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Industry-wide efforts look to control CT dosing levels, but not everyone is convinced the radiation is under control.
Even with the Image Wisely and Image Gently campaigns and the promise to strive for doses as low as reasonably possible, controversy still exists over whether radiology is over-dosing its patients.
Plenty of evidence-based research exists about dosing levels, but there is little agreement on how to interpret what the data mean. It is possible, experts say, to look at the same study findings and conclude that - despite ongoing efforts - radiologists consistently expose patients to radiation levels that are too high, or determine that scanning should continue due to the lack of over-exposure evidence.
The chance of over-dose
The question of dose rates is sticky, said Rebecca Smith-Bindman, MD, radiology and biomedical imaging profess at the University of California San Francisco School of Medicine, because little research has been done into whether low dosages are really low enough to avoid contributing to future cancers. By extrapolating from existing data on high dose exposure, she said, it’s likely that low-dose efforts don’t go far enough.
“We’re not minimizing risk at all,” she said, speaking at the recent RSNA 2013 in Chicago. “We’re using doses higher than needed for diagnosis and are exposing patients to unnecessary risks.”
The population at greatest risk, she said, is patients over age 75. Because more health problems emerge in older age, this group receives a large number of CT scans that any other age range. This is cause for concern, she said, because cancer risk begins to climb after age 50.
However, existing research also shows a relationship between CT exposure and higher cancer rates in children, she said. One study of more than 78,600 children who received multiple CT scans with doses larger than 60 milligray (mGy) found these patients had a 24 percent higher risk of developing leukemia or brain tumors than non-exposed patients.
While other studies didn’t find a correlation at all between CT exposure and future cancer risk, she said, it could still be possible to reduce the number of future cancers by driving dose down even further.
“The total cancer burden can likely be reduced by a few percentages just by lowering doses, and if utilization is reduced, as well, the impact can be even greater,” Smith-Bindman said. “If radiologists want to be in medicine, then they must participate in multidisciplinary teams and accept responsibility for care.”
Because the data is inconsistent, there is no industry-wide consensus on the dangers of CT dose, said William Hendee, PhD, professor of radiology, radiation oncology, and biophysics in the Institute for Health and Society at the Medical College of Wisconsin. Until the dangers are proven, radiologists have a responsibility to provide the most effective care to patients.
“More CT scans means more and more patients are benefitting in this country and elsewhere from CT and other procedures,” he said. “By using those procedures, we provide more accurate diagnoses for a variety of conditions, reduce side effects of surgery, lower the number of surgical interventions, and shorten hospital stays. It’s an overall major positive impact.”
Although CT scans are responsible for nearly half of the increase in medical imaging over the past 25 years, he said, existing data shows that these studies are responsible for only 1 percent to 2.2 percent of cancers in the United States each year.
In addition, he said, research conducted in areas with high levels of naturally-occurring radiation, such as China, Brazil, and India, shows these regions don’t experience higher mortality rates than other places with lower radiation levels. Investigations into cancer rates among nuclear power plant workers also found these individuals didn’t suffer higher incidence of the disease.
Without overwhelming evidence that current CT dose levels are still too high, Hendee said, radiologists should continue to educate patients about the modality and perform these studies when they are appropriate. To do otherwise could be harmful because the risk of forgoing an imaging procedure could be much greater than the radiation associated with the scan.
“The risk of medical imaging with doses less than 50 mSv could be too low to be detectable and may not even exist,” Hendee said. “Until we have better evidence, we should err on the side of making sure the patient receives the benefit of CT and other imaging procedures. We shouldn’t get scared off by other estimates of hazard or risk.”