Cardiac CT Angiography May Expose Patients to High Radiation Dose

Use of the imaging technique known as cardiac computed tomography angiography (CCTA) has the potential to expose patients to high doses of radiation, and methods available to reduce radiation dose are not frequently used, according to a new study.

The 64-slice (able to scan 64 images per rotation) CCTA has emerged as a useful diagnostic imaging method for the assessment of coronary artery disease (CAD) and has been proposed to be useful for evaluating patients in emergency departments with chest pain. "With the constantly increasing number of CCTA-capable scanners worldwide, the volume of CCTA scans performed is likely to show substantial further increase,” the investigators reported in their article describing the study's findings, published in the February 4, 2009, issue of the Journal of the American Medical Association (JAMA). They added that the clinical usefulness of CCTA for the assessment of CAD has to be weighed against the radiation exposure of CCTA and the small but potential risk of cancer. Many clinicians may still be unfamiliar with the magnitude of radiation exposure that is received during CCTA in daily practice and with the factors that contribute to radiation dose, according to the researchers.

Jörg Hausleiter, M.D., from the Deutsches Herzzentrum München (Munich, Germany) and the Technischen Universität München (Munich, Germany), and colleagues investigated the magnitude of radiation dose of CCTA in daily practice, factors contributing to radiation dose and the use of currently available strategies to reduce radiation dose. The trial, the Prospective Multicenter Study On Radiation Dose Estimates Of Cardiac CT Angiography In Daily Practice I (PROTECTION I), an international, multicenter study (21 university hospitals and 29 community hospitals), included 1,965 patients undergoing CCTA between February and December 2007. Analysis was used to identify independent predictors associated with radiation dose, which was measured as dose-length product (DLP; equals the average radiation dose over a specific investigated volume multiplied by the scan length), which best mirrors the radiation a patient is exposed to by the entire CT scan, according to the authors.

The researchers found that the median (midpoint) DLP of the patients in the study was 885-mGy x cm (a measurement of absorbed radiation), which corresponds to an estimated radiation dose of 600 chest X-rays. A high variability in DLP was observed between study sites (range of median DLPs per site, 331-2,146 mGy x cm).

Independent factors associated with radiation dose were patient weight (relative effect on DLP, 5%); absence of stable sinus rhythm (type of heart rhythm; 10% effect); scan length (a 1-cm increase in the scan length was associated with a 5% increase in DLP); the use of electrocardiographically controlled tube current modulation (resulting in a reduction of DLP of 25%, applied in 73% of patients); 100-kV (kilo volts) tube voltage (46% reduction of DLP, applied in 5% of patients); sequential scanning (78% reduction; applied in 6% of patients); experience in cardiac CT (1% reduction); number of CCTAs per month; and type of 64-slice CT system (for highest vs. lowest dose system, 97% effect).

The investigators additionally reported, "…the study demonstrates that radiation exposure can be reduced substantially by uniformly applying the currently available strategies for dose reduction, but these strategies are used infrequently…an improved education of physicians and technicians performing CCTA on these dose-saving strategies might be considered to keep the radiation dose ‘as low as reasonably achievable' in every patient undergoing CCTA. As CCTA is being used more frequently worldwide for diagnosing coronary artery disease, all strategies for reducing radiation exposure will finally reduce the patient's lifetime cancer risks. Although the associated risk is small [estimated lifetime attributable risk of death from cancer after an abdominal CT scan is 0.02%] relative to the diagnostic information for most CT studies, this risk needs to be realized especially when repeated CT scans are being performed.”

In an accompanying editorial in the same issue of JAMA, Andrew J. Einstein, M.D., Ph.D., from the Columbia University College of Physicians and Surgeons (New York, NY, USA), wrote that there are a number of implications from this study for patient care. "First, the study results reinforce the observation that cardiac CT angiography is still a potentially high-dose procedure, and like all procedures involving the use of ionizing radiation, a patient-specific benefit-risk analysis should always be performed to justify the imaging study. Second, the findings suggest that dose-reduction methods can be used in the majority of patients, which should serve as a wake-up call to cardiac CT laboratories that do not routinely use these methods…Third, PROTECTION I reveals a degree of variability in radiation dose between sites that had not been previously appreciated, but which offers the potential to decrease radiation burden from cardiac CTA while maintaining diagnostic image quality by instituting quality improvement programs to close the gap. Fourth, the lack of clinically significant association between procedure volume and dose suggests that despite the general association between case volumes and quality of care, even many high-volume centers can benefit from such quality improvement programs. The international system of radiological protection stands on three principles: justification, optimization, and diagnostic reference levels. PROTECTION I provides valuable information pertaining to each of these in the context of cardiac CTA, and as such makes an important addition to the evidence base.”

In another statement regarding the study, the Medical Imaging & Technology Alliance (MITA; Rosslyn, VA, USA) endorsed policies that ensure medical imaging is utilized appropriately and that unnecessary scans are reduced.

The study by Dr. Hausleiter, M.D., in the February 4, 2009, issue of JAMA, correctly, MITA claims, focuses on what providers need to know to ensure that CCTA is utilized appropriately. Criteria to ensure appropriate usage of medical imaging as developed by medical professional societies is the most effective way to ensure that patients get the right scan at the right time. MITA endorses widespread adoption of appropriateness criteria and is encouraged that leading private health systems are currently using or piloting it to guide the proper utilization of medical imaging technology.

MITA also supports efforts to harness health information technology (IT) to reduce duplicative scans and unnecessary risk to radiation exposure. The association looks forward to working with all stakeholders to develop interoperable imaging exchange standards so that health IT can contribute to realizing the imaging community's goal of reducing radiation exposure.

Even with the collective efforts to reduce radiation exposure, it is important, according to MITA, to point out that CCTA, when used appropriately, minimizes other risks that more invasive procedures present to patients. Moreover, peer-reviewed research proves that CCTA is more cost effective than catheterization for some cardiac patients.

MITA also reported that it support the recent recommendation of the American Heart Association that health-care providers should diligently review patient records, including those from other medical institutions, to ensure that imaging studies are not needlessly repeated.

Medical imaging has changed the face of healthcare delivery. From detecting a disease before it becomes deadly to avoiding invasive procedures, physicians and patients rely on the value of medical imaging every day. Medical imaging is not only integral to best practices and professional guidelines, but has reduced hospital stays, returned people to work more quickly, extended lives and kept families together. When patients receive the right scan at the right time, patient outcomes are improved and health care costs are reduced, according to MITA. Researchers from Harvard Medical School (Boston, MA, USA) have demonstrated that every US$1 spent on inpatient imaging translates into approximately $3 in total savings.

MITA is the collective voice of medical imaging equipment manufacturers, innovators, and product developers. It represents companies whose sales comprise more than 90% of the global market for medical imaging technology.

Related Links:
Deutsches Herzzentrum München
Technischen Universität München
Columbia University College of Physicians and Surgeons
Medical Imaging & Technology Alliance