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Radiation Protection in Mammography: Recommended Safety Procedures for the Use of Mammographic X-Ray Equipment - Safety Code 33
8. Quality Control procedures in mammography
There are two types of Quality Control procedures in mammography. Initially, there are procedures performed at the implementation of the Quality Assurance program. Subsequently, there are procedures carried out during the operation of the program. Consultation with a medical physicist or an expert in Quality Assurance for mammography should be done from time to time to reassess the operation of the program.
8.1 Quality Control equipment
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. It is also important that the Quality Control technologist or medical physicist be trained in the proper use of the test equipment.
If the facility elects to perform all Quality Control tests including testing carried out during implementation of the program to establish baseline values, daily Quality Control monitoring, and tests to verify the on-going performance of the mammographic X-ray system, the test equipment listed in Table 3 is required. If a facility elects instead to only perform daily Quality Control testing and some of the tests to verify the on-going performance of the mammographic X-ray system, the equipment listed in Table 4 is recommended. It is, therefore, assumed that the organization or individual which provides the testing service will supply its own test equipment.
8.2 Mammographic X-ray system evaluation
During the implementation phase of the Quality Assurance program, the establishment of baseline information and X-ray equipment performance is necessary. After initial evaluation, and at regular intervals during clinical operation, baseline information should be re-evaluated and X-ray equipment performance should be examined. The more technical evaluation should be performed by a medical physicist or individual specialized in mammographic X-ray equipment testing and evaluation.
- Mammographic X-ray equipment - Initially, equipment performance
must be fully evaluated. The equipment should be
assessed for compliance with the requirements in Section 5.3.
Not all the tests need to be repeated on an annual or semi-annual
basis since equipment performance for some components is not
likely to change during clinical operation. However, if a
component is serviced or replaced, in such a way that performance
may be changed, the performance must be
re-evaluated. Initial technical evaluation is presented below;
Section 8.2.1 presents tests which need to be performed on an
annual or semi-annual basis.
X-ray generation
a. X-ray beam filtration and radiation beam quality
b. X-ray tube voltage accuracy and reproducibility
c. Irradiation timer accuracy and reproducibility
d. Reproducibility of radiation output
e. Focal spot sizeBeam limiting device
f. Proper radiation beam alignment
g. Light field/X-ray image receptor congruenceAncillary components
h. Source to image receptor distance indicators accuracy
i. Compression device design and performance
j. Bucky system and grid performanceOther
k. Stability of equipment
l. Mechanical and electrical performance
m. Inspection and replacement ofworn or broken components
n. Manufacturer's maintenance schedule - Automatic Exposure Control system - Initially, Automatic
Exposure Control system performance must be fully evaluated
for compliance with the requirements in Section 5.3.1, No. 7,
for film-screen X-ray mammographic X-ray equipment, or
Section 5.3.2, No. 7, for Xeromammographic X-ray equipment
and baseline values established. Tests performed during initial
evaluation of the system are presented below. Section 8.2.1
presents tests which need to be performed on a semi-annual
basis.
a. Reproducibility
b. X-ray tube voltage compensation
c. Minimum response time
d. Thickness compensation response
e. Optical Density setting response
f. Backup timer
- Films, screens and cassettes - For film-screen X-ray mammography,
initially, there must be an evaluation of the
appropriateness of the film-screen combination being used. This
evaluation should be done each time a new type of film or screen
is being introduced. Initial evaluation is presented below;
Section 8.2.1 presents tests which need to be performed on an
annual or semi-annual basis.
a. Adequacy of film-screen combination
b. Film-screen speed uniformity
c. Film-screen contact
d. Screen condition
- Image processing - The initial evaluation of image processing
involves the adequacy of the darkroom environment, and the
establishment of baseline values required during Quality Control
monitoring. Initial evaluation is presented below.
Darkroom
a. Light tightness
b. Safelight conditions
c. Cleanliness
d. Temperature control of water supply
e. Ventilation system
f. Fixer recovery system
Film Processing
g. Condition of processing equipment
h. Film speed and contrast
i. Level of film base plus fog
j. Solution temperature
k. Replenishment rate
l. Fixer retention analysis
m. Posting of maintenance schedule and Quality Control test results
Xeromammographic processing
n. Condition of processing equipment
o. Selenium plate defects
p. Posting of maintenance schedule and Quality Control test results
- Viewboxes - The evaluation of performance of all viewboxes
used for mammograms examination must be done on an annual
basis. Initial evaluation is presented below; Section 8.2.1
presents tests performed on an annual basis.
a. Viewbox surface conditions
b. Brightness
c. Light output homogeneity between viewboxes
d. Light output uniformity
e. Image masking
f. Ambient light control
- Imaging characteristics - The imaging performance of the
mammographic X-ray system must be assessed along with the
establishment of representative patient dose values. A phantom,
with image quality evaluation objects, should be used to test
overall performance of the mammographic X-ray system by a
quantitative evaluation of the system's ability to image small
structures such as fibres, specks and masses, at similar
dimensions to those found clinically. The results of phantom
image evaluations can therefore be used to establish a baseline
value for the Quality Control monitoring program. Another
phantom representing compressed breast tissue should be used
to measure breast surface dose to calculate the mean glandular
dose. The tests for the initial evaluation are presented below and
in Section 8.2.1.
