New approaches to reduce radiation exposure
Introduction
Over the preceding three decades, the U.S. population has seen an estimated sevenfold increase in annual medical imaging ionizing radiation exposure [1]. Cardiac imaging procedures are a major contributor to population radiation exposure in the U.S., collectively accounting for nearly one-fifth of the cumulative radiation dose and approximately 40% of the cumulative dose from medical imaging procedures (Fig. 1) [1], [2], [3]. In its 2007 report, the International Commission on Radiologic Protection (ICRP) noted that cardiologists frequently receive inadequate training in radiation protection [4]. Fortunately, this is beginning to change and an increased focus on radiation safety by the cardiology community has led to advances in technology, imaging protocols, and the development of appropriate use criteria to limit radiation exposure. The purpose of this article is to provide an overview of ionizing radiation during medical imaging, including dosing metrics, risk estimation, and strategies to reduce dose and/or mitigate radiation risk during cardiovascular procedures.
Section snippets
How is radiation dose measured?
Radiation dose is a complex topic and there are a slew of different measures that quantify various aspects of radiation (Table 1). Fig. 2 demonstrates how some of these different dose measures used during fluoroscopy will vary depending on the various aspects of radiation dose that are being evaluated. Similarly for other imaging modalities, including CT and nuclear medicine scans, different metrics might be useful depending on the dosing scenario. This review focuses largely on the long-term
How much radiation from medical imaging?
Effective dose is typically reported in units of millisieverts (mSv). In its 2009 report, the National Council on Radiation Protection (NCRP) estimated an average annual exposure to an individual in the U.S. of 6.2 mSv [1], approximately half from medical imaging procedures with the other half from background sources, predominantly radon [5]. For a frame of reference, a single antero-posterior chest radiograph typically requires 0.02 mSv of effective dose. Fig. 2 demonstrates estimated
What is the risk to patients?
Ionizing radiation involves charged particles containing enough energy to displace electrons and break chemical bonds [7]. Any cell or molecule can be damaged; however, this review is primarily focused on the long-term risk of stochastic effects, most importantly iatrogenic cancer. Cancer is believed to result from misrepair of DNA damage. The extent of DNA damage is proportional to the ionizing radiation exposure and this mechanistic relationship underlies the linear, no threshold model of
Are certain populations at increased risk?
On the basis of epidemiologic studies, combined with mathematical modeling, basic science data, and expert consensus, a series of National Academy of Sciences committees on the biological effects of ionizing radiation (known by the acronym BEIR) have published cancer risk estimates for males and females based on age at exposure [7]. The most recent BEIR risk estimates highlight the substantially increased risk to females due to the risk of breast cancer, and to the young due to the increased
How to reduce radiation burden during cardiac imaging?
The principles of justification and optimization form the backbone of medical imaging dose reduction recommendations [2]. Justification means that a medical procedure should be performed only when the anticipated clinical benefits exceed all anticipated risks, including radiation risk. For individual patients the long-term risks associated with radiation exposure are extremely low. Nonetheless, according to established appropriate use criteria [16], [17], [18], a significant percentage (from
Conclusions and future directions
For the foreseeable future, procedures involving ionizing radiation will remain a vital part of cardiovascular practice; despite the great benefits of these procedures, there are inherent risks to patients and the estimated public health burden is substantial. Therefore, the cardiology community must continue to strive to minimize radiation burden but without compromising diagnostic accuracy or procedural safety. Immediate gains are achievable with improved study justification and by optimizing
Acknowledgments
The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or other funding groups.
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Dr. Hill is supported in part by Grant KL2TR001115-02 from The National Center for Advancing Translational Sciences of the National Institutes of Health, USA and a grant from the Mend A Heart Foundation. Dr. Einstein is supported in part by Grant R01 HL10971 from the National Heart Lung and Blood Institute and by a Herbert Irving Associate Professorship.
The authors have indicated there are no conflicts of interest.