Radiation Occupational exposures and protection

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Radiation Occupational exposures and protection

• A. H. Mehrparvar, MD
• Occupational Medicine department
• Yazd University of Medical Sciences

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Key Scientific Organizations

• International Commission on Radiological
  Protection (ICRP)
• International Atomic Energy Agency (IAEA)
• International Commission on Radiological Units
  and Measurements (ICRU)
• National Council on Radiation Protection and
  Measurements (NCRP)
• Occupational Safety and Health Administration
  (OSHA)

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Guidelines for protection

• There must be at least one person designated as
  the responsible user to undertake responsibility
  for
• ensuring that the equipment is maintained
  properly and functions correctly
• ensuring that the equipment is used and
  maintained only by competent personnel
• ensuring that the equipment is used correctly
• establishing safe operating procedures for the
  equipment and ensuring that operating staff are
  adequately instructed in them
• ensuring that staff are made aware of radiation
  rules
• investigating any high x-ray exposures received
  by personnel
• ensuring that radiation levels outside controlled
  areas are below the maximum permissible limits

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Guidelines for protection

• Protection of operating personnel and others
  working in the vicinity of x-ray equipment should
  be achieved by
• ensuring that the useful beam is always directed
  towards adequately shielded areas.
• constructing shielding to form an unbroken
  barrier.
• providing a control booth for the protection of
  the operator.
• The control booth, and the viewing window in the
  booth, must have shielding properties such that
  no operator is occupationally exposed to more
  than 20 mSv per year.
• Mobile protective screens must not be considered
  adequate as a control booth for radiographic
  rooms containing stationary x-ray equipment

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• locating the control booth, whenever possible,
  such that the radiation has to be scattered at
  least twice before entering the booth.
• use of warning signs, which must be posted on all
  entrance doors of each radiographic room.
• The dimensions of the shielding and the materials
  used must be indicated on the plans. The plans
  must also show the positions of all windows,
  doors, pipes and louvres that may affect the
  protection requirements. Adjacent rooms, as well
  as rooms above and below, must also be noted

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General requirements

• 1. Warning Signs

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• 2. Markings All controls, meters, lights and
  other indicators relevant to the operation of the
  equipment must be readily discernible and clearly
  labelled or marked as to function.
• 3. Indicator Lights There must be readily
  discernible, separate indicators on the control
  panel that respectively indicate
• (i) when the control panel is energized and the
  machine is ready to produce xrays,and
• (ii) when x-rays are produced.

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• 4. Filtration The total permanent filtration in
  the useful beam must be equivalent to at least
  the following thicknesses of aluminum
• (i) 0.5 millimetre of aluminum, for machines
  designed to operate with x-ray tube potentials
  below 50 kilovolts peak
• (ii) 1.5 millimetres of aluminum, for machines
  designed to operate with x-ray tube potentials
  from 50 kilovolts peak to 70 kilovolts peak
• (iii) 2.5 millimetres of aluminum, for machines
  designed to operate with x-ray tube potentials
  above 70 kilovolts peak

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• 5. Exposure Control exposure switch, timer, or
  other device to initiate and terminate x-ray
  production. Where an exposure switch is provided,
  the exposure switch must
• (i) require continuous pressure by the operator
  to produce x-rays
• (ii) if in the form of a footswitch, be so
  constructed that if overturned inadvertent
  exposures do not result
• (iii) be so located that convenient operation
  outside of a shielded area is not possible
• (iv) for mobile x-ray equipment, be equipped with
  a cable at least three meters long.

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Mobile radiographic equipment

• 1. Target-to-Skin Distance The equipment must
  be equipped with means to prevent operation at
  target-to-skin distances of less than 30
  centimeters.
• 2. Exposure Control The exposure switch must be
  of the dead-man type and must be provided with a
  cable at least 3 meters long.

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General recommendations

• 1. An x-ray room must not be used for more than
  one radiological investigation simultaneously.
• 2. Except for those persons whose presence is
  essential, no person must be in the xray room
  when the exposure is carried out.
• 3. Personnel must at all times keep as far away
  from the useful beam as is practicable. Exposure
  of personnel to the useful beam must never be
  allowed unless the beam is adequately attenuated
  by the patient and by protective clothing or
  screens.

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• 4. All personnel must take full advantage of the
  protective devices available.
• 5. Operators should remain inside the control
  booth or behind protective screens when making an
  x-ray exposure.
• In cases where there are reasons that make this
  impractical, protective clothing must be worn.
• 6. If parents, escorts or other personnel are
  called to assist, they must be provided with
  protective aprons and gloves, and be positioned
  so as to avoid the useful beam.
• No one person should regularly perform these
  duties.

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• 7. When a lead equivalent protective apron is
  worn, the personnel dosimeter must be worn under
  the apron.
• 8. All operators of x-ray equipment, together
  with personnel (e.g. nurses) who routinely
  participate in radiological procedures, must wear
  personnel dosimeters.
• 9. X-ray machines which are energized and ready
  to produce radiation must not be left unattended.

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• 10. X-ray equipment must only be operated by, or
  under the direct supervision of, qualified
  individuals.

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Guidelines for general radiology rooms

• 1.The radiation levels in controlled areas that
  are occupied routinely by radiation workers only,
  must be such that no radiation worker is
  occupationally exposed to more than 20 mSv per
  year.
• 2. The radiation levels in uncontrolled areas
  must be such that no person can receive more than
  1 mSv per year.

