ASN Report 2017

266 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 09  - Medical uses of ionising radiation 1. Medical and dental radiodiagnosis installations 1.1 Presentation of the equipment Medical diagnostic radiology is based on the principle of differential attenuation of X-rays by the organs and tissues of the human body. The information is collected on digital media allowing computer processing of the resulting images, and their transfer and filing. Diagnostic X-ray imaging is one of the oldest medical applications of ionising radiation; it encompasses all the methods of morphological exploration of the human body using X-rays produced by electric generators. It occupies an important place in the field of medical imaging and comprises various techniques (conventional radiology, radiology associated with interventional practices, computed tomography, mammography) and a very wide variety of examinations (radiography of the thorax, chest-abdomen- pelvis computed tomography scan, etc.). The request for a radiological examination by the physician must be part of a diagnostic strategy taking account of the patient’s known medical history, the question posed, the expected benefit for the patient, the examination exposure level and the dose history and the possibilities offered by other non-irradiating investigative techniques. An updated guide intended for medical doctors (Guide to good medical imaging examination practices) indicates the most appropriate examinations to request according to the clinical situations (see box). F ore more than a century now, medicine has made use of ionising radiation produced either by electric generators or by radionuclides in sealed or unsealed sources for both diagnostic and therapeutic purposes. The benefits and usefulness of these techniques have long been proven, but they nevertheless contribute significantly to the exposure of the population to ionising radiation. They effectively represent the second source of exposure for the population (behind exposure to natural ionising radiation) and the leading source of artificial exposure (see chapter 1). Protection of the staff working in facilities using ionising radiation for medical purposes is regulated by the provisions of the Labour Code. The medical facilities and devices emitting ionising radiation, including sealed and unsealed sources, must satisfy technical rules and procedures defined in the Public Health Code (see chapter 3). The protection of patients undergoing medical imaging examinations or receiving treatments using ionising radiation is regulated by specific provisions of the Public Health Code. The principles of justification of procedures and optimisation of the doses delivered are the basis of these regulations. However, contrary to the other applications of ionising radiation, the principle of dose limitation does not apply to patients due to the need to adapt the dose delivered to each individual patient according to the therapeutic objective or to obtain an image of adequate quality to make the diagnosis. 1.1.1 Medical radiodiagnosis Conventional radiology Conventional radiology (producing radiographic images, or radiographs), if considered by the number of procedures, represents the large majority of radiological examinations performed. The examinations mainly concern the bones, the thorax and the abdomen. Conventional radiology can be carried out in fixed facilities reserved for diagnostic radiology or, in certain cases, using portable devices if justified by the clinical situation of the patient. Angiography This technique, used for exploring blood vessels, involves injecting a radio-opaque contrast agent into the vessels which enables the arterial tree (arteriography) or venous tree (venography) to be visualised. Angiography techniques benefit from computerised image processing (such as digital subtraction angiography). Mammography Given the composition of the mammary gland and the fineness of the details required in order to make a diagnosis, specific devices (mammography units) are used. They operate at low voltage and provide high resolution and high contrast. They are used in particular in the national breast cancer screening programme. The use of a new technique for three-dimensional imaging of the breast called “tomosynthesis”, which reconstructs the breast from