Radiation Protection in Mammography: Recommended Safety Procedures for the Use of Mammographic X-Ray Equipment - Safety Code 33

Appendix VII

Radiation Emitting Devices Regulations for Diagnostic X-ray Equipment

Item 12 of Schedule I to the Radiation Emitting Devices Regulations establishes standards of design, construction and functioning for diagnostic X-ray equipment such as

"12. Diagnostic X-ray equipment being X-ray machines designed primarily for the examination of humans but excluding dental X-ray equipment, photofluorographic chest X-ray equipment, radiation therapy simulators and computer assisted tomographic equipment."

The specific portions related to mammographic X-ray equipment within the requirements for Diagnostic X-ray Equipment of the Regulations, at the time of printing of the Safety Code, are reproduced below.

Part XII Diagnostic X-ray Equipment

Interpretation

1. In this Part,

"aluminium equivalent" in respect of a material under specified conditions, means the thickness of aluminium (Aluminum Association type 1100 alloy) that, under those conditions, affords the same attenuation as that material; (équivalence en aluminium)

"attenuation" means a decrease in radiation intensity caused by absorption and scattering in a medium; (atténuation)

"automatic exposure control" means a device that automatically controls one or more technique factors to obtain a required amount of radiation; (contrôle d'exposition automatique)

"beam limiting device" means a device that restricts the dimensions of the useful beam; (dispositif de limitation du faisceau)

"coefficient of variation" means the ratio of the standard deviation to the mean value of a series of measurements, calculated by using the following equation:

where	×i	=	ith measurement
	×	=	mean value of the measurements
	S	=	estimated standard deviation
	n	=	number of measurements
	C	=	the coefficient of variation; (coefficient de variation)

"control panel" means those parts of the X-ray control having switches knobs, push buttons or other controls necessary for manually setting the technique factors; (tableau de commande)

"field emission equipment" means equipment that has an X-ray tube in which electron emission from the cathode is due solely to the action of an electric field; (équipement d'émission par effet de champ)

"filter" means material placed in the useful beam to preferentially attenuate certain parts of the X-ray spectrum; (filtre)

"half-value layer" or "HVL" means the thickness of specified material that attenuates the beam of radiation to such an extent that the exposure rate is reduced to one-half of its original value; (couche de demi-atténuation or CDA)

"image receptor" means a device that converts incident X-radiation into a visible image or into a form that can be made into a visible image by further transformation; (récepteur d'image)

"lead equivalent" in respect of a material under specified conditions, means the thickness of lead that, under those conditions, affords the same attenuation as that material; (équivalence en plomb)

"leakage radiation" means any radiation,

1. other than the useful beam, coming from within the tube housing assembly while the exposure switch or timer is activated, or
2. produced when the exposure switch or timer is not activated; (rayonnement de fuite)

"light field" means the area of light in the plane of the image receptor that is directly outlined by the beam limiting device, the perimeter of which is the locus of points at which the illumination is one-fourth of the maximum in the plane of the image receptor; (champ lumineux)

"mobile equipment" means transportable equipment designed to be moved from one location to another, between periods of use, on its own wheels or similar means of support; (équipement mobile)

"stationary equipment" means equipment that is permanently installed in one location; (équipement stationaire)

"technique factors" means the conditions of operation of the diagnostic X-ray equipment and includes the peak tube potential in kilovolts, the tube current in milliamperes, the exposure time in seconds, the exposure in milliroentgen or combinations of those measurements; (paramètres d'exposition)

"tube housing assembly" means the X-ray tube housing with the X-ray tube installed; (système radiogène)

"useful beam" means the X-radiation passing through the tube housing port and the aperture of the beam limiting device when the exposure switch or timer is activated; (faisceau utile)

"X-ray field" means the area of the intersection of the useful beam and any one of the set of planes parallel to and including the plane of the image receptor, the perimeter of which is the locus of points at which the exposure rate is one fourth of the maximum in the intersection. (champ des rayons X)

Standards of Design and Construction

General Requirements

2. Every diagnostic X-ray machine shall be designed and constructed in such a manner that when installed and maintained in accordance with the instructions referred to in paragraph 3(a), it functions in accordance with section 19 for as long as the device has its original components or has replacement components recommended by the manufacturer.

3. Every diagnostic X-ray machine shall be equipped with

1. installation and maintenance instructions supplied by the manufacturer of the device that, if followed by trained and experienced persons, will enable the device to comply with the requirements of these Regulations; and
2. the following written information from the manufacturer with respect to the device:
   1. the maximum power requirements or maximum line current;
   2. the nominal focal spot size of the X-ray tube target and the method of its determination;
   3. adequate instructions for assembly and installation, including specification as to adequate line voltage and line impedance; and
   4. where the device is battery powered, the minimum state of charge necessary for operation.

