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    The Radiographer2009; 56 (3): 3237

    Australian Institute of Radiography

    Literature review

    Introduction

    The objective of establishing diagnostic reference levels (DRL)

    in diagnostic imaging (also previously known as Guidance Levels

    or Reference Values1,2) is to provide radiology and other depart-

    ments that use x-ray imaging with a convenient DRL dose com-

    parison to ensure that radiation doses to patients are kept withinreasonable limits.

    The main task of radiation protection is not only to mini-

    mise the stochastic risks but also to avoid deterministic injuries.

    Stochastic refers to effects whose probability increases with

    increasing dose and for which there is no threshold dose. Any

    dose, no matter how small, has the potential to cause harm and

    this becomes apparent years after the exposure. Examples are

    leukaemia and hereditary effects. Deterministic effects are those

    in which the severity of the effect, rather than the probability,

    increase with increasing dose and for which there is a threshold

    dose. Examples are epilation, erythema and hematologic damage

    and are known as early effects.3

    A DRL, as defined by the International Commission on

    Radiological Protection (ICRP), is a form of investigation level,

    applied to an easily measured quantity, usually the absorbed dose

    in air, or tissue-equivalent material at the surface of a simple

    phantom or a representative patient.4

    The ICRP recommends the establishment of reference levels

    as a method of optimising the radiation exposure to patients. This

    is accomplished by comparison between the numerical value of

    the diagnostic reference level (derived from relevant national,

    regional or local data) and the mean or other appropriate value

    observed in practice for a suitable reference group of patients or a

    suitable reference phantom.

    Another definition by the Council of the European Union in its

    Council Directive 97/43 defines DRL as dose levels in medical

    radiodiagnostic practices or, in the case of radio-pharmaceuticals,

    levels of activity, for typical examinations for groups of standard-

    sized patients or standard phantoms for broadly defined types

    of equipment. These levels are expected not to be exceeded for

    standard procedures when good and normal practice regarding

    diagnostic and technical performance is applied.36 It reinforces

    the concept of references doses applying only to standard or

    representative patients. DRL therefore are not dose limits but

    a guide of good practice. It is not a dose constraint and the DRL

    values are not used for regulatory or commercial purposes. DRL

    act as an investigation trigger if the numerical values are consis-

    tently exceeded.

    Background

    The need for DRL

    Patient exposures in diagnostic radiology are increasing at a

    disquieting rate for certain radiographic, fluoroscopic and CT

    examinations. Regulla and Elder5 pointed out that data obtained

    from the United Nations Scientific Committee on the Effects of

    Atomic Radiation (UNCEAR) show that there are significant

    differences in national radiation exposures and a very unevendistribution of patient doses among world population for the same

    or similar procedures. Mean annual x-ray effective dose of the

    population can vary by up to a factor of 60. In the United States,

    studies such as the Nationwide Exposure X-ray Trends (NEXT)

    surveys also showed that patient doses in radiology vary consider-

    ably from one facility to the next.6 Gray, et al.1 posed the question,

    why one radiology facility should use an exposure that is 10,

    20 or 126 times greater than another facility to produce a radio-

    graphic image? Johnston and Brennan7 and Carroll and Brennan8

    also reported wide variations in patient doses for the same radio-

    graphic examinations among hospitals in the UK and Europe.

    These patient doses are attributed to a wide range of factors such

    as type of image receptor, exposure factors, fluoroscopic times,

    number of images, type of anti-scatter grid and level of quality

    control as reviewed by Seeram,9 Bushong10 and Parry, et al.11

    In Australia, theAustralian Radiation Protection and Nuclear

    Safety Agency (ARPANSA) Code of Practice, Section 3.1.8

    Diagnostic reference levels as a quality assurance tool

    KD Edmonds

    Medical Physics Section, Medical Radiation Branch, Australian Radiation Protection and Nuclear Safety Agency,

    Yallambie, Victoria 3085, Australia.

