2008 ISBN: 978-1-100-10289-4 Cat. No.: H128-1/08-545E Show
HC Pub.: 4000 Table of ContentsExplanatory Notes
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.
This Safety Code has been prepared to provide specific guidance to large medical radiological facilities where diagnostic and interventional radiological procedures are routinely performed using radiographic, radioscopic or computed tomography equipment. Large facilities generally operate more than one type of radiological equipment, or have several suites of the same type of equipment. Most hospitals and computed tomography facilities fall within this category.
The requirements and recommendations of this safety code do not apply to radiation therapy facilities and the equipment used in radiotherapy, including radiation therapy simulators, for localization and treatment planning.
This Safety Code replaces Safety Code 20A and Safety Code 31.
The information in this Safety Code is intended for owners of healthcare equipment, physicians, technologists, medical physicists and other personnel concerned with equipment performance, image quality and the radiation safety of the facility.
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 specified under their statutes. The authorities listed in Appendix V 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.
This Safety Code does not address radiation protection for dental and mammography facilities or small radiological facilities such as chiropractic, podiatry, physical therapy and bone densitometry facilities. For these facilities refer to Health Canada publications "Safety Code 30, Radiation Protection in Dentistry", "Safety Code 33, Radiation Protection in Mammography," and the Safety Code for Small Medical Radiological Facilities.
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. Acknowledgements
This document reflects the work of many individuals. It was prepared and compiled by Mr. Christian Lavoie and Ms. Narine Martel of the Medical X-ray and Mammography Division, Consumer and Clinical Radiation Protection Bureau. Appreciation is expressed to Mr. Yani Picard and other members of the Medical X-ray and Mammography Division for their assistance and advice during the preparation of this code.
The contributions of the following organizations, agencies and associations whose comments and suggestions helped in the preparation of this code are gratefully acknowledged:
Introduction
Diagnostic and interventional radiology, are an essential part of present day medical practice. Advances in X-ray imaging technology, together with developments in digital technology have had a significant impact on the practice of radiology. This includes improvements in image quality, reductions in dose and a broader range of available applications resulting in better patient diagnosis and treatment. However, the basic principles of X-ray image formation and the risks associated with X-ray exposures remain unchanged. X-rays have the potential for damaging healthy cells and tissues, and therefore all medical procedures employing X-ray equipment must be carefully managed. In all facilities and for all equipment types, procedures must be in place in order to ensure that exposures to patients, staff and the public are kept as low as reasonably achievable.
Diagnostic X-rays account for the major portion of man-made radiation exposure to the general population. Although individual doses associated with conventional radiography are usually small, examinations involving computed tomography and radioscopy can be significantly higher. However, with well-designed, installed and maintained X-ray equipment, and through use of proper procedures by trained operators, unnecessary exposure to patients can be reduced significantly, with no decrease in the value of medical information derived. To the extent that patient exposure is reduced, there is, in general, a decrease in the exposure to the equipment operators and other health care personnel.
The need for radiation protection exists because exposure to ionizing radiation can result in deleterious effects that manifest themselves not only in the exposed individuals but in their descendants as well. These effects are called somatic and genetic effects, respectively. Somatic effects are characterized by observable changes occurring in the body organs of the exposed individual. These changes may appear within a time frame of a few hours to many years, depending on the amount and duration of exposure to the individual. Genetic effects are an equal cause for concern at the lower doses used in diagnostic radiology. Although the radiation dose may be small and appear to cause no observable damage, the probability of chromosomal damage in the germ cells, with the consequence of mutations giving rise to genetic defects, can make such doses significant for large populations.
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 radiology, 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, including clinical examination, 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 medical imaging service. Principal Objectives of the Safety Code
This Safety Code is concerned with the protection of all individuals who may be exposed to radiation emitted by X-ray equipment used in a large radiological facility. The aim of this Safety Code is to provide radiological facilities with the necessary information to achieve the following principal objectives:
To assist personnel in achieving these objectives, this Safety Code:
This Safety Code is composed of three sections:
This section sets out the responsibilities of the owner, responsible user, operators and other staff for the safe installation, operation and control of the equipment, and sets out practices to minimize radiation doses to patients, staff and the public.
This section sets out requirements for the facility design and minimum equipment construction and performance standards.
This section sets out requirements for quality assurance programs including acceptance testing and quality control procedures. Section A: Responsibilities and Protection1.0 Responsibility of Personnel
Although staff responsibilities described below 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. 1.1 Owner
The owner is ultimately responsible for the radiation safety of the facility. 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 described below. 1.2 Responsible User
The main role of the responsible user is to monitor and manage the radiation safety program of the facility including personnel requirements, equipment performance and safety procedures and to communicate program information with the appropriate staff. There must be at least one person designated as the responsible user. If the responsible user also performs patient examinations, then all of the requirements listed in section A1.3 for the X-ray equipment operator must also be met. The responsible user must:
1.3 X-ray Equipment Operator
All X-ray equipment operators have the responsibility of carrying out prescribed radiological procedures in a manner which does not cause any unnecessary exposures to patients, themselves and other workers in the facility. Depending on the type of radiological procedure, the equipment may be operated by a physician, a physician/practitioner or a radiation technologist.
1.4 Medical Physicist/Radiation Safety Officer
There must be a Medical Physicist or Radiation Safety Officer to act as an advisor on all radiation protection aspects during the initial stages of construction of the facility, installation of the equipment, and during subsequent operations. Medical physicists are health care professionals with specialized training in the medical applications of physics. A radiation safety officer is the title commonly assigned to a radiation safety specialist who routinely manages a facilities radiation protection program.
The medical physicist /radiation safety officer must:
1.5 Referring Physician/Practitioner
The referring physician/practitioner is the individual authorised to prescribe diagnostic or interventional X-ray procedures. The main responsibility of the referring physician/practitioner is to ensure that the use of X-rays is justified. In some jurisdictions, a registered nurse or nurse practitioner may be authorised by legislation to order X-ray examination. In such cases, the responsibilities of the referring physician/ practitioner listed below would apply to those individuals. It is recommended to contact the appropriate provincial or territorial radiation safety agencies, listed in Appendix V, for information on any applicable provincial or territorial statutes or regulations.
The referring physician/practitioner must:
1.6 Information Systems Specialist
Facilities performing digital image processing should have access to an individual who is trained and experienced in maintenance and quality control of information technology software and hardware such as those for PACS and teleradiology equipment. 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 used in the facility. In all situations, the information systems specialist must ensure confidentiality of patient records.
