The irradiation sessions are always preceded by preparation of the treatment plan which, for each patient, details the dose to be delivered, the target volume to be treated, the dosimetry, the irradiation beam ballistics and the duration of each treatment. Preparation of this plan, which aims to set conditions for achieving a high, uniform dose in the target volume while protecting sound tissues, requires close cooperation between the radiotherapy specialist and the person specialising in medical radiophysics (PSRPM), previously known as the radiophysicist.

Irradiation is performed either using particle accelerators producing photon or electron beams with an energy of between 4 and 25 MeV and delivering dose rates varying between 2 and 6 Gy/mn, or - albeit now to a lesser extent - telegammatherapy appliances equipped with a cobalt 60 source, the activity of which is about 200 terabecquerels (TBq). The number of these latter appliances is declining rapidly in France, where they are being systematically replaced by particle accelerators whose superior performance offers a wider range of treatments. Given the characteristics of these machines, they must be installed in rooms specially designed to guarantee radiation protection of the personnel, turning them into true bunkers (the ordinary concrete walls can vary from between 1 to 2.5 m thickness). A radiotherapy installation comprises a treatment room including a technical area containing the appliance, a control station outside the room and, sometimes, auxiliary technical premises.

It should be noted that experiments should shortly be conducted in France into new irradiation techniques (tomotherapy and radiosurgery). Section 4.4.1 of this chapter gives details on these changes, in which the ASN is keenly interested, in order to anticipate their consequences on radiation protection of both operators and patients.

The protection of the premises, in particular the treatment room, must be determined in order to respect the annual exposure limits for the workers and/or the public around the premises. A safety case must be produced for each installation by the supplier of the machine, together with the PSRPM and the person with competence for radiation protection (or the department with competence for radiation protection) of the establishment in which it is to be installed. This study defines the thicknesses and nature of the various protections required, which will be determined according to the conditions of use of the appliance, the characteristics of the radiation beam and the use of the adjacent rooms, including those vertically above and below. This study should be included in the file presented to support the application for a licence to use a radiotherapy installation, examined by the ASN.

In addition, safety systems must indicate the machine status (operating or not) or must switch off the beam in an emergency or if the door to the irradiation room is opened.