Cat. No.: H129-32/36-2013E-PDF
HC Pub.: 130377
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This document is one of a series of Safety Codes prepared by Health Canada to set out requirements for the safe use of radiation emitting equipment.
The information in this Safety Code has been prepared to provide specific guidance to owners of mammography equipment, radiologists, mammography radiological technologists, medical physicists, and other personnel concerned with the safety procedures, equipment performance, image quality, radiation protection and the overall quality of a mammography facility.
The scope of this safety code includes mammography technologies such as film/screen, computed radiography (CR), digital radiography (DR) and tomosynthesis. Other breast imaging modalities not employing x-ray radiation are excluding from this code.
This Safety Code replaces Safety Code 33, Radiation Protection in Mammography (HC 1995), and the Canadian Mammography Quality Guidelines (HC 2002).
The personnel requirements, safety procedures, equipment and facility guidelines and quality assurance measures detailed in this Safety Code are primarily for the instruction and guidance of persons employed in Federal Public Service departments and agencies, as well as those under the jurisdiction of the Canada Labour Code. Facilities under provincial or territorial jurisdiction may be subject to requirements under their statutes. The authorities listed in Appendix I should be contacted for details of the regulatory requirements of individual provinces and territories.
The words must and should in this Code have been chosen with purpose. The word must indicates a requirement that is essential to meet the currently accepted standards of protection, while should indicates an advisory recommendation that is highly desirable and is to be implemented where applicable.
In a field in which technology is advancing rapidly and where unexpected and unique problems continually occur, this Code cannot cover all possible situations. Blind adherence to rules cannot substitute for the exercise of sound judgement. Recommendations may be modified in unusual circumstances, but only upon the advice of experts in radiation protection. This Code will be reviewed and revised from time to time, and a particular requirement may be reconsidered at any time, if it becomes necessary to cover an unforeseen situation. Interpretation or elaboration on any point can be obtained by contacting the Consumer and Clinical Radiation Protection Bureau, Health Canada, Ottawa, Ontario K1A 1C1.
This Safety Code reflects the work of many individuals. It was prepared and compiled by Ms. Narine Martel of the Medical Imaging Division, Consumer and Clinical Radiation Protection Bureau. The assistance of Mr. Richard Tremblay, Mr. Charles Steiner and the members of the Medical Imaging Division during the preparation of this Code is acknowledged.
Sincere appreciation is expressed for the contributions of the members of the Canadian Mammography Standards and Accreditation Working Group established by the National Committee of the Canadian Breast Cancer Screening Initiative:
Elaine Dever, Canadian Association of Medical Radiation Technologists
Brenda Mitchell, Cancer Care Ontario (formerly)
Tom Butterworth, Canadian Association of Radiologists (formerly)
Andrea Nelson, Canadian Association of Radiologists
Jay Onysko, Public Health Agency of Canada
Rasika Rajapakshe, Canadian College of Physicist in Medicine
Rene Shumak, Cancer Care Ontario
Richard Tremblay, Ministère de la Santé et des Services sociaux du Québec (formerly)
Nancy Wadden, St-Clare's Mercy Hospital, Newfoundland
The contributions of the following organizations, agencies and associations, whose comments and suggestions during the consultation of this document helped in the preparation of this final Code, are gratefully acknowledged:
Alberta College of Medical Diagnostic and Therapeutic Technologists
Association des physiciens et ingénieurs biomédicaux du Québec (APIBQ), Comité de radioprotection
Breast Centre Radiology, Edmonton Alberta
British Columbia Centre for Disease Control
British Columbia Interior Health Authority, Diagnostic Imaging Services
Canadian Association of Radiologists
Federal/Provincial/Territorial Radiation Protection Committee
Health Canada, Medical Devices Bureau
Health Prince Edward Island, Provincial Diagnostic Imaging Services
Horizon Health Network New Brunswick, Saint John Regional Hospital
Horizon Health Network New Brunswick, Upper River Valley Hospital
Imaging Research Program, Sunnybrook Research Institute
Ministère de la Santé et des Services sociaux, Laboratoire de Santé Publique du Québec
Northern Alberta Institute of Technology, School of Health Sciences
Ontario Breast Screening Program, Cancer Care Ontario
Ontario Ministry of Health and Long Term Care
Radiology Consultants Associated, Alberta
Saskatchewan Ministry of Labour Relations and Workplace Safety, Radiation Safety Unit
Saskatchewan Cancer Agency, Screening Program for Breast Cancer
Thunder Bay Regional Health Sciences Centre, Linda Buchan Centre for Breast Screening and Assessment
Vancouver Coastal Health Authority, Department of Radiology
Mammography is an effective imaging method used for the detection of breast cancer. It has been proven to detect breast cancer at an early stage and, when followed up with appropriate diagnosis and treatment, to reduce mortality from breast cancer. Over the past 20 years, technological developments have greatly impacted mammography equipment design and performance and have resulted in improvements in image quality and reduction in radiation dose. Mammographic x-ray procedures are one of the most carefully managed radiological procedures. This is necessary in order to ensure optimization of image quality for interpretation of mammograms and to minimize radiation exposure to patients.
Breast cancer is the most frequently diagnosed cancer among Canadian women. In 2013, it is estimated that 23,800 women will be diagnosed with breast cancer. While the incidence of breast cancer in Canada has stabilized since 1999, the rate of breast cancer mortality has fallen by more than 30 percent since 1986. This is likely to be due to improvements in screening and advances in treatment. It is estimated that in 2013 5,000 women will die of breast cancer. Ensuring the quality of mammography, both screening and diagnostic, is an important component in the management of breast cancer. In order to have an effective mammography program, it is essential that mammography be performed to meet rigorous quality requirements. The responsibility for the quality of mammography in Canada is shared among federal, provincial and territorial governments, and the medical professionals who maintain the equipment, carry out the procedure and interpret the mammograms.
The purpose of this document is to provide guidance to mammography facilities, both screening and diagnostic, on radiation protection and quality assurance in mammography. The contents of this document are built upon and harmonized with existing Canadian and international standards pertaining to mammography. This includes the Diagnostic X-ray Equipment Regulations, Part XII of the Radiation Emitting Devices Act, which regulates the design, construction and functioning of mammographic x-ray equipment, the requirements of the Mammography Accreditation Program of the Canadian Association of Radiologists, provincial requirements and recommendations of the International Commission on Radiological Protection (ICRP) and the International Agency on Atomic Energy (IAEA). It should be noted that other provincial or territorial requirements may exist that supersede or add to provisions of this document.
Currently in Canada, mammography is performed using film-screen and digital mammography systems. Both systems utilize low energy x-rays to penetrate breast tissue, but differ in the image receptor, or detector, that is used to create the image. In film-screen mammography, x-ray film is placed in direct contact with a screen. The x-ray photons are captured by the screen which then emits light that exposes the film. The film is then chemically developed to produce the mammogram. Digital mammography systems use detectors with various technologies to produce the mammographic image. These technologies are generally categorized into two groups: direct and indirect conversion detectors. In systems employing direct conversion detectors, x-ray photons incident on the image receptor interact with a photoconducting material which directly converts the x-ray energy into an electrical signal carrying the image information. The electrical signal is processed and displayed almost instantaneously. In systems employing an indirect detector, a scintillator is used to capture the x-ray energy and then convert it to light. Light photons are then converted into an electrical signal. Computed radiography (CR) mammography systems are a type of indirect digital imaging technology. These systems consist of a cassette, an imaging plate containing photostimulable phosphor and an imaging plate reader. The CR cassette is exposed as in film-screen mammography. The latent image is stored in the imaging plate which is then read to produce the mammographic image.
The radiation dose from a properly carried out mammographic examination is very low and is essentially only delivered to the breast tissue. Due to the very low x-ray energies used in mammography, there is very little dose to other tissues. However, any procedure involving exposures to ionizing radiation must be carefully managed as it is presumed that even small doses of radiation may produce some deleterious health effects. Somatic effects may manifest themselves in the exposed individuals and are characterized by observable changes occurring in the body organs of the individuals. Genetic effects may arise in the descendents of exposed individuals. In mammography, the risk of genetic defects in well-conducted examinations is very small, and for post-menopausal women, there is no genetic risk.
Since it is not possible to measure carcinogenic effects at low doses, estimates of the incidences of radiation effects at low doses are based on linear extrapolation from relatively high doses. Due to the uncertainties with respect to radiological risk, a radiation protection risk model assumes that the health risk from radiation exposure is proportional to dose. This is called the linear no-threshold hypothesis. Since the projected effect of a low dose increases the incidence of a deleterious effect only minimally above the naturally occurring level, it is impossible to prove by observation either the validity or falsity of this hypothesis. However, the linear no-threshold hypothesis has been widely adopted in radiological protection and has led to the formulation of the ALARA (As Low As Reasonably Achievable) principle. The ALARA principle is an approach to radiation protection to manage and control exposures to radiation workers and the general public to as low as is reasonable, taking into account social and economic factors.
In mammography, there are four main aspects of radiation protection to be considered. First, patients should not be subjected to unnecessary radiographic procedures. This means that the procedures are ordered with justification, and when the diagnostic information cannot be obtained otherwise. Second, when a procedure is required, it is essential that the patient be protected from excessive radiation exposure during the examination. Third, it is necessary that personnel within the facility be protected from excessive exposure to radiation during the course of their work. Finally, personnel and the general public in the vicinity of such facilities require adequate protection.
While regulatory dose limits have been established for radiation workers and the general public, these limits do not apply to doses received by a patient undergoing medical x-ray procedures. For patients, the risk associated with the exposure to radiation must always be weighed against the clinical benefit of an accurate diagnosis or treatment. There must always be a conscious effort to reduce patient doses to the lowest practical level consistent with optimal quality of diagnostic information. Through close cooperation between medical professionals, technologists, medical physicists, and other support staff it is possible to achieve an effective radiation protection program and maintain a high quality mammography program.
This Safety Code provides guidance to all mammography facilities, both screening and diagnostic, to achieve and maintain effective mammography programs and to ensure radiation protection. The aim of this Safety Code is to provide mammography facilities with the necessary information to achieve the following principal objectives:
To assist in achieving these objectives, this Safety Code:
This Safety Code is composed of three sections:
Section A: Responsibilities and Protection
This section sets out the responsibilities of the owner, the interpreting radiologists, the mammography radiological technologists, the medical physicist and the information systems specialist for the safe installation, operation and control of the equipment, and sets out practices to minimize radiation doses to patients, staff and the public.
Section B: Facility and Equipment Requirements
This section sets out requirements for the facility design and minimum equipment construction and performance standards.
Section C: Quality Assurance Program
This section sets out requirements for quality assurance programs including acceptance testing and quality control procedures.
This section sets out the qualifications and responsibilities of all personnel involved in mammography. Initial qualifications, continuing experience and education, and re-establishing qualifications are provided and are based upon a 3 year cycle. Although personnel responsibilities are grouped separately, to obtain the optimal level of radiation safety and image quality, it is imperative that full cooperation exists among all concerned parties.
The owner is ultimately responsible for the radiation safety of the facility. The owner is defined as the person or group of persons in control of the possession and use of mammography equipment. The owner may be an individual, a corporation, a district, a province or some other entity. It is the responsibility of the owner to ensure that the equipment and the facilities in which such equipment is installed and used meet all applicable radiation safety standards, and that a radiation safety program is developed, implemented and maintained for the facility. The owner may delegate this responsibility to qualified staff. How this responsibility is delegated will depend upon the number of staff members, the nature of the operation and on the number of x-ray equipment owned. In any event, the owner must ensure that one or more qualified persons are designated to carry out the roles of the personnel described below.