The information systems specialist should:
1.7 Repair and Maintenance Personnel
The repair and maintenance personnel are individuals authorised to perform hardware and software 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 required qualification of this individual will depend highly on the type of facility and the type of equipment used in the facility.
The repair and maintenance personnel should:
2.0 Procedures for Minimizing Radiation Exposure to Personnel
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, responsible users and equipment operators must make every reasonable effort to keep exposures to themselves and to other personnel as far below the limits specified in Appendix I as reasonably achievable. 2.1 General Requirements and Recommendations
2.2 Requirements and Recommendations for Operation of Mobile Equipment
2.3 Requirements and Recommendations for Operation of Radiographic Equipment
2.4 Requirements and Recommendations for Operation of Radioscopic Equipment
2.4.1 Requirements and Recommendations for Performing Angiography.
Angiography is potentially one of the greatest sources of exposure to personnel in radiology, since it requires the presence of a considerable number of personnel close to the patient, radioscopy for extended periods of time and multiple radiographic exposures. For such procedures, all personnel must be aware of the radiation hazards involved and make every effort to adhere to the following requirements and recommendations.
3.0 Procedures for Minimizing Radiation Exposure to Patients
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 physician/practitioner, radiologist, and technologist. They are intended to provide guidelines for elimination of unnecessary radiological examinations and for minimizing doses to patients when radiological examinations are necessary. 3.1 Guidelines for the Prescription of X-ray Examinations
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 2005Footnote 5). 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/practitioner 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 offering comparable diagnostic testing accuracy. 3.2 Guidelines for Radiological Examinations of Pregnant Women
Radiological examinations of the pelvic area of a woman known to be pregnant simultaneously irradiate the patient's gonads and the whole body of the foetus. Irradiation of the unborn foetus increases the infant's risk of somatic effects and also carries the risk of genetic effects in subsequent offspring. Therefore, every effort should be made to avoid unnecessary irradiation of any woman known to be, or who might be pregnant. Clearly, however, in spite of the possibility of radiation damage, if a radiological examination is required for the diagnosis or management of an urgent medical problem, it must be done, irrespective of whether the patient may or may not be pregnant.
The following recommendations apply to X-ray examinations involving pregnant or potentially pregnant women:
3.3 Guidelines for Carrying Out X-ray Examinations
Next to elimination of unnecessary X-ray examinations, the most significant factor in reducing patient exposure is ensuring that only necessary examinations are performed with good technique. It is possible, for example, to obtain a series of diagnostically-acceptable radiographs and have the patient exposures vary widely because of choice of technique and loading factors used. It is the responsibility of the operator and radiologist to be aware of this and to know how to carry out a prescribed examination with the lowest possible exposure to the patient.
The requirements and recommendations that follow are intended to provide guidance to the operator and radiologist in exercising their responsibility toward reduction of patient exposure. 3.3.1 General Requirements and Recommendations
3.3.2 Requirements and Recommendations for Radiographic Procedures
3.3.3 Requirements and Recommendations for Radioscopic Procedures
3.3.4 Requirements and Recommendations for Angiography
3.3.5 Requirements and Recommendations for Computed Tomography Procedures
3.4 Guidelines for Reduction of Dose to Sensitive Tissues
Ionizing radiation has the ability to produce gene mutations and chromosome aberrations in cells. These effects are especially important in two circumstances, exposures to reproductive cells, and rapidly dividing cells. When such effects occur in a reproductive cell(gametes and the stem cells they arise from), undesirable mutations may be transmitted to subsequent generations. If damage is caused in rapidly dividing cells mutations will rapidly be passed on to the cell progeny, amplifying the deleterious radiation effects.
Medical X-ray exposures are, at present, the major contributor of gonadal radiation exposure to the population. By reducing the gonadal dose to individual patients one can, in fact, make a significant contribution toward the reduction of the genetically significant dose to the population. It is generally presumed that there is no threshold dose below which genetic effects cannot occur. Therefore, it is important that even small radiation exposures to the sensitive tissues of patients be avoided, unless such exposures can be shown to be medically necessary.
Individuals performing X-ray examinations of patients must pay special attention to the following factors that are important for reducing doses to sensitive organs:
3.5 Diagnostic Reference Levels (DRLs)3.5.1 Introduction
Doses for medical diagnostic procedures can vary widely between equipment and facilities. Numerous surveys have demonstrated that, for typical procedures, the difference in radiation doses can be as wide as a factor of 50 to 100. For interventional procedures, this difference can be even wider. In diagnostic radiology, the use of surface air kerma limits is not sufficient since these dose limits are usually set at a level high enough so that any doses greater than the limit is clearly unacceptable, but this limit does not help in optimising patient doses. For this reason, the concept of Diagnostic Reference Levels (DRLs) is introduced, instead of using maximum dose limits.
The purpose of DRLs is to promote a better control of patient exposures to X-rays. This control must be related to the clinical purpose of the examination. DRLs must not be seen as limits but instead as guidance to optimise doses during procedures. DRLs are based on typical examinations of standardized patient or phantom sizes, and for a broad type of equipment. While it is expected that facilities should be able to attain these levels when performing procedures using good methodologies, it is not expected that all patients should receive these dose levels but that the average of the patient population should. DRLs are useful where a large reduction in patient doses may be achieved, such as for computed tomography (CT) procedures, where a large reduction in collective doses may be achieved, such as for chest X-rays, or where a dose reduction will result in a large reduction in risk, such as for paediatric procedures. However, interventional procedures are not going to be addressed at this time since it is difficult to establish DRLs for them due to the variability in techniques, the frequency of procedures, the difficulty in dose measurement, and the lack of published data. 3.5.2 Application
The tables shown in section A3.5.3, list representative ranges of DRLs for radiographic procedures, performed on adults and children, radioscopic procedures and CT procedures. It is obvious that not all facilities will perform all of the listed procedures. Therefore, each facility should establish DRLs for those procedures relevant to them and where the number of patients undergoing the procedures is sufficiently high. A facility may set DRLs for other procedures not presented in the tables but which are being performed. At least one procedure should be evaluated for each X-ray equipment.
DRL measurements can be performed in two different ways; with a phantom specifically designed for the procedure, or using patients. In general, it is preferable to use phantoms since the measurements can be more easily replicated and offer more flexibility in the type of procedures which can be performed. Appropriate phantom, such as phantoms for chest, lumbar spine and abdomen representing a patient thickness, in the PA projection, of 23 cm are acceptable for DRL measurements, as long as they are consistently used. DRLs for CT are based on the weighted CT Dose Index, or CTDIw which can be determined by using CT Dosimetry Phantoms, described in Table 22, section C3.6.3.
