The number of computed tomographic (CT) scans performed in the United States has increased dramatically in recent years, and there's concern over a consequent increase in the risk of cancer in those patients. Fully evaluating the "long-term risks from CT scans directly would require very large-scale studies with lifelong follow-up," write the authors of a recent report, who used data on CT scans performed in 2007, risk-projection models, and insurance records to determine the risk of future cancer from CT scan exposure. The researchers determined that among the 72 million U.S. patients who underwent CT scanning in 2007, approximately 29,000 future cancers may be caused by the excess radiation they received.

According to the authors' calculations, about one-third of the projected cancers (the largest percentage) will likely occur in patients who were between the ages of 35 and 54 when the scans were performed, which runs contrary to conventional wisdom, which holds that pediatric patients are at greater risk. The study also found that two-thirds of the expected cancers are likely to arise in women because of the higher risk of lung and breast cancers associated with exposure of the chest to radiation. Researchers found that the area being scanned or the type of scan affected the risk, with the highest risk seen in those undergoing scans of the abdomen and chest CT angiography. The authors noted that these are estimates and that a direct correlation between CT scans and cancer hasn't been demonstrated, but they cited studies showing that large doses of radiation-like those delivered by numerous CT scans-do increase cancer risk.

Although many variables can influence such estimates and these types of projections can be difficult, Marita Lazzaro, an NP in the Cancer Prevention Center at M. D. Anderson Cancer Center in Houston, said that the study poses the question of whether we're using too many CT scans and defines the possible consequences of overuse. "Whenever we see a risk factor for cancer, we try to limit it as much as possible," she said. Echoing the study authors' own conclusions, she said she hoped that the study findings would make clinicians consider using other tests that use less radiation-or none.

Nurses should make sure that patients are aware of the risks associated with CT scans, keep abreast of research in this area, and talk with radiologists to determine the best options for patients. "What needs to be taken from this study is not that CT scans aren't good," Lazzaro said. "But we need to weigh the risk of treatment and testing against the benefit we might be getting."

Tammy Worth