   4. Every diagnostic X-ray machine shall bear

   1. on the external surface of the main X-ray control panel
      1. a warning sign that
         1. includes a statement prohibiting unauthorized use, and
         2. indicates that hazardous radiation emission is produced when the device is in operation,
      2. the X-radiation warning sign described in section 20, and
      3. a readily discernible and clearly visible permanent mark or label that sets out with respect to the X-ray control and X-ray generator combination
         1. the name of the manufacturer,
         2. the model designation,
         3. the serial number,
         4. the date of manufacture, and
         5. the country of manufacture;
   2. on the external surface of the X-ray tube housing, a readily discernible and clearly visible permanent mark or label that sets out
      1. with respect to the X-ray tube,
         1. the name of the manufacturer,
         2. the model designation,
         3. the serial number,
         4. the date of installation of the tube in the housing, and
         5. the country of manufacture, and
      2. with respect to the X-ray tube housing assembly, the minimum permanent filtration in the useful beam provided by the assembly, expressed as millimetres of aluminium equivalent at a specified peak tube potential;
   3. on the external surface of the X-ray tube housing
      1. a permanent mark or marks that define or indicate to within + 4 millimetres
         1. the location of the focal spot, in the case of single focus X-ray tubes, and
         2. the location of the point midway between the centres of the two focal spots, in the case of double focus X-ray tubes, and
      2. permanent marks or labels that indicate clearly the anode and cathode terminals; and
   4. on the external surface of any beam limiting device that adds filtration to the useful beam, a permanent mark or label that sets out, with respect to the beam limiting device, the total permanent filtration, expressed in millimetres of aluminium equivalence at a specified peak tube potential.

   1. Every diagnostic X-ray machine shall be designed and constructed in such a manner that

   1. all marks, labels and signs required by these Regulations are securely fixed to the device and clearly visible;
   2. all controls, meters, lights or other indicators required by these Regulations are readily discernible and clearly labelled or marked as to function;
   3. the X-ray tube is securely fixed and correctly aligned within the tube housing;
   4. the X-ray tube housing maintains its required exposure position or movement without excessive drift or vibration during operation; and
   5. where more than one X-ray tube is controlled by one control panel, except in the case of a diagnostic X-ray machine specifically designed for two-tube techniques,
      1. it shall not be possible to energize more than one X-ray tube at the same time; and
      2. there shall be
         1. on or near each tube housing, so as to be clearly visible to the operator, a visible indication when that X-ray tube is connected and ready to be energized, and
         2. at the control panel, a visible indication of which X-ray tube is connected and ready to be energized.

      2. Every diagnostic X-ray machine shall be designed and constructed to include

      1. means to compensate for variations in X-ray tube potential caused by line voltage fluctuations, such that the device complies with the standard of functioning prescribed by subparagraph 19(b)(ii);
      2. either
         1. a visible or audible indicator that warns the operator; or
         2. a device that prevents X-rays from being produced, when the variation in line voltage exceeds the limits prescribed by subparagraph 19(b)(ii);
      3. a control panel having the following safety features:
         1. separate warning lights, in clear view of the operator, that respectively indicate
            1. when the control panel is energized and the device is ready to produce X-rays, and
            2. when X-rays are produced;
         2. where the device has adjustable technique factors, electrical meters or other indicators that enable the following factors, or any combination thereof, to be determined before the irradiation is initiated, that is to say,
            1. operating tube potential, in kilovolts,
            2. tube current, in milliamperes, and
            3. the irradiation time, in seconds;
         3. where the device has non-adjustable technique factors, permanently affixed marks or labels, or electrical meters or other indicators that enable, at specified target-to-image receptor distances, the following factors, or any combination thereof, to be determined before the irradiation is initiated, that is to say,
            1. operating tube potential, in kilovolts,
            2. tube current, in milliamperes, and
            3. the irradiation time, in seconds; and
         4. where the device is battery-powered, a visual indicator that shows whether the battery is adequately charged for proper operation;
      4. an exposure switch, timer or other mechanism to initiate and terminate the irradiation;
      5. an audible signal to indicate termination of an irradiation;
      6. radiation filters that
         1. are permanently affixed to the exit port of the X-ray tube housing, or beam limiting device or both; and
         2. for a given X-ray tube potential, result in a half-value layer of the useful beam that is not less than the values given in or obtained by linear interpolation or extrapolation of the table to this section;
      7. keyed filter interlock switches or other positive means to ensure that necessary added filtration is in place in any tube housing assembly that
         1. has permanent inherent filtration of 0.5 millimetre or less aluminium equivalence; and
         2. is designed to be operated with added filtration; and
      8. where the device is designed to move under remote control around or across a patient, provision for an emergency stop switch, the activation of which immediately terminates both the motion of the device and the production of X-rays.
         
