When used in appropriate situations and with careful attention to dosage, leading experts agree that the potential benefit of cancer imaging outweighs the risk. However, there has been mounting concern that several increasingly common imaging modalities may expose patients and health care workers to potentially unsafe radiation doses, the consequences of which only become evident with long-term population-based research.
Computed tomography (CT) has come under intense scrutiny because the number of procedures has skyrocketed to more than 60 million annually, a nearly threefold increase since the early 1990s, and the average number of scans per patient is also increasing. The wider use of CT can be traced in large part to its speed and its remarkably clear images of organs and tissues. But the downside, explains Dr. Elaine Ron, a senior investigator in NCI's Division of Cancer Epidemiology and Genetics (DCEG), is that CT requires significantly greater doses of radiation compared to a conventional x-ray. In the case of abdominal CT, for example, the dose is 50 times higher.
Among the chief concerns is use of CT in children. With their still-developing bodies, experts warn, they are more prone to radiation-induced effects that can increase cancer risk. Such concerns led NCI to partner with the Society for Pediatric Radiology to develop a brochure, recently updated, to help educate health care workers about appropriate CT use in children and the potential risks of CT-emitted ionizing radiation. DCEG researchers are also collaborating with researchers from Newcastle University in the United Kingdom and Maccabi Healthcare Services in Israel to investigate the risk of cancer in children and adolescents who have undergone CT scans.
CT is not the only radiologic procedure that NCI researchers are studying. Other diagnostic techniques and treatments that rely on a type of x-ray technology called fluoroscopy, especially coronary angiograms and angioplasty, are proliferating. Because of the length of these procedures, the cumulative exposure to radiation is considerable. In conjunction with five medical societies, NCI has launched a study to determine whether radiologists and cardiologists, among others, who are involved in fluoroscopy-guided procedures have a higher risk of cancer.
The research began because of reports of certain cancers that appear to arise more often among physicians who perform fluoroscopy, explained Dr. Amy Berrington de Gonzalez, an investigator in DCEG's Radiation Epidemiology Branch. There have been efforts by NCI and other medical societies to educate medical personnel about the potential radiation-related risks associated with these procedures. However, the available evidence, including some surveys conducted by the FDA, suggests the message still isn't getting through, particularly to those without extensive radiology training, she stressed.
The long-term study will compare cancer-related deaths between physicians regularly involved in radiation-related procedures and those who are not involved in such procedures. "Then we'll be able to determine whether increasing use of these new imaging technologies are associated with an elevated cancer risk," she says.