Radiologists remain unaware of radiation reduction strategies

Most radiologists know about the medical risks associated with patient exposure to ionizing radiation, but many are still in the dark about basic steps they can take to reduce patient exposure. A University of Michigan survey presented at the RSNA meeting found that a surprising percentage were unaware of methods to adjust mA and kVp during CT procedures.

Only indirect evidence makes a connection between ionizing radiation exposure and cancer risk. Most radiological authorities, however, accept the international linear no-threshold model that establishes a direct link based on the experience of Hiroshima atomic bomb survivors, according to Dr. Kimberly Applegate, an associate professor of radiology at Indiana University.

The implications of that model for radiological practice have widened with the dramatic growth of CT. In 2007, an estimated 62 million CT scans were performed in the U.S. More than seven million of those were performed on children, who are known to be particularly susceptible to ionizing radiation, she said.

Public attention increased after the publication of a study in November 2007 by David J. Brenner, Ph.D, and Eric J. Hall, D.Phil, in The New England Journal of Medicine (2007;357:2277-2284). They estimated that, without restraints, current CT procedures will ultimately be responsible for up to 2% of cancers.

The findings led Dr. Ella A. Kazerooni and colleagues in the radiology department at the University of Michigan to survey radiologists to ascertain their general knowledge about radiation exposure and CT and about strategies known to reduce it.

Their efforts led to the CT Awareness of Radiation Exposure Study, a web-based survey of 150 radiologists conducted in spring 2008. CARES found that radiologists generally do not rate radiation dose minimization as a practice priority. They ranked it below obtaining top image quality, maximizing diagnostic confidence, avoiding repeat scans, promoting the perception that their practice offered the latest technology, and providing patient comfort and optimal throughput speed, Kazerooni said.

Though 89% of radiologists were aware that reducing mA would reduce radiation exposure, Kazerooni was surprised that 11% were not aware of that common precautionary practice.

The survey found that 87% were aware of the value of reducing kV setting during routine CT and 82% knew about progressive gating triggering to reduce radiation exposure during cardiac CT procedures. The respondents believed they had limited access to most dose reducing strategies, however. Only 61% said they could lower the mAs setting on their machines.

"I find it very sobering that 39% of radiologists didn't know that they could go to the scanner to reduce the mA," Kazerooni said. "This is a tool that is available on all CT scanners, independent of generation."

Only 49% of respondents said that they had access to a mechanism to reduce kVp, another standard CT feature.

Slightly over half (55%) of the respondents said they had actually used dose reduction technologies in the previous six months. Utilization was highest among academic radiologists (73%).

About half of the respondents said that they had used either lower mA or low kVp scanning, about one in four applied a triggering mechanism for cardiac CT, and 7% or less had taken advantage of newer technologies such as 3D dose modulation, noise indexing, or bowtie filters.

Radiologists were more likely to reduce dose for teenagers and young adults, children, and women of child-bearing age, compared with older patients. They were also more likely to use dose reduction when it was built into a standard protocol.

In her concluding comments, Kazerooni noted that Dr. Philip Cascade, professor emeritus of radiology at the University of Michigan, had said a decade ago that the time was right for dose reduction in radiology. The results of Kazerooni's survey suggest there is still much more work to do.