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Canadian Journal of Cardiology

Canadian Cardiovascular Society Position Statement on Radiation Exposure From Cardiac Imaging and Interventional Procedures

Published:September 12, 2013DOI:https://doi.org/10.1016/j.cjca.2013.06.002

      Abstract

      Exposure to ionizing radiation is a consequence of many diagnostic and interventional cardiac procedures. Radiation exposure can result in detrimental health effects because of deterministic (eg, skin reaction) and stochastic effects (eg, cancer). However, with the levels experienced during cardiac procedures these risks can be difficult to quantify. Healthcare providers and patients might not fully appreciate radiation-related risks. Though in many cases radiation exposure cannot be avoided, a practice of minimizing exposures to levels “as low as reasonably achievable” (ALARA principle) without compromising the utility of the procedure is encouraged. The purpose of this document is to inform health care providers on the key concepts related to radiation risk from common cardiac procedures and provide specific recommendations on ensuring quality of care.

      Résumé

      L'exposition au rayonnement ionisant est la conséquence de plusieurs actes de cardiologie diagnostique et interventionnelle. L'exposition au rayonnement peut entraîner des effets préjudiciables à la santé en raison d'effets déterministes (par ex. la réaction cutanée) et stochastiques (par ex. le cancer). Cependant, moyennant les niveaux d'intensité subis durant les actes de cardiologie, ces risques peuvent être difficiles à quantifier. Les prestataires de soins et les patients pourraient ne pas réaliser pleinement les risques liés au rayonnement. Bien que dans plusieurs cas l'exposition au rayonnement ne puisse être évitée, la pratique d'une radioprotection par une exposition à une intensité « aussi faible que raisonnablement possible » (principe ALARA : as low as reasonably achievable) ne compromettant pas l'utilité de l'acte est encouragée. Le but de ce document est d'informer les prestataires de soins sur les concepts principaux liés au risque du rayonnement provenant des actes habituels en cardiologie et de fournir des recommandations particulières pour assurer des soins de qualité.

      Introduction

      The medical use of ionizing radiation for diagnostic and interventional procedures and the subsequent exposure burden to the population is ever increasing. For example, estimates in the United States show a 15-fold increase in the number of radiologic and nuclear medicine procedures over the past half century.
      • Mettler F.A.
      • Bhargavan M.
      • Faulkner K.
      • et al.
      Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources—1950-2007.
      Likewise, use of computed tomography (CT) has increased at an estimated rate of 10% per year and the number of cardiac catheterization procedures has doubled over the decade ending in 2006.
      • Mettler F.A.
      • Bhargavan M.
      • Faulkner K.
      • et al.
      Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources—1950-2007.
      Because of the combination of increased procedure volumes and, in some cases, increased individual procedure-related (acute) radiation exposure,
      • Mercuri M.
      • Xie C.
      • Levy M.
      • Valettas N.
      • Natarajan M.K.
      Predictors of increased radiation dose during percutaneous coronary intervention.
      the total per capita effective exposure from medical sources now outweighs that from natural background sources in the United States.

      United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR 2000 Report to the General Assembly, with scientific annexes. UNSCEAR 2000 Report Vol. II: Sources and Effects of Ionizing Radiation: Annex G: Biological Effects at Low Radiation Doses. New York, NY: United Nations, 2000.

      Furthermore, a small number of patients undergo multiple procedures that have relatively high radiation exposure in a short period of time. These repeat procedures can result in high cumulative exposures.
      • Eisenberg M.J.
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      • Lawler P.R.
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      • Pilote L.
      Cancer risk related to low-dose ionizing radiation from cardiac imaging in patients after acute myocardial infarction.
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      Exposure to low-dose ionizing radiation from medical imaging procedures.
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      • Bernheim A.
      • et al.
      Multiple testing, cumulative radiation dose, and clinical indications in patients undergoing myocardial perfusion imaging.
      However, the increased use of ionizing radiation-emitting medical modalities, and the potential risks they carry must be viewed in the context of the benefits to patients. For example, in the United States where advanced diagnostic imaging procedures increased rapidly, there was a concomitant increase in life expectancy in the exposed population

      Lichtenberg FR. The Quality of Medical Care, Behavioral Risk Factors and Longevity Growth. National Bureau of Economic Research. Working Paper 15068, 2009.

      (Supplemental Text S1).