The owner has the responsibility of:
All interpreting radiologists shall meet the following qualifications:
Before beginning to interpret mammograms independently, the interpreting radiologist must:
All interpreting radiologists must maintain their qualifications by meeting the following requirements:
Interpreting radiologists who fail to maintain the required continuing experience or continuing education requirements must re-establish their qualifications before resuming the independent interpretation of mammograms, as follows:
All interpreting radiologists must participate fully in the quality assurance program by:
All mammography radiological technologists must:
All practicing mammography radiological technologists must maintain their competence in the practice of breast imaging by meeting the following requirements:
Mammography radiological technologists who fail to meet the continuing experience requirements must:
Mammography radiological technologists must participate fully in the quality assurance program by:
All medical physicists conducting surveys of mammography facilities and providing oversight of the facility quality assurance program must meet the following requirements:
All medical physicists conducting surveys of mammography facilities and providing oversight of the facility quality assurance program must obtain the following continuing experience and education, in accordance with the requirements of the CCPM.
Medical physicists who fail to maintain the required continuing qualifications may not perform surveys without the supervision of a qualified medical physicist. Before independently surveying another facility, medical physicists must re-establish their qualifications in accordance to the requirements of the CCPM as follows:
The medical physicist must:
Facilities performing digital image processing must have access to an individual who is trained and experienced in installation, maintenance and quality control of information technology software and hardware. Depending on the facility, the individual may be on-site or available upon request. The required qualification of this individual will depend highly on the type of facility and the type of equipment. Ideally the individual should have both information technology and radiation technology expertise.
ISSs who fail to maintain the required continuing qualifications may not carry out their duties without the supervision of a qualified ISS. Before carrying out independent work, the ISS must re-establish their qualifications.
The ISS must:
The repair and maintenance personnel are individuals authorized to perform repairs and maintenance on X-ray generators, control systems, imaging systems and their operating software. Depending on the facility, these individuals may be on-site or available upon request, but in general, this function is sometime contracted to an outside organization, or to the equipment manufacturer.
The repair and maintenance personnel must:
Facilities must maintain records to document the qualifications of all personnel who worked at the facility as interpreting radiologists, mammography radiological technologists, medical physicists and information systems specialists. The retention time must be in accordance with any relevant federal/provincial/territorial statutes and regulations. Records of personnel, including those no longer employed by the facility, should not be discarded as they may be required by the facility to demonstrate the qualifications of all personnel to the accreditation body.
The required and recommended procedures outlined in this section are primarily directed toward occupational health protection. However, adherence to these will also, in many instances, provide protection to visitors and other individuals in the vicinity of an x-ray facility. The safe work practices and procedures should be regarded as a minimum, to be augmented with additional requirements, when warranted, to cover special circumstances in particular facilities.
To achieve optimal safety, equipment operators must make every reasonable effort to keep exposures to themselves and to other personnel as far below the limits specified in Appendix II as reasonably achievable.
The largest single contributor of man-made radiation exposure to the population is dental and medical radiography. In total, such use of x-rays accounts for more than 90% of the total man-made radiation dose to the general population.
The risk to the individual patient from a single radiographic examination is very low. However, the risk to a population is increased by increasing the frequency of radiographic examinations and by increasing the number of persons undergoing such examinations. For this reason, it is important to reduce the number of radiographs taken, the number of persons examined radiographically, and the doses associated with the examinations.
To accomplish this reduction, it is essential that patients must only be subjected to necessary radiological examinations and, when a radiological examination is required, patients must be protected from excessive irradiation during the examination.
The required and recommended procedures for the protection of the patient, outlined in this section, are directed toward the health care professionals, radiologist, and technologist. They are intended to provide guidelines for elimination of unnecessary mammographic examinations and for minimizing doses to patients when mammography is necessary.
Unnecessary radiation exposures of patients can be significantly reduced by ensuring that all examinations are clinically justified. This can be done by adhering, as much as possible, to certain basic recommendations. These recommendations are presented below.
More specific guidance for the prescription of imaging examinations is available from the Canadian Association of Radiologists (CAR) in their Diagnostic Imaging Referral Guidelines (CAR 2012). These guidelines provide recommendations on the appropriateness of imaging investigations for the purpose of clinical diagnosis and management of specific clinical/diagnostic problems. The objective of these guidelines is to aid the referring physician / health care professional to select the appropriate imaging investigation and thereby reduce unnecessary imaging by eliminating imaging that is not likely to be of diagnostic assistance to a particular patient and by suggesting alternative procedures that do not use ionizing radiation but offer comparable diagnostic testing accuracy.
3.2 Guidelines for Screening Mammography
Next to elimination of unnecessary x-ray examinations, the most significant factor in reducing dose is ensuring that examinations are performed with good technique. It is possible, for example, to obtain a series of diagnostically acceptable mammograms and have the organ dose vary widely due to the choice of technique and loading factors. It is the responsibility of the technologist, the medical physicist and the radiologist to be aware of this and to know how to carry out a mammographic x-ray examination with the lowest possible radiation exposure to the patient or breast screening participant.
The requirements and recommendations that follow are intended to provide guidance to the technologist, the medical physicist and radiologist in exercising their responsibility towards reduction of patient exposure.
In the planning of any medical x-ray facility it must be ensured that persons in the vicinity of the facility are not exposed to levels of radiation which surpass the current regulatory exposure limits. Appropriate steps must be taken to ensure adequate shielding is present to meet the following requirements:
Appendix II provides a detailed description of the regulatory dose limits. For mammography facilities, controlled areas are typically in the immediate areas where the mammographic x-ray equipment is used. The workers in these areas are primarily equipment operators such as medical radiation technologists who are trained in the proper use of the equipment and in radiation protection. Uncontrolled areas are those occupied by individuals such as patients, visitors to the facility, and employees who do not work routinely with or around radiation sources (NCRP 2004).
In general, radiation levels directly beside the image receptor of mammographic x-ray equipment are such that the above limits could be exceeded, depending on the design of the equipment, the techniques used and the total workload. However, because mammographic x-ray equipment uses low x-ray tube voltage, reduction in radiation intensity can be easily accomplished with the presence of a suitable shielding barrier between the patient and the technologist, a suitable combination of distance from the sources of radiation and shielding barriers, and restriction of persons from all areas in which the respective recommended dose limit could be exceeded.
In the early stages of designing and planning a mammography facility, three steps should be taken to ensure adequate shielding is in place to provide the necessary level of radiation protection:
In order to determine the shielding requirements for an x-ray facility a floor plan must be prepared, clearly identifying the following components:
When designing the layout of the mammography facility, the following general recommendations must be considered.
The thickness of the shielding material, such as lead, concrete, or gypsum wallboard, required to reduce radiation levels to the recommended dose limits can be determined through calculations. In general, the radiation exposure to individuals depends primarily on the amount of radiation produced by the source, the distance between the exposed person and the source of the radiation, the amount of time that an individual spends in the irradiated area, and the amount of protective shielding between the individual and the radiation source.
Given that mammography is performed at low operating potentials, permanent mammography facilities may not need shielding in addition to the level of protection provided by typical gypsum wallboard construction. Special consideration must be given to radiation protection when using mobile or temporary mammography equipment. For all types of mammography equipment, a qualified expert must be consulted to ensure that the level of radiation safety of the facility is adequate.
The parameters listed below must be considered for the calculation of barrier thicknesses. Allowance should be made for possible future changes in any one or all of these parameters, including increases in use and occupancy factors, in operating tube voltage and workload, as well as modifications in techniques that may require ancillary equipment.
1. The maximum x-ray Workload, (W) or the workload distribution.
The workload is a measure of the operational time or the amount of use of the x-ray equipment. A workload distribution indicates the workload across a range of operating voltages. The workload and workload spectrum can be determined by recording the operating voltage and current-time product of each irradiation taken in each mammography room over a set period of time (i.e., week). If actual workload values are not available, Table 1 presents estimated total workload in a mammography facility (NCRP 2004).
|Total Workload per patient
|Typical Number of Patients
(per 40 hour week)
|Total Workload per week
2. The Occupancy Factor (T)
The occupancy factor is the fraction of time that the area under consideration is occupied by the individual (employee or public) who spends the most time at that location while the x-ray equipment is operating. The following table presents recommended occupancy factors.
|T=1||Administrative offices and receptionist areas, laboratories, pharmacies and other areas fully occupied by an individual, attended waiting rooms, children's indoor play areas, adjacent x-ray rooms, image viewing areas, nurses' stations, x-ray control rooms, living quarters.|
|T=1/2||Rooms used for patient examinations and treatments.|
|T=1/5||Corridors, patient rooms, staff lounges, staff rest rooms.|
|T=1/20||Public toilets, unattended vending areas, storage rooms, outdoor areas with seating, unattended waiting rooms, patient holding areas.|
|T=1/40||Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators, janitor's closets.|
3. The Use Factor (U)
The use factor is the fraction of the workload during which the x-ray beam is pointed in the direction under consideration. In mammography the image-receptor assembly acts as a primary beam stop, and therefore U=0. Only secondary radiation needs to be considered. The use factor for secondary protective barriers is always taken to be 1.
In mammography rooms, shielding calculations must be made for secondary protective barriers. As the image receptor assembly of mammography equipment acts as a primary protective barrier, additional primary barriers are not needed. Secondary protective barriers are required to provide shielding from scattered and leakage x-rays.
Comprehensive shielding calculations for mammography facilities should only be performed by individuals with current knowledge of structural shielding design and the acceptable methods of performing these calculations. It is recommended that shielding calculations be performed using the methodology presented in the National Council on Radiation Protection and Measurements (NCRP) Report No. 147: Structural Shielding Design for Medical x-ray Imaging Facilities (NCRP 2004). However, it must be noted that the shielding design goals specified in NCRP Report 147 are not adopted in this Safety Code. The shielding design goal values may be lower but must not exceed the limits set out in section B1.1 for controlled and uncontrolled areas. Due to the extensiveness of the information, the methodology of NCRP 147, including equations, tables and figures, is not provided in this Safety Code.
The information outlined in sections B1.1 and B1.2 along with the final plans of the installation must be submitted for review by the appropriate responsible government agency. Radiological facilities that fall under provincial or territorial jurisdiction should contact the responsible agency in their respective province or territory listed in Appendix I.
Film storage containers must be adequately shielded to ensure that excessive exposure of film by X- rays does not occur. Sufficient film shielding must be in place to reduce the radiation level to stored film to less than 0.1 mGy over the storage period of the film. Once films are loaded into cassettes, radiation exposure levels should be less than 0.5 µGy and the resulting increase in the base-plus-fog should be less than 0.05 O.D. Appendix IV provides guidance on the shielding requirements for storage of radiographic film. The shielding requirements presented in Appendix IV are very conservative but will protect films from radiation exposure for most circumstances. Given that CR Cassettes are used more frequently and therefore stored for shorter periods of time, the limit of 0.5 μGy is also considered to provide sufficient shielding for CR cassettes (NCRP 147). In general, CR cassettes are stored behind the transparent shield of the mammography radiological technologists. The transparent shield should have a permanent label indicating the lead equivalence of the panel.
All new, used and refurbished mammographic x-ray equipment, and accessories for such equipment, which are sold, imported or distributed in Canada, must conform to the requirements of the Radiation Emitting Devices Act and the Food and Drugs Act and their promulgated regulations. These are the Radiation Emitting Devices Regulations and the Medical Devices Regulations. The Radiation Emitting Devices Regulations, Schedule II, Part XII (Diagnostic x-ray Equipment) sets out the requirements for information and labelling, construction and performance of mammographic x-ray equipment. The Medical Devices Regulations encompass all other safety and effectiveness considerations. It is the responsibility of the manufacturer or distributor to ensure that their equipment complies with the requirements of these regulations prior to importation and/or sale in Canada. Mammography facilities under provincial or territorial jurisdiction may be subject to requirements specified under their statutes and regulations. In addition, the Canadian Standards Association and provincial electrical utility should be consulted for further information.
