CT Radiation Dose Levels Vary Across Countries

A new international study shows a wide variation in the radiation dose levels used for computerized tomography (CT) scans, exposing patients to unnecessary radiation.

Researchers at the University of California, San Francisco (UCSF; USA), St. Luke’s International Hospital (Tokyo, Japan), Maastricht University Medical Center (MUMC; The Netherlands), and other institutions conducted an observational, prospective cohort study of over two million adults CT scans performed between November 2015 and August 2017 at 151 institutions across seven countries (Switzerland, Netherlands, Germany, United Kingdom, United States, Israel, and Japan).

The main outcome measures were mean effective doses and proportions of high dose examinations for abdomen, chest, combined chest and abdomen, and head CT, as determined by patient characteristics (sex, age, and size), type of institution (trauma center, care provision 24/7 centers, and academic or private locales), institutional practice volume, machine factors (manufacturer and model), country, and how scanners were used--before and after adjustment for patient characteristics--using hierarchical linear and logistic regression.

The results revealed that mean effective dose and the proportion of high dose examinations varied substantially across institutions. Even after adjusting for patient characteristics, wide variations in radiation doses across countries persisted, with a fourfold range in mean effective dose for abdomen CT examinations and a 17-fold range in proportion of high dose examinations. Similar variations were observed for chest and combined chest and abdomen CT, but doses for head CT varied less. In contrast, doses varied modestly by type of institution and machine characteristics. The study was published on January 2, 2018, in BMJ.

“We were surprised to learn that the type of machine mattered so little; it is how the machines are used that matters, telling us that there is tremendous opportunity to lower doses, without acquiring the newest machine make and model,” said lead author Professor Rebecca Smith-Bindman, MD, of UCSF. “Our analysis of assessing the variation in dose for specific clinical indications and limited to patients scanned in a single type of machine was the most surprising and highlights this finding.”

“The variation between patients was extremely high…but dose levels could be reduced virtually overnight if there was the will to do so. There is a safety imperative to standardize the protocols used for CT,” concluded Professor Smith. “Developing optimized protocols that balance image quality and dose and of standardizing and updating protocols needs to be simplified, and manufacturers need to get involved in this role. Currently, optimized protocols are not freely shared, and there is a huge role that manufacturers can play in advancing this.”

Various approaches have been used to optimize CT radiation doses. For example, doses for individual patients can be minimized by refining the scan coverage, altering technical parameters, or by software techniques such as iterative reconstruction. One widely used approach to standardize radiation doses is the creation of target dose levels or diagnostic reference levels.

Related Links:
University of California, San Francisco
St. Luke’s International Hospital
Maastricht University Medical Center