2018 ACC/HRS/NASCI/SCAI/SCCT - Heart Rhythm Society

 
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2018 ACC/HRS/NASCI/SCAI/SCCT - Heart Rhythm Society
JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY                                                                                    VOL.   -, NO. -, 2018
                    ª 2018 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
                    PUBLISHED BY ELSEVIER

                    EXPERT CONSENSUS DOCUMENT

                   2018 ACC/HRS/NASCI/SCAI/SCCT
                   Expert Consensus Document on
                   Optimal Use of Ionizing Radiation
                   in Cardiovascular Imaging—
                   Best Practices for Safety and
                   Effectiveness, Part 2: Radiological
                   Equipment Operation, Dose-Sparing
                   Methodologies, Patient and Medical
                   Personnel Protection
                    A Report of the American College of Cardiology Task Force on Expert Consensus Decision Pathways

                    Developed in Collaboration With Mended Hearts

Writing             John W. Hirshfeld, JR, MD, FACC, FSCAI, Chair                                  Gilbert L. Raff, MD, FACCk
Committee           Victor A. Ferrari, MD, FACC, Co-Chair                                          Geoffrey D. Rubin, MD, MBA, FNASCI{
Members                                                                                            Donnette Smith#
                    Frank M. Bengel, MD*                                                           Arthur E. Stillman, MD, PHD, FNASCI
                    Lisa Bergersen, MD, MPH, FACC                                                  Suma A. Thomas, MD, MBA, FACC
                    Charles E. Chambers, MD, FACC, MSCAIy                                          Thomas T. Tsai, MD, MSC, FACC
                    Andrew J. Einstein, MD, PHD, FACC                                              Louis K. Wagner, PHD
                    Mark J. Eisenberg, MD, MPH, FACC                                               L. Samuel Wann, MD, MACC
                    Mark A. Fogel, MD, FACC
                    Thomas C. Gerber, MD, FACC
                                                                                                   *Society of Nuclear Medicine and Molecular Imaging Representative.
                    David E. Haines, MD, FACCz
                                                                                                   ySociety for Cardiovascular Angiography and Interventions
                    Warren K. Laskey, MD, MPH, FACC, FSCAI                                         Representative. zHeart Rhythm Society Representative. xAmerican Society
                    Marian C. Limacher, MD, FACC                                                   of Nuclear Cardiology Representative. kSociety for Cardiovascular
                    Kenneth J. Nichols, PHDx                                                       Computed Tomography Representative. {North American Society for
                                                                                                   Cardiovascular Imaging Representative. #Mended Hearts Representative.
                    Daniel A. Pryma, MD

                        This document was approved by the American College of Cardiology Clinical Policy Approval Committee in November 2017 and the approval bodies of
                    the Heart Rhythm Society, North American Society for Cardiovascular Imaging, Society for Cardiovascular Angiography and Interventions, and Society
                    of Cardiovascular Computed Tomography in January 2018.
                        The American College of Cardiology requests that this document be cited as follows: Hirshfeld JW Jr, Ferrari VA, Bengel FM, Bergersen L, Chambers CE,
                    Einstein AJ, Eisenberg MJ, Fogel MA, Gerber TC, Haines DE, Laskey WK, Limacher MC, Nichols KJ, Pryma DA, Raff GL, Rubin GD, Smith D, Stillman AE, Thomas
                    SA, Tsai TT, Wagner LK, Wann LS. 2018 ACC/HRS/NASCI/SCAI/SCCT expert consensus document on optimal use of ionizing radiation in cardiovascular
                    imaging—best practices for safety and effectiveness, part 2: radiologic equipment operation, dose-sparing methodologies, patient and medical personnel
                    protection: a report of the American College of Cardiology Task Force on Clinical Expert Consensus Documents. J Am Coll Cardiol 2018;71:XXXX–XXXX.
                        Copies: This document is available on the World Wide Web site of the American College of Cardiology (www.acc.org). For copies of this document,
                    please contact Elsevier Reprint Department via fax (212) 633-3820 or e-mail (reprints@elsevier.com).
                        Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express
                    permission of the American College of Cardiology. Requests may be completed online via the Elsevier site (http://www.elsevier.com/about/our-
                    business/policies/copyright/permissions).

ISSN 0735-1097/$36.00                                                                                                            https://doi.org/10.1016/j.jacc.2018.02.018
2018 ACC/HRS/NASCI/SCAI/SCCT - Heart Rhythm Society
2   Hirshfeld Jr. et al.                                                                                                                          JACC VOL.     -, NO. -, 2018
    Radiation Safety ECD, Part 2                                                                                                                                  -, 2018:-–-

    ACC Task Force             James L. Januzzi, JR, MD, FACC                                            Pamela Bowe Morris, MD, FACC
    on Expert                  Luis C. Afonso, MBBS, FACC                                                Robert N. Piana, MD, FACC
    Consensus                  Brendan Everett, MD, FACC                                                 Karol E. Watson, MD, FACC
    Decision                   Adrian F. Hernandez, MD, MHS, FACC                                        Barbara S. Wiggins, PHARMD, AACC
    Pathways**                 William Hucker, MD, PHD
                               Hani Jneid, MD, FACC
                                                                                                         **Formerly named ACC Task Force on Clinical Expert
                               Dharam Kumbhani, MD, SM, FACC
                                                                                                         Consensus Documents.
                               Joseph Edward Marine, MD, FACC

    TABLE OF CONTENTS

    ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -      4. MODALITY-SPECIFIC DOSE REDUCTION
                                                                                                 STRATEGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -
    PREAMBLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -
                                                                                                  4.1. General Principles . . . . . . . . . . . . . . . . . . . . . . . . . .       -

                                                                                                        4.1.1. Case Selection . . . . . . . . . . . . . . . . . . . . . . . . .     -
     1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -
                                                                                                        4.1.2. Dose-Determining Variables . . . . . . . . . . . . .                 -

    2. PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -              4.1.3. Image Quality Issues . . . . . . . . . . . . . . . . . . .           -

                                                                                                  4.2. X-Ray Fluoroscopy . . . . . . . . . . . . . . . . . . . . . . . . . .        -
    3. MODALITY-SPECIFIC RADIATION                                                                      4.2.1. General Principles . . . . . . . . . . . . . . . . . . . . .         -
       EXPOSURE DELIVERY . . . . . . . . . . . . . . . . . . . . . . . . . . -                          4.2.2. Digital X-Ray System Operating Modes . . . .                         -

        3.1. General Principles . . . . . . . . . . . . . . . . . . . . . . . . . . .       -           4.2.3. X-Ray System Calibration, Operation,
              3.1.1. Characteristics of Medical                                                                and Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   -

                     Diagnostic Radiation . . . . . . . . . . . . . . . . . . . .           -           4.2.4. Determinants of Total Dose for an
              3.1.2. Tools Used to Estimate Absorbed Dose . . . . .                         -
                                                                                                               Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   -

                                                                                                        4.2.5. Procedures and Practices to Minimize
        3.2. X-Ray Fluoroscopy . . . . . . . . . . . . . . . . . . . . . . . . . .          -                  Patient and Personnel Exposure . . . . . . . . . .                   -

               3.2.1. X-Ray Fluoroscopy Subject and                                                     4.2.6. Pregnant Occupationally Exposed
                      Operator Exposure Issues . . . . . . . . . . . . . . .                -                  Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    -

              3.2.2. Basics of Operation of an X-Ray                                                    4.2.7. Alternative Imaging Techniques . . . . . . . . . .                   -
                     Cinefluorographic Unit . . . . . . . . . . . . . . . . . .              -
                                                                                                        4.2.8. Summary Checklist for Dose-Sparing in
              3.2.3. Measures and Determinants of                                                              X-Ray Fluoroscopy . . . . . . . . . . . . . . . . . . . .            -

