Size-adjusted dose benchmarks: Is your facility in the danger zone?

 - NEMA takes strides toward reducing CT dose

The world’s largest dose index is being put to work for the benefit of physicians and patients everywhere in the form of national dose guidelines for the most common CT exams preformed in the U.S.

Americans have been exposed to increasingly large amounts of radiation: The average American adult received seven times the annual dose in 2006 when compared to the 1980s. While concerns over radiation dose always been reflected by regulators and advisory boards, the American College of Radiology (ACR)’s Dose Index Registry (DIR) was the first national compendium of patient dose.

Researchers from the University of Washington examined data from the 10 most common CT exams, including head and brain without contrast and abdomen and pelvis with contrast. They developed the first diagnostic reference levels (DRLs) to incorporate patient size, allowing imaging providers to compare doses at their facility with national benchmarks. The research was published in Radiology.

“Because smaller patients require lower doses than larger ones to yield adequate image quality, the new size-specific DRLs and achievable doses (ADs) will enable facilities to more effectively optimize their CT protocols for the wide range of sizes of the patients they examine and thus to appropriately reduce dose to patients,” wrote the authors.

Of the 5.7 million CT exams collected by the DIR in 2014, 3.4 million were in the top 10 most frequently preformed. After filtering for multiphase exams or exams with missing data, researchers were left with 1.3 million CT scans to sift through. Abdominal exams were the most common, making up 45 percent of study-eligible scans. Chest and head were next, claiming shares of 25 percent and 17 percent, respectively.

“This extensive participation and totally automated complete capture of all patient examinations enabled the development of robust, clinically based national DRLs and ADs,” said Kalpana M. Kanal, PhD, professor of diagnostic physics at the University of Washington School of Medicine and lead researcher on the study.

The size-specific dose estimate for abdominal examinations was 16 mGy, compared to 56 mGy for head and brain exams. These refined DRLs closely match benchmarks set by countries around the world, showing that adults in the U.S. have about the same levels of radiation exposure as other countries.

“DRLs should be used to determine if a facility’s dose indexes are unusually high; they should not be used as target doses,” wrote Kanal et al. “Implementation of DRLs and ADs is most effective if the facility has a system to automatically monitor patient dose indexes so that aggregate results may be evaluated.”

DRLs combined with an effective dose-tracking system can help move the goalposts for patient dose, according to the authors.

“While improvements in equipment dose efficiency may be reflected in these dose reductions, investigations triggered when DRLs are exceeded can often result in new, lower-dose protocols that provide sufficient image quality for the diagnostic task,” they wrote. “Thus, data points above the 75th percentile are, over time, moved below the 75th percentile—with the net effect of a narrower dose distribution and a lower median dose.”

Learn more about how to participate in the ACR’s Dose Index Registry here.