When patients are be used to establish DRLs, measurements should be done only on patients whose individual weight is 70 ± 20 kg, and the average weight measurement of the patients should be 70 ± 5 kg. It is recommended that the minimum sample size for a specific procedures or equipment be 10 patients. Patients should not be used for paediatric procedures.
Entrance surface doses for establishing DRLs can be measured using thermoluminescent dosimeters (TLDs) placed on the tube side of the patient, by using dose area product (DAP) meters, or through information retrieved from the Radiology Information System (RIS) , or other means. The use of DAP is more practical since the whole procedure is recorded and their use is less complicated than TLDs, while with the use of RIS, the patient weight may not be available.
The values presented in section A3.5.3 are provided to facilities for guidance. The values presented are dependent of patient size and, as such, a facility will need to evaluate whether their patient population falls within the range of patient size for the procedure. While this safety code recommends representative DRLs, a hospital or clinic can set their own local DRLs if enough data is available. The facility should create a list of reference doses for their patient population and use these values within their quality assurance program. DRL values should be reviewed from time to time to assess their appropriateness. It is recommended that this review be done annually.
Radiological facilities which fall under provincial or territorial jurisdiction should contact the responsible agency in their respective region for information on any provincial or territorial statutory or regulatory requirements concerning dose limits. A listing of these responsible agencies is provided in Appendix V.
DRL values must not be used for comparison with individual patients. The values should be compared only with the average of a collection of patients of a specific weight. The evaluation of conformity with DRLs should be done at the X-ray room level or X-ray equipment type, i.e., mobiles, CT. For each examination under consideration, the mean patient doses for each room should be compared to the DRL for the examination. If the mean dose is found to significantly and consistently exceed the suggested DRL, an investigation of the performance of the equipment, the radiological technique used, and the methodology of dose measurement should be done in order to reduce patient doses. It is recommended that this action level be set at a defined proportion (i.e., 25% of the mean) and at least twice the standard error of the mean of the measurements. 3.5.3 Recommended DRL Values
Table 1 presents representative DRL values for radiographic procedures performed on adults. Table 2 presents DRL values for a 5 year old child along with the mean body thicknesses for each examination. It should be noted that the range of values provided for the entrance surface dose is reflective of the variation of values found in published data. Representative DRLs for radioscopic and CT examinations are shown in Table 3 and Table 4 respectively.
Section B: Facility and Equipment Requirements1.0 Facility Requirements1.1 General Criteria
In the planning of any medical X-ray facility the main priority is to ensure that persons in the vicinity of the facility are not exposed to levels of radiations which surpass the current regulatory exposure limits. Appropriate steps must be taken to ensure adequate shielding is present to meet the following requirements:
Appendix I provides a detailed description of the regulatory dose limits. For medical X-ray imaging facilities, controlled areas are typically in the immediate areas where X-ray equipment is used such as the procedure room and X-ray control booths. The workers in these areas are primarily equipment operators such as radiologists and 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 2004Footnote 18).
In general, attention to the basic principles of distance, time and shielding are required to determine shielding needs. 1.2 Design and Plan of X-ray Facility
In the early stages of designing and planning a medical X-ray facility, three steps should be taken to ensure adequate shielding is in place to provide the necessary level of radiation protection:
1.2.1 Preparation of Facility Plan
In order to determine the shielding requirements for an X-ray facility a floor plan must be prepared, clearly identifying the following components:
1.2.2 Considerations for Room Design and Layout
When designing the layout of the X-ray facility, the following general recommendations must be considered.
1.2.3 Determination of Parameters Governing Structural Shielding Requirements
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.
The parameters listed below must be considered for the calculation of barrier thicknesses. Allowance should be made for possible future changes in anyone 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.
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 X-ray suite over a set period of time (i.e., week). For irradiations made under Automatic Exposure Control, the operating voltage, procedure type and patient thickness should be recorded to be used later to estimate the current-time product. If actual workload values are not available, Table 5 presents estimated total workloads for various medical X-ray facilities (NCRP 2004Footnote 18).
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 present recommended occupancy factors.
Table 6: Occupancy Factors
The use factor, is the fraction of the workload during which the X-ray beam is pointed in the direction under consideration. The following table present recommended occupancy factors.
1.3 Shielding Calculations
Shielding calculations must be made for both primary and secondary protective barriers. Primary protective barriers provide shielding from the direct X-ray beam and therefore must be placed in such an orientation as to intersect the X-ray beam. Secondary protective barriers are required to provide shielding from scattered and leakage X-rays.
Comprehensive shielding calculations for large radiological 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 2004Footnote 18). 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. Alternatively, the methodology presented in NCRP Report No. 49 (NCRP 1976Footnote 16) is also acceptable and presented in Appendix III.
Under the methodology used in NCRP Report 147, the following are assumptions made in the shielding calculation:
The information outlined in sections B1.1 and B1.2 along with the final plans of the installation must be submitted for reviewed by the appropriate responsible government agency. For installations under federal jurisdiction, the responsible agency is the Consumer and Clinical Radiation Protection Bureau, Health Canada, Ottawa, Ontario K1A 1C1. Radiological facilities that fall under provincial or territorial jurisdiction should contact the responsible agency in their respective province or territory listed in Appendix V. 1.3.1 Radiographic Films
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. The values presented in Appendix IV are very conservative but will protect films from radiation exposure for most circumstances. 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. Refer to Appendix IV for storage guides for radiographic film. 1.3.2 Radiographic X-Ray Equipment and Dedicated Chest Radiographic Equipment
Primary and secondary shielding must be provided for radiographic equipment where the tube can be manipulated in several directions. The walls and floor where the X-ray tube can be directed are considered primary barriers whereas the other walls and ceiling are secondary barriers. The primary barrier includes the wall behind the vertical image receptor, or "wall or chest bucky", and the floor under the radiographic table. For dedicated chest radiographic equipment, the wall behind the image receptor is considered a primary barrier.