      Terminology

      When biological tissue is exposed to ionizing radiation some of the energy might be absorbed. The amount of energy deposited in the tissue per unit mass is known as the absorbed dose (measured in greys; Gy). The equivalent dose is obtained by multiplying the absorbed dose by a radiation weighting factor; for x-rays the weighting factor is 1. This is distinct from the effective dose (measured in sieverts; Sv), which accounts for the different radiosensitivities of various biological tissues. The effective dose is estimated by multiplying the equivalent dose with a tissue weighting factor. The sum of the tissue weighting factors over all tissues in the body is equal to 1. The cumulative effective dose (Sv) is the summation of all (effective) doses to an individual over a specified period of time. The collective effective dose is the summation of all (effective) doses to a specified population over a specified period of time. Collective effective dose is generally used for optimization and comparison of radiological technologies or procedures. Collective effective dose is not intended and should not be used for epidemiological studies or for risk projections.
      The 2007 Recommendations of the international commission on radiological protection. ICRP publication 103.
      The different categories of dose are outlined in Table 1. It is important to realize that absorbed dose is a physical quantity, whereas equivalent and effective dose are derived quantities used for radiological protection purposes.
      Table 1Basic dose definitions
      QuantityDescriptionEquivalencyUnit
      Absorbed dose (D)Energy absorbed per unit massNumber of J absorbed per kilogram of material1 J/kg = 1 Gy
      Equivalent dose (H)Takes into account the effectiveness of different radiation types in doing damage to tissue using a dimensionless radiation weighting factor wrH = wr × DSv
      Effective dose (E)Takes into account the potential for detrimental effects to the various organs and tissues using a dimensionless tissue weighting factor wtE = wt × HSv
      There are 2 general classes of radiation-induced effects: deterministic, and stochastic. Deterministic effects are threshold-dependent, largely because of cell death, with the severity increasing relative to the exposure. Tissue reactions, including cataract induction, lung fibrosis, and skin depilation, erythema, and necrosis, are considered deterministic in nature.
      • Fritz-Niggli H.
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      • Koenig T.R.
      • Wolff D.
      • Mettler F.A.
      • Wagner L.K.
      Skin injuries from fluoroscopically guided procedures: part 1, characteristics of radiation injury.
      • International Commission on Radiological Protection (ICRP)
      The Biological Basis for Dose Limitation in the Skin. ICRP Publication 59. Annals of the ICRP Vol. 22, No. 2.
      Stochastic effects are those in which the severity of the effect is not determined by the magnitude of the exposure. However, there is a greater chance of stochastic effects as the radiation exposure increases. Radiation-induced genetic disorders and cancers (eg, solid tumour, leukemia) because of DNA alterations in living cells are considered stochastic in nature.
      • Rao B.S.
      Stochastic effects of radiation. In: IAEA Regional Basic Professional Training on Radiation.
      There is debate over (1) the magnitude of risk at low levels of radiation exposure (in the range of many medical procedures), and (2) how to best extrapolate risks from relatively higher exposures (eg, atomic bomb survivors) in which such data exist to lower levels for which there is no robust epidemiologic evidence. A common method is to use a linear projection of risk extrapolated from exposures of atomic bomb survivors (ie, linear nonthreshold model [LNT]; Fig. 1 and detailed in Supplemental Text S2). However, the current evidence suggests no conclusive proof of risk at very low exposures, and weak evidence at less than acute doses of 50 mSv and protracted doses of 100 mSv. Though the literature suggests potential for skin injury from fluoroscopic procedures, the overall radiation-related risks to the patient should at this time be considered very low.
      Recommendation
      • 1.
        That Canadian cardiologists adopt the LNT model for purposes of general radiation protection (Strong Recommendation, Low-Quality Evidence).
      Values and preferences. Though the evidence is weak, considering the general acceptance of the LNT model among major radiation protection agencies and for encouragement of the “as low as reasonably achievable” (ALARA) principle, there was broad consensus that cardiologists and radiologists should adopt this model. However, meaningful thresholds in clinical practice might include:
      • i.
        Patient skin doses exceeding 4 Gy are at risk of skin injury.
      • ii.
        Acute whole body effective doses of greater than 50 mSv or whole body cumulative effective doses of greater than 100 mSv are at risk of stochastic effects, with risk being inversely proportional to age because of tissue radiosensitivities. Furthermore, we suggest that more large epidemiological studies be undertaken to determine the magnitude of risk of radiation-induced injury from cardiac procedures.
      Figure thumbnail gr1
      Figure 1General characteristics of typical risk model curves. The curves are not intended to be compared quantitatively with each other. It is also worthy to note that the curves are representative of shape and do not indicate any particular risk-response as a function of (arbitrary) dose. All models, except for the threshold model, assume that there is risk at all doses greater than zero. The hormesis curve, inset at low dose, shows positive effect as a function of dose at low dose. The downward curve depicts the effect of attenuation as a result of cell killing at higher doses. RR, relative risk.

