Radiation Occupational exposures and protection A. H. Mehrparvar, MD Occupational Medicine department Yazd University of Medical Sciences

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)

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

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

 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

General requirements  1. Warning Signs

> 5 mrem/hour > 100 mrem/hour > 500 rem/hour Depends on radionuclide: > 10 mCi H-3, 1 mCi S-35, 0.1 mCi P-32, mCi I-125

 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.

 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

 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.

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.

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.

 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.

 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.

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

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.

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/ft ² ) lead.

 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.

 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.

Room layout (general)

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  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.

 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.

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 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.

 Unexposed x-ray film is stored in a film bin, lined with at least 0.8mm (2 lb/ft ² ) 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).

 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).

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.

 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.

 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).