The X-ray tube should never be directed towards the control booth. Therefore the walls of the control booth are calculated as secondary barriers. The information required for calculation of the shielding of radiographic X-ray equipment and dedicated chest radiographic equipment is found in Table AII.1 of Appendix II. 1.3.3 Radioscopic X-Ray Equipment and Angiographic X-Ray Equipment
The design of radioscopic X-ray equipment is such that only secondary shielding must be provided for these types of systems. However, in systems where an X-ray tube for radiography is also present, the shielding for this X-ray tube must be evaluated independently, as in Section B1.3.2. When equipment include more than one X-ray tube, such as in cardiac systems, the shielding calculation must take into account each X-ray tube independently. The information required for calculation of the shielding of radioscopic X-ray equipment is found in Table AII.2 of Appendix II. 1.3.4 Computed Tomography Equipment
The design of computer tomography equipment is such that only secondary shielding must be provided. The calculation of shielding for CT rooms should not rely on workload values as defined in Section B1.2.3 and therefore it is recommended that shielding requirements be calculated using the methodology of NCRP 147 for CT equipment. The information required for calculation of the shielding of CT equipment is found in Table AII.3 of Appendix II. 2.0 Medical X-ray Equipment Requirements2.1 Regulatory Requirements for Medical X-ray Equipment
All new, used, and refurbished medical 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, 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 specify standards for information, labelling, construction and performance of equipment, with respect to radiation safety. The Medical Devices Regulations encompass all other safety considerations and the question of efficacy for all medical X-ray equipment sold in Canada. It is the responsibility of the manufacturer or distributor to ensure that the equipment conforms to the requirements of these regulations. In addition, X-ray equipment must meet any applicable requirements under provincial or territorial jurisdictions for such equipment. The Canadian Standards Association and provincial electrical utility should be consulted for further information.
Part XII of the Radiation Emitting Devices Regulations addressing medical X-ray equipment, in effect at the time of publication of this Safety Code, is reproduced in Appendix VI. These regulations may be amended from time to time, to keep up-to-date with changing technology in the field. Information on the applicability and currency of the Radiation Emitting Devices Regulations may be obtained by contacting the Consumer and Clinical Radiation Protection Bureau, Health Canada, Ottawa, Ontario K1A 1C1. 2.2 Equipment Purchasing
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. 2.2.1 Needs Analysis
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 to 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. 2.2.2 Equipment Specifications
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 identity 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. 2.2.3 Analysis of Vendor Quotation and the Purchase Contract
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 purchasers 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. 2.2.4 Acceptance Testing
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. It is recommended that acceptance testing 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 radiographic, radioscopic and CT equipment is available in publications from the International Electrotechnical Commission (IEC 1999Footnote 9), (IEC 2004Footnote 11).
X-ray performance tests performed 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. 2.3 Existing Medical X-ray Equipment
Whenever possible, existing medical X-ray 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 that time. It should be noted that it is a requirement of the Radiation Emitting Devices Act that replacements for any component or subassembly of an X-ray machine, for which a construction or performance standard has been specified in the Regulations applicable to the class of X-ray equipment, must comply with the standards in effect at the time of replacement. 2.4 Retrofitting with Computed Radiography (CR) and Digital Radiography (DR) Systems
When purchasing a CR system for a new or existing X-ray system or an after market DR detector to be installed on an existing system, both CR and DR systems must meet 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 existing X-ray system, onto which the CR or DR systems is fitted, must meet the current requirements of Part XII of the Radiation Emitting Devices Regulations. CR and DR image receptors must only be installed on X-ray systems which have an automatic means of controlling exposures, such as an automatic exposure control. The system must be calibrated to reflect the sensitivity of the digital receptor. Part XII of the Radiation Emitting Devices Regulations, in effect at the time of publication of this Safety Code, is presented in Appendix VI. For radiography, it is recommended that the detector pitch be equal or better than 200 µm, and the system radiation sensitivity should be greater than an equivalent 200 speed film screen system for equivalent diagnostic images. 2.5 Equipment Specific Requirements
Construction and performance requirements are listed below for radiographic, radioscopic and CT equipment. The Radiation Emitting Devices Regulations, Part XII (Diagnostic X-ray Equipment) should be referred to for more detailed information on each requirement including, for some requirements, measurement conditions and methodologies. 2.5.1 General Requirements
The following requirements must be met by all radiographic, radioscopic, and CT equipment. It is important to note that these requirements are reflective of the requirements of Part XII, Diagnostic X-ray Equipment, Radiation Emitting Devices Regulations, effective at the time of publication of this Safety Code. Therefore any future amendments to the regulations may also affect the requirements of this section.
2.5.2 Radiographic Equipment Requirements
2.5.3 Radioscopic Equipment Requirements
2.5.4 Computed Tomography Equipment Requirements
2.5.5 Dose and Image Quality Information for Computed Tomography Equipment
The initial or baseline dose and image information required to assess the continuing performance of a CT X-ray system is normally obtained from the manufacturer at the time of purchase. For existing equipment, baseline values should be established by a medical physicist.
The following safety and technical information regarding the X-ray dose delivered by the radiation beam must be determined: (US CFR 1020.33Footnote 22), (IEC 2002Footnote 10).
3.0 Image Processing Systems
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. 3.1 Film-Based Systems
The ability to produce a radiograph 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. 3.1.1 X-ray Film
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. 3.1.2 Cassette and Screen
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 should be replaced.
Manufacturers' recommended screen cleaner should be used. To avoid artifacts caused by dirt and dust, the intensifying screens and cassettes should be cleaned at least monthly. The intensifying screens should 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 should be numbered for identification and matching, both inside the cassette and on the outside of the cassette. 3.1.3 Darkroom
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:
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 artifacts caused by dirt, dust, or improper handling of film. An ultraviolet light should be used to find dust areas around the darkroom. No one should eat or drink in the darkroom area. 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 the darkroom; any filter should be changed on a regular basis. 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. 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. 3.1.4 Film Processing
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. 3.1.5 Viewbox
The conditions of viewboxes must be checked regularly along with the conditions under which radiologists and other health care professionals examine radiograms 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. 3.2 Digital Imaging Systems
As an increasing number of imaging modalities are being introduced based on digital technology, imaging facilities are migrating from film-based to filmless digital imaging systems. Digital images can be acquired using either computed radiography or digital radiography systems. Computed radiography systems, or CR systems, consist of a cassette, an imaging plate and imaging plate reader. The CR cassette, loaded with an imaging plate, is positioned in the X-ray system, as it is done with film cassettes. Upon X-ray exposure, the imaging plate, which contains a photostimulable storage phosphor, stores the latent image. The imaging plate is then read and a digital image is produced. For digital radiography systems, or DR systems, the image receptor is a flat panel detector which converts the X-ray signal into an electronic signal carrying the image information. The electronic signal is sent to a digital image processor and the image is displayed almost instantaneously. Digital imaging systems together with systems for storage and communication of digital images have the potential to significantly improve patient care by increasing the efficiency of patient examinations, facilitating rapid electronic communication between health care providers, both within and outside a facility, and ultimately increasing patient throughput .