    Correspondence [email protected]

    Abstract The objective of diagnostic reference levels (DRL) in radiology is to assist in the optimisation of radiation dose

    to patients, while maintaining diagnostic image quality, and to detect unusually high doses that do not contribute signifi-

    cantly to the clinical outcome of a medical imaging examination. DRL have been in existence overseas for more than a

    decade and its influence has contributed to a steady decline in dose for general radiography and fluoroscopic procedures.

    High dose modalities such as CT and interventional procedures are increasing dramatically both locally and internation-

    ally resulting in the unwanted outcome of a significant increase in population cumulative effective dose. This calls forurgent dose reduction and dose constraint measures. Utilising DRL is one method of optimising patient dose. Some local

    and international DRL dose levels for some common radiographic, interventional and CT examinations are presented as

    a suggestion for the application of this methodology in Australian radiology practice.

    Keywords: diagnostic reference levels, guidance levels, radiation dose, reference values, quality assurance.

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    The Radiographer 33

    (Radiation Protection Series No.14) states that the Responsible

    Person must establish a program to ensure that radiation doses

    administered to a patient for diagnostic purposes are:

    1 Periodically compared with DRL for diagnostic procedures for

    which DRL have been established in Australia

    2 If DRL are consistently exceeded, reviewed to determine

    whether radiation has been optimised.12

    In addition, the ARPANSA Safety Guide, Section 7.8

    (Radiation Protection Series No.14.1), suggests that as part of

    the QA program, patient dose surveys are undertaken periodically

    to establish that the doses are acceptable when compared with

    published DRL. It also recommends that accrediting bodies such

    as RANZCR and the Australian Council on Healthcare Standards

    consider including compliance with DRL for a core set of exami-

    nations. If the radiology department observes dose values consis-

    tently exceeding the DRL, then this warrants further investigation

    however some flexibility should be allowed if higher doses are

    indicated by sound clinical judgement.13,14

    However, at this point in time, there are no DRL published in

    the Code of Practice or the Safety Guides. It would seem logical

    therefore to use published values from the literature from exten-

    sive surveys in countries with similar healthcare settings e.g.

    similar levels of education and training for imaging technologists,

    radiologists and similar provision of imaging equipment.15

    History of DRL

    National surveys of patient doses from x-ray examinations in

    Europe and the USA since the 1950s have demonstrated wide

    variations in doses between radiology departments and illustrated

    the need for quantitative guidance on patient exposure. It was only

    at this stage that dose measurements to patients began in earnest.

    National surveys in the USA and UK concentrated on measuring

    entrance surface doses with or without backscatter for commonradiographic projections. The Nationwide Evaluation of X-ray

    Trends in the USA in the 1970s measured entrance skin expo-

    sure free-in-air for average exposure technique factors or used

    a standard phantom. The NRPB national patient dose survey in

    the UK in the 1980s measured entrance surface dose directly on

    the surface of the patient (including backscatter) using thermolu-

    minescence dosemeters. A European trial supporting the Quality

    Criteria for Diagnostic Radiographic Images in 1991 used the

    same technique.37

    Dose guidelines began to appear in late 1980s. First was the

    USA, promoted by the Centre for Devices and Radiological Health

    (CDRH) in conjunction with the Conference of Radiation ControlProgram Directors Inc. Then in the UK it was conducted by the

    National Radiation Protection Board in collaboration with relevant

    professional bodies. Europe then followed with reference doses

    incorporated into Working Documents by EC Study Groups.38

    International recommendations then appeared on how to

    measure and set reference dose levels based on the initiatives led

    by the USA and the UK. The ICRP Publication 60 first made

    mention of the concept of investigation levels in 1990followed

    by the current definition of DRL inICRP Publication 73 in 19964

    and theEC Medical Exposure Directive in 1997.36

    The United Kingdom introduced DRL in 1990 for common

    diagnostic examinations based on a national patient dose survey

    in the mid-1980s conducted by the NRPB, now known as the

    Health Protection Agency (HPA). They are now based on the

    five-yearly reviews of the National Patient Dose Database and are

    currently in their third review.16

    The International Atomic Energy Agency (IAEA) in 1996 and

    2002 also issued advice on the use of DRL (or guidance levels)