                     Subject and Operator Exposure . . . . . . . . . .                      -
                                                                                                  4.3. X-Ray Computed Tomography . . . . . . . . . . . . . . . .                    -
              3.2.4. Measures and Determinants of Physician                                             4.3.1. X-Ray CT General Principles . . . . . . . . . . . . .                -
                     Operator and Healthcare Worker
                                                                                                        4.3.2. Equipment Quality and Calibration . . . . . . .                      -
                     Occupational Exposure . . . . . . . . . . . . . . . . .                -
                                                                                                        4.3.3. Variables That Affect Patient Dose
        3.3. X-Ray CT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   -                  for X-Ray CT . . . . . . . . . . . . . . . . . . . . . . . . .       -

               3.3.1. X-Ray CT Subject and Operator                                                     4.3.4. Summary Checklist of Dose-Sparing
                      Dose Issues . . . . . . . . . . . . . . . . . . . . . . . . . . .     -                  Practices for X-Ray CT . . . . . . . . . . . . . . . . . .           -

              3.3.2. Basics of Operation of an                                                   4.4. Nuclear Cardiology Techniques . . . . . . . . . . . . . . . .                 -
                     X-Ray CT Unit . . . . . . . . . . . . . . . . . . . . . . . .          -
                                                                                                        4.4.1. Nuclear Cardiology General Principles . . . . .                      -
              3.3.3. X-Ray CT Measures of                                                               4.4.2. Nuclear Cardiology Equipment Quality,
                     Subject Exposure . . . . . . . . . . . . . . . . . . . . . .           -                  Calibration, and Maintenance . . . . . . . . . . . .                 -

              3.3.4. X-Ray CT Measures of Effective Dose . . . . .                          -           4.4.3. Nuclear Cardiology Spatial Resolution and
                                                                                                               Image Detector Dose . . . . . . . . . . . . . . . . . . .            -
       3.4. Patient and Medical Personnel Exposure in
                                                                                                        4.4.4. Procedures and Practices to Minimize
            Nuclear Cardiology . . . . . . . . . . . . . . . . . . . . . . . . . .          -
                                                                                                               Patient Exposure . . . . . . . . . . . . . . . . . . . . . .         -
              3.4.1. Patient Exposure in Nuclear Cardiology . . . .                         -
                                                                                                        4.4.5. Procedures and Practices to Protect
              3.4.2. Personnel Exposure in Nuclear                                                             Occupationally Exposed Healthcare
                     Cardiology . . . . . . . . . . . . . . . . . . . . . . . . . . . .     -                  Workers in Nuclear Cardiology Facilities . . .                       -
2018 ACC/HRS/NASCI/SCAI/SCCT - Heart Rhythm Society
JACC VOL.     -, NO. -, 2018                                                                                                                      Hirshfeld Jr. et al.   3
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          4.4.6. Summary Checklist of Dose-Sparing                                            ABSTRACT
                 Practices for Nuclear Cardiology . . . . . . . . .                       -

   4.5. Summary of Dose Minimization Strategies in                                            The stimulus to create this document was the recogni-
        X-Ray Fluoroscopy, X-Ray CT, and                                                      tion that ionizing radiation-guided cardiovascular pro-
        Cardiovascular Nuclear Scintigraphy . . . . . . . . . . .                         -   cedures are being performed with increasing frequency,
                                                                                              leading to greater patient radiation exposure and,

5. SUMMARY, CONCLUSIONS, AND
                                                                                              potentially, to greater exposure to clinical personnel.

   RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . -
                                                                                              While the clinical benefit of these procedures is sub-
                                                                                              stantial, there is concern about the implications of
    5.1. The Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    -   medical radiation exposure. ACC leadership concluded
          5.1.1. Patient Participation in Clinical                                            that it is important to provide practitioners with an
                 Imaging Decisions . . . . . . . . . . . . . . . . . . . . . .            -
                                                                                              educational resource that assembles and interprets the
                                                                                              current radiation knowledge base relevant to cardiovas-
   5.2. Clinical Value of Radiation-Based Imaging Studies
        and Radiation-Guided Therapeutic Procedures . . .                                 -   cular procedures. By applying this knowledge base, car-
                                                                                              diovascular    practitioners    will    be     able      to    select
   5.3. Individual Patient Risk and Population Impact                                         procedures optimally, and minimize radiation exposure
        (Including Occupationally Exposed Workers) . . . . .                              -
                                                                                              to patients and to clinical personnel.
   5.4. The ALARA Principle . . . . . . . . . . . . . . . . . . . . . . . .               -     “Optimal Use of Ionizing Radiation in Cardiovascular
                                                                                              Imaging - Best Practices for Safety and Effectiveness” is a
   5.5. The Potential to Minimize Exposure to
                                                                                              comprehensive overview of ionizing radiation use in
        Patients and Personnel . . . . . . . . . . . . . . . . . . . . . . .              -
                                                                                              cardiovascular procedures and is published online. To
          5.5.1. Imaging Modality Choice . . . . . . . . . . . . . . . .                  -
                                                                                              provide the most value to our members, we divided the
          5.5.2. Procedure Conduct Choice . . . . . . . . . . . . . .                     -
                                                                                              print version of this document into 2 focused parts.
          5.5.3. Protecting Occupationally Exposed                                            “Part I: Radiation Physics and Radiation Biology” ad-
                 Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .      -
                                                                                              dresses radiation physics, dosimetry and detrimental
   5.6. Physician Responsibilities to Minimize                                                biologic effects. “Part II: Radiologic Equipment Operation,
        Patient Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . .            -   Dose-Sparing      Methodologies,       Patient     and        Medical
          5.6.1. Case Selection . . . . . . . . . . . . . . . . . . . . . . . . .         -   Personnel Protection” covers the basics of operation and
          5.6.2. Procedure Conduct . . . . . . . . . . . . . . . . . . . . .              -   radiation delivery for the 3 cardiovascular imaging mo-
          5.6.3. Facility Management . . . . . . . . . . . . . . . . . . .                -   dalities (x-ray fluoroscopy, x-ray computed tomography,
                                                                                              and nuclear scintigraphy). For each modality, it includes
   5.7. Patient Radiation Dose Tracking . . . . . . . . . . . . . . .                     -   the determinants of radiation exposure and techniques to
   5.8. Need for Quality Assurance and Training . . . . . . . .                           -   minimize exposure to both patients and to medical
                                                                                              personnel.
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -

APPENDIX A
                                                                                              PREAMBLE
   Author Relationships With Industry and Other Entities
   (Relevant) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   -
                                                                                              This document has been developed as an Expert
                                                                                              Consensus Document by the American College of Cardi-
APPENDIX B
                                                                                              ology (ACC) in collaboration with the American Society of
   Peer Reviewer Relationships With Industry and                                              Nuclear Cardiology, Heart Rhythm Society, Mended
   Other Entities (Relevant) . . . . . . . . . . . . . . . . . . . . . . . . .            -
                                                                                              Hearts,   North    American    Society     for    Cardiovascular
                                                                                              Imaging, Society for Cardiovascular Angiography and
APPENDIX C
                                                                                              Interventions, Society for Cardiovascular Computed To-
   Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .      -   mography, and Society of Nuclear Medicine and Molecu-
                                                                                              lar Imaging. Expert Consensus Documents are intended to
APPENDIX D                                                                                    inform practitioners, payers, and other interested parties
   Operator Education, Quality Assurance,                                                     of the opinion of ACC and document cosponsors con-
   Radiation Dose Monitoring, and Tracking . . . . . . . . . . .                          -   cerning   evolving    areas    of   clinical     practice      and/or
2018 ACC/HRS/NASCI/SCAI/SCCT - Heart Rhythm Society
4   Hirshfeld Jr. et al.                                                                                           JACC VOL.   -, NO. -, 2018
    Radiation Safety ECD, Part 2                                                                                                -, 2018:-–-