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, some general quality control tests have been included for digital imaging systems. In addition to these test, all equipment- specific, manufacturer-specified tests must also be performed. 3.2.1 Computed Radiography Imaging Plates
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 artifacts are perceived. In general, a weekly visual inspection for dust and dirt is recommended. 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. 3.2.2 CR Cassette
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. 3.2.3 Electronic Display Devices
The performance of medical electronic display devices must be checked routinely. 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 (AAPM, 2005Footnote 2). An overall assessment should be made daily prior to clinical use. It is recommended that geometric distortion, luminance and resolution be evaluated monthly and a detailed evaluation be performed annually by a medical physicist. 3.2.4 Picture Archiving and Communications System
In digital imaging, a system must be in place to manage patient images so that secure storage and timely retrieval of images is possible. 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 a 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. However, once established, a PACS offers a number of advantages such as improved productivity, widespread, simultaneous access to images and image manipulation. Radiologists are able to interpret more cases in shorter periods of time, resulting in shorter waiting times for patients and quicker access to results by the referring physicians. 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. 3.2.5 PACS Implementation
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 system the following key components should be considered.
3.2.6 Teleradiology
Teleradiology is the electronic transmission of radiological images from one location to another for the purposes of interpretation and/or consultation. Through teleradiology, digital images and patient information can be accessed electronically from multiple sites simultaneously. The benefits of teleradiology 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 teleradiology 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 teleradiology.
4.0 Other Equipment
Consideration must be given to other equipment, such as those used for personnel protection and equipment testing, which are necessary for ensuring the radiation safety of a radiological facility. Personnel protective clothing must provide adequate protection without being unduly restrictive and heavy. All test equipment must be properly maintained and carefully stored. 4.1 Protective Equipment
4.2 Test Equipment
5.0 Radiation Protection Surveys
A radiation protection survey is an evaluation, conducted by an expert, of the radiation safety of a radiological facility. The survey is intended to demonstrate that the 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. 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 inspected at regular intervals. 5.1 General Procedures
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. Such inspections should include determination of thickness of lead and/or concrete thickness and density, degree of overlap between lead sheets or between lead and other barriers, as well as thickness and density of leaded glass used in viewing windows.
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. The frequency at which radiation protection surveys are to be conducted is dependant on the type of facility, the type of equipment used and the type of examinations performed. 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. 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. 5.2 Survey Report
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:
6.0 Disposal of X-ray Equipment
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. 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. For example the X-ray tube may contain polychlorinated biphenyls (PCBs) and lead may be present in the X-ray tube housing. 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 radiological 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 V. Section C: Quality Assurance Program1.0 Introduction
All radiological facilities must develop and maintain an effective quality assurance program. Quality assurance in radiology is defined as the planned and organized actions necessary to provide adequate confidence that the X-ray equipment and its related components reliably produce diagnostic information of satisfactory quality with minimum doses to the patients and staff. A quality assurance program includes quality control procedures for the monitoring and testing of X-ray equipment and related components, and administrative methodologies 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 which examines all practices of the facility which effect:
1.1 Goals of the Quality Assurance Program
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 X-ray equipment must be of utmost quality to ensure accurate diagnosis and treatment. If critical elements are missing or artifacts are added to images, the image is considered to be of poor quality. The consequence of poor quality diagnostic information may be incorrect diagnosis resulting in repeat radiographic procedures, unnecessary radiation doses to the patient, delayed or improper patient treatment and increased cost. 1.2 Costs-Benefits of the Quality Assurance Program
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. 1.2.1 Costs of Quality Assurance Program
Some of the costs associated to the quality assurance program are as follow:
1.2.2 Benefits of Quality Assurance Program
In addition to improved diagnostic quality some of the savings associated with the quality assurance program are as follow:
1.3 Implementation of Quality Assurance Program
The implementation of a quality assurance program need not be complicated. It consists in establishing quality control procedures for the equipment along with an administrative methodology to ensure that monitoring, evaluation and corrective actions are properly performed. 1.3.1 Policies and Guidelines Development
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:
1.3.2 Establishment of Quality Control Procedures
The following four steps must be included for the establishment of quality control procedures:
1.3.3 Establishment of Administrative Procedures
The following administrative procedures must be included in the establishment of an effective quality assurance program.
2.0 Acceptance Testing
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. It is recommended that acceptance testing be performed by a medical physicist, or other individuals, with knowledge of the particular type of X-ray equipment and the relevant regulations prior to any clinical use of the equipment. The owner may wish to 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 X-ray equipment. These baseline values and limits are essential to the quality assurance program. 2.1 Acceptance Testing Evaluation
Acceptance testing for radiographic, radioscopic and CT equipment should evaluate at least the following items below. 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. More detailed information on acceptance testing on radiographic, radioscopic and CT equipment is available from the International Electrotechnical Commission (IEC 1999Footnote 9), (IEC 2004Footnote 11).
3.0 Quality Control Testing Procedures and Equipment
Quality control testing must be carried out during routine operation of a radiological facility. This section sets out the required and recommended quality control tests, the associated test equipment and testing frequencies.
Quality control testing of a medical X-ray system includes several major steps. They are:
Test equipment required to perform daily to monthly quality control tests, must be readily available to the individuals responsible for performing these 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.
In the following sections, the descriptive text for each test indicates 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. For example, for film-based systems, the evaluation of noise is not necessary since this item is for the evaluation of digital systems. The type of imaging system, whether film-based, CR, DR, radioscopic or CT, to which the quality control tests apply is identified. Note that both radiographic and radioscopic imaging equipment employing CR and DR digital image acquisition technologies must perform the required tests listed for these systems. 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. 3.1 Daily Quality Control Testing3.1.1 Quality Control Tests List
Daily quality control tests are listed in Table 11. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.1.2, are provided. 3.1.2 Daily Quality Control Tests
Daily Quality Control Tests. Daily Quality Control tests must be performed at the beginning of each day before commencing patient examinations.
3.1.3 Daily Quality Control Test Equipment
Test equipment for the daily quality control testing are listed in Table 12.
3.2 Weekly Quality Control Testing3.2.1 Quality Control Tests List
Weekly quality control tests are listed in Table 13. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.2.2, are provided. 3.2.2 Weekly Quality Control Tests
3.2.3 Weekly Quality Control Test Equipment
Test equipment for the weekly quality control testing are listed in Table 14.
3.3 Monthly Quality Control Testing3.3.1 Quality Control Tests List
Monthly quality control tests are listed in Table 15. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.3.2, are provided. 3.3.2 Monthly Quality Control Tests
3.3.3 Monthly Quality Control Tests Equipment
Test equipment for the monthly quality control testing are listed in Table 16.
