Simple Steps Can Reduce Radiation Dose with Computed Tomography Angiography

ROYAL OAK, MICHIGAN, June 10, 2009 — Amid the mounting popularity of cardiac computed tomography (CT) scanning coupled with concerns over increased radiation exposure, authors of a new study say that very simple steps can reduce radiation by more than 50%, without investing in some of the newer machines that have incorporated dose-reducing technology. But they also caution that centers performing CT angiography may not realize just how much radiation their patients are exposed to.

Writing in the June 10, 2009, issue of the Journal of the American Medical Association, Dr Gilbert L Raff from Beaumont Hospital in Royal Oak, Michigan, et al reported results from a 1-year study examining dose-reducing strategies implemented in almost 5000 patients at 15 hospitals. They used a "best-practice" cardiac CT angiography model, which called for minimizing the physiological scan range, reducing the heart rate in tandem with using electrocardiography (ECG)-gated tube-current modulation, or "pulsing," and lowering the tube voltage in suitable patients.

For the primary outcome of the study—dose length and effective radiation dose—Raff et al were able to lower patients' estimated median radiation dose from 1493 mGyxcm to 697 mGyxcm (P <.001), a 53.3% reduction over an 8-month period. Effective radiation dose was also radically reduced, from 21 mSv to 10 mSv (P <.001). Over the same period, there were no changes in median image quality or in the frequency of diagnostic-quality scans, as compared with the period prior to the implementation of the dose-reducing measures.

In an interview with Heartwire, Raff pointed out that although there have been a raft of recent publications on reducing radiation dose, particularly with cardiac CT, most of them have focused on using the bells and whistles on newer CT scanners—such as step-and-shoot or dual-source technology. But the bulk of CT angiography being performed in the United States is being done on older scanners, he pointed out. "The things we wanted to look at were more basic things like limiting the physical length of the scan, using ECG pulsing, and reducing voltage. So those were the areas that we really thought implementation would be likely to reduce dose."

All of these, he said, "are still pertinent" and have "not been obviated" by newer scanners, with the exception of ECG pulsing, which has essentially been replaced by innovations like nonhelical step-and-shoot, which emits radiation only in predefined snapshots during the cardiac cycle, rather than during the whole cycle.

Raff believes a lack of awareness of these particular dose-reducing techniques is likely the main reason why people aren't using them. The number of imaging centers in the Michigan-based CT registry has "slowly and steadily" been increasing, Raff said, and each new center has come in with effective radiation doses in the range seen at baseline in his study, around 20 mSv. This number is substantially higher than rates reported in other recent studies, he noted.

An even bigger issue, he said, is that people aren't even aware of what their radiation doses are and so aren't taking any steps to reduce them. As the authors noted in the paper: "Baseline data obtained in this study support the concern that [cardiac] CTA testing may result in relatively high radiation doses, but the rapid improvement in radiation dose in the first three intervention months [a decrease of 48%] demonstrates how use of existing technology and technical methods is associated with dramatically reduced dosages."

"One of the things that we're convinced is a major issue here is whether or not you're even measuring your doses and looking at those measurements," he said. Simple things, he told Heartwire, like giving an adequate β-blocker dose to slow the heart for ECG pulsing or taking into account a person's size and weight to reduce the voltage—these are very basic strategies that people are not even aware of.

"If you turn the voltage down from 120 kVp to 100 kVp, you reduce the voltage by 20%, which reduces the dose by 40%," Raff explained. Reducing voltage from 120 kVp to 100 kVp was the strongest variable associated with achieving target radiation doses of less than 15 mSv in the study, the authors noted. Monthly volume of imaging procedures and using lower heart rates were also important factors. The weakest of the dose-reducing strategies turned out to be ECG pulsing, potentially because this was already widely in use at the study outset (74% of the time), although this usage rose to 94% by the end of the study.

Source: Heartwire