Patient exposure to radiation during coronary CT angiography (CTA) has dropped nearly 80% over the last 10 years, largely because of innovations in technique allowed by hardware and software advances, suggests a new installment in a series of surveys documenting these changes.

The improvements in radiation exposure, seen consistently throughout the world, had no apparent practical effect on image quality, say researchers from the Prospective Multicenter Registry on Radiation Dose Estimates of Cardiac CT Angiography in Daily Practice in 2017 (PROTECTION VI).

The new report compares its findings, based on 4502 patients undergoing cardiac CT during one calendar month in 2017, to those of a similar survey from the same group based on 2007 data.

In another finding, the median site-specific CTA radiation dose per procedure varied 37-fold across the 42 university-affiliated hospitals and 19 community hospitals in 32 countries participating in the survey. Ten years earlier, it had varied by only a factor of 7.

The wider range of dosing in the new survey highlights the need for "further site-specific training and adoption of contemporary cardiac-scan protocols," said Jörg Hausleiter, MD, Klinikum der Universität München, Germany, when presenting the analysis here at the European Society of Cardiology (ESC) Congress 2018.

No Apparent Drop in Image Quality

The median dose-length product, a measure of radiation exposure, was 885 mGy × cm for coronary CTA scans in 2007. It fell to 195 mGy × cm by 2017, a decline of 78% (P < .001).

But in that period, the proportion of scans considered nondiagnostic did not significantly change (1.7% and 1.9%, respectively; P = .55); scans were evaluated at core labs.

Imaging was for coronary artery assessment in 89% of cases; the remaining cardiac CT cases were for evaluating bypass grafts or planning electrophysiologic procedures. In a multivariate comparison of the 4006 coronary CTA cases in 2017 vs. 1611 in 2007, six significant correlates of radiation dose emerged.

Of the patient-related factors, a 10-kg increase in body weight was associated with a 7% dose increase; a 10-beats/min increment in heart rate meant an 8% rise in radiation exposure, and the dose went up 21% in the absence of sinus rhythm (P < .03 for all three predictors).

Also, a 10-kVp decrease in tube potential was associated with a 21% reduction and iterative image reconstruction programming with a 30% drop in radiation dosing (P < .01 for both).

Finally, the use of electrocardiographic (ECG) gated low-pitch helical scan techniques in the 2007 survey was associated with a 313% jump in radiation exposure (P < .001) compared with the prospective ECG-triggered axial-scan techniques that later became more common.