3.4 Quarterly Quality Control Testing3.4.1 Quality Control Tests List
Quarterly quality control tests are listed in Table 17. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.4.2, are provided. 3.4.2 Quarterly Quality Control Tests
3.4.3 Quarterly Quality Control Tests Equipment
Test equipment for the quarterly quality control testing are listed in Table 18.
3.5 Semi-Annual Quality Control Testing3.5.1 Quality Control Tests List
Semi-annual quality control tests are listed in Table 19. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.5.2, are provided. 3.5.2 Semi-Annual Quality Control Tests
3.5.3 Semi-annual Quality Control Tests Equipment
Test equipment for the semi-annual quality control testing are listed in Table 20.
3.6 Annual Quality Control Testing3.6.1 Quality Control Tests List
Annual quality control tests are listed in Table 21. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.6.2, are provided. 3.6.2 Annual Quality Control Tests
3.6.3 Annual Quality Control Tests Equipment
Test equipment for annual quality control testing are listed in Table 22.
Appendix I: Dose Limits for Occupational Ionizing Radiation Exposures
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 AI.1. These dose limits are based on the latest recommendations of the International Commission on Radiological Protection (ICRP) as specified in ICRP Publication 60 (ICRP, 1991Footnote 8).
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.
Appendix II: Shielding Information Guides
Appendix III: NCRP #49 Methodology for Calculation of Shielding Requirements for Diagnostic X-ray Installations
This appendix presents the methodology of NCRP #49 for determining the shielding necessary in a diagnostic X-ray installation. The required thickness of shielding can be calculated using the formulae contained in this Appendix, in conjunction with Figures 1 to 3 and the answers to the following questions:
Formulae for Calculation of Shielding Requirements
The thickness of shielding required can be calculated using the formulae given below. This method requires knowing the Workload W, in mA-minutes per week, the use factor U, the occupancy factor T and the distance d, in metres, from the source to the occupied area.
This method involves computation of an average value for the exposure per unit workload at unit distance, K, (in R/mA-min at 1 metre) and then using the curves shown in Figures AIII.1 and AIII.2 and to determine the thickness of lead or concrete required to reduce radiation levels to the required value. 1. Primary Protective Barriers
For primary protective barriers, the value K can be computed from the following equation:
Example: Determine the thickness of primary barrier required to protect a controlled area 3 metres from the target of a 150 kVp diagnostic unit having a weekly workload of 2000 mA-min. The wall has a use factor of 1 and the occupancy factor of the area beyond the wall is 1.
The 150 kVp curves of Figures AIII.1 and AIII.2, respectively show that the required barrier thickness is 2.65 mm of lead or 23.5 cm of concrete.
Figure AIII.1: Attenuation in lead of X-rays from 50 to 150 kVp The minimum half-value layer of aluminum, measurement without the compression paddle in place, calculated by the equation "HVL (mm of Aluminum) greater than or equal to, X-ray Tube Voltage (kV) divided by 100".
Figure AIII.2: Attenuation in concrete of X-rays generated at 50 to 150 kVp This graph presents the attenuation of 50, 70, 100, 125 and 150 kVp X-rays as a function of concrete thickness. The vertical axis is logarithmic and represents K, the quotient of exposure at a unit distance and workload in units of Roentgens per milliampere-minute (R per mA-min at 1 metre). The horizontal axis represent the thickness of concrete in centimetres (cm). The graph shows that logarithm of K decreases as the thickness of concrete increases. 2. Secondary Protective Barriers
Secondary protective barriers are required to provide shielding against both leakage and scattered radiation. Since these two types of radiation are of different qualities, it is necessary to determine the barrier thickness requirements for each separately. If the computed barrier thicknesses for leakage and scatter radiations are about the same, one half-value layer should be added to the larger one to obtain the total secondary barrier thickness. If the computed leakage and scattering thicknesses differ by at least three half-value layers, the larger of the two will be adequate. 2.1 Barrier Against Leakage Radiation
To determine the barrier thickness required to protect against leakage radiation it is necessary to calculate the transmission factor, B, required to reduce the weekly exposure to P. For a diagnostic-type tube housing, where the maximum allowable leakage from the housing is 0.115 roentgen per hour at 1 metre, the transmission factor is given by the following formula:
Having calculated the transmission factor, B, the barrier thickness, as a number of half-value layers or tenth-value layers, can be determined from Figure AIII.3. The required barrier thickness in millmeters of lead or centimeters of concrete can be obtained from Table AIII.1, for the appropriate energy.
Example: Determine the thickness of barrier required to protect a controlled area 2 metres from the housing of a 100 kVp diagnostic unit having a weekly workload of 2000 mA-min. Assume that the tube operates at 5 mA and that the area in question has an occupancy factor of 1. For this case,
From Figure 3, a transmission of 0.209 corresponds to 2.4 HVL's or 0.7 TVL's. From Table AIII.1 the HVL for 100 kVp is 0.27 mm lead or 1.6 cm concrete. Therefore, the required barrier thickness for protection against leakage radiation is
Figure AIII.3: Relationship between the transmission factor B and the number of half-value layers, N, or tenth-value layers, n This triangular graph presents the relationship between the transmission factor B and the number of half-values, N or tenth-values layers, n of a barrier. The vertical axis is logarithmic and represents the relative transmission factor, B. The horizontal axis represents the number of half-value layers, N. The diagonal axis represents the number of tenth-value layers, n. The graph shows that as the transmission factor increases, the corresponding number of half-value layers or tenth-value layers decrease.
2.2 Barrier Against Scatter Radiation
Scattered radiation has a much lower exposure rate than that of the incident beam and usually is of lower energy. However, for X-ray equipment operating below 500 kVp it is usually assumed that the scattered X-rays have the same barrier penetrating capability as the primary beam. For X-rays generated at kVp's of less than 500 kV, the values for K can be determined from the following formula:
Having computed K from equation (3), the curves shown in Figures AIII.1 and AIII.2 are then used to determine the thickness of lead or concrete required in the same way as for the primary barrier.
If the barrier thickness for leakage and for scattered radiation differ by at least 1 TVL, the thicker of them will be adequate. If they differ by less than 1 TVL, 1 HVL should be added to the thicker one to obtain the required total secondary barrier thickness.
Appendix IV: Shielding Guides for Storage of Radiographic Film
To reduce the radiation level to the film to 1.75 μGy (0.2 mR) for weekly workloads of:
Table AIV.1 presents the amount of shielding required to reduce radiation level to 1.75 μGy. In general, for most facilities, the storage time for secondary barriers is adequate.