      Cardiac Diagnostics and Procedures Using Ionizing Radiation

      In total, cardiology is the source of one-third of the collective dose from medical modalities.
      • National Council on Radiation Protection and Measurements
      Ionizing Radiation Exposure of the Population of the United States: 2006. NCRP Report No. 160.
      Furthermore, the magnitude and proportion of the collective exposure directly attributable to cardiology practice is variable and likely increasing, because myocardial perfusion imaging, cardiac CT, and percutaneous coronary intervention procedures are on the rise. Though these estimates are based on U.S. data, Canadian figures are similar.
      • Scott-Montcrieff A.
      • Yang J.
      • Levine D.
      • et al.
      Real-world estimated effective radiation doses for commonly used cardiac testing and procedural modalities.
      Typical doses for various cardiac procedures are listed in Table 2.
      • Mettler F.A.
      • Bhargavan M.
      • Faulkner K.
      • et al.
      Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources—1950-2007.
      Table 2Effective doses for various cardiac imaging procedures
      ExaminationAverage effective dose (mSv)Range in literature (mSv)
      Chest X-ray0.10.05-0.24
      CT calcium scoring31.0-12
      CCTA (initial reports)165.0-32
      CCTA (achievable)5.03.0-7.6
      Coronary angiogram
      Effective doses might vary significantly according to complexity of procedure (eg, simple single-vessel PCI < complex multi-vessel or CTO PCI; simple EPS procedure vs complex EPS ablations).
      72.0-15.8
      Coronary PCI or EPS
      Effective doses might vary significantly according to complexity of procedure (eg, simple single-vessel PCI < complex multi-vessel or CTO PCI; simple EPS procedure vs complex EPS ablations).
      156.9-57
      Nuclear Stress-rest study
      Effective dose varies significantly based on protocol. Data from Mettler et al.15
      99mTc-sestamibi9.4 (1100 MBq) (0.0085 mSv/MBq)
      99mTc-tetrofosmin11.4 (1900 MBq) (0.0076 mSv/MBq)
      Rest ventriculography
      99mTc-labelled rbc7.8 (1110 MBq) (0.007 mSv/MBq)
      Cardiac PET
      18F-FDG5.0-14.1 (740 MBq) (0.019 mSv/MBq)
      Rubidium-822.0-7.5
      CCTA, cardiac computed tomography angiography; CT, computed tomography; CTO, chronic total occlusion; EPS, electrophysiology studies; FDG, fluorodeoxyglucose; PCI, percutaneous coronary intervention; PET, positron emission tomography; rbc, red blood cell; 99mTc, technetium.
      Effective doses might vary significantly according to complexity of procedure (eg, simple single-vessel PCI < complex multi-vessel or CTO PCI; simple EPS procedure vs complex EPS ablations).
      Effective dose varies significantly based on protocol. Data from Mettler et al.
      • Mettler F.A.
      • Huda W.
      • Yoshizumi T.T.
      • Mahesh M.
      Effective doses in radiology and diagnostic nuclear medicine: a catalog.

      Fluoroscopy-driven diagnostic tests and procedures

      The reported radiation doses for fluoroscopic procedures vary widely because of operator and procedural characteristics.
      • Mercuri M.
      • Xie C.
      • Levy M.
      • Valettas N.
      • Natarajan M.K.
      Predictors of increased radiation dose during percutaneous coronary intervention.
      • Mercuri M.
      • Mehta S.
      • Xie C.
      • Valettas N.
      • Velianou J.L.
      • Natarajan M.K.
      Radial access as a predictor of increased radiation exposure during a diagnostic cardiac catheterization procedure.
      These procedures are somewhat distinct from other modalities that use ionizing radiation in that the operator also receives a meaningful radiation exposure. Operator exposure in Canada is carefully regulated and monitored by governmental agencies.
      Numerous radiation exposure and dose metrics have been developed specifically for this class of procedures. The most basic is fluoroscopy time, which measures the total time the fluoroscopy device is active. Fluoroscopy time is not considered a good measure, because it does not account for the intensity of output from the x-ray tube. Air kerma (Gy), measured at a defined interventional reference point, and the related dose area product (Gy-cm2) are the preferred measures. These measures can be used in conjunction with spatial parameters and tissue weighting factors to estimate organ and whole body effective doses.
      • National Council on Radiation Protection and Measurements
      Radiation Dose Management by Fluorocopically-Guided Interventional Medical Procedures. NCRP Report No. 168.
      However, these more discriminatory measures are not routinely or reliably captured and reported. Collection of such information in prospective registries could identify procedures that exceed the 95th percentile for exposure based on national benchmarks.
      • Doyle T.
      • Bergersen L.J.
      • Armstrong A.L.
      • et al.
      Radiation exposure metric. Paper presented at: The Annual Scientific Session of the American College of Cardiology.

