RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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RADIATION PROTECTION INDIAGNOSTIC
ANDINTERVENTIONAL RADIOLOGY
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology

• L15.2 Optimization of protection in radiography
  Radioprotection aspects

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Introduction

• Optimization of patient radiation protection
  requires periodic evaluation of doses and image
  quality.
• Operators of the X Ray system should be aware of
  the interdependence between technical parameters,
  dose and image quality
• Procedures should be established for each
  examination to ensure a proper use of equipment.

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Topics

• Practical rules to protect patients
• Generators and X Ray production related
  parameters
• Imaging devices related parameters (film,
  intensifying screens)
• Examination procedures related parameters (number
  of radiographic projections, technical settings..)

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Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology

• Topic 1 Practical rules to protect patients

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Existing past images

• Before beginning an examination, it is advisable
  to compile the existing past images of similar
  examinations in or outside the institution, in
  order to minimize the number of radiological
  examinations that the patient has to bear.

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Periodic measurement of the entrance patient dose

• The periodic measurement (at least once a year)
  of the entrance patient dose (or similar
  quantity) and the comparison with the guidance
  (or reference) levels and with values from
  previous controls will permit the detection of
  equipment malfunctions
• When the entrance doses (or other dosimetric
  parameters) are clearly in excess of the guidance
  levels (or of those previously obtained), it is
  necessary to check the generator and associated
  devices, as well as the procedures and techniques
  used for the examination.

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Periodic evaluation of the image quality

• A periodic evaluation (at least once a year) of
  the image quality obtained in each room allows
  the detection of malfunctioning in the imaging
  chain or in the generator (almost always
  associated to high patient doses and poor image
  quality)
• A periodic evaluation of the number of rejected
  and repeated radiographs and the analysis of the
  causes of rejects and retakes allow the detection
  of failures in the X Ray equipment, associated
  image devices, as well as in the examination
  procedures and in the skill and training of the
  staff

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Corrective actions

• When some corrective measures are proposed after
  the detection of a malfunctioning, recording the
  follow up of their implementation is advisable
  (in a logbook)
• On the contrary, most of them will not be carried
  out.

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Skin focus distance and others

• In general radiography (except dental) and
  fluoroscopy with X Ray mobile equipment, the
  skin-focus distance should not be lower than 30
  cm
• In radiography and fluoroscopy with fixed
  equipment, the skin-focus distance should not be
  lower than 45 cm
• The fluoroscopy equipment without image
  intensifiers must be replaced, or upgraded with
  an image intensifier

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Practical rules to protect patients

• When there are suspicions about a malfunctioning
  of the X Ray unit or of the imaging chain in a
  room that might affect the protection of the
  patient (i.e., because the images become over or
  underexposed without changing the technique),
  this should be reported to the responsible of the
  room in order to reevaluate the equipment if
  necessary and to introduce corrective actions.

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Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology

• Topic 2 Generators and X Ray productionrelated
  parameters

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With reference to generators and X Ray tubes
filtration

• Whether imported into or manufactured in the
  country where it is used, the equipment should
  conform to applicable standards of the
  International Electrotechnical Commission (IEC)
  and the ISO or to equivalent national standards
• A correct filtration (minimum 2.5 mm Al, in
  general radiology), significantly reduces the
  patient dose due to low energy X Rays which do
  not contribute to the image formation
• In tubes equipped with removable aluminum filters
  (added filtration), it is important to verify
  whether they are still in place after any
  possible maintenance or repairing of X Ray tube

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With reference to generators and X Ray tubes (I)

• In tubes in which filters are not accessible
  neither visible from the outside, it is advisable
  to verify, at least once in the tube lifetime,
  that the correct filtration is in place. After
  each repairing or maintenance during which the
  tube housing is removed, a certificate should be
  obtained proving that filters have been restored
• In mammography, very low voltages are used and
  the filtration requirements are different (0.03
  mm thickness of Molybdenum recommended, in
  equipment with anode of the same material).

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With reference to generators and X Ray tubes (II)

• In examinations with fluoroscopy, a clock should
  be available allowing the measurement of the
  fluoroscopy elapsed time, with audible
  indications at 10 or 5 minutes.
• Fluoroscopy should be controlled with a switch of
  a "dead man" type.

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With reference to generators and X Ray tubes (III)

•  When using mobile equipment in intensive care
  units, in patient rooms or in other different
  locations such as general diagnostic radiology
  rooms, one must not forget that generators
  require a high instantaneous electric power
  supply
• A too low power supply will affect image quality.

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With reference to generators and X Ray tubes (IV)

• For the same reason, in order to avoid retakes,
  it is very important to guarantee that the
  battery attached to the equipment is properly
  charged
• For units connected to the mains, one must be
  sure that the required power is actually supplied.

