Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities

Explanatory 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:

• Alberta Cancer Board
• Alberta College of Medical Diagnostic and Therapeutic Technologists
• Alberta Employment, Immigration and Industry
• British Columbia Centre for Disease Control
• Canadian Association of Radiologists
• Canadian Nuclear Safety Commission
• Cancercare Manitoba
• College of Physicians and Surgeons of Alberta
• Hôpital D^r G.-L Dumont, Moncton, New Brunswick
• Ontario Association of Medical Radiation Technologists
• Ontario Safety Association for Community and Healthcare
• Queen Elizabeth Hospital, Charlottetown, Prince Edward Island
• Saskatchewan Association of Health Organizations
• Vancouver General Hospital, British Columbia
• WorkSafe BC
• Workers'Compensation Board Northwest Territories and Nunavut

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:

1. to minimize patient exposure to ionizing radiation while ensuring the necessary diagnostic information is obtained and treatment provided;
2. to ensure adequate protection of personnel operating X-ray equipment;
3. to ensure adequate protection of other personnel and the general public in the vicinity of areas where X-ray equipment is used.

To assist personnel in achieving these objectives, this Safety Code:

1. sets out relative responsibilities of the owner, the X-ray equipment operator, the responsible user, the medical physicist or radiation safety officer, the referring physician, the information systems specialist, and the repair and maintenance personnel;
2. presents practices and procedures to minimize doses from X-ray equipment to operators and the public;
3. presents practices and procedures for minimizing radiation doses to patients while maintaining adequate image quality;
4. presents practices and procedures for ensuring the X-ray equipment is used in a safe manner;
5. provides information on facility design and shielding requirements;
6. specifies minimum standards of construction and performance for X-ray equipment;
7. supplies information required to implement and operate a quality assurance program for the facility;
8. provides a list of acceptance tests and quality control tests for various types of X-ray equipment and their accessories; and
9. provides a schedule for performing quality control tests.

This Safety Code is composed of three sections:

Section A: Responsibilities and Protection

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.

Section B: Facility and Equipment Requirements

This section sets out requirements for the facility design and minimum equipment construction and performance standards.

Section C: Quality Assurance Program

This section sets out requirements for quality assurance programs including acceptance testing and quality control procedures.