offer any survival benefits for cystic fibrosis patients, the editorialists note. “Studies of the potential survival benefits, preferably randomized controlled trials, therefore now need to be initiated so that any future risk of cancer will be justified by the benefits of the test,” they conclude.
SOURCE: American Journal of Respiratory Critical Care Medicine, January 15, 2006.
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