The Radiation Emitting Devices Act, the Food and Drugs Act and their promulgated regulations are available on the Department of Justice online source of the consolidated Acts and regulations of Canada (http://laws-lois.justice.gc.ca/eng/acts/R-1/index.html, http://laws-lois.justice.gc.ca/eng/acts/F-27/index.html).
The purchase of medical imaging equipment is one of the most significant expenditures of an imaging facility. It is therefore essential to ensure that the desired design and level of performance are being obtained in a cost-effective manner. Below is an outline of the recommended process for purchasing medical imaging equipment.
A needs analysis must be performed to identify the type and specifications of equipment required to meet the clinical x-ray imaging needs. When performing a needs analysis, the main points which should be considered are the types of investigations that the facility intends to perform with the equipment, and the level of performance needed from the equipment. Other points which should be addressed are whether the staff of the facility possesses the expertise to use the equipment, whether adequate space is available for installation of the new equipment, and the date on which the equipment must be installed and operational at the facility. All staff members who will be routinely using the equipment should be consulted for input at this stage.
Equipment specifications must be prepared with full knowledge of the clinical needs and operational conditions, as well as manufacturer's specifications, and regulatory requirements. Equipment specifications supplied to the vendor should identify the type of x-ray equipment needed and the types of clinical procedures intended to be performed with the equipment. It should also identify all system components and provide a complete description of the design, construction and performance features of each component. The level of performance should be such that most manufacturers should be able to meet these performance requirements with readily available components and product lines. All relevant requirements stated in this Safety Code and any further requirements as specified by the agency responsible for the facility should also be addressed in the equipment specifications. Any electrical, mechanical and environmental conditions which may affect the performance of the equipment should also be included.
The equipment specifications should also include other relevant information such as the details concerning the equipment installation and calibration by the vendor and the associated deadlines, the type of warranty and service plan needed, and whether training of staff is required from the manufacturer. In general, the equipment specifications must identify all criteria which must be met for acceptance of the equipment.
Testing equipment required to perform daily to monthly quality control procedures, which are not already available, must be purchased at the same time as the x-ray unit.
Vendor quotations must be thoroughly reviewed to ensure that the vendor supplied equipment specifications address the identified needs of the facility. The vendor's quotation should include the installation and calibration of the equipment, warrantees, delivery time, maintenance plans, quality control testing equipment, staff training and all other criteria included in the purchaser's equipment specifications.
The purchase contract should set out all items and conditions of the purchase specified in the equipment specifications and vendor's quotation which have been agreed upon by the purchaser and vendor. All conditions for acceptance of the equipment must be clearly specified, as well as, action to be taken if conditions for acceptance are not met. A detailed and concise purchase contract will ensure the delivery of equipment in a timely and cost-effective manner.
Acceptance testing must be performed prior to any clinical use of the equipment. Acceptance testing is a process to verify compliance with the performance specifications of the x-ray equipment as written in the purchase contract. It must also verify that the equipment performance meets the manufacturer's specifications and complies with federal and provincial or territorial regulations. Acceptance testing must be performed by, or under the supervision of, a medical physicist, with in-depth knowledge of the particular type of x-ray equipment and the relevant regulations. This individual must be independent of the manufacturer.
Acceptance testing of a medical x-ray system includes several major steps: They are:
More detailed information on acceptance testing of mammographic x-ray equipment is available in publications from the International Electrotechnical Commission (IEC 2007).
X-ray performance tests carried out during the acceptance testing should also reflect the requirements described in subsection B2.5. The results from the acceptance testing should be used to establish baseline values and limits of acceptance on operational performance of the x-ray equipment. These baseline values and limits are essential to the quality assurance program.
Whenever possible, existing mammography equipment should be upgraded to incorporate as many as possible of the safety and performance features required of new medical x-ray equipment, as specified in the Radiation Emitting Devices Regulations, in effect at the time. It should be noted that it is a requirement of the Radiation Emitting Devices Act that replacements for any component or subassembly of mammography equipment, for which a construction or performance standard has been specified in the regulations, must comply with the standards in effect at the time of replacement. In addition, the upgraded components and/or software must be licensed by Health Canada. Information on licensing of mammography equipment, accessories or software is available from the Therapeutic Products Directorate, Medical Devices Bureau of Health Canada (contact information available in Appendix I). The owner of a mammography facility must ensure that any upgrades/changes to the equipment or software meet all applicable federal, provincial and territorial requirements. Any changes/upgrades of equipment affecting image quality and/or radiation dose must undergo acceptance testing by a medical physicist.
When retrofitting a digital image receptor ( ex. CR system) onto a new or existing mammography system, the owner of the facility must ensure that the digital image receptor meets the requirements of the Radiation Emitting Devices Act and Regulations, as well as the Food and Drugs Act and the Medical Devices Regulations. Furthermore, the mammography system, onto which the digital image receptor is fitted, must meet the requirements of Part XII of the Radiation Emitting Devices Regulations in effect at that time. Digital image receptors must only be installed on x-ray systems which have an automatic exposure control. The system must be calibrated to reflect the sensitivity of the digital image receptor.
Mammography must only be performed using radiographic equipment designed specifically for mammography. Radiographic equipment designed for general purpose or special nonmammography procedures are prohibited from use in mammography. This prohibition includes systems that have been modified or equipped with special attachments for mammography.
The information, labelling, construction and function requirements set out in this section are based upon the current Radiation Emitting Devices Regulations, Part XII (Diagnostic X-ray Equipment) and the standard of the International Electrotechnical Commission (IEC), 60601-2-45 (IEC 2011). These requirements are applicable to manufacturers of all new mammography equipment and are presented here in an effort to promote awareness of equipment standards for individuals involved in the acquisition of new mammography equipment. The Radiation Emitting Devices Regulations and the IEC standards applicable to mammography equipment should be referred to for complete and detailed information on equipment standards.
Operating Range for Normal Use (kV)
X-ray Tube Voltage (kV)
Half-Value Layer of Aluminium (mm)
|50 or less||(a) 30||0.30|
2. An irradiation switch of mammography equipment must permit the emission of x-rays only when the operator exerts continuous pressure on the switch.
3. Controlling timers of mammography equipment must:
4. When a support table (including all layers, excluding the grid) is positioned between the patient and the x-ray image receptor, the aluminium equivalence of the support table shall not exceed 0.3 mm, as determined using an x-ray beam that
Any sensor used in automatic exposure control is considered to be part of the x-ray image receptor.
5. For mammography x-ray equipment,
6. Mammography equipment that is equipment with automatic exposure control must have
7. Mammography equipment must have
8. Mammography equipment with a removable fixed-aperture beam limiting device must display on its external surface the dimensions of the image reception area and the focal spot to image receptor distance at which the beam limiting device must be used.
1. Radiation Output Reproducibility
For any combination of x-ray tube voltage, x-ray tube current and irradiation time, or for any selected exposure to the x-ray image receptor, when the line voltage for each measurement is accurate to within one percent of the mean line voltage value of all measurements, and when all variable controls for the loading factors are adjusted to alternate settings and reset to the test setting before each measurement,
2. Accuracy of Loading Factors
The loading factors set out in column 1 of an item of Table 4 must not deviate from the selected value, for any combination of loading factors, by more than the quantity set out in column 2 of that item.
|Item||Column 1||Column 2|
|Loading Factor||Maximum Deviation from the Selected Value|
|1.||X-ray tube voltage||±5%|
|2.||Irradiation time||±(10% plus 1 ms)|
|3.||X-ray tube current||±20%|
|4.||Current time product||±(10% plus 0.2 mAs)|
3. Controlling Timer and Automatic Exposure Control
Measured value of the selected quantity must not differ by more than ±15% of the mean value of the test loadings or, as appropriate, the manufacturer specification.
4. Radiation Output Linearity
5. Dosimetric Indications
For all mammographic x-ray equipment with an integrated digital x-ray image receptor, the mean glandular dose must be indicated for each acquired image.
6. Residual Radiation behind Image Receptor
For mammographic x-ray equipment, the residual radiation behind the image receptor supporting device must not exceed an air kerma measurement of 1.0 µGy or an exposure measurement of 0.115 mR per irradiation when the equipment is operated at
The air kerma or exposure measurement must be averaged over a detection area that is 100cm2, of which no linear dimensions is greater than 20cm, centred at 5 cm from any accessible surface beyond the image receptor supporting device.
7. Minimum Radiation Output Rate
Mammography equipment without an integrated digital x-ray image receptor must have a minimum rate of radiation output of 7.0 mGy/s or 802 mR/s when the equipment is operated,
8. Leakage Radiation in the Loading State
The leakage radiation from the x-ray source assembly of mammographic x-ray equipment must not exceed an air kerma rate of 1.0 mGy/h or an exposure rate of 115 mR/h when the assembly is operated at the nominal x-ray tube conditions of loading that correspond to the maximum specified energy input in one hour.
The rate must be averaged over a detection area of 100 cm2, of which no linear dimension is greater than 20 cm, that is centred at 1 m from the focal spot.
9. Leakage Radiation when not in the Loading State
If high voltage can appear across the x-ray tube of mammographic x-ray equipment, then the radiation emitting from the x-ray source assembly of the equipment must not exceed an air kerma rate of 20.0 µGy/h or an exposure rate of 2.3 mR/h when the equipment is operated with its beam limiting device fully open and the automatic exposure control or the irradiation switch has not been activated.
The rate must be averaged over a detection area of 10 cm2, of which no linear dimension is greater than 5 cm, that is centred at 5 cm from any accessible surface of the x-ray source assembly.
10. Radiation from Other Components
Under any operating condition, the radiation from any component of mammographic x-ray equipment, other than the x-ray source assembly, must not exceed an air kerma rate of 20 µGy/h or an exposure rate of 2.3 mR/h.
The rate must be averaged over a detection area of 10 cm2, of which no linear dimension is greater than 5 cm, that is centred at 5 cm from any accessible surface of the component.
Image processing includes both film and digital processing of radiological images. Film processing systems have been extensively used in the past. Recently with advances in digital technology, digital image processing systems are being used in many radiological facilities. No matter the type of system used, optimization of image quality at an acceptable dose to the patient is a priority for radiological facilities. This is achieved by ensuring image processing is an integral component of the facility's quality assurance program.
The ability to produce a mammogram of satisfactory diagnostic quality at an acceptable dose to the patient depends on the technique used when performing the examination, the appropriate selection of loading factors, the film-screen employed, the handling and processing of the film, and on the conditions of viewing the image. Good image quality requires proper darkroom techniques, routine processor quality control monitoring, and careful adherence to film and processor manufacturers' instructions.
X-ray films are sensitive to light, heat, humidity, chemical contamination, mechanical stress and X-radiation. Unexposed film must be stored in such manners that it is protected from stray radiation, chemical fumes and light. The level of optical density from the base material and film fog from all causes must not be greater than 0.30 O.D. Generally, x-ray films should be stored on edge, in an area away from chemical fumes, at temperatures in the range of 10°C to 21°C and humidity between 30% and 60%. The film manufacturers' instructions must be followed. Sealed film packages must be allowed to reach room temperature before opening to prevent condensation on the films. Loaded cassettes must be stored in an area shielded from exposure to radiation. Radiation exposures to stored film must be limited to 0.1 mGy and, for loaded cassettes, to 0.5 µGy. This area is usually in or near the x-ray room. The location of loaded and unexposed cassettes must be clearly marked. The area should be large enough to accommodate the required supply of cassettes needed during the operation of the facility.
