Cardiac CTA radiation exposure declining, but variation persists

MUNICH — New data from the PROTECTION VI study indicate that radiation exposure from cardiac CTA has declined during the past decade, but there remains significant variability in radiation dose in clinical practice.

The international, prospective, observational PROTECTION VI study sought to investigate the radiation dose of cardiac CTA, the utilization and efficacy of established dose-saving strategies, and the independent predictors of radiation dose in real-world practice in 2017. The study included 4,502 consecutive patients undergoing diagnostic cardiac CTA at 61 international sites in 32 countries.

In 2007, data from PROTECTION I showed that the median dose-length product was 885 mGy-cm. In 2017, however, the median dose-length product was 195 mGy-cm, translating to a 78% reduction in radiation exposure during the 10-year time period (P < .001). Additionally, the median effective dose estimates decreased from 12.4 mSv in 2007 to 2.7 mSv in 2017 when using the dose conversion factor of 0.014 mSv/mGy-cm.

During this time period, the number of nondiagnostic scans did not increase and remained below 2% in 2007 and 2017, Jörg Hausleiter, MD, from Klinikum der Universität München in Germany, said during his presentation of the data at the European Society of Cardiology Congress.

Study details

Patients were enrolled consecutively during one calendar month at each individual site according to local standards of care, and all images were analyzed by a core lab in Munich. From 2007 to 2017, as expected, site experience in performing cardiac and coronary CTA increased by approximately 7 years. The number of CTAs performed per month also increased from 26 to 51 during this time period.

Modern equipment had been used in the studies, with 64-slice scanners being used in 96% of scans in 2007 and 128-slice scanners being used in 91% of scans in 2017. Distribution among manufacturers was evenly balanced.

The median patient age was 60 years, 58% were men, BMI was approximately 26 kg/m² and the main indication for performing cardiac CTA was assessment for CAD. Two-thirds of patients were given beta-blockers and the median heart rate was 60 bpm.

From 2007 to 2017, scan length increased by about 6 mm; use of tube potential of 100 kV or less increased from 5% to 56%; use of low-pitch helical protocol decreased from 94% to 11%; use of axial scan protocol increased from 6% to 78%; use of high-pitch helical scan protocol increased from 0% to 11%; and iterative image reconstruction, which was not available in 2007, was used in 83% of patients in 2017.

High variability, independent predictors

Hausleiter highlighted significant radiation dose variability during both time periods. In 2007, the median dose-length product at the site with the most radiation exposure was sevenfold higher than that at the lowest site. Despite the 78% decrease in median dose-length product from 2007 to 2017, the inter-site variability increased to 37-fold in 2017 when comparing the sites with the lowest vs. highest radiation exposure. Even after exclusion of two outliers, there was still a 10-fold difference in radiation dose, he noted.

The data also demonstrated variability in radiation exposure among regions. The median dose-length product was lowest in East Asia and Australia (169 mGy-cm) and highest in Latin and South America (295 mGy-cm).

In terms of predictors, the researchers found that an increase in patient weight, an increase in heart rate and the absence of sinus rhythm independently correlated with increased radiation exposure.

When axial scan mode was used as a reference, low-pitch helical scan mode was associated with a more than threefold increase in radiation exposure, whereas tube potential and use of iterative image reconstruction techniques significantly reduced radiation exposure. High-pitch helical scan was also associated with a reduction in radiation exposure, but it was not statistically significant.

“The current PROTECTION VI survey demonstrates that radiation exposure from cardiac CTA has been considerably reduced by almost 80% over the past 10 years. This was mainly accomplished by increased use of low tube potential scan protocols, prospectively ECG-triggered axial and high-pitch scan protocol and iterative image reconstruction,” Hausleiter said.

“With this, given the high diagnostic accuracy and low radiation dose, coronary CTA should be considered as a first-line diagnostic test in many patients. However, the large inter-site variability in median radiation dose underlines the need for site-specific training an adaptation of contemporary cardiac scan protocols.” – by Melissa Foster

Reference:

Hausleiter J, et al. Late-Breaking Science in Imaging. Presented at: European Society of Cardiology Congress; Aug. 25-29, 2018; Munich.

Disclosure: Hausleiter reports he has research contracts with Abbott Vascular.