Radiation Dose for Coronary CTA Plummets With New Scanner Technology

Marlene Busko

August 13, 2013

ROYAL OAK, MI — When imaging centers adopted advanced scanning technology tools, the median radiation dose from coronary computed tomography angiography (CTA) dropped by 31%, without any significant loss in acceptable image quality, a new study reports[1]. After 15 centers in Michigan that participated in the Advanced Cardiovascular Imaging Consortium (ACIC) adopted new CT-scanner hardware and software technology, the median effective radiation dose dropped from 9.5 mSV to 6.6 mSv.

The sites already had a 53% drop in effective radiation dose after a year of adopting an ongoing intensive education program based on a best-practice algorithm, as previously published [2] and reported by heartwire .

"Advanced technology in CT scanning makes a huge difference in dose," lead author Dr Kavitha M Chinnaiyan (William Beaumont Hospital, Royal Oak, MI) told heartwire . "All physicians performing CTA need to be aware of [advanced technologies] and apply them," she said. In addition, "best-practice algorithms are essential, monitoring the radiation dose should be a part of every CT lab, and monitoring a patient's total dose from all their imaging studies is extremely important again." This study also suggests that having a collaborative quality-improvement program, carefully selecting appropriate patients, and having a feedback loop to correct practice deficiencies are other valuable ways to improve CTA safety, she added.

The study was published online August 7, 2013 in Circulation: Cardiovascular Imaging.

Collaborative Quality Improvement Initiative

ACIC is a collaborative CTA quality-improvement initiative sponsored by the Blue Cross Blue Shield/Blue Care Network in Michigan, which began in July 2007 with 15 hospital and outpatient imaging centers and now includes 43 centers.

The investigators performed a prospective, controlled, nonrandomized study of 11 901 patients seen at the original 15 centers, in three time periods:

  • May to June 2008: Control period.

  • July 2008 to June 2009: Follow-up 1.

  • July 2009 to April 2011: Follow-up 2, after sites had adopted new scanner hardware or software.

The sites used seven scanners from four manufacturers. The advanced technologies introduced in follow-up 1 included a high-pitch helical CT scanner (one site), adaptive statistical iterative reconstruction (three sites), a volumetric 320-slice CT scanner (one site), and prospective gating (six of the remaining 10 sites).

"Prospective gating is like a 'step-and-shoot' approach . . . where the scanner is turned on only during the part of the cardiac cycle when we know the heart will be still . . . so the [radiation] dose is really low compared with retrospective gating, where the scanner is on throughout the cardiac cycle," Chinnaiyan explained. This technique "requires more stringent preparation of the patient--the heart rate needs to be low . . . [and] . . . steady [with] no arrhythmia--and it requires a [CT-scanner] software update."

Each quarter, site physicians received lectures and individualized on-site education about new scan technology and obtained performance feedback. Sites that did not achieve the target of a 10-mSv radiation dose were contacted to discuss ways to improve.

By the final bimonthly dose measurement, the median effective radiation dose was 4.9 mSv.

Lowering the radiation dose did not significantly decrease the percentage of scans that had diagnostic-quality images, which remained at around 92% throughout the study.

Lower Tube Voltage, Prospective Gating, Feedback Loop

The most significant variables that were associated with achieving a median radiation dose of <10 mSv were: a lower peak tube kilovoltage (kvP) of 100 kVp (odds ratio 3.12), nonretrospective gating (OR 2.236), body-mass index (BMI) <30 kg/m2 (OR 1.731), high monthly scan volume (OR 1.384), and female sex (OR 1.092).

If the tube voltage is decreased from 120 kVp to 100 kVp, the radiation dose decreases by 40%, Chinnaiyan explained. Ensuring stringent prescan heart-rate control with beta blockade and minimizing the scan length were two other strategies to reduce the radiation dose that had the highest impact.

"Selecting the appropriate patients for this test is important, because it's a radiation-based test and we don't want to use it indiscriminately," Chinnaiyan added. Coronary CTA performs best to rule out disease, so according to the guidelines, it should not be used for asymptomatic patients or very high-risk patients, she noted.

Physicians need to constantly reevaluate the procedure to set the acceptable median radiation dose. "In our registry, we started off with 15 mSv as acceptable. We came down to 10 mSv, and now we are lowering it even more--it needs to be below 7 or 8 mSv," she said. This type of dose reduction "is achievable . . . in any setting where radiation dose is monitored and there is a feedback loop," according to Chinnaiyan.

Blue Cross/Blue Shield of Michigan provided research funding. Chinnaiyan received grant support from the American Heart Association. Disclosures for the coauthors are listed in the paper.

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