CT radiation doses for lung-cancer screening vary widely

By Will Boggs MD

NEW YORK (Reuters Health) - 25/9/2019

CT radiation doses used for lung-cancer screening vary widely within and between institutions, researchers report.

"It is important for radiology practices to evaluate their current protocols and ensure that there is standardization and that they install a process/system that can limit such wide variation in radiation doses for a scan as specific as the low-dose lung-cancer screening scan," said Dr. Joshua Demb of the University of California, San Diego.

"While some variation in radiation dose might be anticipated due to patient differences, it is concerning that the within-facility variation is so large such that multiple radiologists might be using markedly different protocols within the same institution," he told Reuters Health by email.

Lung-cancer screening is potentially beneficial when low-dose CT techniques are used, but doses similar to those used for routine chest CT scans can cause almost as many cancers as are detected early by screening.

The American College of Radiology (ACR) recommends that lung cancer screening scans have a volume of CT dose index (CTDIvol) of 3 mGy or lower and an effective dose (ED) of 1 mSv or lower.

Dr. Demb and colleagues used data from an international CT radiation dose registry to assess how often patients received appropriate low-dose lung-cancer screening according to ACR guidelines.

Among more than 12,500 patients at 72 institutions, the mean CTDIvol adjusted for patient size was 2.4 mGy, and the mean ED adjusted for chest diameter was 1.2 mSv.

Overall, 15 institutions (21%) had a median adjusted CTDIvol higher than the ACR guideline, and 47 institutions (65%) had a median adjusted ED higher than the ACR guideline; 18% of CT scans had a CTDIvol higher than guidelines, and 50% of CT scans had an ED higher than guidelines, the researchers report in JAMA Internal Medicine, online September 23.

The odds of exceeding ACR CTDIvol dose benchmarks were 6.1-fold higher when the medical physicist was external instead of being on staff at the institution and were 12 times higher at institutions where any radiologist could establish protocols.

Institutions where lead radiologists altered protocols had a 27% lower CTDIvol, and institutions that updated protocols as needed had 27% higher doses. Results were similar in a separate analysis of ED.

Co-author Dr. Rebecca Smith-Bindman of the University of California, San Francisco, told Reuters Health by email, "The current US Preventive Services Task Force (USPSTF) guidelines call for annual CT scans among adults ages 55-80. This means that patients who are following this recommendation will undergo a lot of CT scans. If CT scans are performed with higher radiation dose than recommended, this will limit the margin of benefit of lung cancer screening."

"While the risk of radiation-induced cancer from CT is, in general, lower than the benefit conferred from finding lung cancer early through low-dose lung cancer screening, the risks of radiation-induced cancer rise when doses rise," she said. "Radiologists who perform lung-cancer screening should follow the ACR guidelines to consistently use low-dose techniques and to consistently perform only a single evaluation of the lung. This is currently not the case and we need to do better."

Dr. Demb added, "Our findings only serve as the first step to better understand why such large dose variations exist. This is part of a larger project to better understand factors associated with higher radiation dose and develop tailored strategies to optimize doses for many types of CT scans."

"In addition to this work," he said, "we believe it is important for radiology practices to internally review their practices and investigate their methodologies to see whether they can optimize their current practices to ensure that patients are getting quality CT scans with radiation doses 'as low as reasonably achievable.'"

SOURCE: https://bit.ly/2mvVVZx

JAMA Intern Med 2019.

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