Dec. 2, 2010 (Chicago) -- Embracing the medical creed to "do no harm," experts today outlined a series of steps aimed at curbing exposure to unnecessary radiation during imaging tests, most notably CT scans.
Radiation, particularly repeated high-dose exposures, has been linked to a small increased risk of cancer years later.
Called "Image Wisely," the new campaign aims to ensure "we use the right procedure at the right dose for the right patient," panel member William R. Hendee, PhD, distinguished professor of radiology, radiation oncology, biophysics, and bioethics at the Medical College of Wisconsin in Milwaukee, tells WebMD.
Speaking at the annual meeting of the Radiological Society of North America, the expert panel says there has been a sevenfold increase in the use of radiation-based imaging in the past 25 years.
Also, a study presented at the meeting suggests that the average person is being exposed to higher doses of radiation from X-rays, angiography, and CT scans than in the past. But another study suggests that the cancer risk from CT scans may be overestimated, at least in the elderly.
Increase in Imaging
Despite the growth in imaging tests over the past three decades, there has not been a similar rise in cancer cases or deaths in the U.S., says panel member Christoph Wald, MD, PhD, executive vice chairman of the department of radiology at the Lahey Clinic in Burlington, Mass., and associate professor of radiology at Tufts University in Boston.
Nevertheless, radiation is frequently portrayed negatively in the press, with headlines in newspapers and on broadcast media screaming out its risks, Wald says.
Hendee says cancer risks have largely been estimated using a National Academy of Sciences study of Japanese survivors of atomic bombs dropped on Hiroshima and Nagasaki in 1945. People at the far edge of those blasts who absorbed about 50 millisievert (mSv) of radiation appear to have an increased lifetime cancer risk of 0.05%, he says.
A series of CT exams might expose a person to that much radiation, Hendee says. Since the lifetime risk of cancer for the average American’s is about 33%, the 0.05% increased risk associated with that exposure is basically negligible on the individual level, he says. But from a public health point of view for the entire population, it could be noteworthy, he says.
According to the medical literature, 50 to 100 mSv of radiation is associated with "some increase in cancer incidence," according to Pat Basu, MD, of Stanford University. He presented the new study on cancer risks in the elderly, but was not on the panel.
By comparison, 10 continental round-trip airplane flights expose a passenger to 1 mSv of radiation and an astronaut is exposed to about 200 mSv per year, Basu says. Health care workers are limited to 20 mSv of radiation per year, he says.
Campaign to Reduce Radiation
Hendee says that the Image Wisely campaign is built on the highly successful Image Gently initiative aimed at reducing radiation exposure to children.
"If we can do it for kids, why not do it for everyone?" Hendee says.
As part of the initiative, the panel hopes all institutions that offer radiation tests put up signs with its icon, the owl, and a pledge to use radiation wisely, he says. "It's a constant reminder."
Practices that the panel hopes to eliminate include the use of tests to protect against malpractice suits, Hendee says. Also, sometimes doctors with a financial stake in a radiation center refer patients to that center.
Another problem: With technology changing so quickly, doctors may not always know which exam is most appropriate, he says. As part of the campaign, a computerized "decision system" has been developed to help guide doctors.
If you’re not sure why your doctor is ordering a test, ask, Hendee advises.
Also, bring a record of what imaging tests you have received when you visit a new facility, suggests James A. Brink, MD, chairman of diagnostic radiology at the Yale University School of Medicine.
The Image Wisely initiative is supported by RSNA, the American College of Radiology, the American Association of Physicists in Medicine, and the American Society of Radiologic Technologists.
Annual Radiation Doses
At the meeting, University of California, San Francisco researchers reported that the average annual radiation dose we receive nearly tripled over 15 years, from 0.80 mSv in 1994 to 2.3 mSv in 2008.
"A small but increasing proportion of patients received high doses," says researcher Ingrid Burger, MD, PhD.
In 1994, 0.49% and 0.04% of those studied received doses of more than 50 and 100 mSv, respectively. In 2008, 2.4% and 0.47% received doses exceeding these thresholds, she says.
The researchers reviewed nearly 24 million radiation exams of people enrolled in seven HMOs across the country.
CTs and the Elderly
In the other study, Basu and colleagues used Medicare claims data on over 10 million patients to estimate cancer risks related to CT scans.
They found a risk of between 0.02% and 0.04%, "surprisingly lower than we expected," Basu tells WebMD.
The researchers also found that the proportion of patients who had imaging studies increased over time. From 1998 to 2001, for example 42% of patients had scans, compared with 50% of those in 2002 to 2005.
Although only elderly people were studied, the findings could apply to middle-age people whose biological sensitivity to radiation is similar, Basu says.
Max Wintermark, MD, of the University of Virginia in Charlottesville, agrees. He notes that elderly people account for the greatest use of CT imaging.
A limitation of the study was that cancer risk was estimated using the National Academy of Sciences data. Patients were only followed for up to four years, a short period during which radiation-associated cancers might not develop.
Also, "you would expect cancer risk to be lower in the elderly, who may die due to other reasons before a secondary cancer has time to manifest," Hendee says.
Basu says a study in which people's radiation exposures and subsequent cancers are tracked over time is needed.
The new studies were presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.