      National Cardiovascular Data Registry—IMPACT Registry. Available at: https://www.ncdr.com/webncdr/impact/. Accessed August 6, 2013.

      • Jenkins K.J.
      • Beekman III, R.H.
      • Bergersen L.J.
      • et al.
      Databases for assessing the outcomes of the treatment of patients with congenital and paediatric cardiac disease–the perspective of cardiology.
      Technique plays an important role in the magnitude of radiation exposure (and thus dose) to the patient and operator during fluoroscopy procedures. Hirshfeld et al. provide a review of how to reduce exposure by optimizing technique and ensuring best practice in using personal protective equipment.
      • Hirshfeld Jr., J.W.
      • Balter S.
      • Brinker J.A.
      • Kern M.J.
      • Klein L.W.
      • Lindsay B.D.
      • et al.
      ACCF/AHA/HRS/SCAI clinical competence statement on physician knowledge to optimize patient safety and image quality in fluoroscopically guided invasive cardiovascular procedures.

      Catheter-based interventions in pediatric patients

      Cardiac catheterization in children has become a critical component of diagnosis and therapy. The principles of radiation safety take a predominant role in planning and execution of such procedures because of the repeated exposures over a lifetime, increased radiosensitivity of children, and a longer time for side effects to manifest. Radiation exposure can be very high in the pediatric patient because of the complexity of interventions, small body size, higher heart rates requiring faster frame rates, and wide anatomical variations.
      The precautions recommended for adult patients apply equally to children. Children born with congenital heart disease frequently undergo numerous diagnostic and therapeutic catheterizations, with potential harmful cumulative long-term effects of radiation exposure.
      • Andreassi M.G.
      • Ait-Ali L.
      • Botto N.
      • Manfredi S.
      • Mottola G.
      • Picano E.
      Cardiac catheterization and long-term chromosomal damage in children with congenital heart disease.
      • de Gonzalez A.B.
      • Mahesh M.
      • Kim K.
      • et al.
      Projected cancer risks from computed tomographic scans performed in the United States in 2007.
      The complex 3-dimensional anatomy of these lesions frequently necessitates multiple digital acquisitions, which increase the radiation exposure. Imaging equipment used for pediatric procedures should be designed and configured for image acquisition modified to accommodate variable procedural requirements and wide age and weight range as seen in the pediatric laboratory.
      • Strauss K.J.
      Pediatric interventional radiography equipment: safety considerations.
      Strategies for radiation exposure reduction and image quality in pediatric populations have been well described
      • Justino H.
      The ALARA concept in pediatric cardiac catheterization: techniques and tactics for managing radiation exposure.
      and the importance of exposure reduction is emphasized in the Image Gently and Step Lightly campaigns.
      • Sidhu M.K.
      • Goske M.J.
      • Coley B.J.
      • et al.
      Image gently, step lightly: increasing radiation exposure awareness in pediatric interventions through an international social marketing campaign.