    in their safety standard series and included guidance levels for

    typical adult patient doses for general radiography, CT, fluoros-

    copy and mammography.2,14,

    Many countries worldwide have now incorporated the European

    Community Directive in national legislative documents.1Several

    organisations currently providing guideline documents for estab-lishing DRL include the ICRP,4,20 the Health Protection Agency in

    the UK,16,21 the Commission of European Communities22 and the

    American College of Radiology.23

    Aim

    The overall aim of DRL are to better manage patient dose in

    diagnostic radiology using the principle of optimisation which is

    defined as exposure to radiation from justified activities should

    be kept as low as reasonably achievable, social and economic

    factors being taken into account. The European Commission and

    the ICRP provide a range of tools to achieve this. 15,24

    Data obtained from patient dose surveys show that typical

    patient doses for the same type of x-ray examinations can varyconsiderably from one radiology practice to another. The estab-

    lishment of DRL therefore is to give an indication of unusually

    high values. The DRL are usually set at the third quartile value of

    the distribution of typical doses derived from dose surveys both

    nationally and internationally. Using the third quartile or 75th

    percentile is a compromise between being overly stringent and

    overly complacent.3

    Essentially, if mean doses exceed a reference level dose an inves-

    tigation should take place to establish the cause and take corrective

    action, unless the dose was clinically justified. Reference doses were

    also used to provide a trigger for practices in need of investigation

    and hopefully lead to dose optimisation. ICRP 734 recommended

    that DRL values be selected by professional bodies, be reviewed at

    regular intervals and be specific to a country or region.

    Wide variations in patient doses are to be expected and it

    is only sensible to compare mean or median values, which is

    less influenced by extreme outliers, on representative groups of

    patients to monitor trends with time, equipment or technique.

    Method

    From a practical perspective, the DRL should be expressed

    as a readily measurable patient-related quantity for the specified

    procedure. For example,

    1 General radiographic examinations either entrance skin dose

    (ESD) or the dose area product (DAP)

    2 Fluoroscopic examinations dose area product (DAP)

    3 CT examinations computed tomography dose index ( CTDIw

    or CTDIvol

    ) and the dose length product (DLP).

    New CT scanners in accordance with Australian Standards,

    AS/NZS 32002.4,25 should display the volume CTDIvol

    and/or the

    DLP on the operators console after the selection of technique

    factors and prior to the initiation of x-rays.13

    DRL used for film-screen technology should not necessarily be

    used for new digital radiography without prior adjustment. 26

    Dosimetry methods

    International guidance on patient dosimetry techniques for

    x-rays used in medical imaging is published by the International

    Commission on Radiation Units and Measurements in ICRU

    Report 74.27 This report contains advice on the relevant dosimet-

    ric quantities and how to measure or calculate them in a clinical

    setting which is directly applicable to the patient dose surveys

    needed to estimate population exposure.

    Diagnostic reference levels as a quality assurance tool

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    The Radiographer34

    There are various methods of recording dose levels.

    Thermoluminescent dosimeters (TLD) are often used for plain

    film examinations and include dose contribution from backscat-

    ter if placed on the patient or phantom surface. The small TLD

    sachets are usually placed in the centre of the irradiated field on

    the entrance surface of the patient or phantom. The TLD can be

    stuck directly and unobtrusively to the patients skin with verylittle interference in patient mobility or comfort. They do not

    interfere with the examination or obscure important diagnostic

    information on the radiographic image. They need to be calibrated

    with respect to radiation qualities used in diagnostic radiology.

    TLD are also prone to some inaccuracy due to signal fade, non-

    linear response and dependency on beam energy.3 Ionisation

    chambers are bulky and more difficult to attach to patients. The

    parallel plate ionisation chambers measure back scatter but the

    lead backed solid state detectors do not. They are not recom-

    mended for direct measurement of entrance surface dose on the

    skin of the patient. They can, however, be used to make measure-

    ments of the absorbed dose to air, in free air, without a patient

    or phantom present. The measurements can then be correctedusing appropriate backscatter factors and the inverse square law

    to estimate the entrance surface dose. Newer technology such as

    optically stimulated luminescence dosimeters (OSLs) and radio-

    chromic film may replace TLD. Radiochromic film is currently

    being evaluated by ARPANSA.