    technologies that are widely available or new to the                   1. INTRODUCTION
    practice community. Topics chosen for coverage by expert
    consensus documents are so designed because the evi-                   1.1. Document Development Process and Methodology
    dence base, the experience with technology, and/or clin-               1.1.1. Writing Committee Organization
    ical    practice       are     not   considered   sufficiently   well
                                                                           The writing committee consisted of a broad range of
    developed to be evaluated by the formal ACC/American
                                                                           members representing 9 societies and the following areas
    Heart Association practice guidelines process. Often the
                                                                           of expertise: interventional cardiology, general cardiol-
    topic is the subject of considerable ongoing investigation.
                                                                           ogy, pediatric cardiology, nuclear cardiology, nuclear
    Thus, the reader should view the Expert Consensus
                                                                           medicine, electrophysiology, cardiac computed tomogra-
    Document as the best attempt of the ACC and document
                                                                           phy (CT), cardiovascular imaging, and the consumer pa-
    cosponsors to inform and guide clinical practice in
                                                                           tient perspective. Both a radiation safety biologist and
    areas where rigorous evidence may not yet be available
                                                                           physicist were included on the writing committee.
    or evidence to date is not widely applied to clinical
                                                                             This writing committee met the College’s disclosure
    practice.
                                                                           requirements for RWI as described in the Preamble.
       To avoid actual, potential, or perceived conflicts of
    interest that may arise as a result of industry relation-              1.1.2. Document Development and Approval
    ships or personal interests among the writing committee,
                                                                           The Writing Committee convened by conference call and e-
    all members of the writing committee, as well as peer
                                                                           mail to finalize the document outline, develop the initial
    reviewers of the document, are asked to disclose all cur-
                                                                           draft, revise the draft per committee feedback, and ulti-
    rent healthcare-related relationships, including those
                                                                           mately approve the document for external peer review.
    existing 12 months before initiation of the writing effort.
                                                                           All participating organizations participated in peer review,
    The ACC Task Force on Expert Consensus Decision
                                                                           resulting in 21 individual reviewers submitting 299
    Pathways (formerly the ACC Task Force on Clinical Expert
                                                                           comments. Comments were reviewed and addressed by
    Consensus Documents) reviews these disclosures to
                                                                           the writing committee. A member of the ACC Task Force on
    determine which companies make products (on market or
                                                                           Expert Consensus Decision Pathways served as lead
    in development) that pertain to the document under
                                                                           reviewer to ensure that all comments were addressed
    development. Based on this information, a writing com-
                                                                           adequately. Both the writing committee and the task force
    mittee is formed to include a majority of members with
                                                                           approved the final document to be sent to the ACC Clinical
    no relevant relationships with industry (RWI), led by a
                                                                           Policy Approval Committee. This committee reviewed
    chair with no relevant RWI. Authors with relevant RWI are
                                                                           the document, including all peer review comments and
    not permitted to draft or vote on text or recommenda-
                                                                           writing committee responses, and approved the document
    tions pertaining to their RWI. RWI is reviewed on all
                                                                           in November 2017. The Heart Rhythm Society, North
    conference calls and updated as changes occur. Author
                                                                           American Society for Cardiovascular Imaging, Society for
    and peer reviewer RWI pertinent to this document are
                                                                           Cardiovascular Angiography and Interventions, and Soci-
    disclosed in Appendixes A and B, respectively. Addi-
                                                                           ety of Cardiovascular Computed Tomography endorsed the
    tionally, to ensure complete transparency, authors’
                                                                           document in January 2018. This document is considered
    comprehensive disclosure information— including RWI
                                                                           current until the Task Force on Expert Consensus Decision
    not pertinent to this document—is available online
                                                                           Pathways revises or withdraws it from publication.
    (see Online Appendix). Disclosure information for the
    ACC Task Force on Clinical Expert Consensus Documents                  2. PURPOSE
    is also available online, as is the ACC disclosure policy for
    document development.                                                  This print-published document is part 2 of an abbreviated
       The work of the writing committee was supported                     version of a larger, more comprehensive document that is
    exclusively by the ACC without commercial support.                     published concurrently online. The online version con-
    Writing committee members volunteered their time to                    tains additional technical detail for readers who wish to
    this effort. Conference calls of the writing committee                 understand a topic in greater depth. The online published
    were confidential and attended only by committee                        document, in addition to covering the topics in the 2
    members and ACC staff.                                                 print-published documents in greater depth, also covers
                                                                           additional topics not covered in the print-published doc-
                                           James L. Januzzi, MD, FACC      uments including 1) dose reduction strategies; 2) operator
                            Chair, ACC Task Force on Clinical Expert       education and certification; 3) quality assurance; and
                                                 Consensus Documents       4) patient radiation tracking.
JACC VOL.   -, NO. -, 2018                                                                                                                           Hirshfeld Jr. et al.   5
-, 2018:-–-                                                                                                                               Radiation Safety ECD, Part 2

  This document covers equipment operation for the 3                                  1% to 5% of the incident x-ray penetrates the subject
cardiovascular procedure classes that employ ionizing                                 reaching the image detector to form the image.
radiation: x-ray fluoroscopy, x-ray CT, and radionuclide
scintigraphy. For the 3 modalities, it includes discussions                           3.1.2. Tools Used to Estimate Absorbed Dose
of radiation delivery and strategies to minimize dose both                            Estimates of absorbed dose for x-ray fluoroscopy and
to patients and to occupationally exposed medical                                     x-ray CT are based on models developed by exposing
personnel. In addition, it covers issues of quality assur-                            instrumented phantoms to incident x-ray beams that
ance, radiation monitoring, and tracking.                                             replicate the beams used in diagnostic imaging and
  The document’s purpose is to provide a comprehensive                                measuring absorbed dose at different points within the
information source about ionizing radiation use in car-                               phantom. Estimating absorbed dose from radionuclides is
diovascular procedures. The writing group has assembled                               an entirely different discipline that is discussed in Section
this information to assist cardiovascular practitioners to                            4.4 of “Part I: Radiation Physics and Radiation Biology”.
provide optimal cardiovascular care when employing
ionizing radiation-based procedures. The goal is to
                                                                                      3.2. X-Ray Fluoroscopy
enhance cardiovascular practitioners’ ability to select the
optimal imaging technique for a given clinical circum-                                3.2.1. X-Ray Fluoroscopy Subject and Operator Exposure Issues

stance, balancing a technique’s risk and benefits, and to                              X-ray fluoroscopy differs from other ionizing radiation
apply that technique optimally to generate high-quality                               imaging techniques in that the beam entrance port is
diagnostic images of greatest clinical value and minimal                              relatively small. Consequently, the skin at the beam
radiation exposure.                                                                   entrance port is the most intensely exposed tissue.
                                                                                      Subject skin doses can reach levels that cause skin tissue
                                                                                      reactions. X-ray photons are also scattered within the
3. MODALITY-SPECIFIC RADIATION
                                                                                      subject. These deliver dose to subject tissues outside of
   EXPOSURE DELIVERY
                                                                                      the imaging field (Figure 1). Scattered photons that exit
                                                                                      the     subject     can     expose       nearby      medical       personnel
3.1. General Principles
                                                                                      (Figure 2). Consequently, assessment of the implications
3.1.1. Characteristics of Medical Diagnostic Radiation                                of    subject      exposure       from      x-ray     fluoroscopy           must
For all 3 imaging modalities (x-ray fluoroscopy, x-ray CT,                             consider entrance port skin dose, which is the dose
and nuclear scintigraphy), 95% to 99% of radiation energy                             received by internal structures within the imaging field
that enters or is released within the subject is either                               and by other internal structures outside of the imaging
absorbed or scattered within the subject. The remaining                               field.

   F I G U R E 1 Diagrammatic Representation of an X-Ray Fluoroscopy System to Illustrate X-Ray Exposure Modality

   The primary beam, collimated to a rectangular cross section, enters the patient, typically through the patient’s back. It is attenuated and scattered within the
   imaging field. The primary beam exposes the subject within the imaging field. The scattered primary beam radiation can expose structures within the subject
   that are remote from the imaging field.
6   Hirshfeld Jr. et al.                                                                                                        JACC VOL.   -, NO. -, 2018
    Radiation Safety ECD, Part 2                                                                                                             -, 2018:-–-

        F I G U R E 2 Diagrammatic Representation of the Pattern of X-Ray Scatter From a Subject Undergoing X-Ray Fluoroscopy

        Note that scattered x-ray emanates from the subject in all directions.

