Cancer risk from CT low, but can be further reduced

The risk of cancer is slightly elevated in patients who undergo computed tomography (CT) scans, according to the authors of an international study, who reported that incidence was significantly increased for urinary tract cancer and six other solid tumors.

While risk of any cancer linked to CT is low, reducing the radiation dose would lead to a long-term reduction in cancer incidence, said John D. Mathews, MBBS, MD, PhD, the study’s lead author from the University of Melbourne, Australia. Meanwhile, at least one U.S. institution has launched a new program to accurately measure patients’ lifetime exposure to radiation from diagnostic imaging.

In the study of more than 600,000 Australians, Dr. Mathews and colleagues found that, for every 1,800 people who underwent CT scans before the age of 20 years, there was one extra case of cancer over the following 10 years. This small increase in cancer risk must be weighed against the benefits of CT in diagnosing and monitoring disease, Dr. Mathews said.

Study findings, reported online in the British Medical Journal (May 21, 2013), involved researchers at eight other centers in Australia as well as Oxford University in Oxford, UK, and the International Agency for Research on Cancer in Lyon, France.

“In most cases, the benefits of having a scan clearly outweigh the risk of a later cancer. Nevertheless, our new findings will remind doctors to order CT scans only when there is a definite medical reason, and to insist that CT scans use the lowest possible x-ray dose,” Dr. Mathews said.

“It is clear from our study that if we reduce the number of scans performed in a large population, and continue to reduce the doses from individual scans, there will be a small but corresponding reduction in the number of cancers in later years.”

In the study, researchers linked Medicare records of CT exposures for the entire population of young Australians, aged 0-19 years between 1985 and 2005, to cancers diagnosed up to the end of 2007. Overall cancer incidence was 24% greater for exposed than for unexposed individuals, after accounting for age, sex, and year of birth (incidence rate ratio [IRR]: 1.24; 95% confidence interval: 1.20-1.29; p<.001). The IRR increased significantly for urinary tract cancer and other types of solid cancer: digestive organs, melanoma, soft tissue, female genital, brain, and thyroid.

The risk of cancer increased with the number of CT scans, and the proportional increase in risk was greater for those exposed at younger ages.

In the United States, one hospital system has addressed concerns about the safety of radiation from imaging tests, as outlined in the British Medical Journal study and a recent study in JAMA Pediatrics. Salt Lake City-based Intermountain Healthcare has launched a program that compiles the cumulative radiation patients receive from about 220,000 higher-dose procedures and imaging exams each year, starting with exams performed in the last quarter of 2012. That information is now readily available to both physicians and patients.

Physicians can review the cumulative radiation a patient has received through Intermountain’s electronic medical record system. Patients can view their own radiation history via a password-protected portal on the Internet. In addition to providing the cumulative radiation history, patients and physicians are also given access to educational materials on the risks and benefits of medical radiation.

"We are very excited to begin see the benefits of monitoring cumulative radiation," said Donald Lappé, MD, of Intermountain’s Cardiovascular Clinical Program. "With this information, clinicians and staff have reduced radiation, avoided unnecessary treatments, and found alternatives which do not involve x-rays."

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