Cassettes or screens in poor conditions will impair diagnostic quality. Problems are caused by dirty or damaged screens, warped cassettes, fatigue of foam compression material or closure mechanism, light leaks, and poor film-screen contact. Cassettes should be checked regularly for wear and cleanliness and any damaged cassettes must be replaced. Manufacturers' recommended screen cleaner should be used. To avoid artefacts caused by dirt and dust, the intensifying screens and cassettes must be cleaned at least monthly. The intensifying screens must be inspected with an ultraviolet light to find dust particles. Cleaning tools include a screen cleaner with antistatic solution, lint-free cloths, compressed air, and a camel hair brush. Cassettes and screens must be numbered for identification and matching, both inside the cassette and on the outside of the cassette.
With the exception of daylight automatic image processors not requiring darkrooms, automatic film processors require properly designed darkrooms. While specific details may vary from installation to installation, all darkrooms must include certain basic features listed below. Detailed information on the design of mammography darkrooms is provided by the International Atomic Energy Agency (IAEA, 2009).
Cleanliness in the darkroom and of the screens and cassettes is essential. It is important to maintain the cleanest environment possible in order to minimize any artefacts caused by dirt, dust, or improper handling of film. An ultraviolet light should be used to find dust areas around the darkroom. Eating or drinking in the darkroom area must not be permitted. All working surfaces, tops of counters and the floor should be cleaned regularly, at least once a day. Tops of cabinets, vents, light fixtures and any other areas which can collect dust should be cleaned on a regular basis. The ventilation system should be checked to make sure that no dust is carried from it to the inside of the darkroom; any filter should be changed on a regular basis. Except for in an auto-mixer, chemicals should not be mixed inside the darkroom since this operation can result in chemical splashes onto the equipment or working surfaces. Personnel should wear personal protection devices (gloves, masks, etc.) when handling chemicals.
To avoid putting fingerprints on the film and to avoid dirtying the screens, it is important to wash hands frequently with soap that does not leave any residue. Hand lotions and creams may also result in fingerprints on films. Clutter which may collect dust should be eliminated. Corrugated cardboard boxes containing film boxes, chemicals, and other supplies should not be stored or opened inside the darkroom as they will create a lot of dust. The boxes should be opened outside the darkroom, and films and supplies carried inside. Any articles of clothing made of loose fibres or which are static generating, such as wool, silk, some cottons or cotton blend fabrics, should not be worn in the darkroom or should be covered with a laboratory coat.
Improper or careless processing of exposed radiographic films can result in films of poor diagnostic image quality and consequently increase the possibility of wrong diagnosis or requests for repeat x-ray examinations. To achieve full development, the film must be processed in chemically fresh developer, at the correct temperature and for sufficient time to ensure that the silver in exposed silver halide crystals in the film emulsion is completely reduced. If this is not done, the blackening of the film will not be optimum and the tendency will be to increase radiation exposure to achieve proper image density.
Other factors can also affect the quality of the processed film. These include cleanliness of the processing system, film immersion time, and the efficiency of the rinsing. To ensure proper processing of films certain basic procedures must be followed:
X-ray film processing generates silver containing wastes. Silver containing chemicals must not be disposed of directly into the sewer system. These chemicals must be collected and released to the appropriate waste management agency for disposal and/or recycling. The management of silver containing waste must be carried out in accordance to provincial and municipal requirements.
The conditions of viewboxes must be checked regularly along with the conditions under which radiologists and other health care professionals examine mammograms since this may influence diagnostic accuracy. Problems with improper illumination due to the non-uniformity of fluorescent tubes or degradation and discolouration of the viewing surface must be corrected.
An increasing number of Canadian mammography facilities are transitioning from film-screen mammography to digital mammography. Various digital mammography systems are available using different types of detector technologies to produce the digital images. In general, digital mammography equipment are categorized into two groups: Computed Radiography (CR) systems or Digital Radiography (DR) systems.
Quality control testing of digital image systems is essential. Verification of the proper functioning of the x-ray imaging equipment along with appropriate selection of technique and loading factors remains essential for obtaining a satisfactory image at a minimal dose to the patient. For digital systems, specific quality control testing must also be performed on the image acquisition, storage, communication and display systems. In section C of this Safety Code, general quality control tests have been included for digital imaging systems. In addition to these tests, all equipment-specific, manufacturer-specified tests must also be performed. Facilities under provincial or territorial jurisdiction may be subject to other testing requirements.
Computed radiography (CR) imaging plates are reusable and can be exposed, read and erased repeatedly. For this reason, it is necessary to evaluate the conditions of imaging plates on a regular basis. With normal use, the accumulation of dust, dirt, scratches and cracks may reduce image quality. Exposure to chemical agents, such as non-approved imaging plate cleaners, handling with dirty or wet hands or contact with hand lotions are all possible causes of imaging plate damage. It is recommended that a log book be maintained to track the physical conditions of all imaging plates and cassette assemblies. The cleaning frequency depends on patient volume, plate handling, and the frequency at which artefacts are perceived. A weekly visual inspection for dust and dirt must be performed. The imaging plates must be cleaned monthly following manufacturer recommended procedures and using manufacturer recommended cleaners. Cleaner must not be poured directly onto the plates as this may cause staining.
Under normal conditions of use, dust and dirt can accumulate on cassettes. It is recommended that a log book be maintained to track the physical conditions of all cassettes. In general, a weekly visual inspection for dust and dirt is recommended and monthly cleaning of CR cassettes following manufacturer recommended procedures and using manufacturer recommended cleaners. The outside of the cassette can easily be cleaned with water and soap or a non-aggressive cleaner. The inside must not be cleaned with soap and water, since soap residue may be left on the protective coating after cleaning.
When not in use, CR cassettes, loaded with an imaging plate, must be stored in a location such that the level of radiation exposures is limited to 0.5 µGy.
Digital breast tomosynthesis (DBT) is a new three dimensional (3D) breast imaging technique. DBT equipment acquire multiple projection images of a breast over a range of tomographic angles. The number of images acquired and the tomographic angle varies between manufacturers of DBT equipment. Reconstruction algorithms are then used to produce images of tomographic planes through the breast. Typically plane thicknesses range from 0.5 to 3mm. Images can be viewed on a display monitor of individual planes or of sequential scrolls over all slices through the breast.
DBT has the potential to improve visualization of breast tissues by overcoming limitations of current mammographic techniques resulting from overlapping breast tissue into a single two dimensional image. The dose delivered to the patient during one tomosynthesis scan is comparable to one mammographic exam (Gennaro 2010). The potential benefits of DBT include improvement in screening sensitivity, improvement in lesion size at detection, improvement in characterization, and decrease in recall rates ( Helvie 2010).
For DBT equipment, quality assurance and quality control procedures as well as dosimetry must be performed in accordance with the recommendation of the manufacturer.
In order to realize the full potential of digital mammography it is important to ensure that the electronic display devices on which mammograms are viewed for interpretation provide optimal visualization of breast tissues. The mammography review workstation must meet the following minimum specifications (AAPM 2005, CAR MAP 2011, Van Ongeval 2010):
A monochrome monitor with a minimum spatial resolution of 3 megapixels should be used for technologist or other health care professional for mammography consultation.
It is important to ensure that display devices undergo acceptance testing and their ongoing performance is verified through routine and annual quality control testing. Detailed information on acceptance and quality control testing of display devices is available from the American Association of Physicists in Medicine (AAPM, 2005). The cleanliness of the display surface must be maintained. Manufacturer recommended cleaners and cleaning procedures must be followed. The performance of the display must be verified using test patterns designed for evaluating various characteristics of display performance. An overall assessment should be made daily prior to clinical use. A weekly visual evaluation must be performed by the technologists and a detailed annual evaluation must be performed by a medical physicist. Section C of this document provides a description of these quality control tests. Attention must be given to reading room viewing conditions when performing quality control tests of display monitors.
In digital imaging, a system must be in place to manage patient images so that secure storage and timely retrieval of images is possible. A Picture Archiving and Communications System (PACS) is one such system which is widely used in radiology. A PACS in an imaging facility connects digital image acquisition devices with systems which can store, retrieve and display digital images within and outside the facility. The transition to PACS requires a significant amount of planning, time and resources. Once established, a PACS offers a number of advantages such as improved productivity, widespread, simultaneous access to images and image manipulation. However, attention must be given to ensure that the quality of patient images is maintained and that patient information is not lost or unintentionally altered. Such situations can lead to repeat radiological examinations and misdiagnoses of patients.
When deciding whether to implement a PACS, a number of key issues should be addressed. A PACS is a very high capital investment. It requires resources for hardware, software and additional staff such as a PACS administrator and any consultants which may be necessary. Early in the planning stages of a PACS, parties should be consulted from all areas which will be affected by the changes. This should include departmental administrators, PACS specialists, medical physicists, radiologists, technologists, referring physicians and any existing information technology (IT) staff. The information obtained during the consultation should be used to perform an intensive cost/benefit analysis prior to making a decision. Early consulting with all involved parties will facilitate the clinical acceptance of the system. When deciding upon the specifications of a PACS the following key components should be considered.
Integrating the Healthcare Enterprise is an initiative whose goal is to make all necessary information about any given patient readily available to a care provider in order to ensure optimal medical care to the patient. IHE defines Integration Profiles that use established information technology (IT) standards to integrate systems from multiple vendors for effective interoperability and efficient workflow in day-to-day work scenarios of health professionals (users), using information from patients' records. (IHE 2007)
An IHE Integration Profile describes precisely how to solve given real-world clinical problems through functional system components, called IHE Actors. These are based on standards such as Digital Imaging and Communication in Medicine (DICOM) and Health Level 7 (HL7). Integration Profiles do not create standards; rather they clearly, carefully define how "Actors", or component devices, use established standards unambiguously in order to be interoperable and work together (e.g. how to acquire and display a digital mammography image).
IHE Mammography Image Profile (MAMMO)
The IHE Mammography Image Profile as applied to the digital mammography modality ensures that the acquired digital mammography images contain all relevant information that is necessary for further image processing, application of computer assisted detection (CAD), storage, review and printing. This profile is absolutely necessary for generating correct digital mammography image content to ensure optimal presentation of images at a mammography review workstation.
Mammography facilities should request support for the MAMMO profile by the digital mammography modality. This will provide the following benefits to the healthcare enterprise:
The IHE Mammography Image Profile as applied to the mammography diagnostic review workstation assures the correct display of digital mammography images from any digital mammography modality claiming conformance to the same profile. This profile is absolutely necessary to allow the display of digital mammography images from different vendors in a similar way as it was previously done with analog mammography.
The IHE Mammography Image Profile ensures proper image orientation, justification, contrast display and image sizing. This profile dictates provisions leading to the accurate display of CAD mark and the display of all relevant technical and identification information on image base. The profile also requires that the displays used for image interpretation are correctly calibrated for optimal image review.
The IHE Mammography Image Profile requires that a mammography diagnostic review workstation be able to display mammography images in several standard ways: fit to viewport, true size, same size and view actual pixels. The fit to viewport display is intended to allow up to eight images to be displayed simultaneously on the display pair, primarily for temporal comparison. True size display is useful for percutaneous biopsy, surgical planning or size comparison to prior films. Same size display allows easy comparison of digital mammography images acquired at different resolutions or using different detector sizes. View actual pixels display allows for display of all captured data or "full resolution," which is especially useful when evaluating micro-calcifications or subtle masses.
The IHE Mammography Image Profile, however, does not define hanging protocols or how images of different matrices should be sized relative to each other.