    3.2.2. Basics of Operation of an X-Ray Cinefluorographic Unit                      to image formation. Layers of aluminum and copper in
    An x-ray cinefluorographic unit generates controlled x-                            the x-ray tube exit port filter out these “undesirable”
    rays in an x-ray tube that are collimated to regulate the                         photons.
    size and shape of the beam. The beam passes through the
    subject forming images that are detected by a flat panel                       3.2.3. Measures and Determinants of Subject and
    detector (Figure 1). The x-ray tube output (and accord-                               Operator Exposure
    ingly the exposure to the subject) is modulated by feed-
                                                                                  There are 2 different x-ray fluoroscopic system parame-
    back circuitry from the unit’s imaging chain to achieve an
                                                                                  ters (described in detail in Section 4.4.1 of Part 1) that
    optimally exposed image.
                                                                                  characterize x-ray exposure and dose:
    X-Ray Cinefluorographic Unit Operating Parameters
    There are multiple imaging parameters that influence the                        1) Cumulative air kerma at the interventional reference
    x-ray exposure associated with an x-ray cinefluorographic                          point. Kerma is an acronym for “kinetic energy
    examination. These are:                                                           released in material.”
                                                                                  2) Cumulative kerma-area product (KAP).
    1. X-ray image detector dose per pulse. The dose for each
        x-ray pulse (typically measured in nanogray [nGy])
        that reaches the x-ray system detector. This parameter                    Cumulative Air Kerma at the
        is set by the x-ray unit calibration. It determines image                     Interventional Reference Point
        clarity and detail.                                                       A procedure’s cumulative air kerma at the interventional
    2. X-ray unit framing (pulsing) rate. The number of pul-                      reference point is a more meaningful measure of subject
        ses that the x-ray system generates per unit time. This                   exposure than the total fluoroscopic time, which does
        is an operator-selectable parameter that generally                        not account for selected detector dose, subject density,
        ranges between 4 and 30 pulses/s. It determines image                     cine acquisition time, or changes in frame rate and
        temporal resolution.                                                      angulation.
    3. Imaging field size. The area of the x-ray beam that                             X-ray exposure to the subject is not uniform. As an
        impinges on the subject.                                                  x-ray beam passes through a subject, tissue absorption
    4. X-ray beam filtration. An x-ray tube produces a                             attenuates it. Tissue closer to the beam entrance port
        spectrum           of   x-ray     photon        energies.       Photon    receives a larger dose than deeper-lying tissue (Figure 3).
        energies
JACC VOL.   -, NO. -, 2018                                                                                                       Hirshfeld Jr. et al.   7
-, 2018:-–-                                                                                                            Radiation Safety ECD, Part 2

                                                                              3.2.4. Measures and Determinants of Physician Operator and
   F I G U R E 3 Diagram Showing the Estimated Decreasing Intensity of
   X-Ray Exposure With Depth Within the Subject
                                                                                    Healthcare Worker Occupational Exposure
                                                                              Application of KAP in Cardiovascular X-Ray Fluoroscopy
                                                                                to Estimates of Effective Dose to Medical Personnel
                                                                              Medical personnel who conduct x-ray fluoroscopic pro-
                                                                              cedures are exposed by scattered radiation (Figure 2). The
                                                                              cumulative quantity of scattered radiation is directly
                                                                              related to the procedure’s cumulative KAP.
                                                                                The quantity of scattered radiation that reaches and
                                                                              delivers dose to medical personnel is determined by:

                                                                              1. The distance of the exposed medical personnel from
                                                                                the x-ray source—scattered x-ray intensity decreases
                                                                                proportionately to the square of the distance from the
                                                                                source.
                                                                              2. The effectiveness of shielding employed by the
                                                                                exposed medical personnel.

                                                                              Physician and Medical Personnel Exposure Monitoring
   In this example, (right anterior oblique projection), the beam enters      Estimates   of   radiation   dose   to     exposed        medical
   the left side of the subject’s back. Beam intensity decreases with depth   personnel are based on measurements made by personal
   within the subject due to a combination of beam divergence with
                                                                              radiation monitors (formerly known as “film badges”).
   distance (inverse square law) and absorption within the subject. The
   overall effect of these processes is to attenuate the beam intensity
                                                                              The outside badge mounted at collar level outside
   that exits the subject to 5% or less of the incident intensity.            protective garments) measures the dose that reaches
                                                                              unshielded structures of the head. A badge worn
                                                                              underneath protective garments measures the dose that
tissue within the imaging area, but is not negligible
                                                                              penetrates the protective apron reaching the subject.
(Figure 1).
                                                                              These measure total exposure in mGy. The personal
Kerma-Area Product
                                                                              radiation monitor readings are converted using an
KAP, the product of air kerma output and image field size,
                                                                              algorithm to estimate effective dose to the subject
sometimes referred to as dose-area product, is commonly
                                                                              in mSv (2–5). The details of these measurements and
used as a metric to estimate a subject’s total absorbed
                                                                              calculations are included in the full version of this
dose. It incorporates both dose intensity and exposed
                                                                              document published online.
tissue volume into a single measurement. KAP is also
directly related to the quantity of scattered radiation that                  Exposure Levels for Operating Physicians
leaves the subject’s body and, accordingly, to the                            Most studies of operating physician dosimetry find a
magnitude of exposure to nearby medical personnel                             range of 0.02 to 0.12 m Sv/Gy$cm 2 KAP for the procedure
(Figure 2).                                                                   with typical values clustering about 0.1 mSv/Gy$cm 2 (6,7).
                                                   2
  KAP is expressed in units of Gy$cm . It is calculated by                    (Note that the estimated patient exposure is 200 m Sv/
multiplying the beam air kerma by its cross-sectional                         Gy$cm 2, indicating that operator exposure is roughly
area. Some x-ray system manufacturers report KAP in                           1/2,000 of patient exposure.) Applying these values, a
units of m Gy$m 2 (1 Gy$cm 2 ¼ 100 m Gy$m 2). It should also be               “typical” combined coronary arteriogram and straight-
noted that air kerma and KAP represent cumulative doses                       forward coronary interventional procedure utilizing a
from an exposure, not exposure rates.                                         cumulative KAP of 50 Gy$cm2 would deliver a 5-m Sv
Application        of      KAP       in     Cardiovascular            X-Ray   effective dose to the physician operator standing roughly
Fluoroscopy to Estimates of Effective Dose to Patients                        1 m from the center of the primary beam while delivering
The most commonly used estimate of the relationship                           10 mSv to the patient.
between KAP exposure to the thorax in Gy$cm 2 and                               Special considerations for occupationally exposed
effective dose in Sieverts (Sv) is 0.20 mSv/Gy$cm2 (1). By                    workers who are pregnant or may become pregnant are
this estimate, a combination coronary arteriography and                       discussed in Section 4.2 of this document and in greater
percutaneous coronary intervention that delivers a KAP                        detail in section 5.4.4 of “Part I: Radiation Physics and
exposure of 50 Gy$cm 2 would impart an effective dose to                      Radiation Biology” and in the longer, online-published
the subject of 10 mSv.                                                        version of this document.
8   Hirshfeld Jr. et al.                                                                                                                JACC VOL.    -, NO. -, 2018
    Radiation Safety ECD, Part 2                                                                                                                       -, 2018:-–-

        F I G U R E 4 Comparison of Retrospective ECG Gating With Prospective ECG Gating

        With retrospective gating, the intensity-modulated x-ray beam is on for the entirety of the R-R intervals during imaging. With prospective gating, the x-ray
        beam is on for about 26% of every other R-R interval. Reproduced with permission from Shuman et al. (8).

