Inconsistent imaging: CT radiation doses vary around the world

CT protocols and radiation doses vary significantly across different countries, according to a new study published in the BMJ. The authors added, however, that developing a consistent standard “should be possible.”

“It is important to minimize exposure from medical imaging and reduce unnecessary variation by optimizing examination protocols,” wrote author Rebecca Smith-Bindman, MD, of the University of California San Francisco, and colleagues. “Evidence suggests that in many instances, CT doses can be reduced by 50 percent or more without reducing diagnostic accuracy.”

The authors used data from the University of California San Francisco CT International Dose Registry to learn more about the various factors that can influence CT radiation dose. CT examinations of the abdomen, chest, combined chest and abdomen, and head were used for the study. All examinations were performed on adult patients between Nov. 1, 2015, and August 22, 2017. Data was collected from a total of 151 different institutions from the United States, the United Kingdom, Switzerland, the Netherlands, Germany, Israel and Japan.

Overall, after the researchers accounted for various patient characteristics, the median effective dose for abdominal CT from these institutions ranged from 5 to 32 millisievert (mSv). The mean effective dose for abdominal CT ranged from 7 mSv to 25.7 mSv, with similar differences noted for chest and combined chest and abdomen CT. Dose variation in head CT was “more modest, with a relative mean dose between the highest dose and lowest dose countries of 1.3.”

Smith-Bindman and colleagues also noted that most factors their team observed “had only a small effect on the dose variation across different machines in the registry or between the different countries.”

“Using an international registry of CT doses, we found large variation in doses across the included countries even after accounting for patient characteristics, numerous institutional characteristics, average machine and institutional practice volumes, and machine factors,” the authors wrote. “The variation in dose persisted when we limited our analysis to one clinical question where the radiation dose requirements would have been the same across the included countries.”

Ultimately, the researchers found that these significant dose differences were “almost entirely associated with how institutions used the machines,” which means a more consistent standard across the board could have a huge impact and help get these countries on the same page moving forward.

“Optimizing doses to a more consistent standard should be possible both within and between countries by modifying the decisions made by radiology teams in developing CT protocols for patients,” the authors concluded. “Future research should focus on understanding factors that drive institutions, and scientifically comparing different approaches for optimizing doses.”