When radiation dose isn’t proportional with patient size, patient exposure inevitably runs the risk of exceeding — or falling beneath — the amount necessary for good image acquisition. A two-year study published in the journal Radiology used the world’s largest CT dose index registry to establish national CT dose levels based on patient size.

Previous national diagnostic reference levels (DRLs) only provided one value per exam based on a standard-size phantom that represented an average patient. But Kalpana M. Kanal of the University of Washington School of Medicine and her colleagues realized that CT protocols need to be optimized for the wide range of patient sizes.

The American College of Radiology launched its Dose Registry Index in 2011, and by 2016 it expanded to include 30 million-plus exams from over 1,500 facilities. Kanal and her team evaluated more than 1.3 million registry exams that were conducted in 2014 at 538 health care facilities in the U.S.
DRLs and achievable doses (Ads) were developed for 10 of the most common adult CT exams. For head exams, the team used lateral thickness to determine patient size, and water-equivalent diameter was used for neck and body exams.

Kanal stated that the use of DRLs is associated with a reduction in the overall dose and range of doses observed in clinical practice. But she warned that DRLs should not be used as target doses, but instead, to determine if a facility’s doses are too high.

Facilities can assess and compare their median and size-grouped dose indexes with the respective size-based ADs and DRLs. If they don’t have access to size-grouped dose indexes, they can compare their overall median indexes with the average DRLs and ADs for all patient sizes.

“DRLs and ADs are not intended to be used for comparisons with dose indexes for individual patients,” Kanal said in a statement. “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.”

The team is planning to conduct additional research that will include high-dose exams and different scanner configurations. They also are aiming to develop DRLs and ADs for pediatric patients.

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