    3.3. X-Ray CT                                                                             Electrocardiographic gating, which can have a major
    3.3.1. X-Ray CT Subject and Operator Dose Issues                                     impact on dose, is important in cardiovascular imaging to
                                                                                         minimize motion artifact.
    Although x-ray CT, like x-ray fluoroscopy, is an external
                                                                                              There are 2 types of gating (Figure 4):
    beam exposure technique, unlike x-ray fluoroscopy the
    incident beam is distributed circumferentially around the                             n   Retrospective gating involves x-ray exposure contin-
    subject. Consequently, x-ray CT subject skin doses should                                 ually over the cardiac cycle. Because exposure occurs
    never approach levels that could cause skin injury, and                                   continuously, retrospective gating delivers greater
    subject-harm issues should be confined to stochastic risk.                                 exposure than prospective triggering.
    The dose delivered by an x-ray CT examination is not                                  n   Prospective triggering involves synchronizing expo-
    uniform, delivering greater dose to more superficial lo-                                   sure to a selected portion of the cardiac cycle. The goal
    cations compared with deeper locations closer to the                                      of prospective triggering is for exposure to occur only
    exposed volume center.                                                                    when cardiac motion is minimal.

    3.3.2. Basics of Operation of an X-Ray CT Unit                                       3.3.3. X-Ray CT Measures of Subject Exposure
    The dose delivered by an x-ray CT examination can vary                               The dose delivered by an x-ray CT examination should be
    substantially depending on patient characteristics and                               considered from 2 perspectives:
    the settings of multiple scanner operating parameters.
                                                                                          n   Dose Intensity: Dose per unit mass of tissue. This is a
    Configurable CT technique parameters that can affect
                                                                                              measure of the intensity of the dose used to generate
    dose include x-ray tube potential (measured in kV), x-ray
                                                                                              the images.
    tube current (measured in milliamperes [mA]), scan pro-
                                                                                          n   Volume of Tissue Exposed. The total dose delivered to
    tocol (e.g., axial or helical), pitch, gating protocol, scan
                                                                                              a subject is the product of the dose intensity and the
    rotation time, beam width, scan length, and beam
                                                                                              volume of tissue exposed.
    filtration.
       Image quality is affected by imaging parameter selec-                                  Although CT dose metrics are derived from the mea-
    tion. This selection involves a conscious balancing of                               surement of x-ray tube air kerma, in the CT lexicon, the
    image quality and dose. Other parameter selections, such                             term “dose” is widely used.
    as gating protocol, do not necessarily affect image quality                          CT Dose Index—A Measure of Dose Intensity
    but do affect the amount of radiation used to acquire an                             Computed tomography dose index (CTDI) was first
    image set.                                                                           defined in 21 CFR 1020.33(c) as the average dose detected
JACC VOL.   -, NO. -, 2018                                                                                          Hirshfeld Jr. et al.   9
-, 2018:-–-                                                                                               Radiation Safety ECD, Part 2

over a 100-mm scan length from an imaging acquisition of          phantoms for the determination of DLP. For that reason,
14 slices. It is a measure of dose intensity, that is, the dose   when reporting CTDI or DLP in children, the phantom size
imparted by a unit scan length.                                   used should always be specified. In addition, in children,
CTDI100                                                           sensitivity to a stochastic event varies substantially with
CTDI 100 is a refinement of CTDI that standardizes all dose        subject age. Consequently, in children, European guide-
index measurements to a scan length of 100 mm.                    lines for chest CT conversion factors (19), based on the 32-
Weighted CTDI 100                                                 cm phantom, range from 0.013 mSv $ mGy 1 $ cm 1 (age 10
The CTDIw, or weighted CTDI 100, is an index developed to         years) to 0.039 mSv $ mGy 1 $ cm 1 (age 0 years). Only 2
approximate the average radiation dose delivered to a             studies using contemporary cardiac scanners have deter-
cross section of a subject’s body, allowing for dose vari-        mined cardiac CT-specific conversion factors for children.
ation with depth.                                                 Normalized to the 32-cm phantom, conversion factors (20)
Volume CTDI                                                       range from 0.092 to 0.099 mSv $ mGy 1 $ cm 1 for age 1
CTDI vol is the weighted absorbed dose to air of a 1 cm           year, 0.049 to 0.082 mSv $ mGy 1 $ cm 1 for age 5 years,
axial length of the examined subject located in the               (19) and 0.049 mSv $ mGy 1 $ cm 1 for age 10 years.
middle section of a 100-mm length scan of an acrylic
cylinder for a specific CT technique. It accounts for both         3.4. Patient and Medical Personnel Exposure in
the exposure directly delivered to the 1-cm thick slice               Nuclear Cardiology
and the exposure to that slice by scatter from adjacent           3.4.1. Patient Exposure in Nuclear Cardiology
imaged tissue.
                                                                  Unlike x-ray imaging, which principally exposes the
CTDI vol Special Considerations for Exposure in Children
                                                                  imaged structures, an injected radioactive tracer exposes
It is noteworthy that for identical techniques, smaller
                                                                  the entire body. Organs receiving the highest radiation
subjects receive a higher dose than larger subjects. Esti-
                                                                  dose may not be the imaged structures. The patient’s
mates of CTDI vol for body imaging made utilizing a 32-cm
                                                                  behavior after study completion can alter the rate of
thick phantom underestimate the dose received by
                                                                  radiopharmaceutical excretion, affecting the overall ra-
smaller individuals by a factor of 2.
                                                                  diation dose.
Size-Specific Dose Estimate
                                                                    Estimating the effective dose from a radiopharmaceu-
Size-specific dose estimate is a normalization of CTDIvol
                                                                  tical exposure incorporates:
that takes into account subject size. Its incorporation into
practice is still to be determined.                               1. Quantity of radioactivity administered.
Dose-Length Product—A Measure of the Total Dose                   2. Radiopharmaceutical distribution within the subject.
  Absorbed by the Subject                                         3. Kinetics of distribution to and elimination from each
Dose-length product (DLP) is the product of CTDI vol and             organ.
the axial scan length. It is a measure of total dose to the       4. Radiosensitivity of each exposed organ.
subject and is analogous to KAP for x-ray fluoroscopy.             5. Physical half-life of the radionuclide and its emitted
Accordingly, for x-ray CT, DLP is the best predictor of              photon or particle energy.
stochastic risk.
                                                                    Medical internal radiation dose is a commonly used
                                                                  framework for estimating the radiation dose from radio-
3.3.4. X-Ray CT Measures of Effective Dose
                                                                  pharmaceuticals. The medical internal radiation dose
For   CT     imaging,     European    Commission–sponsored
                                                                  method uses the radiopharmaceutical’s “effective” half-
guidelines from 2000 (9) and 2004 (10) have suggested a
                                                                  life—the combination of radionuclide organ residence
simple approximation of the effective dose that can be
                                                                  times and physical decay rates—to estimate the total dose
obtained by multiplying the DLP by a conversion factor k
                    1       1
                                                                  (in mGy) received by each organ. These values are
(unit: mSv $ mGy         $ cm ) that varies dependent on the
                                                                  multiplied by the individual organ radiation sensitivities
radiation sensitivity of different body regions and patient
                                                                  to yield the individual organ equivalent doses, which are
ages. There are specified conversion factors for CT of the
                                                                  then summed to calculate the whole-body effective dose
head, neck, chest, abdomen, pelvis, and legs (11). The
                                                                  for the subject in mSv.
most common conversion factor for adult chest CT is
                                                                    Additional dose issues:
0.014 mSv $ mGy 1 $ cm1 (12), with values for children
being greater. For CT examinations confined to the car-            1. A renally excreted radiopharmaceutical will deliver a
diac region, estimated conversion factors are greater, with         radiation dose to the bladder wall. If the subject voids
an average value of 0.026 mSv $ mGy 1 $ cm 1 (13–18).             infrequently, the dose to the bladder will be higher.
X-Ray CT Measures of Effective Dose in Children                   2. Radiopharmaceutical imaging studies, both positron
Pediatric CT dosimetry is complicated by the fact that              imaging (positron emission tomography [PET]) and
scanners and studies have variably used 32- or 16-cm                single-photon      emission      computed        tomography
10   Hirshfeld Jr. et al.                                                                                                   JACC VOL.   -, NO. -, 2018
     Radiation Safety ECD, Part 2                                                                                                        -, 2018:-–-

        (SPECT), which employ attenuation correction, utilize a                        is important always to seek to minimize patient radiation
        hybrid radiation-based technique to estimate attenua-                          exposure (this is a particular consideration in younger
        tion. This delivers an additional exposure.                                    patients who have long natural life expectancies), it is
                                                                                       equally important to not withhold appropriate studies
     3.4.2. Personnel Exposure in Nuclear Cardiology                                   due to undue concern of the radiation-related risk.