         Top of Page

   Table
   Design operating range (kilovolts peak)		Measured potential (kilovolts Peak)	Half-value Layer (Millimetres ofaluminium)
   Below 50		30	0.3
   		40	0.4
   		49	0.5
   50 to 70		50	1.2
   		60	1.3
   		70	1.5

   6.

   1. An exposure switch provided with a diagnostic X-ray machine
      1. shall be designed so that it requires continuous pressure by the operator to produce X-rays
      2. where it is a foot-switch, shall be so constructed that an unintended exposure does not occur if the switch is overturned;
      3. shall be located so that it cannot be conveniently operated outside a shielded area, except in the case of an exposure switch used in conjunction with mobile X-ray equipment, with spot-film devices, in fluoroscopy or in special procedures; and
      4. where it is part of a mobile machine, shall be equipped with a cable at least 3 metres long.
   2. A radiographic timing device provided with a diagnostic X-ray machine shall be designed so that
      1. it terminates an irradiation on completion of any one of the following;
         1. a preset time interval
         2. a preset product of current and time, (mAs), or
         3. a preset number of pulses;
      2. it permits the operator to terminate the irradiation at any time;
      3. it automatically resets to its original position or zero at the termination of the irradiation; and
      4. when it is at the zero or OFF position, an irradiation cannot be initiated.
   3. Permanent diaphragms, cones or other beam limiting devices provided with a diagnostic X-ray machine, as permitted by these Regulations, to collimate the useful beam shall afford the same degree of shielding as that required of the tube housing assembly.

   Radiographic Machines

   7. Every radiographic machine equipped with an automatic exposure control shall

   1. be designed to include, on the control panel, a clear indication as to when the automatic exposure control mode of operation has been selected;
   2. where the X-ray tube operating potential is 50 kilovolts peak or greater, be designed and constructed to have minimum exposure time capability
      1. in the case of a field emission machine rated for pulsed operation, equal to or less than the time interval equivalent of two pulses, or
      2. in the case of all other machines, equal to or less than 1/60 second or the time interval required to deliver 5 milliampere-seconds, whichever is the greater;
   3. be equipped with a means for ensuring that
      1. where the X-ray tube potential is less than 50 kilovolts peak, the product of the X-ray tube current and the exposure times does not exceed 2,000 milliampereseconds per exposure, or
      2. where the X-ray tube potential is 50 kilovolts peak or more;
         1. the product of the X-ray tube current and the exposure time does not exceed 600 milliampereseconds, or
         2. the product of the peak X-ray tube potential, current and exposure time does not exceed 60 kilowatt-seconds per exposure;
   4. be equipped with a back-up timer having a maximum setting.
      1. in the case of a tomographic machine of 10.0 seconds and
      2. in the case of any other machine, 3.0 seconds; and
   5. be designed
      1.  
      2. to include, on the control panel, a visible light indicator that will warn the operator, and
      3. to require manual resetting of the machine before another automatically timed exposure can be made, when termination of automatically timed exposure occurs because the limits specified in paragraph (c) or (d) have been reached.

      11.

      1. Every radiographic X-ray machine designed specifically for mammography shall be designed and constructed to include
         1. an X-ray beam limiting device that limits the size of the useful beam so that, at any target-to-image receptor distance specified for the machine, the X-ray field in the plane of the image receptor
            1. does not exceed the edge of the image receptor next to the chest wall of the patient by more than 2 percent of the target-to-image receptor distance, and
            2. does not extend beyond any other edge of the image receptor; and
         2. an image receptor supporting device with sufficient shielding to ensure that the device complies with the standard of functioning prescribed by paragraph 19(e).
      2. Where a radiographic X-ray machine designed specifically for mammography is equipped with a removable fixed aperture beam limiting device, the device shall bear on its external surface clearly visible permanent marking stating
         1. the image receptor size; and
         2. the target-to-image receptor distance for which the devices is designed.

12. Every general purpose radiographic X-ray machine equipped with special attachments for mammography shall be designed and constructed in such a manner that when the attachments are in service, the machine meets the requirements of section 11.

Limits on Material Between Patient and Image Receptor

18.

