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

6. Equipment Specifications

6.1 X-Ray Equipment

All veterinary X-ray equipment and accessories for such equipment sold in Canada must conform to the Radiation Emitting Devices Act and the Food and Drugs Act. There are no specific standards promulgated for veterinary X-ray equipment under the Radiation Emitting Devices Act, but this equipment must comply with the general provisions of the Act. The requirements of the Food and Drugs Act are specified in the Medical Devices Regulations promulgated under this Act. It is the responsibility of the manufacturer or distributor to ensure that the equipment conforms to the requirements stated in these Acts.

Modifications to these requirements may be made from time to time to keep abreast of changing technology in the field of radiation protection and veterinary medicine. Information on the applicability and currency of the Radiation Emitting Devices Act and the Medical Devices Regulations may the obtained by contacting the Bureau of Radiation and Medical Devices, Department of National Health and Welfare, Ottawa, Ontario K1A 1C1.

Whenever possible and to the extent that is practical, existing X-ray equipment should be upgraded to incorporate as many as possible of the safety and performance features described below. New X-ray equipment should also incorporate as many as possible of the safety and performance features described.

To ensure maximum protection for staff and visitors, all X-ray equipment should at least meet certain basic requirements.

1. Warning Signs: the X-ray control panel must bear a permanent and conspicuous sign prohibiting unauthorized use and warning that hazardous X-radiation is emitted when the equipment is in operation.
2. Markings: all controls, meters, lights and other indicators relevant to the operation of the equipment must be readily discernible and clearly labelled as to function.
3. Irradiation Light: there must be a readily discernible separate indicator on the control panel that indicates when X-rays are being produced.
4. Mechanical Stability: the X-ray tube must be securely fixed and correctly aligned within the X-ray tube housing. The X-ray source assembly must maintain its required position without excessive drift or vibration during operation.
5. Irradiation Control: there must be an irradiation switch, timer, or other device to initiate and terminate X-ray production. This control must automatically terminate the irradiation after a preset time, product of tube current and time, or irradiation value has been reached. Where an irradiation switch is provided, it must require continuous pressure by the operator to produce X-rays. A foot switch is to be constructed so that no X-ray can be produced if it is inadvertently overturned. The irradiation timer must be an electronic type: mechanical timers must not be used.
6. Indication of Loading Factors: for X-ray equipment having adjustable loading factors, the control panel must incorporate indicators that allow these loading factors to be determined. For equipment having non-adjustable loading factors, permanent marks or labels may be used to indicate these parameters.
7. Timer Accuracy: the irradiation timer should be such that at each setting it is accurate to 1/60 second or 7% of that setting, whichever is greater.
   
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8. X-Ray TubeVoltage Accuracy: the generator should be such that at each voltage setting it is accurate to 5% of that setting.
9. Irradiation Reproducibility: for any selected combination of X-ray tube voltage, current and time greater than 1/10 second, the coefficient of variation of any 10 consecutive irradiations taken at the same distance within a period of 1 hour should not exceed 0.1. The coefficient of variation is defined as the ratio of the standard deviation to the mean value of a series of irradiation measurements calculated using the following equation:

• 10. X-Ray Tube Shielding : the X-ray tube must be enclosed in a shielded housing. The leakage radiation from the X-ray tube housing must not exceed 0.873 mGy (100 mR) in 1 hour at 1 metre at the nominal X-ray tube voltage on the equipment.
• 11. Beam Limiting Device : the X-ray tube housing must be equipped with a beam limiting device that enables adjustment of the size of the X-ray field. The beam limiting device should incorporate means to indicate the size of the X-ray field at the image reception area.
• 12. Half-Value Layer : for a given kilovoltage, the measured value of half-value layer of the useful beam must follow the limits below:

• For equipment designed to operate with X-ray tube potentials below 70 kilovolts, the half-value layer must not be less than 1.5 millimetre of aluminium (mmAl).
• For equipment designed to operate with X-ray tube potentials at and above 70 kilovolts peak the half-value layer must not be less than:
  
  
  • 2.1 mmAl at 70 kVp,
  • 2.3 mmAl at 80 kVp,
  • 2.5 mmAl at 90 kVp,
  • 3.0 mmAl at 110 kVp,
  • 3.2 mmAl at 120 kVp,
  • 3.5 mmAl at 130 kVp,
  • 3.8 mmAl at 140 kVp, and
  • 4.1 mmAl at 150 kVp.

6.2 Protective Clothing

Protective aprons, gloves and thyroid shields used for veterinary X-ray examinations must provide attenuation equivalent to at least 0.5 mm of lead at X-ray tube voltages of up to 150 kVp. The lead equivalent thickness of the material used must be permanently and legibly marked on the protective device. Protection must be provided throughout the glove, including fingers and wrist.

Protective aprons, gloves and thyroid shields must be stored and maintained according to manufacturers' recommendations. It is also recommended that protective aprons, gloves and thyroid shields are checked by radiographing them annually or when damage is suspected.

6.3 Darkroom and Film Processing

The irradiation necessary to produce a radiogram of satisfactory diagnostic quality depends not only on the loading technique and the film-screen combination employed but also on the handling and processing of the film. Improper processing of radiographic film can cause films of poor diagnostic quality that may require an increase in loading factors or repeat irradiations. This would lead to an increase in the exposure level of scatter and leakage radiations to the staff. Adherence to the following guidelines on darkroom design, film processing and film storage will improve the diagnostic quality of films and ultimately reduce radiation levels in the facility.

1. The darkroom must be impervious to light.
2. A warning light or sign should be located outside the darkroom to indicate when the room is in use.
3. Safelights, fitted with light bulbs of correct intensity, and filters appropriate to the specifications of the film used must be provided above the work area within the darkroom.
4. Manufacturers' recommendations about the strengths and temperatures of the solutions and immersion times must be followed to ensure optimum film processing.
5. Manufacturers' recommendations about the operation and servicing of automatic film processors must be followed to ensure optimum film processing.
6. Developing solutions should be replenished and changed according to the manufacturers' recommendations.
7. Unexposed radiographic films must be stored in such a manner that they are shielded from stray radiation. Storage should be provided such that no film can be exposed to more than 1.75 µGy (0.2 mR) of stray radiation before use. The amount of shielding required will depend on the storage time and the workload of the facility. It can be determined from the table in Appendix III.
8. Films should be stored on end in a cool, dry area.