Mammography facilities should request support for the MAMMO profile by the mammography diagnostic review workstation. This will provide the following benefits to the healthcare enterprise:
IHE Portable Data for Imaging (PDI) Integration Profile (IHE 2009)
The IHE Portable Data for Imaging (PDI) Profile enables creating DICOM-compliant image CDs on the modality. Requesting support for the PDI profile by the digital mammography modality will provide the following benefits to your organization:
Computer-aided detection (CADe) and computer-aided diagnosis (CADx) are image analysis methods used to assist radiologists when interpreting mammographic images. CADe techniques involve the use of computer algorithms to locate (using distinctive signs such as a triangle, a circle, a square or others) and identify suspicious regions of an image with the ultimate goal of increasing cancer detection. CADx techniques involve the use of computer algorithms to indicate the likelihood that a known lesion is malignant.
The use of computer aided detection and diagnosis systems must be carefully managed in order to assess the resulting effects on the overall quality of the mammography program. Various approaches can be used to asses CADe and CADx systems (Bick 2010). Quality determinants such as specificity, sensitivity, positive predictive value, and overall accuracy should be included in the assessment of computed aided systems for detection and diagnosis.
Telemammography is the electronic transmission of mammographic images from one location to another for the purposes of interpretation and/or consultation. Through telemammography, digital images and patient information can be accessed electronically from multiple sites simultaneously. The benefits of telemammography include more efficient delivery of patient care and the ability to provide radiological services to facilities in remote areas which do not have radiologists available on-site. Since telemammography involves the acquisition and interpretation of patient images at different sites, it is important that policies and procedures be in place at all locations to ensure image quality is optimized and comparable among all facilities accessing patient images. This is especially important when official authenticated written interpretations are made through telemammography. All workstations used for interpretation of telemammography images must be included in the quality assurance program of the facility to ensure performance meets minimum requirements for mammography workstations. All telemammography workstations must meet the same level of performance and undergo the same quality control testing as those of the facility where images are acquired. The relevant workstation quality control tests set out in Section C must be performed at the required frequencies. The information in this section is based on the CAR Standards for Teleradiology (CAR 2008).
The use of telemammography must be documented. Periodic reviews must be made for the appropriateness, problems and quality of the transmitted data. The data must be collected in a manner which complies with the statutory and regulatory requirements.
Increasing amounts of data are generated by digital mammography equipment. The costs associated with storage and transmission of this data has resulted in significant interest in compression methods of digital images. There are two types of compression: reversible (also called lossless) compression and irreversible (also called lossy) compression. Using lossless compression, images may be compressed and decompressed and there is no alteration of the original image data. Using lossy compression, decompressed images are modified and pixel values may be different from their original values.
Until scientific studies provide evidence that lossy compression does not compromise accurate diagnosis of patients, there must be no lossy compression of digital mammography images.
Consideration must be given to test equipment necessary for ensuring the performance of mammographic equipment and their accessories as well as for ensuring the radiation safety of the facility.
A radiation protection survey is an evaluation, conducted by the regulatory authority, of the radiation safety of a mammography facility. The survey is intended to ensure compliance with the requirements of this Safety Code, to demonstrate that x-ray and auxiliary equipment function properly and according to applicable standards, and that the equipment is installed and used in a way which provides maximum radiation safety for operators, patients and others. It is important to note that radiation protection surveys described in this section are primarily for the instruction and guidance of persons employed in Federal Public Service departments and agencies, as well as those under the jurisdiction of the Canada Labour Code. Facilities under provincial or territorial jurisdiction may be subject to requirements under their statutes. The authorities listed in Appendix I should be contacted for details of the regulatory requirements of individual provinces and territories.
During the investigation, the regulatory authority may request reports of quality control performed by the physicist or by the technologist, safety measures such as protective equipment and shielding are also examined to ensure that they are present and provide the required protection. It is important, therefore, that x-ray facilities are surveyed at regular intervals.
Routine operation of any new installation or an installation which has undergone modifications should be deferred until a complete survey has been made by an expert. The expert is an individual who is qualified by education and experience to perform advanced or complex procedures in radiation protection that generally are beyond the capabilities of most personnel within the facility. These procedures include evaluation of the facility design to ensure adequate shielding is in place, inspection and evaluation of the performance of x-ray equipment and accessories, and evaluation and recommendation of radiation protection programs. The owner of the facility (or another delegated staff member such as the Radiation Protection/Safety Officer) must contact the appropriate regulatory agency to ascertain inspection and acceptance testing procedures in that jurisdiction. Some jurisdictions may require that the facility be declared in compliance with applicable governmental regulations prior to operations.
For a new facility, it is particularly advantageous to make visual inspections during construction, to ensure compliance with specifications and to identify faulty material or workmanship, since deficiencies can be remedied more economically at this stage than later.
For existing installations, a survey must be carried out after any changes are made which might produce a radiation hazard. This includes alteration of protective barriers, equipment modification and replacement, changes in operating procedures, or increased workloads.
Finally, radiation protection surveys must be carried out at regularly scheduled intervals during routine operations to detect problems due to equipment failure or any long-term trends toward a decrease in the level of radiation safety. Facilities should contact the applicable regulatory authority to establish the survey schedule.
The results of such surveys, including conclusions drawn by the expert, must be submitted to the owner or responsible user in a written report. The written report should be available, 30 days after testing.
All such reports must be retained by the owner or responsible user. For federal facilities, radiation survey reports should be maintained for 5 years and personnel dosimetry records for the lifetime of the facility.
The survey report must present, in a clear systematic way, details and results of the measurements carried out, as well as the conclusions drawn and recommendations made by the surveyor. Any unusual findings about the equipment itself, the facility or operating procedures, which could affect the safety of operators or other persons in the vicinity of the x-ray facility, must be clearly identified.
The survey report must include the following:
When x-ray equipment is considered for disposal, an assessment should be made as to whether the equipment can be refurbished and/or recycled. Communication with the manufacturer or supplier of the equipment should be made as to whether the equipment or components of the equipment can be recycled or returned. It must be noted that if the equipment contains any patient information, this information must be adequately removed. Once the decision has been made to dispose of x-ray equipment, an assessment must be made to determine if any equipment components contain hazardous materials. To ensure equipment is not unsafely operated after disposal, it should be made inoperable before disposing. The cables that power the equipment and other electrical connections should be disconnected and removed. It is recommended that mammography facilities, under provincial or territorial jurisdiction contact the responsible agency in their respective province or territory for further information. A listing of these responsible agencies is provided in Appendix I.
All mammography facilities must develop and maintain an effective quality assurance program. In mammography, a quality assurance program is defined as the planned and organized actions necessary to provide adequate confidence that mammography equipment and related components reliably produce quality mammograms with minimum dose to patients and staff. A quality assurance program must include quality control procedures for the monitoring and testing of mammographic equipment and related components, and administrative procedures to ensure that monitoring, evaluation and corrective actions are properly performed. The owner of an x-ray facility has the responsibility of establishing a quality assurance program that examines all practices of the facility which affect:
The ultimate goal of a quality assurance program is to ensure accurate and timely diagnosis and treatment at the minimum dose to the patient and staff. In order to have a successful quality assurance program it is essential that equipment is in proper working condition and all staff members understand the goals of the program and are committed to the implementation of the program through full participation.
Information obtained from mammography equipment must be of utmost quality to ensure accurate diagnosis and treatment. If critical elements are missing or artefacts are added to images, the image is considered to be of poor quality. The consequence of a poor quality mammogram may be incorrect diagnosis resulting in repeat mammography, unnecessary radiation doses to the patient, delayed or improper patient treatment and increased cost.
The initial implementation and the general operation of a quality assurance program will involve cost in both money and time from staff. However, savings from the operation of the program will offset some of these costs. For some facilities, there may be a reduction in the overall operating costs.
Some of the costs associated to the quality assurance program are as follow:
In addition to improved diagnostic quality some of the savings associated with the quality assurance program are as follow:
The implementation of a quality assurance program need not be complicated. It consists of establishing quality control procedures for the equipment along with an administrative methodology to ensure that monitoring, evaluation and corrective actions are properly performed.
One useful step is to develop a series of policies and guidelines where various issues are addressed. The following list presents some of these policies and guidelines. Each facility may require different sets of policies and guidelines depending on the type of work being performed and the organizational structure of the facility. These policies should be established by management with participation from staff. It is recommended that all safety policies, procedures and processes be reviewed by a joint health and safety committee. The policies should be present in the quality assurance (QA) manual. The following information should be readily available to radiology staff:
The following four steps must be included for the establishment of quality control procedures:
The following administrative procedures must be included in the establishment of an effective quality assurance program.
Accreditation is a formal process through which a mammography facility can demonstrate that the quality of mammography performed in their facility meets accepted standards. Accreditation requires both self-evaluation by the mammography facilities and external evaluation by a reviewing body. It involves an assessment of personnel qualifications, policies and procedures, equipment design and performance, and the facility's quality assurance program including quality control testing. Through accreditation, a mammography facility can provide additional reassurance in their commitment to quality of care.
In Canada, mammography accreditation programs have been established by provincial organizations and nationally by the Canadian Association of Radiologists. It is strongly recommended that all Canadian mammography facilities are accredited by a recognized standard such as that of the Canadian Association of Radiologists or its equivalent.
Acceptance testing is a process to verify compliance with the performance specifications of the x-ray equipment as written in the purchase contract and that the equipment performance complies with federal and provincial or territorial regulations. Acceptance testing must be performed prior to any clinical use of the equipment. Acceptance testing must be performed by or under the supervision of, a medical physicist, with in-depth knowledge of the particular type of mammography equipment and the relevant regulations prior to any clinical use of the equipment. The owner must have acceptance testing performed by an individual or organization independent of the manufacturer.
Acceptance testing of a medical x-ray system includes several major steps: They are:
The results from the acceptance testing should be used to set baseline values and acceptance limits on operational performance of the mammography equipment. These baseline values and limits are essential to the quality assurance program.
Acceptance testing for mammography equipment should evaluate at least the items in Table 5. Not all equipment will be subject to the full set of tests. The type of equipment and its configuration will dictate the sets of tests to be performed.