    Alternatively, the entrance skin dose may also be calculated

    from x-ray tube output measurements (mGy/mAs) and the expo-

    sure parameters, kVp, filtration and mAs. The incident air kerma

    is calculated from the tube output using the inverse square law and

    then multiplied by the backscatter factor to obtain the entrance

    skin dose.

    A dose area product (DAP) meter consists of an ionisationmeter that is usually attached to the x-ray tube collimator and

    measures the dose in Gy. square centimetre (Gy cm2) which is

    proportional to the beam area and incident air kerma. The unit

    unfortunately does not measure backscatter which is important

    in higher dose examinations such as cardiac and vascular inter-

    ventional procedures. However DAP meters can be used for

    radiographic and fluoroscopic procedures such as barium meals,

    angiography and on mobile image intensifiers.2,3,28

    For CT machines, the CTDIw

    and /or CTDIvol

    (mGy) and the

    DLP values(mGy cm) are conveniently provided at the opera-

    tor console before or after the examination. The CTDIw

    is the

    weighted sum of the CT dose (or air kerma ) index measured

    in the centre and periphery (1 cm under the surface) of a 16 cm

    diameter (head) or a 32 cm diameter (trunk) standard polymeth-

    ylmethacrylate (PMMA) CT dosimetry phantom. The CT dose

    index is measured with a 100mm long pencil ionization chamber

    inside a standard PMMA CT dosimetry phantom.

    CTDIw

    = CTDIc+ CTDI

    pwhere

    cis the centre position

    andp

    is the peripheral position of the phantom. Units: mGy

    CTDIw

    corrected for pitch is the CTDIvol

    .

    CTDIvol

    = Units: mGy

    The DLP is the product of CTDIvol

    and the scan length of the

    examination.

    Thus DLP = CTDIvol

    x length irradiated. Units: mGy cm15

    As a starting point it is suggested that the UK 2000 survey

    review of DRL for general radiography for adults (Table 1) and

    fluoroscopy for adults (Table 2), Paediatric procedures (Table

    3), the UK 2003 CT survey (Table 4), and mammography (Table

    5), be adopted and /or adapted in the Australian context as there

    are currently no established national DRL.29 Some state regula-

    tors though have provided local DRL guidance on radiography,

    fluoroscopy and CT.

    34

    Dose values should be reviewed as com-puted/digital radiography becomes more widespread in order to

    minimise the detrimental influence of exposure creep.30 This

    phenomenon occurs after the change over from film-screen

    radiography to digital radiography where exposure factors may

    actually increase in order to reduce image noise. Uncoupling of

    display from acquisition in digital radiography introduces the

    potential for systematic overexposure without necessarily com-

    promising image quality.31 The wide exposure latitude and linear

    response to x-ray energy provides an image appearance that

    remains consistent throughout the exposure range and this in turn

    provides little feedback to the technologist. Underexposed images

    typically have a grainy, mottled appearance that causes radiolo-

    gists to reject images. Over-exposed images, on the other hand,have a crisp, sharp appearance. In order to prevent repeating the

    image, the technologist may increase exposure factors especially

    for manual and mobile radiography. Exposure indices or expo-

    sure indicators provided by the various CR/DR manufacturers

    also have a wide range of acceptable values and are currently not

    standardised throughout the industry.

    In the case of CT examinations, care should be taken when

    following overseas DRL because of the wide variety of CT scan-

    ners and local examination protocols employed. In addition, the

    rapid advances in CT technology have also resulted in constantly

    changing scanning protocols. Nevertheless, the DRL provided in

    Tables 15, serve as a rough guide until new DRL emerge fromcurrent surveys in Australia.

    In future, a web based interactive dose survey software pro-

    gram will be provided by ARPANSA where each radiology

    department can access it to calculate their dose levels and com-

    pare them with DRL.