      Cardiac CT

      CT imaging has rapidly increased in use, and become an invaluable tool for the diagnosis of a broad spectrum of disease entities.
      • Shrimpton P.C.
      • Edyvean S.
      CT scanner dosimetry.
      • Lee C.I.
      • Haims A.H.
      • Monico E.P.
      • Brink J.A.
      • Forman H.P.
      Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks.
      • Mayo J.R.
      • Leipsic J.
      Radiation dose in cardiac CT.
      Developments in CT gantry technology in the past 10 years (eg, slip rings, z-axis segmented detector arrays, subsecond gantry rotation) have provided faster image acquisition that facilitated development of cardiac-gated CT angiography (CCTA).
      • Achenbach S.
      • Ulzheimer S.
      • Baum U.
      • et al.
      Noninvasive coronary angiography by retrospectively electrocardiographic-gated multislice spiral CT.
      • Becker C.
      • Knez A.
      • Ohnesorge B.
      • Schöpf U.
      • Reiser M.
      Imaging of noncalcified coronary plaques using helical CT with retrospective EKG gating.
      • Nieman K.
      • Oudkerk M.
      • Rensing B.J.
      • et al.
      Coronary angiography with multi-slice computed tomography.
      CCTA has rapidly been adopted for noninvasive coronary artery imaging because it provides high-contrast cross-sectional views of the coronary arteries without limitations on the imaging plane or field of view. Utilization of CCTA has a historically high price: increased radiation exposure to the population. Multiple technological advancements have, however, resulted in a steady decrease in radiation dose over the past decade.
      • Galiwango P.
      • Chow B.J.
      Cardiac computed tomography and risks of radiation exposure: how low can we go?.
      • Heydari B.
      • Leipsic J.
      • Mancini G.B.
      • et al.
      Diagnostic performance of high-definition coronary computed tomography angiography performed with multiple radiation dose reduction strategies.
      Radiation exposure from CCTA is proportional to the tube current, exposure time, and the square of tube voltage and is inversely proportional to the pitch for helical acquisition. Estimated radiation doses for CCTA examinations can be expressed in numerous terms. These are the volume CT dose index (mGy), and dose length product (mGy cm).
      • Lee C.I.
      • Haims A.H.
      • Monico E.P.
      • Brink J.A.
      • Forman H.P.
      Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks.
      The estimated effective dose for a patient is obtained by multiplying dose length product by a conversion factor, k (mSv mGy−1 cm−1) that varies dependent on the body region that is imaged.
      • Hataziioannou K.
      • Papanastassiou E.
      • Delichas M.
      • Bousbouras P.
      A contribution to the establishment of diagnostic reference levels in CT.
      These normalized effective dose coefficients are determined using Monte Carlo techniques and consider the radiation sensitivity of the body region scanned based on exposed organ radiosensitivities.
      Because of the growth in utilization of CCTA, there is increasing scrutiny regarding its appropriateness and associated radiation exposure.
      • Starck G.
      • Lönn L.
      • Cederblad A.
      • Forssell-Aronsson E.
      • Sjöström L.
      • Alpsten M.
      A method to obtain the same levels of CT image noise for patients of various sizes, to minimize radiation dose.
      • Hausleiter J.
      • Meyer T.
      • Hermann F.
      • et al.
      Estimated radiation dose associated with cardiac CT angiography.
      In 2009, a sample of 50 international sites as part of the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography in Daily Practice (PROTECTION) I study highlighted a wide variation in protocols used for CCTA, demonstrating a 6-fold difference in median patient radiation exposure among the participating study sites.
      • Hausleiter J.
      • Meyer T.
      • Hermann F.
      • et al.
      Estimated radiation dose associated with cardiac CT angiography.
      More recently, reported doses in CCTA have been significantly lower than those published in PROTECTION with modern publications reporting effective radiation doses of 1-4 mSv.
      • Leipsic J.
      • LaBounty T.M.
      • Heilbron B.
      • et al.
      Estimated radiation dose reduction using adaptive statistical iterative reconstruction in coronary CT angiography: the ERASIR Study.
      • LaBounty T.M.
      • Leipsic J.
      • Mancini G.B.
      • et al.
      Effect of a standardized radiation dose reduction protocol on diagnostic accuracy of coronary computed tomographic angiography.
      • Achenbach S.
      • Marwan M.
      • Ropers D.
      • et al.
      Coronary computed tomography angiography with a consistent dose below 1 mSv using prospectively electrocardiogram-triggered high-pitch spiral acquisition.
      There are patient- and protocol-related factors that can affect patient exposure. However, it is the CT scan parameters that ultimately determine patient exposure. Optimizing scan parameters to ensure diagnostic image quality is achieved with a reasonable dose is the goal of all cardiac CT examinations. The CT physician must be engaged in the protocol selection. Typically, the acquisition mode, routine helical retrospectively gated, prospective triggering, or high pitch helical acquisition has the greatest effect on radiation exposure. This is followed by the selection of tube potential and tube current and planning of scan length. The lowest radiation exposure for conventional cardiac CT requires use of a lower tube potential, typically 100 peak kilovoltage (kVp), a tube current setting that is appropriate to the patient body habitus, a short x-ray exposure window of ≤ 10 ms, and a scan coverage of 120-140 mm. Routine use of retrospective electrocardiographic gating is associated with a significant increase in radiation exposure and is not recommended unless ventricular function or wall motion assessment is needed.