|Item Under Evaluation for Acceptance Testing||FS||CR||DR|
|1.1 Initial Inspection and Inventory||X||X||X|
|1.2 Inspection of Documentation||X||X||X|
|2.0 Visual and Functional Tests|
|2.1 Mechanical Properties||X||X||X|
|2.2 Safety Systems||X||X||X|
|3.0. Performance Evaluation - X-ray Generator and Control|
|3.1 Focal Spot Size||X||X||X|
|3.2 Source-to-image distance||X||X||X|
|3.3 X-ray Tube Voltage||X||X||X|
|3.4 Current Time Product||X||X||X|
|3.5 Loading Time||X||X||X|
|3.6 Beam Limitation and Indication||X||X||X|
|3.7 X-ray Beam Filtration||X||X||X|
|3.8 Automatic Exposure Control||X||X||X|
|3.9 Radiation Output||X||X||X|
|3.10 Radiation Leakage||X||X||X|
|4.0 Performance Evaluation - Compression|
|4.1 Compression force||X||X||X|
|4.2 Compression force indicator accuracy||X||X||X|
|5.0 Performance Evaluation - Image Acquisition|
|5.1 Response Function||X||X|
|5.3 Missed Tissue at Chest Wall||X||X|
|5.5 Defective Detector Element||X|
|5.6 Uncorrected Defective Detector Elements||X|
|5.7 Inter-Plate Sensitivity||X|
|5.8 Influence of Other Radiation Sources||X|
|5.9 Fading of Latent Image||X|
|5.10 Inter-cassette variation||X|
|5.11 Film/Screen Contact||X|
|5.12 IHE mammography image profile compliance (Acquisition Modality Actor)||X||X|
|6.0 Performance Evaluation - Film Processing|
|6.1 Processor Temperature||X|
|6.2 Processing Time||X|
|6.5 Darkroom Light||X|
|7.0 Performance Evaluation - Image Quality|
|7.1 Contrast Detectability||X||X||X|
|7.2 Spatial Resolution (Modulation Transfer Function (MTF) and Noise Power Spectrum (NPS) for digital systems)||X||X||X|
|7.3 Irradiation Time||X||X||X|
|7.4 Geometric Distortion and Artefacts||X||X||X|
|7.5 Digital Detector Residual Image (Ghost Image)||X||X|
|8.0 Performance Evaluation - Dosimetry|
|8.1 Mean Glandular Dose||X||X||X|
|9.0 Image Presentation - Review Workstations|
|9.1 Ambient light||X||X|
|9.2 Contrast Visibility||X||X|
|9.4 Display Artefacts||X||X|
|9.5 Luminance Range||X||X|
|9.6 Greyscale Display Function||X||X|
|9.7 Luminance Uniformity||X||X|
|9.8 IHE mammography image profile compliance (Image Display Actor)||X||X|
|10.0 Image Presentation - Viewboxes|
|10.1 Ambient Light||X||X||X|
|10.3 Light Output Uniformity||X||X||X|
|10.4 Light Output Homogeneity (between viewboxes)||X||X||X|
|11.0 Image Presentation - Printers|
|11.1 Geometric Distortion||X||X|
|11.2 Contrast Visibility||X||X|
|11.4 Printer Artefacts||X||X|
|11.5 Greyscale Display Function||X||X|
|11.6 Optical Density Uniformity||X||X|
|12.0 Image Presentation - Film Digitizers|
|12.1 Overall image quality||X|
|12.4 Optical Density||X|
Quality Control testing must be carried out during routine operation of a mammography facility. This section sets out the required and recommended quality control tests, the associated test equipment, and the testing frequencies.
Quality control testing of a mammography system includes several major steps. They are:
Quality control tests performed daily to semi-annually are carried out by the mammography radiological technologists. Test equipment required for these tests must be readily available to the individuals responsible for performing those tests. All test equipment must be calibrated and verified to be operating accurately. Individuals performing quality control tests must be trained in the proper operation of the test equipment and in performing the tests. Annual quality control tests must be performed by a qualified medical physicist.
In the following sections, the descriptions of each test indicate whether performance of the test is required or recommended. In addition, not all equipment will be subject to the full set of tests listed in the following sections. The type of imaging system, whether film-based, CR, or DR, to which the quality control tests apply, is identified. The quality control tests and testing procedures provided in this section are based upon existing mammography standards, for film/screen and digital mammography equipment, established by international, national and provincial organizations (IAEA 2009)(IAEA 2011)(CAR MAP 2011)(MSSS 2001)(MSSS 2006). Alternative tests can be performed in place of those specified if it can be shown that the test is capable of verifying the necessary parameter or performance. For some tests, manufacturers' recommended procedures and acceptance criteria are recognized. However, equivalent testing procedures, such as those recommended by a recognized mammography standard setting body may be acceptable. Harmonized testing protocols are desirable as this allows comparison of performance and standardized testing.
Daily quality control tests must be performed at the beginning of each day that mammography is conducted before commencing patient examinations and processing any patient images.
|Quality Control Procedures
|Daily Quality Control Tests|
|Cleanliness of Electronic Display Devices and
Assessment of Viewing Conditions
|Film Processor Function||D6|
|Image Quality Evaluation-Film/Screen Systems||D7|
|Imaging Quality Evaluation - Digital Systems||D8||D8|
|Overall Visual Assessment of Electronic Display Devices||D9||D9|
|Overall Visual Assessment of Printers||D10|
D1. Equipment Warm-up - The manufacturer's recommended warm up procedure must be followed. The warm up procedure must be repeated if the equipment is left idle for an extended period of time. It is important to note that all components of the imaging system which are routinely used must be warmed up, including computer display devices and printers.
D2. Meters Operation - Meters and visual and audible indicators should be checked for proper function.
D3. Equipment Conditions - X-ray equipment conditions should be visually inspected for loose or broken components and cleanliness. The x-ray source assembly should be checked for motion or vibration during operation. Visual inspection should also be conducted of all other components of the imaging system.
D4. Darkroom Cleanliness - In order to maintain the cleanliness of the darkroom, all working surfaces, tops of counters and the floor should be cleaned daily. Dust and debris can more easily be seen using a UV-B lamp.
D5. Cleanliness of Electronic Display Devices and Assessment of Viewing Conditions - A visual inspection for cleanliness should be made of all electronic display devices used for interpretation. Devices must be cleaned as necessary. An assessment must be made of the environment in which mammograms are read. The level of ambient light must be low and consistent, particularly when lightboxes and electronic displays are present in the same room. An assessment should also be made of the temperature, noise and room ergonomics to ensure consistency of the viewing conditions.
D6. Film Processor Function - 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.
D7. Image Quality Evaluation - Film/Screen systems. For film/screen systems an image quality evaluation must 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 artefacts, and a consistent current time product setting. The optical density of the film at the centre of an image of a phantom must 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. The optical density of the film at the centre of the phantom image must not change by more than ±0.20 from the established operating levels.
D8. Image Quality Evaluation - Digital Systems - An image quality evaluation must be performed of a flat field image. Using a uniform phantom representing average breast thickness, evaluate images for significant artefacts that could interfere with clinical interpretations. View the "for presentation" image on the acquisition workstation using appropriate window width and level. The images must have a uniform appearance with not significant artefacts. Note that for CR images it is important to monitor clinical images acquired throughout the day to ensure artefacts do not develop due to accumulation of dust.
D9. Overall Visual Assessment of Electronic Display Devices - The performance of electronic display devices used for the interpretation of mammograms must be assessed. The daily quality control tests recommended by the American Association of Physicists in Medicine (AAPM, 2005), including the TG18 test patterns, test procedures and acceptance criteria should be used. The display system must be warmed up prior to testing. Attention must be given to ensure ambient light levels are appropriate (less than 40 lux) and representative of conditions under which clinical images are viewed. A viewing distance of 30 cm is recommended. Displaying the image of a test pattern, an assessment must be made of the general image quality and for the presence of artefacts. The TG18-QC test patterns can be used for this test and should be displayed using the software routinely used to display clinical images.
D10. Overall Visual Assessment of Printers - The performance of printers must be verified whenever they are going to be used. Note that all printers used for printing of clinical images, whether on-site or in a remote facility, must perform this test. Print and inspect the TG18-QC test pattern and inspect for the following:
|1||Uniform phantom representing average breast thickness (ex. PMMA test object thickness 45 ± 0.5 mm)
(if needed for manufacturer's recommended warm up procedure)
|FS, DR, CR||D1, D7, D8|
(21 steps optical attenuator with densities ranging from approximately 0.00 to 4.80 in steps of 0.15)
Accuracy: ± 0.02 log exposure units
Reproducibility: ± 0.02 log exposure units
Accuracy: ± 0.02 O.D. at 1.0 O.D.
Reproducibility: ± 0.01 O.D. at 1.0 O.D.
|6||Test Pattern Image (TG18-QC)||DR, CR||D9, D10|
|Quality Control Procedures
|Weekly Quality Control Tests|
|Screen Cleanliness and Condition||W1|
|Cassette Cleanliness and Conditions||W2||W2|
|Visual Inspection of Cleanliness of Imaging Systems||W3||W3||W3|
|Darkroom Light Conditions||W4|
|Darkroom Temperature and Humidity Conditions||W5|
|Phantom Image for Film-screen Systems||W7|
|Digital Image Quality Evaluation||W8||W8|
|Electronic Display Device Performance||W9||W9||W9|
|Laser Film Printer Artefacts||W10||W10||W10|
W1. Screen Cleanliness and Condition - 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.
W2. Cassette Cleanliness and Conditions - Cassettes should be checked for cleanliness, wear, warping, fatigue of foam compression material, closure mechanism, and light leaks. The cassette holder tunnel should be checked for dust and dirt. Cleaning frequency and method should be in accordance to manufacturers' recommendations.
W3. Visual Inspection of Cleanliness of Imaging Systems - Imaging systems must be inspected for dust and dirt on or near the image reception area where they may negatively affect image quality. For CR systems, the imaging plates must be inspected. The imaging plate loading and unloading mechanism must be cleaned and lubricated if necessary. The image receptors for direct digital mammography systems must be kept clean of dust, dirt and other items which may come into contact with them. Laser scanning digitizers must also be checked for cleanliness.
W4. Darkroom Light Conditions - A visual test must be performed in the darkroom to ensure the room is light tight and that other sources of light such as illuminated light switches and computer power supplies do not cause film fogging. 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. The assessment of darkroom light conditions should be made after a 10 to 15 minute period of adaptation to the dark conditions with safelights turned off.
W5. Darkroom Temperature and Humidity Conditions - A verification of the darkroom temperature and humidity should be conducted. The temperature should be between 15°C and 23°C and the humidity between 40% and 60%.
W6. Viewbox Conditions - Viewboxes should be inspected visually for cleanliness, viewing area discoloration and improper illumination. Note that this test is also applicable in situations where images acquired from digital mammography systems are printed.
W7. Phantom Image for Film-Screen Systems - A phantom, with image quality evaluation objects, must be used to test the imaging performance of the mammography system. For the RMI-156 mammography phantom, a minimum of the four largest fibers, the three largest speck groups and the three largest masses must be visible.
W8. Digital Image Quality Evaluation - For CR and DR systems, an evaluation must be made of the digital image quality. Acquire an image of a uniform phantom representing average breast thickness and a contrast object (typically an acrylic disk of 2.5 cm diameter and 1 mm thick). The following criteria must be met:
W9. Electronic Display Device Performance - The performance of all electronic display devices used to view images from digital systems, as well as those obtained through scanning of radiographic films, must be checked. This includes display devices used for acquisition and interpretations of images. For this test, it is recommended that a modified TG18-QC test pattern be used which emulates the images produced by each model of digital mammography equipment in the facility, or which might be interpreted at that workstation (i.e., has the same x-y dimensions, number of bits, and a DICOM header containing appropriate values of all relevant tags). Note that when evaluating the display devices of the interpretation workstations, the viewing conditions must be verified. The following criteria must be met:
W10. Laser Film Printer Artefacts - For mammography facilities printing digital images, the quality of images obtained from the laser film printer must be checked for artefacts. Ensure that the viewbox used to assess printed films has sufficient luminance. Print an image of a uniform test pattern (i.e., TG18-UNL80 test pattern). The following criteria must be met:
(as recommended by manufacturer)
Accuracy: ± 0.3 °C Reproducibility: ± 0.1 °C
|4||RMI 156 Phantom, with image quality evaluation objects||FS||W7|
Accuracy: ± 0.02 O.D. at 1.0 O.D.
Reproducibility: ± 0.01 O.D. at 1.0 O.D.
|FS, CR, DR||W7, W10|
|7||Acrylic disk (4 mm thick)||FS||W7|
|8||Acrylic disk (ex. 2.5 cm in diameter and 1mm thick)||CR, DR||W8|
|9||Uniform phantom representing average breast thickness (ex. PMMA of thickness 45 ± 0.5 mm)||CR, DR||W8|
|10||Test Pattern(s) for evaluation of electronic display device performance and laser film printer (ex. TG18-QC, TG-18 UNL80)||CR, DR||W9, W10|
|11||Magnifying lens (4x to 5x magnification)||CR, DR||W9, W10|
|Quality Control Procedures
|Monthly Quality Control Tests|
|Mechanical, Electrical and Overall Safety Inspection||M1||M1||M1|
|Cassette, Screen and Imaging Plate Cleaning||M2||M2|
|Accuracy of Processor Temperature||M3|
|Extended Full Field Artefacts Evaluation||M5||M5|
|Laser Printer Sensitivity||M6||M6|
M1. Mechanical, Electrical and Overall Safety Inspection - A safety inspection must be performed of the following items:
M2. Cassette, Screen and Imaging Plate Cleaning - Cassettes, screens and imaging plates must be cleaned and inspected for damage. Manufacturer recommended cleaners and cleaning procedures should be used.