     Nuclear cardiology personnel receive exposure both from
                                                                                       4.1.2. Dose-Determining Variables
     handling radiopharmaceutical doses and from their
                                                                                       The radiation dose delivered to patients and medical
     proximity to radioactive patients. There are substantive
                                                                                       personnel (regardless of modality) is affected by 3 vari-
     differences, compared with x-ray environments, in the
                                                                                       ables that are under the operator’s control. These are:
     variables affecting personnel exposure:
                                                                                       1. Equipment quality and calibration
     1. The photons emitted from the subject from radio-
                                                                                       2. Equipment operating protocols
        pharmaceuticals are generally of higher energy than
                                                                                       3. Operator conduct
        the x-rays emitted from fluoroscopy or CT devices.
        Therefore, personal shielding devices such as lead                               As each of these variables influences the dose delivered
        aprons or leaded glasses are less effective and, conse-                        to the patient (and also, potentially to operating medical
        quently, are rarely used. Nuclear cardiology personnel                         personnel), each provides an opportunity to reduce dose.
        rely on the principles of time and distance, minimizing
        the time they spend in close proximity to either the                           4.1.3. Image Quality Issues
        dose syringe or the injected patient.                                          Image quality is a major determinant of an examination’s
     2. Unlike x-ray environments, the radiopharmaceutical is                          diagnostic accuracy. Inadequate image quality may cause
        a continuous source of activity that can be excreted via                       either incorrect diagnoses or a need to repeat an exami-
        body fluids or spread during administration. Thus,                              nation—requiring additional patient exposure. Conse-
        subject blood and excreted body fluids are radioactive.                         quently, it is imperative that radiological equipment meet
        An accident or error can cause a healthcare worker to                          current image quality standards, be maintained in prime
        receive an exposure from contamination.                                        working order, and are operated properly to produce
                                                                                       high-quality diagnostic images.
     4. MODALITY-SPECIFIC DOSE REDUCTION                                                 Radiological image quality is strongly influenced by the
         STRATEGIES                                                                    detector dose—the quantity of radiation that reaches the
                                                                                       image detector. Overall image quality is determined by
     4.1. General Principles                                                           spatial and temporal resolution, the signal-to-noise ratio,
     Table 1 indicates core principles to follow for the use of                        the contrast-to-noise ratio, and presence of imaging arti-
     medical ionizing radiation for diagnostic and therapeutic                         facts. Most tactics that increase either spatial resolution (by
     procedures.                                                                       improving signal-to-noise ratio and contrast-to-noise ra-
                                                                                       tio) or temporal resolution (by increasing framing rate) do
                       Core Principles for the Use of Medical Ionizing                 so at the cost of increased dose. The challenge is to optimize
       TABLE 1         Radiation for Diagnostic and Therapeutic                        these properties by balancing the tradeoffs between dose
                       Procedures
                                                                                       and image quality. There are circumstances in which the
     1. The examination should be conducted such that the dose received by the         “best” image that the system can deliver is better than
         patient and attendant medical personnel is the smallest necessary to yield
         satisfactory diagnostic efficacy.                                              needed for diagnosis. Consequently, operators can choose
     2. Diagnostic and therapeutic efficacy should not be compromised in the interest
                                                                                       to accept a lower image quality, which is still sufficiently
         of sparing radiation dose.                                                    diagnostic, to reduce patient (and operator) radiation dose.
     3. If the study’s purpose can be achieved employing a modality that does not      Spatial Resolution—Detector Input Dose, Pulse Width,
         employ ionizing radiation, serious consideration should be given to the
                                                                                         and Nuclear Scan Acquisition
         alternative modality.
                                                                                       Image signal-to-noise ratio is inversely proportional to
                                                                                       the square root of the detector dose. Low signal-to-noise
     4.1.1. Case Selection                                                             ratio images have a “grainy” appearance because the
     The most effective way to reduce patient radiation                                image is formed by a small number of x-ray photons. This
     exposure is to perform a radiation-based procedure only                           grainy quality, termed “quantum mottle,” becomes
     when it is the preferred choice among alternative mo-                             smoother as dose increases, improving the ability to
     dalities that do not involve radiation exposure (e.g., stress                     perceive image detail.
     echo or stress cardiac magnetic resonance). Appropriate                             Examples of the impact of detector dose on image noise
     use criteria should be applied to select patients to un-                          for x-ray fluoroscopic imaging are presented in Figure 5.
     dergo diagnostic and therapeutic procedures. Although it                          These are images of a line pair phantom acquired at different
JACC VOL.   -, NO. -, 2018                                                                                                                       Hirshfeld Jr. et al.   11
-, 2018:-–-                                                                                                                            Radiation Safety ECD, Part 2

   F I G U R E 5 Images of a Line Pair Phantom Acquired in an X-Ray Fluoroscopic System at Different Detector Doses (as Labeled on the Individual Images)

   Note the progressive decrease in image noise and the ability to perceive image detail as the dose increases: 10 nGy/frame, an unacceptably low dose; 18 nGy/
   frame, representative dose for low-dose fluoroscopy; 40 nGy/frame, representative dose for standard-dose fluoroscopy; 200 nGy/frame, representative
   dose for cine acquisition; 1,200 nGy/frame, representative dose for digital subtraction imaging.

detector doses ranging from 10 to 1,200 nGy/frame.                                  counts per unit time, and the image acquisition time, with
As the number of photons reaching the detector increases,                           longer acquisition times acquiring a larger number of
image noise decreases and the image becomes smoother.                               counts.
Over a defined range, as image noise decreases, perceptible                             The     cardiovascular         system      moves.       This     imposes
image spatial resolution increases. For each imaging                                additional requirements on cardiovascular imaging sys-
modality there is an upper limit of dose beyond which                               tems. Spatial resolution is also determined by x-ray
further dose increase, although it may produce a smoother-                          pulse width. Images acquired with pulse durations >8
appearing image, does not yield greater image detail of                             ms will be degraded by motion unsharpness just as
diagnostic importance.                                                              photographs of moving objects are blurred if acquired at
  Similarly, the image noise in x-ray CT images is deter-                           slower camera shutter speeds. Typical pulse durations
mined in part by detector dose. Larger doses will yield                             are 2 to 8 ms.
images with less noise and, within limits, greater spatial                          Temporal Resolution—Pulse Frequency
resolution. For x-ray CT, the spatial resolution required to                        If an image series (such as an x-ray fluoroscopy cine
assess myocardial contours, and, accordingly, the dose                              acquisition) is acquired at too slow of a frame rate, events
needed to achieve it, is smaller than that required to im-                          that occur during time periods shorter than the framing
age coronary arteries.                                                              rate will not be resolved and object motion will cause the
  For nuclear scan images, the number of gamma ray                                  image to have a jerky quality.
counts that are acquired to construct the image de-
termines the image noise and, accordingly, its spatial                              4.2. X-Ray Fluoroscopy
resolution, which improves as the number of counts ac-                              Of the 3 imaging modalities, x-ray fluoroscopy has the
quired increases. The number of counts acquired is                                  greatest variability in dose per procedure and has the
determined by the amount of radioactivity administered                              potential to deliver the largest dose to patients, operators,
for the examination, which determines the number of                                 and nearby medical personnel. Dose is substantially
12   Hirshfeld Jr. et al.                                                                                         JACC VOL.    -, NO. -, 2018
     Radiation Safety ECD, Part 2                                                                                               -, 2018:-–-

