ACC: Radiation dose reduction achievable, needed
NEW ORLEANS—With the risks of radiogenic cancer sparking concerns among patients and cardiologists, Andrew Einstein, MD, PhD, of Columbia University Medical Center in New York City, suggested that stakeholders consider radiation risks in balance with the benefits of the proposed imaging study. Einstein and a panel of presenters shared a list of strategies for reducing radiation dose across the spectrum of cardiovascular imaging modalities during a presentation at the annual meeting of the American College of Cardiology.

“The reason for concern is two-fold,” explained Einstein, who shared that procedure volume is increasing, with some patients receiving very high doses up to 1,000 times that of a chest x-ray.

Typical dose exposures for cardiovascular imaging exams are: 7 mSv during catheterization, 4 to 19 mSv during CT angiography and 4 to 24 mSv during SPECT studies, with cardiac PET studies associated with less radiation than SPECT. However, Einstein acknowledged that dose varies from site to site and from patient to patient. Nevertheless, it is possible to reduce dose in many scenarios and institutions.

Reducing dose during EP studies

With wide variation in radiation exposure during electrophysiology studies (EP), Sony Jacob, MD, assistant professor of cardiology at Wayne State University in Detroit, offered the ABC method of EP dose reduction:
  • Awareness. Operators, lab staff, patients, referring cardiologists and primary care physicians alike need to be aware of radiation exposure.
  • Barriers. Use shielding, aprons, thyroid collars, drapes and curtains.
  • Control the study. Consider patient positioning and fluoroscopy time. Shorter cine runs and cine frame rates can reduce dose but must be balanced with image quality needs, said Jacob.
  • Distance from source. The farther away from the system, the less exposure.
  • Education and training. All staff and trainees should be trained about dose reduction.

Jacob shared a few works-in-progress that may deliver improved dose reduction. For example, global positioning system technology and a helmet-based tracking system are being translated into a medical positioning system, which could facilitate optimal placement for minimal dose.

Other strategies that could address the issue include developing a radiation awareness culture among primary care physicians and general cardiologists; implementing safeguards to display, record and report radiation; promulgating radiation dose alerts that warn operators when dose exceeds a threshold; and developing radiation dose registries.

Reducing dose during invasive coronary angiography

Preet Ramappa, MD, assistant professor of internal medicine at Wayne State University in Detroit, confirmed that the primary goal of dose reduction efforts is to adhere to the ALARA (as low as reasonably achievable) principle.

She recommended multiple strategies: minimizing beam time, using optimal beam collimation and the lowest degree of image magnification and checking positioning of the x-ray tube and receptor. Ramappa also shared that it is possible to image patients at a frame rate of 7.5 frames per second, which can halve dose. However, in this protocol, operators need to ensure that the reduced dose does not compromise image quality.

Ramappa continued with a series of recommendations aimed at raising patients’ awareness, including: record the patient’s estimated dose, maintain x-ray records, ascertain pregnancy status, provide patient education and obtain consent.

Like Jacob, Ramappa also outlined future developments that may help address dose reduction. A robotic device to assist with the insertion of guidewires and stents could reduce dose to the operator, while MR-guided cardiac intervention eliminates dose to both patients and providers.

Appropriate use criteria and dose reduction

“The lack of knowledge of appropriate use criteria (AUC) among referring physicians, radiologists and cardiologists is one factor contributing to the overutilization of imaging,” stated Kavithat Chinnaiyan, MD, of William Beaumont Hospital in Royal Oak, Mich.

AUC can help reduce unnecessary exposure by supporting informed decision-making and eliminating unnecessary studies. In fact, Chinnaiyan emphasized the link between AUC and quality, suggesting, “Obtaining the appropriate study is at the start of the chain of quality.”

Cardiac CT AUC, revised in 2010, address 93 clinical scenarios with 35 indications coded as appropriate, 29 as uncertain and 29 as inappropriate. Early data regarding the impact of AUC appear positive.

The Advanced Cardiovascular Imaging Consortium, a Michigan-based quality initiative, set a target rate of 5 percentor fewer inappropriate CTA studies among its member organizations and implemented a rigorous education program over four years to meet its objective.

Chinnaiyan shared preliminary results; they suggested a greater than 50 percent reduction in inappropriate studies over the four years and a 30 percent increase in appropriate use.

Reducing radiation dose during SPECT, PET imaging

Gary Heller, MD, PhD, of Hartford Hospital in Conn., reported that radiation exposure for PET/CT is surprisingly low and typically falls in the 4 to 8 mSv range. Although SPECT exposure is higher, Heller asserted that nuclear cardiology can employ a number of strategies to curb dose.

Technetium is the tracer of choice for SPECT, with an average dose of 8 to 10 mSv for a rest/stress study, which represents a hefty reduction from the 15 to 20 mSv exposure incurred during thallium studies. Dual-isotope imaging tops the group at 25 mSv. “Nuclear cardiology should be moving away from dual-isotope imaging and thallium imaging,” stated Heller, adding, “Dual-isotope studies should be reserved for myocardial viability studies.” Alternately, PET perfusion studies may be utilized for the same indication.

Heller explained that protocol choice offers another route to dose reduction. Hartford Hospital has performed stress-only imaging for eight years, which has reduced radiation exposure considerably.

Dose reduction extends beyond acquisition and can include post-processing. For example, wide-beam reconstruction can cut acquisition time and reduce dose proportionately.