Appendix V: Federal/Provincial/Territorial Radiation Safety Agencies
Consumer and Clinical Radiation Protection Bureau Health Canada P.L. 6301A 775 Brookfield Road Ottawa, Ontario K1A 1C1
Radiation Protection Service B.C. Centre for Disease Control Government of British Columbia 655, 12th Avenue West Vancouver, British Columbia V5Z 4R4
WorkSafe BC 6951 Westminster Highway Richmond, British Columbia V7C 1C6
Workplace Policy and Standards Development Branch Alberta Employment, Immigration and Industry 8th floor, 10808-99th Avenue Edmonton, Alberta T5K 0G5
Radiation Safety Unit Ministry of Advanced Education, Employment and Labour 400- 1870 Albert St. Regina, Saskatchewan S4P 3V7
Radiation Protection Services Department of Medical Physics CancerCare Manitoba 675 McDermot Avenue Winnipeg, Manitoba R3E 0V9
Ontario (for issues related to patient and public safety)
Ontario Ministry of Health and Long-Term Care X-Ray Inspection Services 5700 Yonge Street, 3rd Floor North York, Ontario M2M 4K5
Ontario (for issues related to worker safety)
Ministry of Labour Radiation Protection Service 81A Resources Road Weston, Ontario M9P 3T1
Direction de la logistique et des équipements Ministère de la Santé et des Services sociaux Gouvernement du Québec 1005, ch. Sainte-Foy, 7e étage Québec (Québec) G1S 4N4
Radiation Protection Services Department of Health and Wellness P.O. Box 5100, Carleton Place 3rd Floor Fredericton, New Brunswick E3B 5G8
Occupational Health and Safety Division Nova Scotia Department of Environment and Labour P.O. Box 697 Halifax, Nova Scotia B3J 2T8
Division of Environmental Health Health and Social Services Government of Prince Edward Island P.O. Box 2000 Charlottetown, Prince Edward Island C1A 7N8
Newfoundland and Labrador
Department of Labour West Block, 4th floor, Confederation Bldg. P.O. Box 8700 St. John, Newfoundland A1B 4J6
Occupational Health and Safety Government of the Northwest Territories Box 1320 Yellowknife, Northwest Territories X1A 2L9
Occupational Health and Safety Yukon Workers' Compensation Health and Safety Board 401 Strickland Street Whitehorse, Yukon Territory Y1A 5N8 Appendix VI: Radiation Emitting Devices Regulations for Diagnostic X-ray Equipment
The Diagnostic X-ray Equipment Regulations, Part XII of the Radiation Emitting Devices Regulations, in effect at the time of publication of this Safety Code, are shown below. The regulations have been included here for convenience of reference only and do not have official sanction. In addition, these regulations may be amended from time to time. For all purposes of interpreting and applying the law, users should consult the regulations, as registered by the Clerk of the Privy Council and published in Part II of the Canada Gazette. The Consumer and Clinical Radiation Protection Bureau of Health Canada can also be contacted for clarification on any of the requirements.
Schedule I of the Radiation Emitting Devices Regulations
12. Diagnostic X-ray equipment, being X-ray devices that are used for the examination of the human body, not including dental X-ray equipment with an extra-oral source that is subject to Part II of these Regulations, photofluorographic X-ray equipment, radiation therapy simulators and computer-assisted tomographic equipment.
PART XII DIAGNOSTIC X-RAY EQUIPMENT Interpretation
1.(1) The definitions in this subsection apply in this Part.
"aluminum" means aluminum that has a degree of purity of 99.9% or higher and a density of 2.70 g/cm3. (aluminium)
"aluminum equivalent" means the attenuation equivalent of an object expressed in thickness of aluminum. (équivalent en aluminium)
"field emission device" means a device in which the emission of electrons from the cathode is due solely to the action of an electric field. (dispositif d'émission par effet de champ)
"general purpose radiographic equipment" means any stationary equipment other than that used solely for the examination of specific anatomical regions. (appareil de radiographie pour usage général)
"loading factor" means a factor the value of which influences the X-ray tube load, and includes
"mammography equipment" means diagnostic X-ray equipment that is used for the examination of breast tissue. (appareil à mammographie)
"mobile equipment" means, with respect to diagnostic X-ray equipment, equipment that is moved between incidents of use. (appareil mobile)
"radiographic equipment" means diagnostic X-ray equipment that implements a technique in which the information contained in the X-ray pattern is obtained, recorded and optionally processed. (appareil de radiographie)
"radioscopic equipment" means diagnostic X-ray equipment that implements a technique in which continuous or periodic sequences of X-ray patterns are produced and simultaneously and continuously displayed in the form of visible images. (appareil de radioscopie)
"radioscopic imaging assembly" means the combination of components in radioscopic equipment that uses X-ray photons to produce a radioscopic image. These components usually consist of the X- ray image receptor, X-ray image intensifier, equipment housings, interlocks and protective shielding. (système d'imagerie radioscopique)
"rectification type" means, with respect to diagnostic X-ray equipment, the process by which the X-ray generator converts high voltage to X-ray tube voltage. (type de redressement)
"stationary equipment" means, with respect to diagnostic X-ray equipment, equipment that is never moved between incidents of use. (appareil fixe)
"X-ray image receptor" means a device that converts incident X-rays into a visible image or into a form that can be made into a visible image by further transformation. (récepteur d'image radiologique)
(2) Unless otherwise defined, words and expressions used in this Part have the same meaning as in the International Electrotechnical Commission Standard entitled Medical radiology --Terminology, Publication 788, First edition, 1984.
Information and Labelling
2. The manufacturer must ensure that the following information accompanies each piece of diagnostic X-ray equipment:
3. Diagnostic X-ray equipment must display the following information in a manner that is legible, permanent and visible on the specified surfaces:
4. The X-ray warning symbol shall
5. All controls, meters, warning lights and other indicators required by this Part must be clearly labelled as to their function.
Construction Standards
6. Diagnostic X-ray equipment must have
7.(1) An irradiation switch for diagnostic X-ray equipment must
(2) The controlling timer for diagnostic X-ray equipment must
8.(1) In the case of diagnostic X-ray equipment, other than mammography equipment, when an object set out in column 1 of an item of the table to this subsection is positioned between the patient and the X-ray image receptor, the aluminum equivalent of the object shall not exceed the amount set out in column 2 of that item, as determined using an X-ray beam that
(2) In the case of mammography equipment, when an object set out in column 1 of an item of the table to this subsection is positioned between the patient and the X-ray image receptor, the aluminum equivalent of the object shall not exceed the amount set out in column 2 of that item, as determined using an X-ray beam that
(3) For the purposes of subsections (1) and (2), any sensor used in automatic exposure control is a part of the X-ray image receptor.