1. Subject to subsections (2) and (3), the aluminium equivalent of each of the items listed in column I of the table to this section that is used between the patient and the image receptor in any diagnostic X-ray equipment shall not exceed the limits shown therefor in column II of the table, as determined using an X-ray beam having a potential of 100 kilovolts peak and a half-value layer of 2.7 millimetres of aluminium.
2. The total aluminium equivalent of all the material, other than the screen and its associated mechanical support panel or grids, that is present between the patient and the image receptor shall not exceed 3.5 millimetres.
3. Commencing one year from the date of the coming into force of these Regulations, the total aluminium equivalent of all the material, other that the screen or grids, that is present between the patient and the image receptor shall not exceed 3.5 millimetres.

Table
Column I	Column II
	Aluminium
	Equivalence
Item	(millimetres)
Front panel(s) of cassette holder (total of all)	1.0
Front panel(s) of film changer (total of all)	1.0
Stationary table top	1.0
Movable table top (including stationary sub-top)	1.5
Cradle	2.0

Standards of Functioning

19. Every diagnostic X-ray machine when fully assembled for use shall function under normal conditions of use in such a manner that

1. for any given combination of X-ray tube potential (in kilovolts peak), tube current (in milliamperes), exposure time (in seconds) of not less than 0.1 second, or for selected radiation exposure to the image receptor (in milliroentgens)
   1. the coefficient of variation of any ten consecutive radiation exposure measurements, taken at the same source-to-detector distance within a time period of one hour, is no greater than 0.05, and
   2. each of the ten radiation exposure measured is within 15 percent of the mean value of the ten measurements, when the line voltage for each measurement is within plus or minus 1 percent of the mean value for all of the measurements;
2. for any selected setting of the peak X-ray tube potential,
   1. the actual peak kilovoltage corresponds to the selected value to within plus or minus 5 percent of the selected value, and
   2. for a line variation of plus or minus 7 percent of its nominal value, the peak kilovoltage, prior to initiation of an exposure, is capable of being maintained to within plus or minus 5 percent of the selected value;
3. the radiographic timer or automatic exposure control
   1. can be set to control irradiations as short as 1/60 second or 5 milliampere-seconds, whichever is greater,
   2. at each setting is accurate to 1/60 second or 7 percent of that setting, whichever is greater, and
   3. at each setting complies with the reproducibility requirements of paragraph(a);
4. for any fixed indicated value of X-ray tube potential (in kilovolts peak) within the range of values of operating tube potential specified for the equipment, the average ratios of exposure (in milliroentgens) to the product of the tube current and exposure time (in milliampere-seconds) obtained at any two consecutive tube current settings do not differ by more than 0.10 times their sum, that is to say,
   
   
   
   where ×₁ and ×₂ are the average mR/mAs values obtained at each of two consecutive tube current settings;
5. the transmission of the primary X-ray beam through the mammographic image receptor support device referred to in paragraph 11(1)(b) results, with the equipment operated
   1. in the mammographic mode,
   2. at the minimum target-to-image receptor distance for which it is designed, and
   3. at the maximum rated peak X-ray tube potential and maximum rated tube current-exposure time product for that peak tube potential,
   in a radiation exposure averaged over a detection area of 100 square centimetres, with no linear dimension greater than 20 centimetres and centred at 5 centimetres from any accessible surface beyond the plane of the support device that does not exceed 0.1 milliroentgen for each activation of the X-ray tube;
6. where it is a radiographic X-ray machine designed specifically for mammography, the exposure rate from leakage radiation averaged over a detection area of 100 square centimetres with no linear dimension greater than 20 centimetres, located at 5 centimetres from any point on the external surface of the X-ray tube housing does not exceed 2 milliroentgens per hour;
7. where there is a possibility of a high voltage appearing across the X-ray tube without the exposure control or timer activated, the emission of X-radiation from the X-ray tube, with the beam limiting device fully open, does not result in an exposure rate, averaged over a detection area of 100 square centimetres with no linear dimension greater than 20 centimetres and centred at 5 centimetres from any accessible external surface of the X-ray tube housing, in excess of 2 milliroentgen per hour;
8. emission of ionizing radiation by any component other than the X-ray housing assembly, when the X-ray tube is operated at its maximum rated tube potential and current, does not result in an exposure rate averaged over a detection area of 100 square centimetres with no linear dimension greater than 20 centimetres and centred at 5 centimetres from any accessible surface of the component, that exceeds 2 milliroentgens per hour, when averaged over a period of 1 hour.

20. The X-radiation warning sign referred to in section 4 of this Part is a sign that

1. is shown in two contrasting colours;
2. is clearly visible and identifiable from a distance of 1 metre;
3. has no outer dimensions less than 2 centimetres;
4. bears the words "CAUTION X-RAYS" and "ATTENTION RAYONS X"; and
5. is designed in accordance with the following diagram: