Canadian Mammography Quality Guidelines

4. Quality Assurance

In mammography, quality assurance programme means the planned and organized actions necessary to provide confidence that mammographic equipment and related components operated in a facility will reliably produce quality mammo-grams providing the necessary information for accurate clinical assessment with minimum dose to patients and staff.

Quality control procedures are an essential component of quality assurance programmes which clearly specify the technical procedures necessary for the monitoring and testing of mammographic equipment and related components.

4.1 Quality Assurance General Recommendations

Each facility must establish and maintain a quality assurance programme.

A. Responsible Individuals. Although all staff members are assigned individual responsibilities, it is imperative that full cooperation exists among all concerned parties.

1. Owner. The owner may be an individual, a corporation, a district, a province or some other entity. The owner has the responsibility of
   
   
   1. implementing and maintaining an effective diagnostic imaging quality assurance programme for the facility, including quality control testing procedures and record keeping;
   2. ensuring the installation complies with all applicable regulatory requirements;
   3. consulting with the appropriate government agencies
      
      
      1. when a new facility is being constructed, or modifications of an existing one are planned, to ensure that radiation safety is adequate,
      2. when mammographic X-ray equipment is purchased to ensure adequate radiation safety, and to register the equipment with the appropriate agency, and
      3. to set periodic scheduled inspections for the facility. In some jurisdictions, the agency responsible for inspections has the mandate for setting inspection schedules;
         
         
   4. establishing safe working conditions;
   5. ensuring that
      
      
      1. the equipment functions properly through ongoing maintenance by competent personnel and replacement of outdated or noncompliant equipment,
      2. safe operating procedures are established and are followed,
      3. quality control monitoring of mammo-graphic X-ray equipment, image processor, and ancillary equipment is carried out,
      4. technologists are properly trained in the operation of the equipment being used, and
      5. technologists-in-training and inexperienced personnel operate mammographic X-ray equipment only under the direct supervision of a licensed or certified technologist; and
         
         
   6. ensuring professional qualifications are maintained.
      
      
2. Interpreting Physicians (Radiologists). All interpreting physicians must
   
   
   1. participate fully in the quality assurance programme
   2. communicate with staff any changes in image quality whether they are due to improper positioning, loading factors or image processing.
      
      
3. Medical Physicists. The medical physicist is responsible for
   
   
   1. verifying the safety of an installation at the time of planning and construction, and ensuring that the installation complies with all applicable regulatory requirements;
   2. providing ongoing evaluations of the safety procedures and recommending to the owner the necessary changes to ensure optimum patient and personnel safety, and instructing personnel in proper radiation protection practices;
   3. participating in the quality assurance programme to
      
      
      1. ensure that the quality assurance programme is properly implemented and operated;
      2. verify whether the optimal level of technical image quality is obtained; and
      3. ensure appropriate quality control monitoring instruments are available and properly calibrated;
         
         
   4. performing the required testing of mammographic X-ray equipment, image processor, and ancillary equipment according to the proper record keeping procedures described in section (B);
   5. providing a complete written report clearly describing survey results; and
   6. prompt oral communication of survey results with a responsible individual within the facility.
      
      
4. Mammography Technologist. Mammography technologists must participate fully in the quality assurance programme by
   
   
   1. ensuring that the optimal level of diagnostic image quality is maintained,
   2. performing daily and routine quality control tests of mammographic X-ray equipment, image processor, and ancillary equipment and keeping records of these tests, and
   3. communicating with staff any changes in image quality.

B. Quality Assurance Records. It is essential that measurements and information gathered for the quality assurance programme be clearly documented and readily available for evaluation.

1. The medical physics report should be circulated to all staff and retained at the facility.
2. As fas as practicable, recorded data must be indicated as data points on a control chart when the measurement is made. In this form, trends can be more easily detected. A log book or other easily identifiable method of recording must be used and records must be keep for a minimum of 3 years.
3. Processor quality control charts should be retained in the Quality Control records for 1 year.
4. Sensitometric films for the last full months Quality Control chart should be retained.
5. One monthly sample Quality Control phantom film must be keep for a minimum of 3 years.

C. Evaluation of Data. Recorded data must be evaluated immediately and necessary action taken expeditiously.

D. Baseline Performance Levels. Baseline performance values of mammographic X-ray equipment and image processing system must be established after verifying that equipment functions properly. Images used for determining baseline performance levels should be obtained using the routine technique for a 4.2 cm compressed breast. This baseline performance will be used to diagnose any changes in equipment performance. It is important to keep records of equipment operation data and baseline performance measurements. These records will be needed to diagnose any changes in image quality.

E. Testing Frequency. The frequency of testing should be increased if the equipment exhibits significant changes between scheduled Quality Control tests, or if the equipment is used for an exceptionally high volume of procedures. Additional testing should be performed if the results of testing fall outside the limits of acceptability for the tests, or after any corrective actions are made. Equipment must be retested after service to any part which may affect the image density, image quality or radiation output from the X-ray tube.

The Quality Control programme should not be discontinued if the results indicate relatively stable equipment performance. The purpose of a Quality Control programme is to control quality, and periodic measurement of equipment performance is essential. The frequency of testing described in sections (3) and (4) should be considered a minimum.

F. Corrective Actions. There must be established repair and calibration procedures to deal with significant problems. A decision tree system should be developed to provide guidance to deal with events such as equipment failure and to deal with circumstances when equipment performance deviates beyond the set limits. A list of individuals having the authority to stop operation of a mammographic unit should be established. The decision tree should include the following steps:

1. repeat test to confirm;
2. what to do if repeated test confirms performance failure;
3. what to do if test fails only marginally;
4. what to do if test shows a history of failure; and
5. what to do if test fails substantially.

4.2 Quality Assurance - Equipment Requirements

It is essential that the necessary quality control test equipment be provided to the quality control technologist or medical physicist. It is suggested that the required test equipment be acquired when mammographic X-ray equipment is purchased. A complete list of test equipment is shown in Table 3 along with purchasing specifications for the accuracy and reproducibility of the equipment.

If the facility elects to perform all quality control tests, including testing carried out during implementation of the programme to establish baseline values, daily quality control monitoring, and tests to verify the ongoing performance of the mammographic X-ray system, items 1-20 of the test equipment listed in Table 3 are required.

If the facility elects instead to only perform daily quality control testing and some of the tests to verify the ongoing performance of the mammographic X-ray system, only items 1-12 of the test equipment listed in Table 3 are required. Although it is recommended that all equipment be available at each facility, only daily quality control equipment, items 1-6, must be present on-site and items 7-12 should be accessible when needed. It is assumed that the organization or individual which provides testing services will be responsible for supplying their own test equipment, items 13-20.

Table 3. Quality Control Equipment

Item		Equipment	Accuracy	Reproducibility
1	Test Equipment for Daily Quality Control Tests	Sensitometer (21 step optical attenuator with densities ranging from approximately 0.00 to 4.80 in steps of 0.15)	± 0.02 log exposure units	± 0.02 log exposure units
2		Densitometer	± 0.02 O.D.at 1.0 O.D.	± 0.01 O.D.at 1.0 O.D.
3		Thermometer	± 0.3 °C	± 0.1 °C
4		Magnifying glass	-	-
5		Ultraviolet light	-	-
6		Uniform 3-5 cm thick cassette-sized phantom (acrylic)	-	-
7	Test Equipment for Monthly and Quarterly Quality Control Tests	Phantom, with image quality evaluation objects (RMI-156 or NA #18-220 are required for accreditation by MAP)	-	-
8		Compression force test device	± 10%	± 5%
9		Stopwatch
10		Film/screen contact test tool (16 mesh/cm or 40 mech/in)
11		Fixer retention test kit
12		Ruler
13	Test Equipment for Annual Quality Control Tests	Dosimeter	± 5%	± 1%
14		Non-invasive X-ray tube voltage meter	± 1.5 kV	± 0.5 kV
15		Irradiation time meter	± 5%	± 1%
16		Light meter (for measurement of luminance and illuminance)	± 10%	± 5%
17		Aluminum filter (> 99.9% purity)	1% thickness	-
18		Resolution test pattern for focal spot assessment (maximum resolution of at least 16 lp/mm)	-	-
19		Sheets of uniform breast equivalent material (at least four 2 cm thick sheets)	-	-
20		Metallic coins	-	-

4.3 Quality Assurance - Mammography Technologists' Quality Control Tests

A. Daily Quality Control Tests. Daily Quality Control tests must be performed at the beginning of each day that mammography is conducted before processing any patient films.

1. In order to maintain the cleanliness of the darkroom all working surfaces, tops of counters and the floor should be cleaned daily.
2. Film processor function must be evaluated every morning before performing clinical examinations, after the processor has been turned on and has reached the required development temperature; and at other times as required, such as after a replenishment rate change.
   
   
   1. The film processing solution levels must be checked to ensure agreement with the manufacturers' recommended baseline levels for the particular processor and film type, for the given number of films processed daily.
   2. The film processing solution temperature must be checked, using a non-mercury thermometer, to ensure agreement with the manufacturers' recommended baseline level for the particular processor and film used.
   3. Sensitometric strip processing must be performed in order to monitor the performance of the image processing system.
      1. The base plus fog shall be within +0.03 of the established operating level.
      2. The mid-density shall be within ±0.15 of the established operating level.
      3. The density difference shall be within ±0.15 of the established operating level.
         
3. Image quality evaluation tests should be performed.
   A uniform phantom representing average breast thickness should be routinely used to monitor and maintain image density to ensure correct optical density, the absence of excessive artifacts, and a consistent current time product setting. While it is strongly recommended that this test be performed daily, this test must be performed at least weekly.
   
   
   1. The optical density of the film at the centre of an image of a phantom shall be at least 1.40 when exposed under a typical clinical condition. It is strongly recommended that the optical density be greater than 1.60.
   2. The optical density of the film at the centre of the phantom image shall not change by more than ±0.20 from the established operating levels

B. Weekly Quality Control Tests

1. A visual test must be performed in the darkroom to ensure the room is light tight. Particular attention must be paid to the door seal and the mounting of the film processor if the film insertion to the processor is done through a wall.
2. Screens should be checked for cleanliness and damage. Manufacturer recommended screen cleaner should be used. An inspection for dust particles should be done with an ultraviolet light.
3. Cassettes should be checked for cleanliness, wear, warping, fatigue of foam compression material and closure mechanism, light leaks.
4. The cassette holder tunnel should be checked for dust and dirt.
5. Viewboxes should be inspected visually for cleanliness, viewing area discolouration and improper illumination.
6. A phantom, with image quality evaluation objects, should be used to test imaging performance of the mammographic X-ray system. While it is strongly recommended that this test be performed weekly, this test must be performed at least monthly for the accreditation phantom.
   
   
   1. A minimum of the four largest fibres, the three largest speck groups and the three largest masses must be visible.
   2. The number of test objects of each group type (fibres, specks, and masses) visible in the phantom image should not decrease by more than one half.
   3. The phantom image background optical density should be at least 1.4 and should not vary by more than ±0.20 from the operating level.
   4. The density difference due to a 4.0 mm acrylic disc should be at least 0.40 and should not vary by more than ±0.05 from the established operating level.

C. Monthly Quality Control Tests

1. X-ray equipment should be visually inspected for loose or broken components.
2. The accuracy of the processor temperature display should be checked regularly against a non-mercury thermometer. The processor developer temperature should be accurate to within 0.5 °C.
3. The replenishment rate must be compared with the manufacturers' recommended baseline level for the particular processor and film type, for the given number of films processed daily and for the method of processing.

D. Quarterly Quality Control Tests

1. Fixer retention tests should be performed to ensure fixer is adequately removed from processed films according to established baseline levels.
2. An analysis must be done of the repeat records to identify and correct any trends or errors. The repeat rate must be between 2 and 5 percent, not including Quality Control films. Facilities must maintain records for every repeat by recording every repeat, including the reason for the repeat along with any corrective actions, immediately after the repeat film is taken. If images contain some patient diagnostic information, they should be maintained in the patient file.

E. Semi-Annual Quality Control Tests

1. Breast Compression Device. A compression force of at least 11.4 kg (25 lbs) shall be provided. Effective October 28, 2002, the maximum compression force for the initial power drive must be between 11.4 kg (25 lbs) and 20.5 kg (45 lbs).
2. Level of Film Base Plus Fog. The level of optical density from the base material and film must not be greater than 0.25 units.
3. Safelight Test for Darkroom Fog. An image of a uniform cassette-sized phantom exposed to a minimum optical density of 1.4 units must not show an increase in optical density greater than 0.05 units in two minutes exposure to the darkroom light environment.
4. Screen/Film Contact. All cassettes used in mam-mography must be tested for screen/film contact using a 16 mesh/cm (40 mesh/in) copper screen. Large areas greater than 1 cm in diameter of poor contact that are not eliminated by screen cleaning and remain in the same location during subsequent tests should replaced. Multiple small areas, less than 1 cm in diameter, are acceptable.

4.4  Quality Assurance - Medical Physicists' Mammographic Quality Control Tests

A. Annual Quality Control Tests

1. X-ray Tube Radiation Output. The X-ray tube radiation output shall be high enough to minimize irradiation time to eliminate perceptible motion artifacts.
   
   
   1. For any combination of operating loading parameters, 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, must be no greater than 0.05, and each of the ten radiation exposure measurements must be within 15 percent of the mean value of the ten measurements.
   2. For film-screen mammography equipment, the X-ray tube output should be at least 7.0 mGy/s (802 mR/s) over a 3 second period of time when operating at 28 kV in the standard mam-mography (Mo/Mo) mode at any clinically used Source to Image Distance (SID).
      
      
2. Radiation Beam Quality. The first half-value layer should be determined for all commonly used clinical X-ray tube voltages and target/filter combinations. The unit should be set to manual timing, with a time sufficiently long to provide an air kerma of approximately 4.5 mGy when there is no aluminum filtration placed in the beam.
   