      Nuclear medicine—radionuclide myocardial perfusion imaging

      The most common technique used for radionuclide myocardial perfusion imaging (RMPI) is called single photon emission CT (SPECT) imaging. This technique uses a gamma-emitting radioisotope (called radionuclide) that is injected into the bloodstream of the patient at peak stress and/or at rest. For RMPI studies, the effective dose ranges between 2 and 32 mSv depending on the radioisotope and protocol used, with dual isotope protocols having the highest effective doses.
      • Mettler F.A.
      • Huda W.
      • Yoshizumi T.T.
      • Mahesh M.
      Effective doses in radiology and diagnostic nuclear medicine: a catalog.
      • Einstein A.J.
      • Moser K.W.
      • Thompson R.C.
      • Cerqueira M.D.
      • Henzlova M.J.
      Radiation dose to patients from cardiac diagnostic imaging.
      With respect to radiation exposure, there are a number of qualitative differences between RMPI and other cardiac imaging modalities.
      • Mercuri M.
      • Rehani M.M.
      • Einstein A.J.
      Tracking patient radiation exposure: challenges to integrating nuclear medicine with other modalities.
      The primary difference is the source of the ionizing radiation (radiopharmaceutical inside the body vs external radiation field), and consequently, how radiation exposure and dose are measured. In RMPI studies, radiation exposure is expressed in terms of administered activity. This is the number of decays per second and is typically measured in millions of becquerels. The International Commission on Radiological Protection (ICRP) outlines methods for estimating radiation dose based on the administered activity.
      Radiation dose to patients from radiopharmaceuticals. ICRP Publication 53.
      Radiation dose to patients from radiopharmaceuticals (addendum 2 to ICRP Publication 53): ICRP Publication 80.
      • ICRP
      Radiation dose to patients from radiopharmaceuticals. Addendum 3 to ICRP Publication 53. ICRP Publication 106. Approved by the Commission in October 2007.
      However, these methods assume standard patient biokinetic characteristics and habitus.
      The newest SPECT systems use cadmium zinc telluride. These have many advantages including a higher sensitivity for gamma-rays because of the high atomic numbers of Cd and Te, and better energy resolution than older scintillator detectors. These advantages facilitate a lower radionuclide dose in patients. Electrocardiographic cardiac gated acquisitions are possible with SPECT to obtain differential information about the heart at any phase of the cardiac cycle. Gated myocardial SPECT can be used to obtain quantitative information about myocardial perfusion, thickness, and contractility, and to allow calculation of left ventricular ejection fraction, stroke volume, and cardiac output.
      Recommendations for reducing dose in RMPI include the use of stress first or stress-only protocols in patients with low pretest probability of coronary artery disease, because a stress-only protocol in conjunction with attenuation correction is likely to provide sufficient information to rule out the disease at a relatively low radiation dose.
      • DePuey E.G.
      • Mahmarian J.J.
      • Miller T.D.
      • et al.
      Patient-centered imaging.
      Dual isotopes have been shown to have much higher radiation exposure rates and when possible technetium agents/isotopes should be used over and above thallium. Attenuation correction and new software acquisition with iterative reconstruction have also facilitated lower dosing of radionuclides.
      Positron emission tomography is an expanding area of RMPI. Ongoing advances in cardiac SPECT and positron emission tomography imaging techniques and incorporation of rubidium-82 has the potential to significantly reduce the radiation exposure per procedure by almost 50% compared with previous techniques.
      • Small G.R.
      • Wells G.
      • Schindler T.
      • Chow B.J.
      • Ruddy T.D.
      Advances in cardiac SPECT and PET imaging: overcoming the challenges to reduce radiation exposure and improve accuracy.
      • Dilsizian V.
      • Bacharach S.L.
      • Beanlands R.S.
      • et al.
      ASNC imaging guidelines for nuclear cardiology procedures: PET myocardial perfusion and metabolism clinical imaging.
      Recommendation
      • 2.
        We suggest that the operator and institution adopt processes to minimize the radiation exposure for each cardiac imaging modality (Strong Recommendation, Low-Quality Evidence).
      • 3.
        We suggest that each site measure radiation exposure for each cardiac imaging modality at regular intervals as a quality initiative (Strong Recommendation, Low-Quality Evidence).
      Values and preferences. In cardiology, there are a variety of imaging modalities and techniques that might provide similar information, making it difficult in many clinical scenarios to recommend a “1 size fits all” approach based solely on risks of radiation exposure. Therefore, a more reasonable approach would be to recommend that clinicians and laboratories adopt processes of protocol selection to match the specific patient needs and follow the “as low as reasonably achievable” principle approach to optimize imaging techniques. These steps would aid in providing optimal diagnostic information and minimizing patient risks.

      Recording and Monitoring Radiation Exposure/Dose to the Patient

      Currently there are established standards in Canada for monitoring and reporting of exposure to healthcare workers from radiation-based procedures. However, similar policy or standards do not exist for patients. Increasingly, many individuals are undergoing several procedures using ionizing radiation, which results in individual cumulative effective doses of greater than 100 mSv. This might be especially true in cardiology, in which acute exposures/doses are relatively high compared with other domains. The concern for potential health risk because of high cumulative doses forms the basis for programs to track procedural exposures and doses. A recent joint statement by several agencies outlines the need and potential benefits of radiation exposure tracking strategies.

      Joint Position Statement on the IAEA Patient Radiation Exposure Tracking By ESR, FDA, IAEA, IOMP, ISRRT, WHO and CRCPD. Available at: https://rpop.iaea.org/RPOP/RPoP/Content/Documents/Whitepapers/iaea-smart-card-position-statement.pdf. Accessed June 2, 2012.