    Discussion

    The development of DRL practice in diagnostic radiology within

    Australia is still at an early stage as no national surveys have been

    carried out for any radiological examinations for the express pur-

    pose of establishing national DRL. At a local level, various organi-

    sations, regulatory authorities and individual practices have carried

    out limited general radiography, fluoroscopy and CT surveys.34

    There is a clear need to manage (optimise) the radiation doses

    from diagnostic radiology in order to minimise the risks from

    radiation induced cancers. The establishment and use of DRL is

    recommended by international radiation protection organisations

    as an important component of the management of these doses

    and many countries have incorporated them into their radiation

    protection regulations12,36

    Data from European countries shows a wide variation in com-

    mon DRL which may be due to differences in socio-economic

    conditions, regulatory regime, activeness of professional bod-

    ies and health care implementation (private/public mix etc).7,32

    International radiation protection bodies such as the IAEA and

    ICRP therefore recommend that each country carry out its own

    national wide scale DRL survey. It is for this reason that Australia

    must develop its own set of common national DRL.

    The introduction of computed and digital radiography in recent

    years has had a significant impact on the potential for higher dose

    KD Edmonds

    1

    3

    2

    3

    CTDIw

    pitch

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    The Radiographer 35

    Table 1: Recommended diagnostic reerence doses or individual radiographs on adult patients.

    Radiograph ESD per radiograph (mGy) DAP per radiograph (Gy cm2)

    Skull AP/PA 3 -

    Skull LAT 1.5 -

    Chest PA 0.2 0.12

    Chest LAT 1 -

    Thoracic spine AP 3.5 -

    Thoracic spine LAT 10 -

    Lumbar spine AP 6 1.6

    Lumbar spine LAT 14 3

    Lumbar spine LSJ 26 3

    Abdomen AP 6 3

    Pelvis AP 4 3

    Adopted rom the UK 2000 DRL survey review. 29

    Note: Adult is dened as a person o average size (7080 kg) ESD = Entrance Skin Dose, DAP = Dose Area Product.

    Table 2: Recommended diagnostic reerence doses or fuoroscopic/interventional examinations on adult patients.

    Examination DAP per exam (Gy cm2) Fluoroscopy time per exam (mins)

    Barium (or water soluble) swallow 11 2.3

    Barium meal 13 2.3

    Barium ollow through 14 2.2

    Barium (or water soluble) enema 31 2.7

    Small bowel enema 50 10.7

    Biliary drainage/intervention 54 17

    Femoral angiogram 33 5

    Hickman line 4 2.2

    Hysterosalpingogram 4 1

    IVU 16 -

    MCU 17 2.7

    Nephrostogram 13 4.6

    Nephrostomy 19 8.8

    Retrograde pyelogram 13 3

    Sialogram 1.6 1.6

    T-tube cholangiogram 10 2

    Venogram (leg) 5 2.3

    Coronary angiogram 36 5.6

    Oesophageal dilation 16 5.5

    Pacemaker implant 27 10.7

    Adopted rom the UK 2000 survey review.29 DAP = Dose Area Product.

    delivery.30,31 In addition, the exponential increase in CT examina-

    tions has lead to the unwanted outcome of a significant increase

    in population cumulative effective dose.35 Other causal agents that

    are linked to high doses include type of image receptor, exposure

    factors, fluoroscopic time, number of images, type of antiscatter

    grid and level of quality control.9,10,11

    DRL depend significantly on local practice and equipment.

    They may also change with time as optimisation strategies become

    successful. The UK experience over the past 20 years has shown

    that the implementation of DRL together with a dose optimisation

    program has resulted in a gradual reduction of doses.29,32

    For DRL to succeed, acceptance and application of the concept is

    required across as many radiology departments as possible. Complex

    calculations will only discourage participation. Furthermore, setting

    DRL is a resource intensive activity and requires a national response.

    Priority should be given to procedures with greatest dose implica-

    tions, i.e. CT and Interventional procedures. DRL should be owned

    by the professions such as the Australian Institute of Radiography and

    the Royal Australian New Zealand College of Radiology. ARPANSA

    will assist in facilitating their development.

