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

7. Quality Assurance program

Quality Assurance in mammography is defined as the planned and organized actions necessary to provide confidence that mammographic X-ray equipment and related components operated in a facility will reliably produce quality mammograms with minimum dose to patients and staff. This means that the radiologist and other health care professionals will be provided with images of diagnostic quality with the least amount of radiation for the examination. A Quality Assurance program for mammography includes Quality Control procedures for the monitoring and testing of mammographic X-ray equipment and related components, and administrative methodology to ensure that monitoring, evaluation and corrective actions are properly performed. A Quality Assurance program shall include all practices established by the owner to ensure that:

1. the mammographic X-ray examination is performed with the lowest possible radiation dose to the patients consistent with clinical diagnostic requirements;
2. the mammograms produced provide for accurate clinical assessment; and
3. all steps leading to accurate diagnosis are taken and the information is made available in a timely fashion to the patient's physicians.

7.1 Goals of Quality Assurance program

Goals of Quality Assurance program The principal goal of a Quality Assurance program is to ensure accurate and timely diagnosis. The secondary goal is to minimize radiation dose to the patient as long as the principal goal is achieved. Two factors will affect the operation of a Quality Assurance program; one deals with the diagnostic imaging equipment and the other with equipment operation. It is essential that the equipment be in proper working condition if any Quality Assurance program is to succeed. All staff members must participate fully in the implementation and operation of the Quality Assurance program, and must understand the goals of the program and must be committed to the concept. Any program initiated only to comply with regulatory requirements is not likely to provide the maximum possible benefit to the patient.

Mammograms of diagnostic quality must contain all information necessary for the diagnosis. If critical elements are missing from the mammogram or artifacts are added to it, the image is considered to be of poor quality. False positive mammograms result in unnecessary anxiety for the patient whereas false negative mammograms provide a false sense of security. The consequence of poor quality mammograms may be incorrect diagnosis resulting in possible premature death of the patient, unnecessary biopsies, repeat mammographic procedure, unnecessary radiation dose to the patient, and increased cost.

7.2 Cost-benefit of Quality Assurance program

The initial implementation along with the general operation of a Quality Assurance program in mammography will involve cost in both time from staff and money. However, savings from the operation of the program will offset some of these costs. For some facilities, there may be a reduction in overall operating costs. Some of the costs associated to the Quality Assurance program are as follow.

1. Personnel - The staff will be required to perform new duties, which include generating test images for their mammographic X-ray equipment and record keeping. It is expected that staff cost beyond the initial cost, including training, incurred during the implementation of the program would be minimal.
   
   
2. Test equipment - Test equipment for photographic, radiographic and diagnostic image Quality Control, such as mammographic phantoms, will be required. However, the cost of such equipment is small compared to the cost of mammographic X-ray equipment and it can be utilized for several mammographic X-ray systems. It would not be necessary to purchase some of the test equipment if the facility decides to have some of the Quality Control tests performed by an external organization or individual.
   
   
3. Test images - Two to five percent of films used by a facility may be required for the performance of sensitometry, phantom imaging, equipment and cassettes testing.
   
   
4. External organizations - If the facility does not have the capacity to perform internally all Quality Control tests, it may choose to contract an external organization or individual to perform some of these tests and equipment assessment. In addition, the facility may retain the service of a medical physicist as an advisor during implementation and for consultation during operation of the facility.

In addition to improved diagnostic quality of mammograms, some of the savings associated to the Quality Assurance program are as follow.

1. Film and processing chemicals - A decrease in the number of retakes may result in the reduction in the number of mammographic films and processing chemicals used.
   
   
2. Equipment - The reduction in the number of mammograms taken will lead to a reduction in workload which in turn will put less stress on mammographic X-ray equipment and image processors. Problems with equipment may be diagnosed earlier before more serious and costly problems occur thus reducing down time and equipment service cost.
   
   
3. Patient flow - The reduction in the number of repeated mammograms, and better diagnostic quality of the mammograms will allow efficient use of time for both radiologists and technologists. This will result in better predictability of scheduling and possibly greater patient throughput.

7.3 Implementation of a Quality Assurance program

The implementation of a Quality Assurance program in mammo-graphy need not be complicated. It consists in establishing Quality Control procedures for the equipment along with an administrative methodology to ensure that monitoring, evaluation and corrective actions are properly performed.

7.3.1 Establishment of Quality Control procedures

The following four steps are needed for the establishment of Quality Control procedures.

1. Equipment operation - It is essential that mammographic X-ray equipment and image processing equipment function properly before a Quality Assurance program is implemented. Manufacturer and vendor should provide proper operating characteristics for their equipment. Film-screen combination and processing should meet manufacturer's speed and contrast values. This may involve replacement, repair, upgrading or calibration of the equipment.
   
   
2. Baseline performance - Baseline performance values of mammographic X-ray equipment and image processing system must be established after verifying that equipment functions properly. 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 measurement. These records will be needed to diagnose any changes in image quality.
   
   
3. Reference test image - To evaluate image quality of mammograms, a reference test image is needed. This reference test image is made by using the mammographic X-ray equipment, image processing system and a mammographic phantom and will be used for comparison of daily test image.
   
   
4. Result evaluation and action levels - An effective Quality Control monitoring program includes not only a routine Quality Control testing schedule, data recording and record keeping, but also test result evaluation, such as determination of acceptable or unacceptable limits of equipment operation coupled with a list of corrective actions that may be required.

A set of limits should be established which indicates a level of operation outside of which the system or the function should be closely monitored but where no immediate action is required. Another set of limits should also be established where immediate remedial action must be taken.

7.3.2 Establishment of administrative procedures

The following administrative procedures are needed for an effective Quality Assurance program.

1. Responsibility - Although the owner of the facility is ultimately responsible for the implementation and operation of the Quality Assurance program, to obtain the optimal level of radiation safety and image quality, it is imperative that full cooperation exist between all concerned parties. Staff members may be assigned duties with regard to equipment monitoring, record keeping and Quality Assurance operation. It is essential that the level of responsibilities and involvement of the owner and staff be indicated and understood.
   
   
2. Record keeping - It is essential that measurements and information gathered for the Quality Assurance program be clearly documented and readily available for evaluation. As far as practicable, recorded data should be indicated as data points on a control chart when the measurement is made. For example, it includes the densitometric results of the sensitometric film strips and the charting of temperature for the film processor. In this form, trends can be more easily detected. A log book or other easily identifiable method of recording must be used.
   
   
3. Evaluation of data - Recorded data should be evaluated immediately and necessary actions taken.
   
   
4. Limits of acceptability of data - Upper and lower limits of acceptability of recorded data must be determined and documented. When these limits are reached, corrective actions must be taken. For example, they can be the range of acceptable temperature for the film processor. These limits should be set such that they are just within the range allowable before diagnostically significant image changes are evident. They should not be so restrictive that they exceed the capability of the equipment, or that frequent corrective actions are taken without any evidence of problems. These limits should be reviewed from time to time.
   
   
5. Testing frequency - Testing frequency must be such that a balance is reached between the cost of testing, the disruption to the operation of the facility and the maintenance of quality.
   
   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 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 program should not be discontinued if the results indicate relatively stable equipment performance. The purpose of a Quality Control program is to control quality, and periodic measurement of equipment performance is essential. The frequency of testing described in Section 8 should be considered a minimum.
   
   
6. 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 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.