     affected by operator choices, behavior, equipment qual-               catheter placement can be accomplished with fluoro-
     ity, and calibration.                                                 scopic frame rates as slow as 4 frames/s. More complex
                                                                           procedures such as coronary and structural interventions
     4.2.1. General Principles                                             require greater temporal resolution and employ frame
     For an x-ray fluoroscopic examination, the total skin dose             rates between 10 and 15 frames/s.
     (in Gy) is determined by the sum of air kermas of all the               Cine acquisition frame rates also vary with the purpose
     frames (fluoroscopy and cine acquisition) in the exami-                of the examination. For coronary arteriography, a frame
     nation. The total effective dose is proportional to the sum           rate of 10 to 15 frames/s is generally adequate. For adult
     of the KAPs of all of the examination’s frames.                       ventriculography, 30 frames/s is preferred to achieve
                                                                           more precise identification of end diastole and end sys-
     4.2.2. Digital X-Ray System Operating Modes                           tole. In pediatric applications, framing rates as fast as 60
     Digital x-ray imaging systems operate in 3 modes that                 frames/s are occasionally needed.
     employ different detector doses to achieve different im-
     age spatial resolution.                                               4.2.4. Determinants of Total Dose for an Exposure
                                                                           Dose per Frame and Framing Rate
     1. Fluoroscopy—the lowest-dose imaging protocol that
                                                                           The     optimal    parameter   settings   for   a    fluoroscopic
        yields images with the lowest spatial resolution.
                                                                           examination or a cine acquisition run are determined by
        Typical fluoroscopic detector doses range between 20
                                                                           the patient’s particular circumstance’s and requirements
        and 40 nGy/frame.
                                                                           for spatial and temporal resolution. For fluoroscopy
     2. Cine acquisition—an intermediate-dose imaging proto-
                                                                           mode, current x-ray units typically provide tableside-
        col intended to provide diagnostic quality images for
                                                                           selectable fluoroscopy detector dose per frame levels
        archiving and diagnostic interpretation. Cine acquisi-
                                                                           that produce different degrees of image noise. They also
        tion images have less image noise than fluoroscopic
                                                                           provide tableside fluoroscopy and cine acquisition frame
        images but should still have visible noise. Typical cine
                                                                           rates ranging from 4 to 30 pulses/s. For cine acquisition
        acquisition detector dose rates are 200 nGy/frame.
                                                                           mode, the detector dose per pulse is set by the service
     3. Digital subtraction—Digital subtraction algorithms are
                                                                           engineer but the operator is able to select the frame
        highly sensitive to image noise and require high doses
                                                                           rate.
        to function effectively. Consequently, digital subtrac-
                                                                           X-Ray Imaging Field Size and System Positioning
        tion algorithms per frame dose rates are the largest
                                                                           Whereas the dose per pulse and the number of pulses
        (typically 1,200 nGy/frame).
                                                                           determine the total dose intensity (in mGy) delivered to
                                                                           the patient, the product of the total dose and the imaging
     4.2.3. X-Ray System Calibration, Operation, and Dose                  field size determines the total amount of radiation energy
     The goals and purposes of an examination determine the                (expressed as the KAP in Gy$cm 2) that the patient re-
     optimal balance between radiation exposure and image                  ceives. In addition to the examination’s total number of
     spatial and temporal resolution. For example, for x-ray               pulses and the detector dose per pulse, the KAP is
     fluoroscopy, the spatial and temporal resolution required              affected by 2 additional parameters that are under the
     for general catheter placement and manipulation is less               operator’s control: the imaging field size selected and
     than that required to perform cardiac interventional                  system positioning.
     procedures.            Current   x-ray   fluoroscopy   systems   are   X-Ray Imaging Field Size
     capable of imaging at multiple frame rates and can adjust             Current    x-ray    systems    link   brightness     stabilization
     detector gain to utilize variable detector doses (21,22).             detection to a collimator position that samples only the
     These capabilities enable the operator to select an optimal           detector area receiving the collimated x-ray beam. Conse-
     imaging protocol for a particular situation.                          quently, the dose per pulse to the detector is not affected
     Temporal Resolution Issues and Dose Tradeoffs                         by collimator position. However, the KAP is directly related
     Because the cardiovascular system moves, x-ray fluoro-                 to the size of the imaged area. The consequence of this
     graphic imaging requires short pulse durations to limit               phenomenon is that, for a given detector zoom (magnifi-
     image motion unsharpness (typically between 3 and 8 ms                cation or input phosphor size) mode, smaller image area
     for adults, as short as 2 ms for children).                           sizes deliver proportionately smaller KAPs. Thus, at a given
        Fluoroscopic temporal resolution requirements vary                 detector zoom mode, reducing exposed field size by colli-
     substantially depending on the examination’s purpose. In              mation to the smallest size necessary minimizes the KAP
     less demanding circumstances, the operator can decrease               that the patient receives. This is not true for changing
     dose by utilizing slower frame rates and lower doses                  detector zoom modes. Detector dose per pulse increases as
     per frame without compromising effectiveness. General                 the zoom magnification increases.
JACC VOL.   -, NO. -, 2018                                                                                                                       Hirshfeld Jr. et al.   13
-, 2018:-–-                                                                                                                            Radiation Safety ECD, Part 2

X-Ray System Positioning                                                            the radiation scattered within the patient that would
There is an optimal distance between the patient’s skin                             otherwise reach medical personnel; accordingly, x-ray
surface and the x-ray source (typically approximately 70                            detector positioning contributes to medical personnel
cm). If the patient is positioned too close to the x-ray                            protection (Figure 6).
source, the x-ray output is concentrated on a smaller area
of the patient’s skin, increasing the patient’s beam                                4.2.5. Procedures and Practices to Minimize Patient and
entrance port exposure rate. This can increase the pa-                                      Personnel Exposure
tient’s skin injury risk. If the patient is positioned too far                      X-Ray Equipment Quality, Calibration, and
from the x-ray source, the image receptor necessarily                                  Maintenance
must also be positioned further away from the source and                            Invasive cardiovascular x-ray imaging facilities have a
the inverse square law requires a greater x-ray output to                           responsibility to maintain and update x-ray equipment to
achieve the requisite detector dose, requiring increased                            produce quality images at the minimum detector dose.
kVp and decreasing image contrast.                                                  Equipment should be well maintained and its calibration
  X-ray     detector      positioning       is   also     an    important           should be surveyed periodically to verify that it is oper-
determinant of dose to the patient as well as the expo-                             ating within appropriate specifications. The x-ray system
sure to medical personnel from scattering. If the detec-                            should provide beam spectral filtering that is consistent
tor is positioned substantially above the thorax, the                               with current standards.
image magnification caused by beam divergence will                                      The x-ray system should provide reduced-dose oper-
decrease the size of the beam entrance port, causing the                            ating protocols for low-dose and low frame rate fluoros-
patient to receive a larger skin dose. In addition,                                 copy imaging programs. Cine acquisition detector input
the x-ray image detector, when positioned close to the                              doses range should be set at the smallest detector dose
patient’s chest, intercepts a substantial portion of                                that provides satisfactory diagnostic quality images.

