A multi-facility program using ECG gating and kV reduction allowed Michigan providers to halve coronary CT angiography (CCTA) radiation dose for thousands of patients with no effect on image quality, according to a study in the June 10 issue of the Journal of the American Medical Association.
Results from multiple studies have suggested that CCTA may definitively exclude the diagnosis of coronary artery disease in a substantial proportion of well-selected patients. However, radiation dose from this procedure remains a concern.
To assess CCTA radiation dose, Blue Cross Blue Shield of Michigan and the Blue Care Network began funding the Advanced Cardiovascular Imaging Consortium (ACIC) in 2006 to provide administrative, logistical, statistical and analytical support for quality improvement. Initially, 15 hospitals of varying sizes were part of the ACIC, and a cohort registry began in July 2007.
Lead investigator Gilbert L. Raff, MD, medical director of the Ministrelli Center for Advanced Cardiovascular Imaging at Beaumont Hospitals in Royal Oak, Mich., revealed that the first two months of the study were spent collecting data to determine the radiation doses. In that time, they found that the average CCTA dose was 21 mSv, which is higher than is commonly accepted.
"Because we collectively wished to improve those statistics, we initiated an intervention phase of the one-year project, during which time we developed and implemented a program of how to properly acquire the scan with minimal radiation dose," Raff explained. "We provided each site with feedback on how each facility compared with the larger group, so they could monitor their own improvement."
The group implemented ECG-gated current dose modulation for every patient across the consortium, except in such impossible cases as atrial fibrillation. "Along with this method recommendation, we also strongly recommended the use of beta blockers to control heart rates," Raff said, adding that the axial scanning method of step-and-shoot was not available at the time of the study.
In addition, the program monitored and recommended the minimum scan length for each patient. "We encourage people to use a concise window that was related to the heart, so as to not overlap the lungs or upper abdomen," Raff said.
The program designers also sought to reduce the voltage levels from 120 kV to 100 kV, if the patient's body weight was normal.
"This turned out to be the single most effective change, because if you reduce voltage by 20 percent, it reduces the radiation dose by 40 percent," Raff stated. "This made such a dramatic difference because ECG pulsing was already being employed at many facilities prior to the study, whereas only 13 percent of the hospitals were using this method at the beginning." By the end of the study period this technique was in use with 43 percent of all patients.
Also, image quality improved. "Importantly, despite the reduction in the radiation doses, there were no significant changes during the control period compared with follow-up period in median image quality rating or the proportion of diagnostic-quality scans (89 percent in the control period vs. 92 percent in the follow-up period)," the authors wrote.
Raff attributed the success of the program to the fact that each institution had a champion or leader who could encourage staff, tweak the methods from within that facility and help communicate the "link of responsibility between the radiologist and the technologist." He also said that the CT manufacturers were very willing to send people to train the hospital staff at each institution in the new methods.
Making providers aware of their median current dose with CCTA was the first step toward reducing dose. "Once a facility became aware, they wanted to improve," Raff noted. "Knowing that they have to report their doses is tremendous impetus to change."
Also, involving an educational aspect to the dose-reduction program at every level in the imaging process contributed to its success.
"Without a feedback loop of regular dose measurements and reports, similar monitoring of patient preparation and appropriate imaging protocols and resultant image quality, there would neither be the opportunity to detect dose elevations nor the ability to improve practice," the authors noted.
During the last two months of the project, the investigators re-evaluated the data from each