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Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology

• Topic 3 Imaging devices related parameters

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With reference to imaging devices screen-film
combination

• The use of the appropriate screen-film
  combination, the "fastest" compatible with the
  type of image that is looked for, is recommended
  to guarantee the lowest patient dose
• Due to human errors, it is not advisable to use
  in the same room, several screen-film
  combinations of different sensitivity class
• An exception is the case when each combination
  has a different film format and the selection of
  radiological technique is made manually (no AEC)  

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With reference to imaging devices (I)

• The use of cassettes, grid holders and tables of
  carbon fiber material, results in important
  patient dose reductions
• The use of intensifying screens with, scratches,
  or cassettes that do not provide the correct
  film-screen contact should be avoided

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With reference to imaging devices automatic
exposure control

• Inappropriate selection of automatic exposure
  control settings might lead to incorrectly
  contrasted images (too dark or too clear).
• Then the automatic exposure control device should
  ALWAYS be checked, in particular when the
  sensitivity of the screen-film combination has
  been changed.
• The correct operation of the automatic exposure
  control device requires, for each projection, the
  selection of the chamber or detector closer to
  the area of interest, so that this area be best
  contrasted.

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With reference to imaging devices (II)

• The patient entrance air kerma rate should not
  usually exceed 50 mGy/min.
• In modern image intensifiers, this value should
  be much lower depending on patient size and
  projection
• The use of devices for memorizing the last image
  (last image hold) is recommended

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With reference to imaging devices (III)

• In either automatic or manual processors, it is
  essential to change the chemicals according to
  the manufacturer instructions, with respect to
  both the expiration time and the number of
  processed films.
• The safelights in darkrooms do not have filters
  with endless life. Replacement is recommendable
  at least once a year (twice a year is optimal).
• When changing to a more sensitive film than the
  former used, it might be advisable to reduce the
  safelight power (or change filters) in the
  darkroom.

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With reference to imaging devices (IV)

• It is very important to have viewing boxes in
  areas with correct environmental light, enough
  brightness and uniformity over the surface and,
  for certain applications (e.g. mammography)
  complementary high intensity light sources.
  Hence, periodic cleaning of the internal and
  external surfaces and replacement of the
  fluorescent tubes are essential
• Make sure that the illuminated area coincides
  with the radiograph size, so that diaphragmable
  viewing boxes are recommended

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Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology

• Topic 4 Examination procedures related
  parameters

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With reference to procedures (I)

• The usual radiological technique for each
  projection on a given equipment, with details of
  the associated image device should be written and
  be readily accessible, close to the control
  panel. It should be specified for patients of
  standard as well as uncommon size
• Thus any personnel (substitutes, night personnel
  or staff after time periods of a different work
  different examinations or work in another room)
  would know those techniques without having to
  resort to "estimates" and retakes 

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With reference to procedures (II)

• With any equipment (manually as well as
  automatically controlled), it is important to
  know which set of parameters (technique) are to
  be selected to obtain a good image
• When changes are introduced on whichever element
  of the imaging chain (generator or tube as well
  as other accessory devices such as film type,
  cassette, intensifying screen, etc), an update of
  technical settings should be performed
• A yearly check of those updates is also advisable

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With reference to procedures (III)

• It is advisable to use the highest kVp (and the
  lowest mAs) compatible with the image that one
  expects to obtain. In this way the patient
  irradiation will be lower, although it might get
  lower image contrast. Therefore the optimization
  is to find the proper balance between contrast
  and dose
• The shortest exposure time as possible should be
  selected, above all when examining non-
  collaborating patients (shorter time means
  reduction in kinetic blurring)

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With reference to procedures (IV)

• Hence, it is recommended to perform the pediatric
  examinations with generators (three-phase or high
  frequency, usually) capable of producing very
  short exposures, in order to avoid retakes due to
  the kinetic blurring and poor image quality
• The radiographic techniques in use in each room
  should be compared on a regular basis with those
  recommended in published guidelines (EEC,BSS)

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With reference to procedures (v)

• Any radiological examination is assumed to have
  been prescribed by a properly accredited
  physician
• When applicable, patients own record as well as
  medical indications that make recommendable the
  radiological examination should be available
  (WHO, EC)
• Then it might be convenient to modify the
  examination procedure (e.g. to substitute it by
  another examination or to revoke it and contact
  the prescriber), in order to adopt the most
  appropriate strategy

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With reference to procedures (VI)

•  It is of extreme importance that the personnel
  operating the equipment is properly trained and
  accredited in radiation protection
• Training criteria shall be specified or be
  subject to approval, as appropriate, by the
  Regulatory Authority in consultation with
  relevant professional bodies
• The personnel should inform the patient on the
  correct positioning and immobilization as well as
  on technical prerequisites of the examination
  (suspended respiration, deep inspiration, etc)

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With reference to procedures (VII)

• It is important to ensure that the radiological
  examination is "justified", taking into account
  the benefits and risks of available alternative
  techniques that do not involve medical exposure
• The patient should wear gonadal protectors, if
  gonads are exposed, assuming that it does not
  interfere with the expected image
• In case of possible foetus irradiation it is
  advisable to adapt the examination procedure of
  pregnant women, together with the radiation
  protection strategy

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With reference to procedures (VIII)

• For that reason, in order to avoid unwanted
  irradiation of the fetus, it is recommended to
  post warnings, both at the X Ray room entrance
  and in the waiting ward such as

"IF YOU THINK THERE IS ANY POSSIBILITY THAT YOU
ARE PREGNANT, PLEASE TELL IT TO THE RADIOGRAPHER
(RADIOLOGICAL TECHNOLOGIST) OR THE RADIOLOGIST,
BEFORE THE X RAY EXAMINATION IS PERFORMED".
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With reference to procedures (IX)

• It should be asked to the female patient about
  the possibility of being pregnant, even to the
  pediatric patient in puberty. In the affirmative
  case appropriate measures should be taken
• When a pregnant patient undergoes a radiological
  examination (in the abdomen), it might be
  advisable to make an individual evaluation of the
  expected fetus dose.