a. Representative breast surface doses with mean glandular dose calculations
b. Image spatial resolution
c. Image contrast
d. Image quality
8.2.1 Description and frequency of tests
Table 5 presents suggested performance criteria and recommended frequency of testing for mammographic X-ray equipment. It must be noted that some facilities may require a different frequency of testing than suggested and that for facilities under provincial jurisdiction, different performance criteria and testing frequency may apply.
| Test | Performance Criteria | Frequency |
| Mammographic X-ray equipment | ||
| Focal spot size | Section 5.3.1 No. 2 or | Annually |
| Section 5.3.2 No. 2 | ||
| Beam limiting device | Section 5.3 No. 9 | Annually |
| Compression plate alignment | Section 5.3 No. 11 | Annually |
| Radiation output | Section 5.3.1 No. 6 or Section 5.3.2 No. 6 | Semi -annually |
| X-ray timer | Section 5.3 No. 7 | Semi-annually |
| Backup timer | Section 5.3 No. 7 | Semi-annually |
| X-ray tube voltage | Section 5.3.1 No. 5 or Section 5.3.2 No. 5 | Semi-annually |
| Radiation beam quality | Section 5.3.1 No. 4 or Section 5.3.2 No. 4 | Semi-annually |
| Automatic Exposure Control system | ||
| Optical density setting response | Section 5.3.1 No. 7 or Section 5.3.2 No. 7 | Semi-annually |
| X-ray tube | Section 5.3.1 No. 7 or | Semi-annually |
| voltage compensation | Section 5.3.2 No. 7 | |
| Thickness | Section 5.3.1 No. 7 or | Semi-annually |
| compensation response | Section 5.3.2 No. 7 | |
| Films, screens and cassettes | ||
| Screen/film speed uniformity | Section 6.5 | Semi-annually |
| Viewboxes | ||
| Brightness | Section 6.4 | Annually |
| Light output uniformity | Section 6.4 | Annually |
| Light output | Section 6.4 | Annually |
| homogeneity | ||
| Ambient light control | Section 6.4 | Annually |
| Imaging characteristics | ||
| Representative breast surface dose and meanglandular dose calculations | Appendix II | Annually |
| Image spatial resolution | Baseline | Annually |
| Image contrast | Baseline | Annually |
| Image quality | Baseline | Annually |
8.3 Quality Control monitoring
Quality Control procedures to be performed in a Quality Assurance program are presented in the following list. Section 8.3.1 presents the tests with the suggested frequency and performance criteria.
- Mammographic X-ray equipment - Mammographic X-ray equipment should be checked for loose or broken components. Breast compression force should be checked.
- Darkroom and image processing operation - There should be regular inspection of darkroom and processing equipment for cleanliness. Light-tightness and correct safelighting should also be assessed on a regular basis. The accuracy of the processor thermometer used should be checked. A daily inspection of film processing solutions levels, and cleanliness of darkroom should be made.
- Film, screen and cassette - Screens should be checked for cleanliness and damage. Cassettes should be checked for cleanliness, wear, warping, fatigue of foam compression material and closure mechanism, light leaks, and film-screen contact. The cassette holder tunnel should be checked for dust and dirt.
- Viewboxes - Viewboxes should be checked for cleanliness, viewing area discoloration and improper illumination.
- Image characteristics - Test images are needed to monitor the performance of the mammographic X-ray system and image processing. A phantom representing breast thickness should be routinely used to monitor and maintain image density. Another phantom, with image quality evaluation objects, should also be used to test imaging performance of the mammographic X-ray system. The image Quality Control monitoring tests and evaluations must be performed on a regular basis.
- Retake record - A record of every retake should be made, including the reason for the retake along with any corrective actions. If images contains some patient diagnostic information, they should be maintained in the patient file. Any trends or repeated errors should be identified and corrected.
8.3.1 Description and frequency of tests
Table 6 presents suggested performance criteria and recom-mended frequency of testing for mammographic Quality Control. It must be noted that some facilities may require a different frequency of testing than suggested and that for facilities under provincial jurisdiction, different performance criteria and testing frequency may apply.
| Test | Performance Criteria | Frequency |
| Mammographic X-ray equipment | ||
| Breast compression device force |
Section 5.3 No. 11 | Semi-annually |
| X-ray equipment conditions |
Visual acceptance | Monthly |
| Darkroom and image processing operation | ||
| Level of film base plus fog | Section 6.3 | Semi-annually |
| Safelight test for darkroom fog | Section 6.2 | Semi-annually |
| Fixer retention in film | Baseline | Quarterly |
| Thermometer accuracy | Section 6.1 | Monthly |
| Darkroom conditions | Visual acceptance | Daily |
| Replenishment rate | Baseline | Daily |
| Film processing solution levels | Baseline | Daily |
| Film processing solution temperature | Baseline | Daily |
| Sensitometric strip processing | Baseline | Daily |
| Films, screens and cassettes | ||
| Screen/film contact | Section 6.5 | Semi-annually |
| Screen conditions | Section 6.5 | Weekly |
| Viewboxes | ||
| Viewboxes conditions | Visual acceptance | Weekly |
| Image characteristics | ||
| Image contrast | Baseline | Weekly |
| Image quality | Baseline | Weekly |
| Image density | Baseline | Daily |
| Retake record | ||
| Retake analysis | Baseline | Monthly |