M3. Accuracy of Processor Temperature - 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.
M4. Replenishment Rate - 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.
M5. Extended Full Field Artefacts Evaluation - A flat field image quality evaluation must be performed using all applicable focal spots, filters, and magnification modes. Image a uniform phantom and evaluate for the presence of significant artefacts that could interfere with clinical interpretation. View the "for processing" image under appropriate window width and level settings. The images must have a uniform appearance with no significant artefacts.
M6. Laser Printer Sensitometry - An evaluation must be made of the consistency of the performance of the laser printer. Printing an image of a sensitometry strip, the following criteria must be met:
Note that this test must be performed monthly for dry processing laser printers. However, for wet processing laser printers, this test must be performed each day prior to clinical images.
Accuracy: ± 0.3 °C Reproducibility: ± 0.1 °C
(as recommended by manufacturer)
|4||Uniform phantom representing average breast thickness (ex. PMMA test object thickness 45 ± 0.5 mm)||CR, DR||M5|
|6||Printer sensitometry strip produced by printer or sent from acquisition workstation.||CR, DR||M6|
|Quality Control Procedures
|Quarterly Quality Control Tests|
|Fixer Retention Analysis||Q1|
|Spatial Resolution/Modulation Transfer Function (MTF) Evaluation of CR Equipment||Q3|
|Laser Printer Quality||Q4||Q4||Q4|
|Film Digitizer Performance||Q5|
Q1. Fixer Retention Analysis - Fixer retention tests must be performed to ensure fixer is adequately removed from processed films according to established baseline levels. The level of residual fixer must not exceed 0.05 g/m2.
Q2. Repeat Analysis - For both film/screen and digital mammography systems an analysis must be done of the repeat records to identify and correct any trends or errors. Repeat images are defined as images taken due to inadequate quality. This does not include images taken for quality control purposes, images taken to acquire additional views, or additional images taken to include tissue which could not be imaged due to breast size. Repeat records must be maintained and analysed individually for each mammography system. Facilities must maintain records for every repeat, the reason for the repeat along with any corrective actions, immediately after the repeat image is taken. If images contain some patient diagnostic information, they should be maintained in the patient file. The repeat rate must less than 5 percent and should be less than 2 percent.
Q3. Spatial Resolution/Modulation Transfer Function (MTF) Evaluation of CR Equipment - An evaluation must be made of the spatial resolution of CR mammography systems. Spatial resolution is the ability to resolve objects in a resultant image when the difference in the attenuation between the objects and the background is large compared to noise. Spatial resolution can be evaluated either by imaging an MTF test device and using appropriate software, following manufacturer's testing procedures or using an alternate method deemed acceptable by a qualified physicist. The MTF must be within the manufacturer's specifications and the established baseline levels. This test may also be performed on DR systems, however, spatial resolution is unlikely to vary significantly on a quarterly basis for these systems.
Q4. Laser Film Printer Quality - An evaluation must be made of the quality of printed images. For this test, it is recommended that a modified TG18-QC test pattern be used which emulates the images produced by each model of digital mammography in the facility, or which could be interpreted at this workstation(i.e., has the same x-y dimensions, number of bits, and a DICOM header containing appropriate values of all relevant tags). Annotate the modified TG18-QC test pattern with 5cm horizontal and vertical rulers. Note that images must be printed from both the acquisition and interpretation workstations. Examine the printed images on a viewbox. The following requirements must be met:
Q5. Film Digitizer Performance - An evaluation must be made of the film digitizer performance to ensure that image quality of digitized images is comparable to that of film. The resolution of the digitized images should correspond to the nominal resolution of the digitizer.
|1||Fixer Retention Test Kit||FS||Q1|
|2||MTF test device and software to calculate MTF||CR||Q3|
|3||Test Pattern(s) for evaluation of electronic display device performance and laser film printer (ex. TG18)||CR, DR||Q4, Q5|
|4||Magnifying lens (4X to 5X magnification)||FS,CR, DR||Q4|
|Quality Control Procedures
|Semi-Annual Quality Control Tests|
|Breast Compression Device||SA1||SA1||SA1|
|Safelight Test for Darkroom Fog||SA2|
|Interplate Sensitivity Variation of Imaging Plates||SA4|
SA1. Breast Compression Device - The compression device must be evaluated to verify the compression force, alignment of the compression plates, and the accuracy of the indicated breast thickness.
SA2. Safelight Test for Darkroom Fog - An image of a mammographic 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.
SA3. Screen/Film Contact - All cassettes used in mammography must be tested for screen/film contact using a 16 mesh/cm (40 mesh/in) copper screen. Cassettes with large areas greater than 5mm in diameter of poor contact that are not eliminated by screen cleaning and remain in the same location during subsequent tests must be replaced. Areas of poor contact greater than 2mm at the chest wall edge are not acceptable.
SA4. Interplate Sensitivity Variation of Imaging Plates - For CR equipment, an evaluation must be made of the variation of inter-plate sensitivity.
|1||Compression force test device (conventional analog scale)||FS, CR, DR||SA1|
|2||Bath towels or blocks of foam rubber (specific mass: about 30 mg/cm3)||FS, CR, DR||SA1|
|3||Tape measure||FS, CR, DR||SA1, SA3|
|4||PMMA slabs of uniform thickness||FS, CR, DR||SA1, SA4|
Accuracy: ± 0.02 O.D. at 1.0 O.D.
Reproducibility: ± 0.01 O.D. at 1.0 O.D.
|7||Film/Screen contact test tool for mammography (40 mesh)||FS||SA3|
|Quality Control Procedures
|Annual Quality Control Tests|
|Accuracy of Tube Voltage||A1||A1||A1|
|Reproducibility of Tube Voltage||A2||A2||A2|
|Radiation Output (Air Kerma) Reproducibility and Linearity||A3||A3||A3|
|Normalized Radiation Output||A4||A4||A4|
|X-ray Beam Filtration||A5||A5||A5|
|Light Field and x-ray Field Alignment||A7||A7||A7|
|Automatic Exposure Control (AEC)||A8||A8||A8|
|Image Receptor Performance||A9||A9||A9|
|Electronic Display Device Performance||A13||A13|
|General Preventative Maintenance||A16||A16||A16|
A1. Accuracy of Tube Voltage - At tube voltages commonly used clinically, the x-ray tube voltage must not deviate from the selected value by more than 5%.
A2. Reproducibility of Tube Voltage - At tube voltages commonly used clinically, the coefficient of variation of the kVp must be equal to or less than 0.02, based on 5 measurements at each tube voltage setting. Note however, that if the percentage difference between the first two measurements is not greater than 5%, only two measurements at each tube voltage setting is acceptable.
A3. Radiation Output (Air Kerma) Reproducibility and Linearity - The reproducibility and linearity of the air kerma must be evaluated using manual mode, a Mo/Mo target filter combination and x-ray tube voltage of 28kVp. Select 3 most commonly used mAs settings. The coefficient of variation of any five consecutive air kerma measurements must be no greater than 0.05. Note however, that if the percentage difference between the first two measurements is not greater than 5%, only two measurements at each mAs setting is acceptable. At each mAs setting, calculate the average air kerma value and the output (Y) by dividing each average air kerma value by the corresponding mAs value. For consecutive pairs of mAs settings, calculate the linearity as L=100(Y1-Y2)/(Y1+Y2). The linearity must be less than ±10%.
A4. Normalized Radiation Output - Using the values of output (Y) obtained in test A3, calculate the normalized output by applying an inverse square law correction to obtain the output at 1.0m. The normalized output at 28kVp with a Mo/Mo target filter combination must be greater than 30µGy/mAs.
A5. X-ray Beam Filtration - The first half-value layer must be determined for all commonly used clinical x-ray tube voltage settings and target/filter combinations. The first half-value layer of aluminium, measurement with the compression paddle in place, must be within the range defined by:
A6. Collimation - As assessment must be made of the collimation to ensure full exposure of the image receptor and alignment of the compression paddle with the chest wall edge of the image receptor. The x-ray field:
The alignment of the compression paddle must be such that the edge of the compression paddle:
A7. Light Field and X-ray Field Alignment - An assessment should be made of the alignment of the light field and the x-ray field. 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.
A8. Automatic Exposure Control (AEC) - The performance of the AEC must be evaluated.
A9. Image Receptor Performance - The performance of the image receptor must be verified against the manufacturer's specifications and the established baseline values.
A10. Image Quality - The quality of mammographic images must be verified against manufacturer's specifications and established baseline levels.
A11. Dosimetry - An assessment must be made of the entrance surface air kerma and the mean glandular dose.
A12. 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.
A13. Electronic Display Device Performance - The performance of all electronic display devices, whether part of the interpretation/review workstation or acquisition workstation must be verified. The annual quality control tests recommended by the American Association of Physicists in Medicine (AAPM, 2005) including the TG18 test patterns, test procedures and acceptance criteria should be used. For this test, it is recommended that modified test patterns be used which emulate the images produced by each model of digital mammography in the facility, or which could be interpreted at this workstation(i.e., have the same x-y dimensions, number of bits, and a DICOM header containing appropriate values of all relevant tags). The display system must be warmed up prior to testing. Attention must be given to ensure ambient light levels are appropriate (20 - 40 lux) and representative of conditions under which clinical images are viewed. A viewing distance of 30 cm is recommended.
A14. Printers - The performance of printers must be evaluated to ensure that the quality of printing is consistent and that the quality of printed images is comparable to that of images on the display monitor. For this test, it is recommended that modified test patterns be used which emulate the images produced by each model of digital mammography system in the facility, or which might be interpreted at that workstation (i.e., has the same x-y dimensions, number of bits, and a DICOM header containing appropriate values of all relevant tags).
A15. General Preventive Maintenance - Preventive maintenance of the x-ray equipment and accessories is necessary to prolong the life of the equipment. An annual inspection must be conducted for structural integrity, cleanliness, ease of movement of all components and any other procedures recommended by the manufacturers.
|1||Non-invasive x-ray tube voltage meter
Accuracy: ± 1.5 kV Reproducibility: ± 0.5 kV
|FS, CR, DR||A1, A2|
Accuracy: ± 5 % Reproducibility: ± 1 %
|FS, CR, DR||A3, A4, A5, A11|
|3||Aluminum filter (> 99.9 % purity)
Accuracy: 1 % thickness
|FS, CR, DR||A5|
|4||Metal plate to shield the detector from x-rays
(ex.: 1 mm steel, 5 mm Aluminium, > 0.1 mm lead)
|FS, CR, DR||A5|
|5||Ruler(s) or measuring tape||FS, CR, DR||A5, A6, A7|
|6||Two Radiographic Rules||CR, DR||A6|
|7||Phosphorescent screen material (approx. 20 mm x 50 mm)||CR, DR||A6|
|8||Contrast Objects (ex. metallic foil or markers, coins, PMMA disk)||FS, CR, DR||A6, A7, A8|
|9||Multiple sheets of uniform, tissue equivalent attenuator
(ex. a set of 10 mm thick PMMA plates covering the complete detector area capable of providing thicknesses of 20, 45 and 70 mm) or uniform phantom representing average breast thickness (ex. PMMA of thickness 45 ± 0.5 mm)
|FS, CR, DR||A6, A8, A9, A10, A11|
(ex: radioluscent U shaped rigid expanded polystyrene
|FS, CR, DR||A8, A11|
|11||Stopwatch||FS, CR, DR||A8, A10|
Accuracy: ± 0.02 O.D. at 1.0 O.D.
