uses three-dimensional images of the target volumes and neighbouring organs obtained with a CT scanner, sometimes in conjunction with other imaging examinations (Positon Emission Tomography – PET, Magnetic Resonance Imaging – MRI, etc.). For several years now, however, the proportion of treatments performed using this techniques is decreasing in favour of Intensity‑Modulated Radiotherapy (IMRT), which saw the day in France in the early 2000s and allows better adaptation to complex tumoral volumes and better protection of neighbouring organs at risk, thanks to modulation of the intensity of the beams during irradiation. Following on from IMRT, Intensity-Modulated Volumetric Arc Therapy (IMVAT) is now being used increasingly frequently in France. This technique consists in irradiating a target volume by continuous irradiation rotating around the patient. Helical radiotherapy, or tomotherapy, enables radiation treatment to be delivered by combining the continuous rotation of an electron accelerator with the longitudinal movement of the patient during the treatment. The possibility of modulating radiation intensity allows equally well the irradiation of large complex-shaped volumes as of highly-localised lesions, if necessary in mutually independent anatomical regions. The system requires the acquisition of images under the treatment conditions of each session for comparison with reference computed tomography images in order to reposition the patient. Stereotactic radiotherapy is a treatment method that aims at delivering high dose radiation to intra- or extracranial lesions with millimetric accuracy through multiple mini-beams which converge at the centre of the target. The total dose is delivered either in a single session or in a hypofractionated manner, depending on the disease being treated. The term radiosurgery is used to designate treatments carried out in a single session. This technique demands great precision in defining the target volume to irradiate, following the shape of the tumour as closely as possible, and uses specific identification techniques in order to locate the lesions with millimetric accuracy. This therapeutic technique chiefly uses three specific types of equipment, such as: ∙ Gamma Knife®, which uses more than 190 cobalt-60 sources. It acts like a veritable scalpel over an extremely precise and delimited zone; ∙ robotic stereotactic radiotherapy; CyberKnife® is a miniaturised linear accelerator mounted on a robotic arm; ∙ multi-purpose linear accelerators equipped with additional collimation means (mini-collimators, localisers) that can produce mini-beams. Since 2018, the combination of a linear accelerator for radiotherapy coupled with an MRI scanner has been developing. Contact therapy or contact radiotherapy is an external-beam radiotherapy technique. The treatments are delivered by an X-ray generator using low-energy beams which are particularly suited to the treatment of skin cancers because the delivered dose decreases rapidly with depth. Intraoperative radiotherapy combines surgery and radiotherapy, with the radiation dose being delivered in the operating theatre to the tumour bed during surgical intervention. This technique is used primarily for treating small cancers of the breast. In April 2016, the HAS published the results of the assessment of this practice and concluded that the conditions necessary to propose coverage by the state health insurance scheme were not satisfied at the time. It considers that the clinical and medicoeconomic studies must be continued in order to have clinical data over the longer term. Nevertheless, some intraoperative electron radiotherapy devices, with the “CE” marking, have been put on the market. They allow optimal irradiation of the tumour while preserving the surrounding healthy tissues to the maximum possible extent. This innovative technique is currently being discussed by the Canpri. Hadron therapy is a treatment technique based on the use of beams of charged particles (protons and carbon nuclei), which can deliver the dose in a highly localised manner during treatments, thereby drastically reducing the volume of healthy tissue irradiated. According to its advocates, hadron therapy with carbon nuclei is more suited to the treatment of the most radiation-resistant tumours and could result in several hundred additional cancer cases being cured each year. 2.1.2 Technical rules applicable to external-beam radiotherapy facilities On account of the high dose rate when delivering the dose to the patient, the devices must be installed in rooms specially designed to guarantee radiation protection of the staff, turning them into veritable bunkers in which the wall thickness can vary from 1 to 2.5 metres of ordinary concrete). A radiotherapy installation comprises a treatment room including a technical area containing the treatment device, a control station outside the room and, for some accelerators, auxiliary technical premises. 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. The current conditions of design of these rooms was reviewed in 2019. A specific study must be carried out for each installation by the machine supplier, together with the medical physicist and the radiation protection advisor. This study defines the thicknesses and nature of the various protections required, which are determined according to the conditions of use of the device, the characteristics of the radiation beam and the use of the adjacent rooms, including those vertically above or below the treatment room. This study must be included in the file submitted to ASN to support the application for a license to use a radiotherapy installation. In addition, a set of safety systems informs the operator of the machine operating status (exposure in progress or not) and switches off the beam in an emergency or if the door to the irradiation room is opened. The bunker with shielding baffle remains the reference insofar as it reduces the shielding required at the ventilation duct and electrical duct inlets and provides greater security in the event of failure of the door motorisation system or if anyone gets accidentally locked inside. However, if the space available to the licensee is limited, which compromises the installation of the accelerator, a smaller shielding baffle, or even none at all, can be envisaged under certain restrictive conditions. The ZAP‑X® gyroscopic platform, a new medical device which obtained the “CE” marking in January 2021, presents the innovative characteristic of being self-shielded. A first machine of this type is currently being installed in France and is planned to start operating in 2023. As part of ASN’s examination of the application for a licence to possess and use this device, it has been put before IRSN and the Canpri will give its opinion on this new technique at the beginning of 2023. 2.1.3 Radiation protection situation in external-beam radiotherapy The installed base of external-beam radiotherapy facilities in 2022 comprises 592 particle accelerators installed in 174 radiotherapy centres subject to ASN licensing (see Graph 1). 214 ASN Report on the state of nuclear safety and radiation protection in France in 2022 • 07 • Medical uses of ionising radiation 07
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