      They confirm that “the major goals of tracking include: (1) supporting accountability for patient safety; (2) strengthening of the process of justification (eg, information available at the point-of-care for the referring practitioner); (3) supporting optimization (eg, use of diagnostic reference levels); (4) providing information for assessment of radiation risks; and (5) establishing a tool for use in research and epidemiology.”

      Joint Position Statement on the IAEA Patient Radiation Exposure Tracking By ESR, FDA, IAEA, IOMP, ISRRT, WHO and CRCPD. Available at: https://rpop.iaea.org/RPOP/RPoP/Content/Documents/Whitepapers/iaea-smart-card-position-statement.pdf. Accessed June 2, 2012.

      ; p. 1 The International Atomic Energy Agency (IAEA) Smart Card/SmartRadTrack program is one way to track individual patient exposure histories and perhaps, cumulative dose.
      • Rehani M.M.
      • Frush D.P.
      Patient exposure tracking—the IAEA smart card project.
      • Rehani M.
      • Frush D.
      Tracking radiation exposure of patients.
      For the operator, technologies that allow personal dose monitoring and feedback in “real-time” are available or under development.
      A cumulative dose-tracking strategy requires at least two important features: (1) a common measure of radiation dose across modalities; and (2) a platform for recording radiation exposures and doses for each procedure and summation of radiation doses across procedures. As previously discussed, each modality has a unique set of radiation exposure and dose metrics. Each of these can be used to estimate an effective dose. Therefore, effective dose might serve as a means to integrate collected information across modalities to estimate an individual's cumulative radiation dose.
      • Mercuri M.
      • Rehani M.M.
      • Einstein A.J.
      Tracking patient radiation exposure: challenges to integrating nuclear medicine with other modalities.
      However, it should be noted that effective dose was developed for population level dosimetry, and thus, might be inaccurate for estimating doses to an individual. When there is agreement on which metrics should be recorded, the means by which they are recorded must allow for communication of information such that cumulative doses across procedures can be calculated for an individual. The Digital Imaging and Communications in Medicine header, which is currently part of most imaging modalities, might be appropriate for this purpose.
      • Mercuri M.
      • Rehani M.M.
      • Einstein A.J.
      Tracking patient radiation exposure: challenges to integrating nuclear medicine with other modalities.
      Currently, there is no standard of practice in Canada for measuring and recording radiation exposures and doses to patients, nor is there a standard process to communicate this information to patients and other health care practitioners. A platform for recording and communicating dosimetry information of patients should be established. Cardiologists and radiologists should provide manufacturers with information on which data elements, specific to radiation dosimetry, should be incorporated into imaging technology.
      Recommendation
      • 4.
        We suggest that a multi-disciplinary committee should be established to develop a consensus on dosimetry standards for cardiac imaging and interventional procedures that use ionizing radiation in Canada (Strong Recommendation, Low-Quality Evidence).
      • 5.
        We suggest that cardiologists, radiologists, administrators, and policy makers should work together with manufacturers to develop a platform for radiation dose tracking across Canada, conforming to health information communication and privacy regulations (Strong Recommendation, Low-Quality Evidence).

      Patient Perspective

      Patients might come to clinic with knowledge regarding the potential risks from ionizing radiation, and in some cases with various biases regarding risks gathered from various nonpeer-reviewed sources and media. Thus, it is imperative that the physician obtaining consent for the procedure has a working knowledge of the expected radiation exposure and the potential specific risks to the patient so that a reasoned discussion may take place. Discussions related to risks of radiation will also help verify to the patient and family that the health care provider and institution has acknowledged the potential risks of radiation exposure in their overall decision process.
      There is little evidence on which is the most effective strategy to communicate the radiation-related risks to the patient. Assessing the actual long-term risks from any one procedure is not easy for any individual and it is difficult to fit “hard numbers” into the discussion. A generic communication strategy that has potential for greater uptake could be adopted. Use of operational quantities or terms (eg, Sv) in discussion regarding radiation risks with the patient should be discouraged. Such specific terminology might be more useful within individual departments when deciding on dosing strategies rather than for use in patient discussions.

      Peck DJ, Samei E. How to understand and communicate radiation risk. Available at: www.imagewisely.org. Accessed August 6, 2013.

      The language of communication of risk should be simple, well understood by the health care providers relaying the information, and placed in context with the specific test or procedure and clinical indication for which it is being performed. It might be reasonable to state that the long-term risk from radiation exposure is less than the other expected risks from the procedure but nevertheless exists, and all necessary precautions have been taken to minimize this risk to obtain the information needed or to complete the interventional procedure.
      A number of articles have reviewed options for discussing radiation risks with patients.