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Guidelines (general)

• The x-ray workload (i.e. number of films exposed)
  does not exceed 960 (on average) in a 40-hour
  work week schedule.
• The x-ray unit is normally operated at up to 125
  kVp, with a maximum film (cassette) size of 35cm
  x 43cm (14 x 17).
• The room containing the unit has dimensions no
  smaller than 3m x 4m.
• Unexposed x-ray film is stored in a film bin,
  lined with at least 0.8mm (2 lb/ft²) lead.

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• Shielding is required to provide protection
  outside the room
• (a) for workers to meet the Action Level of
  1mSv/year
• (b) for members of the public not to exceed the
  recommended public dose limit of 1 mSv/year.
• For workers directly involved in the taking of
  x-rays, this guideline provides an option for
  shielding the control booth to either 20 mSv/year
  (the maximum permissible dose) or to 1 mSv/year
  (the Action Level).
• Control booth shielding is based on providing
  protection against secondary radiation (i.e.
  leakage and scatter) only, but not the primary
  beam.

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• Occupancy behind barriers the shielding
  assessment (over) has taken into account the
  amount of time (occupancy) spent by persons
  outside the barriers (i.e. walls/doors)
• ?? Full occupancy applies to areas occupied by
  workers or other persons for a total of more than
  30 minutes per day, and applies to adjacent rooms
  and tenanted facilities.
• ?? Partial occupancy applies to areas occupied by
  workers and other persons for a total of no more
  than 30 minutes per day, and applies to areas
  such as adjacent stairwells, parkades and parking
  lots, lanes, gardens and infrequently used rooms
  (storage).
• If the facility has accessible areas (e.g. rooms)
  above and/or below the x-ray room, protection for
  these areas must be provided in the intervening
  floors.

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Room layout (general)
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Guideline (mamography)

• The x-ray unit is operated at up to 35 kVp.
• The room containing the unit has dimensions of at
  least 3m x 3m
• The x-ray workload (number of film exposures) per
  40 hour workweek does not exceed 1200.
• Shielding is required to provide protection
  outside the room
• a) for workers to meet the Action Level of
  1mSv/year
• b) for members of the public, to not exceed the
  recommended public dose limit of 1 mSv/year.

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• Operator protection is required to ensure that
  the maximum permissible dose of 20 mSv/year is
  not exceeded and that doses are kept as low as
  reasonably achievable.
• The shielding specified for the operator
  protective shield will ensure the operator does
  not exceed the 1 mSv/year Action Level.

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Guideline (fluoroscopy)

• The current/future x-ray workload in the room
  does not exceed 50 fluoroscopic (radioscopic)
  procedures average fluoroscopy (radioscopy) time
  is 5 minutes per patient and 300 radiographic
  film in a 40 hour workweek schedule.
• The x-ray unit is normally operated in the range
  70-100 kVp, and occasionally at up to 125 kVp.
• The maximum film (cassette) size is 35cm x 43cm
  (14 x 17) and maximum image intensifier size is
  41cm (16).
• The room containing the unit has dimensions no
  smaller than 3m x 4.5m.

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• Unexposed x-ray film is stored in a film bin,
  lined with at least 0.8mm (2 lb/ft²) lead.
• Shielding is required to provide protection
  outside the room
• a) for workers, to meet the Action Level of
  1mSv/year
• b) for the general public, to not exceed the
  recommended public dose limit of 1 mSv/year.
• For workers directly involved in the taking of
  x-rays, this guideline provides an option for
  shielding the control booth to either 20 mSv/year
  (the maximum permissible dose) or to 1 mSv/year
  (the Action Level referred to above).

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• Occupancy outside barriers the shielding
  required (over) takes into account the amount of
  time (occupancy) spent by persons outside the
  barriers (i.e. walls/doors)
• ?? Full occupancy applies to areas occupied by
  workers or other persons for a total of more than
  30 minutes per day, and applies to adjacent rooms
  and tenanted facilities.
• ?? Partial occupancy applies to areas occupied by
  workers and other persons for a total of no more
  than 30 minutes per day, and applies to areas
  such as adjacent stairwells, parkades and parking
  lots, lanes, gardens and infrequently used rooms
  (storage).

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Guideline (CT)

• The current/future x-ray workload does not exceed
  200 patients/week per 40 hour work week schedule.
  
• The CT unit is operated at up to 150 kVp.
• The room containing the unit has dimensions no
  smaller than 3.5m x 6m.
• Shielding is required to provide protection
  outside the room
• a) for workers, to meet the Action Level of
  1mSv/year
• b) for members of the public, to not exceed the
  recommended public dose limit of 1 mSv/year.

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• For workers directly involved in the taking of
  x-rays, this guideline provides an option for
  shielding the control booth to either 20 mSv/year
  (the maximum permissible dose) or to 1 mSv/year
  (the Action Level referred to above).
• No person other than the patient shall be inside
  the room during diagnostic exposures except when
  required to assist the patient, when protective
  lead aprons shall be worn.

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• Occupancy outside barriers the shielding options
  (see over) allow for consideration of the amount
  of time (occupancy) spent by persons outside each
  of the barriers(i.e. walls/doors)
• ?? Full occupancy applies to areas occupied by
  workers or other persons for a total of more than
  30 minutes per day, and applies to adjacent rooms
  and tenanted facilities.
• ?? Partial occupancy applies to areas occupied by
  workers and other persons for a total of no more
  than 30 minutes per day, and applies to areas
  such as adjacent stairwells, parkades and parking
  lots, lanes, gardens and infrequently used rooms
  (storage). Areas that can be converted from
  Partial Occupancy to Full Occupancy (e.g. from
  storage to office) should be considered as Full
  Occupancy for shielding requirements.
• If the facility has accessible areas (e.g. rooms)
  above and/or below the CT room, protection for
  these areas must be provided in the intervening
  floors (see over).

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