Radiation Protection In Veterinary Medicine - Recommended Safety Procedures For Installation And Use Of Veterinary X-ray Equipment - Safety Code 28

4. Building and Installation Requirements

4.1 Design Criteria

In the planning of any veterinary X-ray facility, account must be taken of the expected maximum workload of the equipment, use factors of the barriers and occupancy factors for areas adjacent to the facility. Allowance should be made for possible future changes in any of these parameters, such as increased operating X-ray tube voltage and workload or an increase in the degree of occupancy of surrounding areas.

It is particularly advantageous to make visual inspections during construction of a new facility to ensure compliance with specifications and to identify faulty material or workmanship. Deficiencies can be remedied more economically at this stage than later. Such inspections should verify the thickness and density of all barriers, including lead sheets, concrete walls and shielding glass used in viewing windows.

Certain basic principles must be observed when determining the shielding requirements for a room used routinely for veterinary radiological procedures.

1. The radiation levels in controlled areas that are routinely occupied 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.

In general, radiation levels close to the X-ray equipment are such that the above limits are exceeded even at very low workloads. Reductions in radiation intensity can be accomplished by interposing physical barriers or increasing the distance between the sources of radiation and the persons to be protected.

The shielding required to reduce radiation levels to acceptable values may be determined on the basis of distance, nominal X-ray tube voltage, and workload. To ensure that the radiation levels are always below acceptable limits, the maximum expected workload should be used.

4.2 General Recommendations

The procedures described below must be followed to protect personnel working with or in the vicinity of X-ray equipment.

1. The radiation beam must always be directed toward adequately shielded or unoccupied areas.
2. The radiation beam and scattered radiation should be attenuated as closely as possible to the source.
3. Where necessary, the floors, walls, ceilings and doors must be built with materials providing adequate radiation protection to workers.
4. The shielding should be constructed to form an unbroken barrier. Care should be taken in the use of shielding materials, especially lead, which must be adequately supported to prevent "creeping".
5. When necessary, a control booth must be provided for the protection of the operator. The control booth and its viewing window must have shielding properties such that no operator is exposed to more than 20 mSv per year. Mobile protective barriers are not considered adequate as a control booth except for facilities requiring no shielding at 1 metre from source, or where 1/20 of permissible dose equivalent limits are not likely to be exceeded at 1 metre.
6. The control booth should be located, whenever possible, such that the radiation has to be scattered at least twice before entering the booth. In facilities where the radiation beam may be directed toward the booth the shielding of the booth must be that of a primary barrier.
7. The control booth should be positioned so that during an irradiation no one can enter the radiographic room without the knowledge of the operator.
8. Warning signs must be posted on all entrance doors of radiographic room. The warning signs must incorporate the X-radiation warning symbol and should incorporate the words "Unauthorized Entry Prohibited."
9. The final plans for the facility must be reviewed by the appropriate responsible government agencies before construction. For facilities under federal jurisdiction; the responsible agency is the Bureau of Radiation and Medical Devices of the Department of National Health and Welfare. For facilities under provincial jurisdiction the responsible agencies are listed in Appendix IV. The thickness 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.
10. Mobile X-ray equipment used routinely in one location is considered to be a fixed installation, and the facility should be shielded accordingly.