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With reference to procedures (X)

• The pregnant patient or worker has a right to
  know the magnitude and type of potential
  radiation effects that might result from in utero
  exposure
• Communication should be related to the level of
  risk. Verbal communication may be adequate for
  low dose procedures
• If fetal doses are above 1 mGy, usually a more
  detailed explanation is given

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Approximate fetal doses from conventional X Ray
examinations (data from the UK 1998)
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Approximate fetal doses from fluoroscopic and
computed tomography procedures (data from the
U.K. 1998)
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With reference to procedures (XI)

• The most appropriate projection should be
  adopted, from the patient protection point of
  view, when the diagnostic information so allows.
• For pregnant women, PA abdominal projections are
  preferable to minimize uterus dose
• For skull examinations eye lenses are better
  protected in PA projection

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With reference to procedures (XII)

• The smallest film and cassette size compatible
  with the expected image must be used together
  with automatic collimation. Otherwise the patient
  would be over-irradiated, by receiving radiation
  over a larger volume and transversal surface, and
  the raise in scattered radiation would reduce the
  image quality and increase the operating
  personnel doses.
• When using equipment without automatic X Ray beam
  collimation, it should be verified that the
  radiation field is reduced up to the smallest
  size compatible with the required image, even in
  fluoroscopy applications (the unit usually will
  allow for radiation field reductions both in
  radiography as in fluoroscopy).

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With reference to procedures (XIII)

• The use of the anti-scatter grid improves the
  image quality, but ALWAYS increases patient
  doses. It is advisable to evaluate whether the
  grid is actually necessary in equipment where its
  use is optional according to procedure (e.g.
  mammography) or patient characteristics. In that
  case, one should check its location (some grids
  imply an increase in patient skin irradiation up
  to factors 2, 3 or even higher)
• When the grid is of a focussed type, it is
  important to confirm that the focus-film distance
  has been selected within the correct range

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With reference to procedures (XIV)

• When a change of the usual technique is needed in
  order to improve or maintain the image quality -
  without changing any element of the imaging
  device - it is advisable to check the performance
  of the whole imaging chain. Usually, the change
  implies an increase in patient dose.
• The patient should be visible from the operation
  control panel.
• When possible the fluoroscopy should be used in
  intermittent mode, irradiating the patient only
  when strictly necessary.

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With reference to procedures (XV)

• The use of fluoroscopy for centering the
  radiation field as a preliminary step of the
  radiographic image is not considered as a good
  radiological practice, so that it should be
  avoided.
• Whenever possible a compression device (e.g.
  mammography), should be used as far as the
  patient can bear, since it reduces dose while
  improving image quality.

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With reference to procedures (XVI)

• In general radiology, the patient-tube distance
  should be as long as possible, and the
  patient-image device (detector) distance as short
  as possible (except for air gap scatter reduction
  technique)
• In general radiology using fluoroscopy the
  patient-tube distance is usually determined by
  the collimator, which also operates as beam
  pointer, and the patient-intensifier distance
  should be as short as possible.

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With reference to procedures (XVII)

• In CT, the examinations should be done with the
  minimum possible number of slices giving the
  necessary radiological information. Increasing
  that number implies a higher irradiation over a
  larger volume, and would be equivalent to using
  large fields in conventional radiography,
  resulting in higher doses.
• In general, the radiological examination should
  be performed with the strictly necessary number
  of images. Fluoroscopy time should be as short as
  possible, irrespective of the image support in
  use.

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Summary

• Practical rules to protect patients consist in
  periodic assessment of dose and image quality,
  with remedial action if needed
• The practitioner should be aware of the influence
  on dose and image quality of technical parameters
  (field size, grid type, kV, type of projection)
• Procedures (number of images and technical
  parameters to set) have to be established for
  each examination.

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Where to Get More Information

• International Basic Safety Standards for
  Protection Against Ionizing Radiation and for the
  Safety of Radiation Sources, Safety Series 115,
  IAEA, Vienna, 1996.
• A practical guide on radiological protection and
  quality assurance in diagnostic radiology. CE,
  Value Programme, 1996. Vañó E, Gonzalez L, Maccia
  C, Padovani R. Edited by Cátedra de Física
  Médica, Facultad de Medicina, Universidad
  Complutense de Madrid, 28040 Madrid, Spain.
• Radiological protection of the worker in medicine
  and dentistry. ICRP Publication 57, Pergamon
  Press, 1989.