   
   1. The first half-value layer of aluminum, measured with the compression paddle in place, shall not be less than the values shown in Table 4 for a selected X-ray tube voltages and all target/filter combinations. For other X-ray tube voltages, the half-value layer of the radiation beam must be calculated by linear interpolation from the values in Table 4, by using the following formula:

ii. The first half-value layer of aluminum, measurement without the compression paddle in place, shall not be less than the values shown in Table 4 for selected X-ray tube voltages and all target/filter combinations. For other X-ray tube voltages, the half-value layer of the radiation beam must be calculated by linear interpolation from the values in Table 4, or by using the following formula:

Table 4. Minimum first half-value layer for selected X-ray tube voltage at any combinations of target and filter materials when measured with and without the compression paddle in place.

X-ray Tube Voltage (kV)	Minimum First Half-Value Layer with Compression Paddle in Place (mm Al)	Minimum First Half-Value Layer without Compression Paddle in Place (mm Al)
24	0.27	0.24
26	0.29	0.26
28	0.31	0.28
30	0.33	0.30
35	0.38	0.35

iii.  The first half-value layer of aluminum, measured with the compression paddle in place, should not be greater than the values obtained using the following formula for a selected X-ray tube voltage:

where

• C = 0.12 mm Al for Mo/Mo,
• C = 0.19 mm Al for Mo/Rh,
• C = 0.22 mm Al for Rh/Rh, and
• C = 0.30 mm Al for W/Rh.

Note that these half-value layer upper limits a re bas ed on molybdenum filter thicknesses of 30 µm or less and rhodium filter thicknesses of 25 µm or less.

c. Automatic Exposure Control System - Optical Density Setting Response. The automatic exposure control device must perform in such a way that the variation of optical density in the resultant radiograms does not exceed ± 0.15 of the mean optical density when the thickness of a uniformly attenuating breast tissue equivalent material is varied over a range of 2 to 6 cm and the tube voltage, and anode filter combinations are varied appropriately over the range used clinically in the facility. The optical density of the film in the centre of the phantom image shall not be less than 1.20. If this requirement cannot be met, a technique chart shall be developed showing appropriately loading factors for different breast thickness and compositions that must be used so that optical density within ± 0.15 of the average under automatic exposure control conditions can be produced.

d.  Screen/Film Speed Uniformity. The film optical density must be within ± 0.15 units from the mean for all cassettes used in the facility when tested with identical loading factors.

e.  Representative Breast Surface Dose and Mean Glandular Dose Calculations. Breast phantoms such as RMI-156 or NA #18-220 which represent a breast composed of 50 percent fat and 50 percent glandular tissue and compressed to 42 mm thickness, should be used to determine the representative mean glandular dose for a breast of similar composition. The mean glandular dose should not exceed 3.0 mGy.

f. Focal Spot Conditions - System Resolution. The X-ray system used for mammography, in combination with the mammography screen-film combination used in the facility, shall provide a minimum resolution of

1. 11 line-pairs/mm when a high contrast resolution bar test pattern is oriented with the bars perpendicular to the anode-cathode axis, and
2. 13 line-pairs/mm when the bars are parallel to the axis.

The bar pattern shall be placed 4.5 cm above the breast support surface, centred with respect to the chest wall edge of the image receptor, and with the edge of the pattern within 1 cm of the chest-wall edge of the image receptor.

When more than one target material is provided, the measurement shall be made using all possible combinations of focal spot and target material. When more than one SID is provided, the test shall be performed at the SID most commonly used clinically. The test X-ray tube voltage shall be set at the value used clinically by the facility for a standard breast and shall be performed in the AEC mode, if available.

If necessary, a suitable absorber may be placed in the beam to increase the exposure time. The screen-film cassette combination used by the facility shall be used to test for this requirement and shall be placed in the normal location used for clinical procedures.

g.  Beam Limiting Device. For any focal spot to image receptor distance, the x-ray field does not extend beyond

1. the edge of the patient support next to the chest wall of the patient by more than 5 mm, and
2. any other edge of the image reception area by more than 2 percent of the focal spot to image receptor distance.
   
   

h.  Light Field Alignment. If a light localizer designed to define the outline of the X-ray field is included, the separation between the perimeter of the visually defined field and that of the X-ray field must not exceed 2 percent of the focal spot to image receptor distance.

i. Viewboxes. All viewboxes used for the interpretation of mammograms must be tested for compliance with the following requirements. Ensure all viewboxes have been turned on for a minimum of 30 minutes before obtaining measurements.

1. Brightness. The view box brightness should be at least 3,500 nits (cd/m²).
2. Light Output Uniformity. The light output from the viewboxes should be uniform to within 10 percent.
3. Light Output Homogeneity. The light output homogeneity between all viewboxes used for mammograms should be uniform to within 15 percent of the mean.
4. Ambient Light Control. The ambient light within the reading room must be less than 50 lux. A value of 5-10 lux is recommended.