Radiation Dosing at Coronary CT Angiography Plunged Worldwide in Past Decade

September 07, 2018

MUNICH — 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.

Hausleiter is also senior author on its same-day publication in the European Heart Journal with lead author Thomas J. Stocker, MD, Ludwig-Maximilians-Universität München, Germany.

He said the analysis should help alleviate any lingering concerns that radiation exposure at CTA is so high as to pose a risk for cancer or other disorders, especially cumulatively in patients who need repeated imaging. "At least in the past, there was always that notion," he told theheart.org | Medscape Cardiology.

At the currently lower radiation exposure levels from CTA, Hausleiter said, "the associated risk of cancer is negligible. The benefit outweighs it significantly."

"With these results today, I think it's very clear that we've come down to a level where, at least in the patients we investigated, with a median age of 60, it doesn't really matter if you  use 2 mSv or 4 mSv," he said. "From my perspective, if you are below 5 mSv, then I don't think that you really harm the patient."

Message for Special Cases

Based on such reassurances, the analysis also has a message for managing special cases, observed U. Joseph Schoepf, MD, from the Medical University of South Carolina, Charleston. "There are certain scenarios where you need a little more radiation to create images that are diagnostic," he said in an interview. They include many obese patients or those with arrhythmias, for example.

The current findings suggest "you shouldn't shy away from investing a little more radiation to make sure those patients get the best possible diagnosis that they can get."

Schoepf acknowledged that PROTECTION VI centers were likely among the most sophisticated and high-performing if they offered coronary CTA in the first place and participated in the survey, which may have introduced bias.

But he agrees that the current study, in which he did not take part, should end any remaining safety concerns about CTA radiation exposure. "This study should probably put a nail in the coffin of the radiation discussion. I think what people should focus on right now is to provide the best possible diagnosis for their patients."

The decade since collection of the 2007 data saw dramatic expansion of coronary CTA use and closely followed introduction of 64-slice CT systems, Schoepf said. "They were the first CT platforms that enabled cardiac CT on a larger scale."

In the 2007 survey, 96% of scans were obtained by using 64-slice systems; by 2017, 91% of scans were on systems of at least 128 slices. Four major CT system manufacturers (General Electric, Philips, Siemens, and Toshiba) were similarly represented in both surveys.

The concerns about CTA radiation also grew during the decade, leading to efforts in the imaging community to reassure the public and clinicians that exposures could be reigned in; surveys like those contributing to the current report were one result, Schoepf said.

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).

In addition, 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.

It was a "concerted and conscious effort to reduce radiation that took full advantage of the technical opportunities that advanced CT platforms provided us with," Schoepf said, along with "a willingness of the field to explore and embrace them, that led to those dramatic reductions in radiation doses that we see here."

Hausleiter discloses research support and speaker honoraria from Abbott Vascular and Edwards LifeSciences; disclosures for the other authors are in the report. Schoepf discloses research support from Astellas, Bayer, and Siemens and personal fees for speaking or consulting from Bayer, General Electric , Guerbet, HeartFlow, and Siemens.

European Society of Cardiology (ESC) Congress 2018. Late Breaking Science in Imaging. Presented August 25, 2018.

Eur Heart J. Published online August 25, 2018. 25. Abstract

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