9. For diagnostic X-ray equipment,
10. Radiographic equipment that is equipped with an automatic exposure control must have
(c) when an irradiation under automatic exposure control terminates because the limits specified in paragraph (b) have been reached,
11.(1) General purpose radiographic equipment must have
(2) The X-ray field indicator referred to in paragraph (1)(b) must
12.(1) General purpose radiographic equipment that has a positive beam limiting system must
(2) For the purposes of paragraph (1)(d), the conditions of operation are as follows:
13.(1) Subject to section 14, radiographic equipment, other than general purpose radiographic or mammography equipment, must have a fixed-aperture beam limiting device that, for the combination of image reception area and focal spot to image receptor distance described in subsection (2),
(2) The fixed-aperture beam limiting device referred to in subsection (1) must display on its exterior surface a specified focal spot to image receptor distance and the dimensions of its image reception area at that distance.
14. Mobile radiographic equipment that does not meet the requirements of section 13 must have
15.(1) Mammography equipment must have
(2) Mammography equipment that has a removable, fixed-aperture beam limiting device must display the following information on its external surface:
16. Diagnostic X-ray equipment that has a spotfilm device must have
17. Radiographic equipment, other than equipment described in sections 11 to 16, must have a beam limiting device that, when the axis of the X-ray beam is perpendicular to the image receptor plane, permits
18. Radioscopic equipment must
19. Radioscopic equipment that is used for cineradiography must have visual indicators that continuously display the X-ray tube voltage and the X-ray tube current.
20. A high-level irradiation control for radioscopic equipment must
21. Diagnostic X-ray equipment must function in accordance with the requirements set out in sections 22 to 32 during its operation under normal conditions of use.
22.(1) The definitions in this subsection apply in this section.
"coefficient of variation" means the ratio of the estimated standard deviation to the mean value of a series of measurements calculated using the equation:
"exposure to the X-ray image receptor" means the amount of X-rays, registered by one or more detectors located in a fixed position in proximity to the X-ray image receptor, that is necessary to produce a radiogram of the overall density sought by the operator. (dose d'irradiation au récepteur d'image radiologique)
(2) 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 1% of the mean line voltage value of all the measurements, and when all variable controls for the loading factors are adjusted to alternate settings and reset to the test setting before each measurement,
(3) For the purposes of subsection (2), diagnostic X-ray equipment with an automatic exposure control must have attenuating material in the X-ray beam that is thick enough that the loading factors can be adjusted to provide single irradiations of at least
23.(1) This section applies in respect of diagnostic X-ray equipment that has
(2) In the case of a line voltage regulation of 6% or less, the loading factor set out in column 1 of an item of the table to this subsection 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.
24.(1) The controlling timer or automatic exposure control device of diagnostic X-ray equipment must have a minimum irradiation time capability that does not exceed the greater of:
(2) If the automatic exposure control of diagnostic X-ray equipment is selected, the variation in optical density set out in subsection (3) or (4) must be determined using objects that are made of human-tissue equivalent material and have thicknesses that are representative of the actual range of the body thicknesses of the patients.
(3) The automatic exposure control device of diagnostic X-ray equipment, other than mammography equipment, when the X-ray tube voltage and the thickness of the objects described in subsection (2) are held constant or varied as specified in columns 1 and 2 of an item of the table to this subsection, must limit the variation in optical density of the resulting radiograms to the quantity set out in column 3 of that item.
(4) The automatic exposure control device of mammography equipment, when both the X-ray tube voltage and the thickness of the objects described in subsection (2) are varied, must limit the variation in optical density of the resulting radiograms to 0.15.
25.(1) For any selected value of X-ray tube voltage within a range determined in accordance with subsection (2), the quotients of the average air kerma or exposure measurement divided by the indicated current time product, obtained at the applicable settings specified in subsection (3), must not differ by more than 0.10 times their sum as determined by the formula
(2)The range referred to in subsection (1) is the smaller of
(3)The quotients referred to in subsection (1) must be determined at
(4) If diagnostic X-ray equipment has more than one focal spot, the quotients referred to in subsection (1) must be determined for all combinations of two focal spots that have a nominal focal spot size greater than 0.45 mm, and all combinations of two focal spots that have a nominal focal spot size equal to or less than 0.45 mm at the applicable settings set out in subsection (3).
26.(1) For mammography 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
(2) For the purposes of subsection (1), the air kerma or exposure measurement must be averaged over a detection area that is 100 cm2, of which no linear dimension is greater than 20 cm, centred at 5 cm from any accessible surface beyond the image receptor supporting device.
27.(1) Mammography equipment must have a minimum rate of radiation output of 7.0 mGy/s or 802 mR/s when the equipment is operated
(2) For the purposes of subsection (1), the minimum rate of radiation output must be
28.(1) Radioscopic equipment that has a feature described in column 1 of an item of the table to this subsection, other than when radioscopic images are being recorded, must not operate at any combination of X-ray tube voltage and X-ray tube current that results in an air kerma rate that exceeds that set out in column 2 of that item or an exposure rate that exceeds that set out in column 3 of that item:
(2) For the purposes of subsection (1), the air kerma or exposure rate must be determined at a location along the X-ray beam axis that is
29.(1) The leakage radiation from the X-ray source assembly of diagnostic 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 equipment is operated at the nominal X-ray tube conditions of loading that correspond to the maximum specified energy input in one hour.
(2) For the purposes of subsection (1), 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 point.
30.(1) If high voltage can appear across the X-ray tube of the diagnostic 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
(2) For the purposes of subsection (1), 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.
31.(1) Under any operating condition, the radiation from any component of diagnostic X-ray equipment, other than the X-ray source assembly, must not exceed an air kerma rate of 20.0 µGy/h or an exposure rate of 2.3 mR/h.
(2) For the purposes of subsection 1, 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.
32.(1) In the case of radioscopic equipment, the radiation resulting from the transmission of the X-ray beam through, or scattered from, the entrance window of the radioscopic imaging assembly must not exceed an air kerma rate of 2 mGy/h for an entrance air kerma rate of 1 Gy/min or an exposure rate of 2 mR/h for an entrance exposure rate of 1 R/min.
(2) For the purposes of subsection (1), the rate must be
Appendix VII: Facility Radiation Protection ChecklistAppendix VIII: Radiation Measurement UnitsExposure
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:
Absorbed Dose
The gray (Gy) replaces the rad (rad) as the unit of absorbed dose. The relationship between the two units is as follows:
Equivalent Dose
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 References |