      Peck DJ, Samei E. How to understand and communicate radiation risk. Available at: www.imagewisely.org. Accessed August 6, 2013.

      • Cardinal J.S.
      • Gunderman R.B.
      • Tarver R.D.
      Informing patients about risks and benefits of radiology examinations: a review article.
      • Dauer L.T.
      • Thornton R.H.
      • Hay J.L.
      • Balter R.
      • Williamson M.J.
      • St Germain J.
      Fears, feelings, and facts: interactivity communicating benefits and risks of medical radiation with patients.
      • Fahey F.H.
      • Treves S.T.
      • Adelstein S.J.
      Minimizing and communicating radiation risk in paediatric nuclear medicine.
      • Picano E.
      Informed consent and communication of risk from radiological and nuclear medicine examinations: how to escape from a communication inferno.
      • Verdun F.R.
      • Boclud F.
      • Gudinchet F.
      • Arouna A.
      • Schnyder P.
      • Meuli R.
      Radiation risk: what you should know to tell your patient.
      Options include: (1) expressing risk in comparison with natural background radiation exposure; (2) expressing risk compared with risk of death from natural causes or natural occurrences of cancer itself; or (3) expressing a radiological dose as multiples of a chest x-ray, which might be an even simpler means of communicating risk. This latter method has been suggested by the UK College of Radiologists and has been endorsed in the European Commission's guidelines on imaging.
      • Picano E.
      Informed consent and communication of risk from radiological and nuclear medicine examinations: how to escape from a communication inferno.
      In pediatric practice, examples such as the “Image Gently” campaign have been used to communicate risk to parents of children undergoing radiology-based procedures.
      • Fahey F.H.
      • Treves S.T.
      • Adelstein S.J.
      Minimizing and communicating radiation risk in paediatric nuclear medicine.
      Clinicians should encourage a common framework for communicating risk related to radiation procedures.
      In some cases, patients might receive a “high dose” of radiation that might result in tissue reactions such as skin injury over the subsequent weeks. In such circumstances it is suggested that there should be processes in place to follow-up patient status and enquiries postprocedure. The intensity of follow-up will depend on the magnitude of dose exposure.
      • Koenig T.R.
      • Wolff D.
      • Mettler F.A.
      • Wagner L.K.
      Skin injuries from fluoroscopically guided procedures: part 1, characteristics of radiation injury.
      • Douglas P.S.
      • Carr J.J.
      • Cerqueira M.D.
      • et al.
      Developing an action plan for patient radiation safety in adult cardiovascular medicine: proceedings from the Duke University Clinical Research Institute/American College of Cardiology Foundation/American Heart Association Think Tank held on February 28, 2011.
      Recommendation
      • 6.
        We suggest that health care providers establish a mechanism for follow-up of potential deterministic injuries in patients with “high” exposure (Strong Recommendation, Low-Quality Evidence).
      Values and preferences. In appropriately selected patients the potential mortality and morbidity benefits of a specific cardiac diagnostic test or intervention far outweighs the potential long-term stochastic risks related to radiation exposure. However, considering a more predictable relationship between very high dose of exposure and risk of skin injury from high procedural-related doses, we suggest that there be a mechanism of identification and follow-up of such patients.

      Conclusions

      Radiation exposure from cardiac procedures, primarily fluoroscopy-guided procedures, CCTA, and RMPI, can in rare cases cause skin injury and might even be associated with cancer. However, the nature of resulting injuries is such that they may often go unnoticed by those providers ordering and performing the single (or multiple) procedure(s) that lead to such injuries. There is little robust evidence for definite long-term risks at the levels of radiation exposure experienced by most cardiac patients, particularly considering the age at which most patients receive examinations that use ionizing radiation. All providers should remain vigilant regarding regular surveillance of radiation exposure levels from imaging modalities with a constant review of procedure metrics and techniques to limit exposure to ionizing radiation and maintain quality. It is important to emphasize that small adjustments in procedure metrics, such as reducing fluoroscopy time during interventional procedures by 5%-10%, reducing the scan range for CCTA by 1-2 cm, or reducing the administered dose of injected radioisotopes can have a substantial effect on reducing the cumulative population burden from ionizing radiation. Though exposure reduction strategies have had a significant effect on reducing radiation dose perhaps the most powerful strategy is to limit performing studies that do not meet current appropriateness guidelines.
      • Achenbach S.
      • Ulzheimer S.
      • Baum U.
      • et al.
      Noninvasive coronary angiography by retrospectively electrocardiographic-gated multislice spiral CT.

      Supplementary Material

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