Reproducibility: ± 0.01 O.D. at 1.0 O.D
|FS||A8, A9, A10, A14|
|13||Phantom, with image quality evaluation objects (ex. RMI-156 )||FS||A9, A11|
|14||Magnifying lens (4x to 5x magnification)||FS, CR, DR||A9, A10, A14|
|15||ROI capability or QC software for image analysis||CR, DR||A9|
|16||Geometric Distortion Test Tool||CR||A9|
|17||Spatial Resolution test tool (ex. resolution test pattern up to 20 lp/mm)||FS, CR, DR||A10|
|18||MTF test device and software to calculate MTF||CR, DR||A10|
|19||Light meter (for measurement of luminance and Illuminance)
Accuracy: ± 10 % Reproducibility: ± 5 %
|FS, CR, DR||A12, A13|
|20||Test Pattern(s) for evaluation of electronic display device performance and laser film printer (ex. TG18 or SMPTE)||CR, DR||A13, A14|
|21||Transparent Ruler||CR, DR||A14|
Consumer and Clinical Radiation Protection Bureau
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Ontario (for issues related to patient and public safety)
Ontario Ministry of Health and Long-Term Care
X-ray Inspection Service
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Ministry of Labour
Radiation Protection Service
81A Resources Road
Direction générale de la santé publique
Ministère de la Santé et des Services sociaux
1075, Chemin Ste-Foy, 11e étage
Radiation Protection Services
Department of Health and Wellness
P.O. Box 5100, Carleton Place
Fredericton, New Brunswick
Occupational Health and Safety Division
Nova Scotia Department of Environment and Labour
P.O. Box 697
Halifax, Nova Scotia
Prince Edward Island
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Government of Prince Edward Island
P.O. Box 2000
Charlottetown, Prince Edward Island
Newfoundland and Labrador
Department of Labour
West Block, 4th floor, Confederation Bldg.
P.O. Box 8700
St. John, Newfoundland
Occupational Health and Safety
Government of the Northwest Territories
Yellowknife, Northwest Territories
Occupational Health and Safety
Yukon Workers' Compensation Health and Safety Board
401 Strickland Street
Whitehorse, Yukon Territory
For the purpose of this Safety Code, individuals may be classified in one of two categories: (1) radiation workers, individuals who are occupationally exposed to x-rays and (2) members of the public. The dose limits are given for both categories in Table AII.1. These dose limits are based on the latest recommendations of the International Commission on Radiological Protection (ICRP) as specified in ICRP Publication 103 (ICRP 2007).
Dose limits for radiation workers apply only to irradiation resulting directly from their occupation and do not include radiation exposure from other sources, such as medical diagnosis and background radiation.
|Applicable Body Organ or Tissue||Radiation Workers||Members of the Public|
based on ICRP Statement on Tissue Reactions (ICRP 2011)
|Whole Body||20 mSv effective dose per year averaged average over a defined 5 year period and 50mSv in any single year.||1mSv effective dose|
|Lens of the eye||20 mSv equivalent dose per year averaged over a defined 5 year period and 50mSv in any single year.||15 mSv|
|Skin||500 mSv equivalent dose||50 mSv equivalent dose|
|Hands and Feet||500 mSv equivalent dose||-|
Method 1: Mean glandular dose calculation for breasts represented by PMMA thicknesses of 20, 45 and 70 mm.
The mean glandular dose, MGD which is the absorbed dose to the glandular tissues within the breast can be determined using the following formula:
MGD = Ki,t × gt × ct × s
Ki,t is the entrance air kerma (without backscatter) at the upper surface of the PMMA simulating a standard breast of thickness t mm
gt is the air kerma to MGD conversion factor for a breast having 50% fibroglandular tissue and 50% fat composition with a thickness of t mm (provided in Table AIII.1)
ct is the conversion factor for any difference in the breast composition from 50% glandularity of a standard breast with a thickness of t mm (provided in Table AIII.2)
s is the correction factor for the use of target/filter combinations other than Mo/Mo (provided in Tables AIII.3 and AIII.4)
Note that the factors gt and ct depend on the HVL of the x-ray beam measured with the compression paddle in the beam. The measured valued HVL value of the mammography system must be used. Typical measured HVL values for different tube voltage and target/filter combinations are shown in Table AIII.5.
|PMMA thickness (mm)||Equivalent breast thickness (mm)||g-factors (mGy/mGy)
HVL (mm Al)
|PMMA thickness (mm)||Equivalent breast thickness (mm)||Glandularity of equivalent breast||c-factors
HVL (mm Al)
|Target Filter Combination||Filter thickness (µm)||S Factor|
|PMMA thickness (mm)||Equivalent breast thickness (mm)||S factor|
|HVL (mm Al) for target filter combination|
Some compression paddles are made of Lexan, the HVL values with this type of compression plate are 0.01 mm Al lower compared with the values in the table.
|kV||Mo + 30 μm Mo||Mo +25 μm Rh||Rh +25 μm Rh||W +50 μm Rh||W +0.45 μm Al|
|25||0.33 ± .02||0.40 ± .02||0.38 ± .02||0.52 ± .03||0.31 ± .03|
|28||0.36 ± .02||0.42 ± .02||0.43 ± .02||0.54 ± .03||0.37 ± .03|
|31||0.39 ± .02||0.44 ± .02||0.48 ± .02||0.56 ± .03||0.42 ± .03|
|34||0.47 ± .02||0.59 ± .03||0.47 ± .03|
|37||0.50 ± .02||0.51 ± .03|
Method 2: Mean glandular dose calculation for breasts composed of 50% fibroglandular tissue and 50% adipose tissue representedby a 4.2 cm phantom.
The mean glandular dose (in millirad) is determined by multiplying the entrance exposure in air (in roentgens) by a conversion factor which is dependent upon the x-ray tube voltage (kVp) and the half-value layer for a given target filter combinations, using the following formula:
MGD = K × CF
K is the entrance exposure in air in roentgens
CF is the conversion factor in millirads per roentgen (provided in Tables AIII.6, AIII.7 and AIII.8)
|X-Ray Tube Voltage (kVp)||W/Al Target-Filter Combination|
W/Al conversion factors have been adjusted to the data from (Stanton 1984).
|X-Ray Tube Voltage (kVp)|
|X-Ray Tube Voltage (kVp)|
The following table provides the thicknesses of lead required to reduce the radiation level to film and loaded cassettes to 1.75 µGy (0.2 mR) for a weekly workload of 1000 mA-min at 35 kilovolts peak.
|Distance from x-ray tube to stored films|
|1 m||2 m||3 m||4 m||5 m|
|1 day||0.4 mm||0.3 mm||0.2 mm||0.2 mm||0.1 mm|
|1 week||0.5 mm||0.4 mm||0.4 mm||0.3 mm||0.3 mm|
|1 month||0.6 mm||0.5 mm||0.4 mm||0.4 mm||0.4 mm|
|1 year||0.7 mm||0.6 mm||0.6 mm||0.6 mm||0.5 mm|
It should be noted that CR cassettes loaded with an imaging plate typically have a faster rate of use than loaded film cassettes and therefore are stored for shorter periods of time (NCRP 147). For storage of loaded CR cassettes, the manufacturers' specified shielding levels must be followed.
Following the lead of the International Electrotechnical Commission, the air kerma (in Gray, Gy) replaces the exposure (in Roentgen, R) as the measure of exposure. The relationship between the two units is as follows:
The Gray (Gy) replaces the rad (rad) as the unit of absorbed dose. The relationship between the two units is as follows:
The Sievert (Sv) replaces the rem (rem) as the unit of equivalent dose. The relationship between the two units is as follows:
Note: m = milli = 10-3; µ = micro = 10-6
the mean energy deposited by ionizing radiation to a volume of matter divided by the mass of that volume. The unit of measurement is the gray (Gy)
the energy deposited per unit mass in air. The unit used to measure air kerma is the gray (Gy). For x-rays with energies less than 300 kilo-electron volts (keV) the magnitude of air kerma and absorbed dose in air are equivalent.
any structure or pattern visible in the image that is not part of the object being imaged
reduction of a radiation quantity upon passage of the radiation through matter resulting from all types of interactions with this matter
"automatic exposure control"
in an x-ray equipment, mode of operation in which one or more loading factors are controlled automatically in order to obtain, at a pre-selected location, a desired quantity of radiation
"beam limiting device"
device to limit the radiation field
a light-tight case for holding intensifying screens and film or a CR plate
"coefficient of variation"
the ratio of the estimated standard deviation to the mean value of a series of measurements, calculated by using the following equation:
Xi = the value of the ith measurement
= the mean value of the n measurements
S = standard deviation
n = number of measurements
C = the coefficient of variation
part of equipment for the purpose of controlling all, or some, of the functions of the
equipment. The control panel may contain devices for indicating and displaying operating
an instrument for measuring the optical density or degree of blackening of film
measure of dose designed to reflect the amount of radiation detriment. The effective dose is obtained by multiplying the equivalent dose of each tissue or organ by an appropriate tissue weighting factor and summing the products. The unit of measurement is the sievert (Sv).
measure of the dose to a tissue or organ designed to reflect the amount of harm caused to the tissue or organ. The equivalent dose is obtained by multiplying the absorbed dose by a radiation weighting factor to allow for the biological effectiveness of the various types of radiation in causing harm to tissue. The unit of measurement is the sievert (Sv)
material or device which modifies the characteristics of the radiation beam as the beam passes through it
the unwanted signal added to an image by the exposure of the image receptor to light, radiation or heat
between patient exposures
"half-value layer" or "HVL"
thickness of a specified material, which attenuates, under narrow beam conditions, x-rays with a particular spectrum to an extent such that the air kerma rate, exposure rate or absorbed dose rate is reduced to one half of the value that is measured without the material.
device, intended to convert x-ray patterns into another form, from which a visible image is obtained either directly or indirectly. The x-ray pattern is the information contained in an x-ray beam in which the distribution of intensity has been modulated by the object passed.
ionizing radiation which has passed through the protective shielding of a radiation source as well as that which, for some types of x-ray generators, has passed through the radiation aperture before and after loading.
the area illuminated by light in the plane of the image receptor simulating the radiation field
factor influencing by its value the x-ray tube load, for example x-ray tube current, loading time, continuous anode input power, x-ray tube voltage and percentage
"mean glandular dose"
mean absorbed dose in the glandular tissue (excluding skin) in a uniformly compressed breast of known tissue composition, using a specified calculation method
a device that simulates some aspect of human anatomy
polymethyl methacrylate, also known by the generic name acrylic and the trade names Plexiglas,
Acrylate, Lucite and Perspex
device permitting the exposure of film in a reproducible manner to different levels of light.
"x-ray tube assembly"
the x-ray tube housing with an x-ray tube installed
area on a surface intersected by an x-ray beam within which the radiation intensity exceeds a specific or specified level
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CAR (2008) Canadian Association of Radiologists, CAR Standards for Teleradiology
CAR (2011). CAR Position Statement on the Use of Thyroid Shields. http://www.car.ca/uploads/about/201106_ps_car_thyroid_shield.pdf
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Radiation Emitting Devices Act, R. S., C.34.
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Definitions from various sources (IEC 2008), (MSSS 2001), (IAEA 2011).