    Conclusion

    Overseas experience has shown that the use of DRL have prov-

    en be a useful quality assurance tool in optimising patient dose in

    Diagnostic reference levels as a quality assurance tool

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    The Radiographer36

    Examination Standard age (y) DAP per exam (Gy cm 2)

    MCU 0 0.4

    1 1.0

    5 1.0

    10 2.1

    15 4.7

    Barium meal 0 0.7

    1 2.0

    5 2.0

    10 4.5

    15 7.2

    Barium swallow 0 0.8

    1 1.5

    5 1.5

    10 2.7

    15 4.6

    Table 4: Recommended diagnostic reerence levels or CT examinations (CTDIvol

    and DLP).

    Patient group Scan region CTDIvol

    (mGy)

    single slice/multi slice

    DLP (mGy cm)

    Single slice/multi slice

    Adults Post ossaCerebrum

    Whole exam

    65/10055/65

    760/930

    Abdomen (liver metastases )

    Whole exam

    13/14

    460/470

    Abdomen and pelvis

    (abscess) Whole exam

    13/14

    510/560

    Chest, abdomen and pelvis

    (lymphoma staging or ollow up).

    Whole exam

    22/26

    760/940

    Chest (lung cancer) 10/13 430/580

    Chest Hi-res

    Whole exam

    3/7

    80/170

    Children

    01 year-old

    Head (post ossa)

    Head (cerebrum)

    Thorax

    35

    30

    12

    270 (whole exam)

    200

    5-year-old

    Head (post ossa)

    Head (cerebrum)

    Thorax

    50

    45

    13

    470 (whole exam)

    230

    10-year-old

    Head (post ossa)

    Head (cerebrum)

    Thorax

    65

    50

    20

    620 (whole exam)

    370

    Adopted rom UK 2003 CT dose survey.33

    Dose values or adults relate to the 16 cm diameter CT dosimetry phantom or examinations o the head and the 32 cm diameter CT dosimetry phantom or

    examinations o the trunk.All dose values or children relate to the 16 cm diameter CT dosimetry phantom.

    CTDI vol = Computed Tomography Dose Index Volume, DLP = Dose Length Product.

    Table 3: Recommended diagnostic reerence doses or complete examinations on paediatric patients.

    Adopted rom the UK 2000 survey review.29

    KD Edmonds

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    The Radiographer 37

    diagnostic radiology. It is recommended that local dose surveys be

    performed annually while national surveys every five years.32,33

    The imaging technologist is the main person who decides on

    the exposure factors and the visual image quality for the radi-

    ologist to make a diagnosis. The technologist should therefore be

    aware of the exposure options that minimise radiation doses while

    still maintaining good image quality and monitoring dose levels.

    DRL would therefore serve as an important means of minimising

    radiation doses as well as dose variations at minimal cost to radiology

    departments. They also increase staff awareness and imaging tech-nologists will be better equipped to deal with patient enquiries.3

    ARPANSA is responsible for carrying out national DRL

    surveys in consultation with relevant stakeholders such as the

    Royal Australian & New Zealand College of Radiology, The

    Australian Institute of Radiography, Australasian College of

    Physical Scientists & Engineers in Medicine, Australian & New

    Zealand Society of Nuclear Medicine, Department of Health and

    Aging and the various State/Territory Regulators.

    Acknowledgements

    The author thanks Anthony Wallace for his advice in preparing

    this article.

    The author

    KD Edmonds DCR BHA Grad Dip Pub Health

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    Table 5: Recommended diagnostic reerence level or mammography or a

    typical adult patient.

    For ilm screen examinations using a grid, the mean glandular dose (MGD)

    is 2 mGy based on the 4.2 cm acrylic American College o Radiologists phan-

    tom.17,18,19

    For a 50% adipose, 50% glandular 5 cm thick phantom the MGD is 3 mGy17

    Note: For digital mammography, the values quoted above represent an upperlimit

    Diagnostic reference levels as a quality assurance tool