   F I G U R E 6 Diagrammatic Representation of the Effect of System Positioning on Patient and Operator Radiation Exposure During X-Ray Fluoroscopy

   Note that in the “table too low” circumstance, the entrance port dose delivered to the patient is increased compared with optimal positioning. In the “table
   too low, detector too high” circumstance, the entrance port dose to the patient is further increased. In addition, in the “table too low” circumstance, the
   scattered dose to the operator increases because less of the scattered dose is intercepted by the detector (23).
14   Hirshfeld Jr. et al.                                                                                           JACC VOL.   -, NO. -, 2018
     Radiation Safety ECD, Part 2                                                                                                -, 2018:-–-

     Physician Operator Conduct                                             date, theoretical, based upon anecdotal reports of
     Dose Awareness and Monitoring                                          increased left-sided brain tumors in interventional car-
     Appropriate physician operator conduct begins with a                   diologists (29).
     commitment to minimize radiation exposure to patients                    The protection afforded by lead garments should be
     and to healthcare personnel. Operators should be cogni-                augmented        by   portable   shielding.    Typical   in-room
     zant of the variables that determine image quality and                 shielding includes a ceiling-mounted lead-impregnated
     dose to achieve the best balance of image quality and                  poly (methyl methacrylate) shield that can be placed
     radiation exposure (24,25).                                            between the patient’s thorax and the operator’s upper
        Current x-ray units display real-time values for air                body.      The   importance      of   ceiling-mounted     shields
     kerma dose rates, and cumulative air kerma and KAP. The                cannot be overstated. Proper use of these shields re-
     physician operator should be aware of these values and                 duces operator eye exposure by a factor of 19 (30).
     their interpretation throughout a procedure and consider               Under-table mounted 0.5-mm lead-equivalent shielding
     total accumulated dose in making procedure conduct                     intercepts backscatter off of the patient and the x-ray
     decisions.                                                             table that would otherwise strike the operator’s lower
     X-Ray System Operational Issues                                        body.
     Imaging modality, imaging time, and image field size                      The inverse square law is one of the best sources of
     are 3 important dose-affecting parameters that are under               protection. X-ray intensity decreases as the square of the
     the operator’s direct control. Operators should select the             distance from the source. This relationship has implica-
     lowest-dose imaging modality that is appropriate for a                 tions for physician operators, because the operator’s po-
     particular application. This includes using an image field              sition in relation to the x-ray source can make a large
     size that confines exposure to the structures of interest,              difference in exposure magnitude.
     using the lowest-dose fluoroscopy program, and using the                  Circulating personnel should be positioned remotely
     slowest fluoroscopy pulse rates that yield appropriate                  from the x-ray source and, as a result, should receive
     quality images (26).                                                   negligible exposure. When circulating personnel need to
        Operators should use the x-ray system collimator to                 approach close to the patient, the physician operator
     minimize the exposed field size. Operators should opti-                 has a responsibility to not operate the x-ray system
     mize system positioning with the procedure table at the                (22,31).
     optimal distance from the x-ray tube and the image de-
     tector as close to the patient as possible. In addition,               4.2.6. Pregnant Occupationally Exposed Workers
     operators         should       employ    radiation-sparing   tactics   Uterine     Exposure     Considerations       for   Pregnant   or
     including “last image hold,” virtual collimator position                 Potentially Pregnant Occupationally Exposed Workers
     adjustment, and virtual patient positioning aides.                     As discussed in Section 5.4.4 of Part 1, no measurable
     Physician         and    Medical        Personnel   Shielding   and    increase in adverse fetal outcomes has been detected at
        Protection                                                          fetal or embryonic exposures below 50 mGy. For occu-
     Protective shielding of operators and personnel provides               pationally exposed workers in an x-ray fluoroscopy
     substantial protection. Standard shielding for diagnostic              environment, proper shielding and practices should keep
     x-ray ranges between 0.25 and 0.5 mm of lead or equiv-                 accumulated uterine exposures well below this level.
     alent. A 0.5-mm lead-equivalent apron absorbs 95% of 70                Because the uterus is a deep structure and is inside of
     kVp x-ray and 85% of 100 kVp (27,28).                                  protective garments, the dose to the uterus delivered by
        Medical personnel working in an x-ray procedure                     scattered x-ray is greatly attenuated. Measurements made
     room should wear 0.25- or 0.5-mm equivalent lead                       in phantoms indicate that the uterine dose in a subject
     aprons augmented with neck thyroid shields and hu-                     wearing a 0.25-mm lead apron is
JACC VOL.   -, NO. -, 2018                                                                                                         Hirshfeld Jr. et al.   15
-, 2018:-–-                                                                                                              Radiation Safety ECD, Part 2

4.2.7. Alternative Imaging Techniques                                         nondiagnostic either because of poor image quality or
Alternative imaging techniques, such as intracardiac ul-                      because the images will not answer the clinical ques-
trasound and electromagnetic mapping, can provide                             tions posed. Case selection should incorporate the
structural and guidance information that can supple-                          appropriate use criteria formulated collaboratively by
ment or replace x-ray fluoroscopic imaging. These                              the American College of Cardiology and other organi-
should be employed in place of fluoroscopy when                                zations (37–39).
appropriate.                                                                  Procedure Planning and Patient Preparation
                                                                              In planning the examination, it is important to select the
4.2.8. Summary Checklist for Dose-Sparing in X-Ray Fluoroscopy                acquisition protocol that provides a degree of spatial and
                                                                              temporal resolution that is consistent with the examina-
Checklist of Dose-Sparing Practices for X-Ray Fluoroscopy                     tion’s purpose. Imaging should be confined to the region
Case selection          , Consider patient age, comorbidities, natural life   of interest.
                          expectancy

                        , Consider appropriateness and utility of             4.3.2. Equipment Quality and Calibration
                          nonradiation-based imaging techniques
                                                                              Equipment calibration and preventive maintenance as
Equipment calibration   , Fluoroscopic and cine doses as low as compatible
                          with diagnostic image quality                       part of quality assurance and control programs play an
Procedure conduct       , Minimize beam-on time                               important role in reducing radiation dose by facilitating
                        , Use lowest-dose fluoroscopy setting suitable for     dose optimization. This is discussed in greater detail in
                          a particular task                                   the full online document.
                        , Collimate imaging field size to the area of
                          interest
                                                                              4.3.3. Variables That Affect Patient Dose for X-Ray CT
                        , Use the slowest framing rates suitable for a
                          particular task                                     The radiation dose to a patient is determined by a com-
                        , Minimize cine acquisition run durations             bination of the patient’s physical characteristics and
                        , Minimize patient-detector distance
                                                                              scanner protocol selection. Larger patients require larger
                                                                              exposures.
                        , Maximize employment of operator shielding
                                                                                Operator-selectable imaging protocols that influence
                                                                              patient dose include:
4.3. X-Ray CT
                                                                              1. Scan length. Scan length should be kept to a minimum
4.3.1. X-Ray CT General Principles                                               to encompass only the anatomy of interest.
Achieving optimal images at minimal dose requires an                          2. X-ray beam intensity. Dynamically modulated tube
expert team to coordinate patient management and pro-                            current should be used for cardiovascular acquisitions
tocol selection including image acquisition, reconstruc-                        Tube potential: The single most important factor in con-
tion, and interpretation. The team needs to select the                          trolling radiation dose is adjustment of x-ray tube voltage
imaging protocol most likely to acquire diagnostic-quality                      (in kV) (40–42). Increasing tube voltage increases the x-ray
images that achieve the examination’s goals while                               beam’s mean photon energy level, and increases radiation
exposing the patient to the smallest necessary radiation                        dose roughly proportionally to the square of the voltage.
dose (34–36).                                                                   Increasing x-ray tube voltage decreases image noise.
   The keys to minimizing radiation exposure in cardiac                         Tube current: The x-ray tube current (in milliamperes
CT are:                                                                         [mA]) is proportional to the number of x-ray photons
                                                                                produced per unit time and is linearly proportional to
1. Appropriate case selection.
                                                                                radiation dose. Image noise is inversely proportional to
2. Scanner capability and protocol selection.
                                                                                the square root of the tube current. Thus, decreasing
3. Proper patient preparation.
                                                                                tube current at a given tube potential decreases
4. Appropriate examination conduct.
                                                                                the radiation dose at the expense of increased image
   Greater detail of how to implement these procedures is                       noise.
discussed in depth in the complete document published                         3. Rotation time. The time required for the gantry to
online.                                                                          perform 1 rotation is a selectable parameter. Exposure
Case Selection Appropriateness                                                   increases linearly with rotation time.
The     first     principle      to    reduce      patient      radiation      4. X-ray beam filtration. Greater filtering decreases pa-
exposure         due    to   CT      examinations        is    to    avoid       tient dose. The choice of filter depends on the size of
performing          examinations        that    will    prove       to   be      the patient and the acquisition field of view (36).
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