The American Heart Association (AHA) recently published a scientific statement promoting the enhancement of radiation safety in cardiovascular imaging.¹ The document outlined three approaches for achievement of that goal: through education, justification, and optimization. The education recommendations involve making sure that both patients and clinicians have an understanding of the possible risks and benefits that could result from imaging procedures. Justification represents ensuring that the imaging is clinically necessary and appropriate. Optimization involves the effort to make sure that the lowest possible radiation exposure is achieved while maintaining high diagnostic accuracy. The statement also addresses perceived barriers to the implementation of dose-reduction strategies. The following summarizes these recommendations.

Education

Education is seen as the foundation for any attempts to increase safety in medical imaging. This educational effort should include both patients and clinicians. Studies have shown a lack of awareness on the part of clinicians regarding their knowledge of CT scans increasing the lifetime risk of cancer. The paper proposes that clinicians should be made aware of these issues through educational strategies. Clinicians should be able to weigh the risks versus benefits of imaging for appropriate match-up of patient and testing.

Education in medical schools, residencies, and fellowships should address the following: basic understanding of the available imaging modalities and their accuracy in specific clinical situations; cost-effective, evidence-based usage emphasizing pertinent guidelines and appropriate use principles; basic concepts related to radiation exposure and the concepts of absorbed and effective dose; and radiation dose estimates for commonly used procedures and risk estimates associated with these doses.¹ Enhanced communication skills related to this content is also deemed important for effective communication with patients.

In addition, those performing tests should have a detailed knowledge of how equipment functions, dose-optimization techniques for the types of studies performed, and dose-minimization techniques for operators and staff.¹ Table 1 summarizes this content.

Practicing clinicians should demonstrate knowledge of these competencies through board certification and re-certification. Clinicians should also stay abreast of developments through the published literature and national scientific meetings. 

In many settings, physician assistants or nurse practitioners also order imaging studies. Therefore, these professionals should understand radiation safety principles as well.

Radiation technologists and staff should receive education about radiation sources, patient doses, biological effects of ionizing radiation, radiation protection, dose-optimization techniques, and radiation regulations.¹

Patients and the public need access to resources to educate and inform them in a balanced way. Strategies for effective communication of benefits and risks, shared decision making, and informed consent should be employed. Table 2 contains the recommendation related to shared decision making.

Justification

The key first step in radiation safety is the appropriate selection of the patient for the test. In this scenario, clinical benefits usually outweigh potential risks. However, if a comparable test with less radiation exposure or no exposure is available, that test is preferred. The approaches to implementation of this justification are patient-centered imaging, adherence to pertinent appropriate use criteria (AUC), and use of scientific guidelines.

Patient-centered imaging is individualizing test selection for every patient, looking at the values of the patient, their preferences, epidemiological characteristics, and the clinical scenario. One approach that was discussed to help achieve this in a busy practice was the development of educational materials for patients to help them make more informed decisions. 

AUCs have been developed for cardiac radionuclide imaging (2009), cardiac CT (2010), coronary revascularization (2009), invasive coronary angiography (2012), and ICD and resynchronization therapy (2013).¹ However, these do not deal with exposure to ionizing radiation or comparative effectiveness of modalities. They do, however, address the issue of inappropriate tests. The promotion and development of AUCs is considered a further area of need.

Optimization

Once an imaging test is considered appropriate and necessary, the goal of optimization is to perform the study with minimal radiation exposure while maintaining high diagnostic accuracy.¹ Difficulties related to measuring radiation exposure and dose are discussed in the paper, as are strategies for improvement. In addition, individual differences related to dosing are reviewed.

There are challenges in the measuring of the absorbed radiation dose given to a patient. The amount of radiation delivered by a device may be known, but the amount absorbed by the patient could depend on size, shape, and tissue composition. Discussion focusing on cardiac CT, nuclear cardiology, and fluoroscopy-related issues is included in the statement. The AHA also provides guidance on measuring scanner output for a cardiac CT study, and a method is suggested for determining the volume of CT dose. Fluoroscopic radiation dose metrics and excessive dose quantities are also reviewed. Institutional trigger levels indicative of excessive radiation doses should prompt the need for counseling of patients prior to discharge, to initiate continued follow-up in order to monitor for adverse effects of large dosages. The first recommendation in Table 3 reflects this.

There are also modality-specific optimization techniques to be considered. There have been many technical advances in cardiac CT scanning which have led to higher quality imaging with lower radiation exposure levels. This situation can be improved further through more individualizing of scanning protocols. In nuclear cardiology, testing with positron emission tomography (PET) leads to a lower radiation dose than with single-photon emission CT (SPECT), but SPECT may be preferred in patients who are tested while exercising. The good news is that in SPECT and PET scanning, new hardware and software advances have been made, giving higher image quality and diagnostic accuracy with a lower injected dose. With fluoroscopy, the actual rates of radiation are determined by a combination of selected mode, patient characteristics, and operator behavior. Methods to reduce exposure rates during use of fluoroscopy are summarized in the statement.

There is also a recommendation for evaluation (and eventual public reporting) of the performance of cardiac imaging practices relative to national benchmarks. A great deal of variation exists among and within imaging centers for dosing in the same study type. The statement proposes a public database be developed for comparison of practices to promote quality control and improvement. This would be used for benchmarking data and to assist in the study of radiation reduction methods. This is a recommendation also found in Table 3.

Another area identified is the need for diagnostic reference levels (DRLs) for radiation exposure related to cardiac imaging. DRLs are radiation exposure levels for a standardized procedure, and are used as a quality control tool. They may also be used for comparison of practices. Exceeding DRLs consistently suggests the need to reevaluate practices. Use of DRLs has led to adoption of optimization techniques for decreasing exposure. The paper suggests more development of standards for testing. Some DRLs are currently in development.

There is a recognition that there are limitations to the ability to track patient radiation history. A mechanism for continuous updating needs to be developed. Individuals could keep their own record of exposure, and a card to record this (called a Patient Medical Imaging Record) is available on the FDA website. Health care workers could also be responsible for this recordkeeping, although it is recognized this would take a great deal of manpower. In spite of information gleaned from a cumulative exposure record, benefits and risks of each test should still be determined by a physician and patient based on the current diagnostic challenge.

Future Priorities for Research 

Future research priorities in radiation safety include continued technical developments in imaging; assessing the benefit of imaging in various clinical scenarios using clinical trials and comparative effectiveness studies; continued refinement of AUCs; improving methods of effective communication with patients; epidemiologic studies of the effects of radiation exposure; and identification of cellular biomarkers of radiosensitivity. Table 4 contains the group’s recommendation related to research. 

Summary

Radiation safety is an issue we can all support. This scientific statement from the AHA provides a framework to promote improved practice and increased safety for patients and staff during imaging procedures.

Reference

1. Fazel R, Gerber T, Balter S, et al. Approaches to Enhancing Radiation Safety in Cardiovascular Imaging: A Scientific Statement From the American Heart Association [published online ahead of print September 29, 2014]. Circulation. https://circ.ahajournals.org/content/early/2014/09/29/CIR.0000000000000048.citation. Accessed October 7, 2014.