ACC: Making cuts to rad exposure does not equal loss of diagnostic quality
With six million people in the U.S. currently undergoing CT scans and the number of CT scans alone experiencing an annual growth rate of about 11-13 percent between 2000-2005, the exposure to low-dose ionizing radiation is quite concerning, said Kavitha Chinnaiyan, MD, program director of advanced cardiac imaging education within the division of cardiology at William Beaumont Hospital in Royal Oak, Mich. 

Chinnaiyan presented a case study that used quality initiatives within the Blue Cross Blue Shield of Michigan-sponsored Advanced Cardiovascular Imaging Consortium coronary CT Angiography (ACIC CCTA) registry to reduce radiation in the imaging laboratory.

“When you look at the 2007 data, you see the rise in CT scans has been exponential and just in the age groups of 36-54 years of age, for both men and women but partially in women,” she explained. “More than half of the U.S. population, particularly women are exposed to low or moderate doses of radiation from medical procedures every year.”

Noting that one of the main issues with CCTA is the high radiation dose, Chinnaiyan noted that it is inherently a factor of the low-pitch value that is required for the scanning method. “If you look at the radiation dose with regular coronary CT angiography without dose modulation, it is about 15 mSv, but there is a huge variation in the general community and the dose can actually be double this reported number,” she said.

According to Chinnaiyan, these data have sparked a “cascade of thinking” about radiation dose and the ACIC CCTA improvement project has included 50 hospitals and imaging centers across Michigan, with over 18,000 patients since its conception in July 2007.

For the study, the first quality initiative identified by the researchers was dose reduction, in which an extensive dose reduction protocol was implemented over the course of the first year.  During this year, 15 sites and 4,819 patients were included in the ACIC. Chinnaiyan said that the executive committee of the ACIC nominated a lead technologist and radiation physicist at each of the 15 sites and the project began with an intensive teaching seminar in dose reduction methods at one of the ACIC quarterly meetings.

In addition, Chinnaiyan said that subsequently, confidential reports were sent to each of the sites’ lead technologist about their specific radiation dose in relation to the rest of the consortium and what they needed to do in order to bring the dose down.

In terms of dose reduction methodology, the researchers first minimized scan length, as Chinnaiyan noted, “the greater the scan, the greater the dose.” In addition, rigorous patient preparation, including insisting that heart rate was well- controlled and the requirement that EKG dose modulation must be applied to all patients unless there was an underlying arrhythmia was employed.

Moreover, the researchers set guidelines for the use of kVp according to the patient’s body mass index (BMI). “If the patients had a BMI less than 30, but had a heart rate less than 70 beats per minute than we said to use 100 kVp and if they had a body weight of greater than 185 or BMI greater than 30, we recommended 120 kVp, which is the regular protocol,” she explained.

The 100 kVp dose, according to Chinnaiyan, is the minimum dose, in which the tube current goes down to about 4 percent. “That results in a huge 40-60 percent reduction in radiation,” she noted.

Chinnaiyan noted that the results from the first 12 months of the study were successful, as the average dose of 25 mSv in July 2007 was slashed to an average of 11 mSv by July 2008. “We had substantial reduction in radiation dose,” she said. “A large majority of patients --nearly 20 percent--were receiving about 30 mSv of radiation. During the study period, there was a consistent decline in radiation dose.”

In addition, she said that there was an increase in the number of patients that received the 100 kVp protocol (13 percent, up to 43 percent at end of the study) and EKG dose modulation went up from about 84 to 97 percent by the end of the year.

Chinnaiyan noted that the factor that makes the most difference for the use of 100kVp compared to 120 kVp was if the sites conducted more scans, they were more conscientious of radiation dose.  Also, age and BMI made a difference, since as they increase, the radiation dose rises, she said.

While Chinnaiyan believes that adequate training can result in further dose reduction, she noted that the results of the study translated to a 56 percent reduction from the study’s beginning to its end.  “This was statistically significant, as was the increased use of 100 kVp, and none of this had any change on the diagnostic imaging quality,” she said.