Since ionising radiation was discovered more than a century ago, medical applications have been one of its main uses. Whether for diagnosis or therapy, medicine employs various sources of radiation, produced either by electrical generators or by artificial radionuclides inside sealed or unsealed sources.

In medical applications of ionising radiation, the principle of dose limitation, one of the three fundamental principles of radiation protection, does not apply. Unlike the other types of applications, medical exposure is of direct benefit to the patient exposed, either for diagnostic purposes or for therapeutic reasons. Therefore, it is up to the practitioner to carry out case by case an assessment of the level of exposure to be applied to the patient in order to achieve the specified goal. However, the practitioner must first of all employ the principles of justification and optimisation.

Although the benefits and usefulness of medical applications have been established for many years now, they do contribute significantly to exposure of the population. They are the primary source of artificial exposure, behind natural exposure. This is why medical uses of ionising radiation are subject to a wide-ranging regulatory framework and the ASN is in this area developing specific activities, particularly with respect to installation monitoring.

The work that started in 2001 to overhaul the radiation protection regulations continued in 2005 with the publication of new regulations implementing the Public Health Code (protection of patients) and the Labour Code (protection of workers).

The ASN also focused on putting in place tools for assessing changes to radiation protection in the medical field and reinforcing the information available to health professionals concerning radiation protection regulations.

Radiodiagnosis is the discipline of medical imaging covering all techniques for morphological exploration of the human body using the X-rays produced by electrical generators.

Radiology is based on the principle of differential attenuation of X-rays by the organs of the human body. The information is gathered either on radiological film or more and more often on digital media allowing computer processing of the images obtained.

Radiodiagnosis, which is the oldest of the medical uses of radiation, occupies predominant place in medical imaging area, which now comprises various specialisations which have become increasingly independent as time has gone by. Technological change has also led to the development of imaging techniques which meet a wide variety of user needs.

The variety of types of radiological examination available for modern medicine should not however lead the practitioners to forget that they all involve irradiation of the patient. Therefore, the doctor must only prescribe the examination if it is part of a diagnostic strategy that takes account of the pertinence of the information looked for, the benefit to the patient, the irradiation of the patient and the possibilities of other non-irradiating investigative techniques. Section 1.5 of this chapter gives details concerning the exposure levels of patients during certain radiological examinations.

In the medical field, apart from conventional radiology, more specialised techniques allowing a broader field of investigation are also used.

• Conventional radiology

This uses the principle of conventional radiography and covers the vast majority of radiological examinations carried out. These examinations are primarily of the skeleton, thorax and abdomen and are part of what is called "sophisticated radiodiagnosis", with reference to the performance of the generators used. Conventional radiology can be split into three main families:
• radiodiagnosis performed in fixed installations specifically built for the purpose;
• radiodiagnosis performed occasionally using mobile appliances, particularly at the patient's bedside. This practice should be limited to patients who cannot be moved;
• radiodiagnosis conducted in the operating theatre as a tool to assist the surgeon. In this case, mobile X-ray generators equipped with image intensifiers output images onto a TV screen (radioscopy) for real-time guidance of the surgeon.

It should be noted that radioscopy devices without image intensifiers (simple radioscopy) are now prohibited by the order of 17 July 2003.

• Surgical radiology

They are radiological techniques which use radioscopy with image intensification and require special equipment allowing to replace certain surgical operations, in particular in cardiology (dilation of coronary arteries, etc.). They often require long-term exposure of the patients, who then receive high doses which can sometimes lead to radiation deterministic effects (cutaneous lesions, etc.). The surgical staff usually working in the immediate vicinity of the patient are also exposed to higher levels than during other radiological practices. Then, given the risk of external exposure for the operator and the patient, surgical radiology must be justified by clearly determined medical need and its practice must be optimised in order to improve the radiation protection of both operators and patients.