Little Guidance, CT Dose Variations Common During Pandemic

There is a need for standardized guidance with CT radiation dose when imaging patients who are COVID-19-positive, according to newly published research.

Despite being a widely used diagnostic scan throughout the pandemic, guidance has been lacking with CT, leading to protocol differences and significant variations in standard measurements of radiation dose. In an article published in the Nov. 10 Radiology, a team from Massachusetts General Hospital called for more leadership in the use of CT to reduce the risk of unnecessary radiation.

“We identify an urgent need for a dedicated task force to establish specific guidelines and recommendations on the frequency of CT and specific scan protocols to minimize the effects of cumulative radiation exposure from multiple CT and multi-phase CT protocols,” said the team led by Fatemeh Homayounieh, M.D., radiologist and post-doctoral research fellow.

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To get a better understanding of how CT has been used worldwide during the pandemic, the team conducted a retrospective study, examining data collected from a two-part International Atomic Energy Agency survey that was conducted between May 2020 and July 2020 about CT utilization, protocols, and radiation doses. The team collected details on patient age, weight, and clinical indication; specifics of CT equipment, such as make, model, installation year, and number of detector rows; scan protocols with body region, scan phases, and tube current and potential; and the radiation dose descriptors CT dose index (CTDI_vol) and dose length product (DLP).

Overall, the team assessed data from 782 patients (71 percent of whom had only one CT) from 54 healthcare sites in 28 countries to learn more about how CT and its protocols have been used during the pandemic. According to the survey responses, less than 50 percent of these sites used CT for COVID-19 diagnosis, but approximately 75 percent employed it to determine disease severity.

Once Homayounieh’s team analyzed the collected data, they realized there has been a great deal of variation in the CT dose index across vendor, number of detector rows, reconstruction techniques, and years of installation.

“Our study on variations in CT utilization, protocols, and radiation dose demonstrates a lack of guidance on CT protocols contributing to variable CT practices in COVID-19 pneumonia across different healthcare sites,” the team said, noting that no official guidance on the frequency of CT use, protocol specifics, or need for follow-up exists.

In one country, the team reported, the variations were particularly significant. Not only did they find an eight-fold variation in median CTDI_vol, but they also identified a 10-fold one in median DLP throughout a multitude of sites. In addition, the team determined, some continents -- not just countries -- have also experienced wide variations. Specifically, based on the frequency of multiple follow-up CT scans, they said, cumulative DLP for patients in Latin American was 503 mGy.com, a level that significantly surpassed the same values from three other continents – 306-382 mGy.cm

“This implies an urgent need for optimization of scan protocols and radiation doses for chest CT examination and not only limited to imaging of patients with COVID-19 pneumonia,” they said. “These differences highlight the importance of CT protocol optimization, which is as important as access to latest scanners and dose reduction technologies.”