LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT 2 – Nuclear-based medical activities 2.1 External-beam radiotherapy Radiotherapy, along with surgery and chemotherapy, is one of the key techniques employed to treat cancerous tumours. Radiotherapy uses ionising radiation to destroy malignant cells, as well as nonmalignant and dysfunctional cells, etc. We distinguish external-beam radiotherapy, where the source of radiation (particle accelerator or a sealed radioactive source in the case of Gamma Knife®) is external to the patient, from brachytherapy, where a sealed radioactive source is placed as close as possible to the cancerous lesion, either via the natural cavities or by catheters (see point 2.2). The radiation sessions are always preceded by the preparation of a treatment plan which serves to set the conditions for achieving a high dose in the target volume while preserving the surrounding healthy tissues. The treatment plan defines the dose to deliver, the target volume(s) to treat, the organs at risk to be protected, the ballistics of the radiation beams and the predicted dose distribution (dosimetry). Preparation of the treatment plan requires close cooperation between the radiation oncologist, the medical physicist and, if necessary, the dosimetrists. The main radiation protection risk is linked to the dose delivered to the patient; the change of treatment techniques with the development of hypofractionated radiotherapy (see point 2.1.1), which consists in delivering higher doses during a given session, makes it all the more crucial to control delivery of the dose. This is why ASNR’s oversight focuses on both the ability of the centres to control delivery of the dose to the patient, to adopt and master new artificial intelligence tools, and to learn lessons from the malfunctions that have occurred or could occur. The implementation of the Quality and Safety Management System (QSMS) and patient safety measures, skills management, equipment maintenance, a culture of reporting, and the ability to analyse adverse events thus make OEF central to ASNR inspections. As technical, organisational and human changes are potential risk-generating situations, particular attention is also given to change management during the inspections. 2.1.1 – Description of the techniques Several external-beam therapy techniques are currently used in France. The SFRO considers three-dimension conformal radiotherapy to be the basic technique in its Guide to recommendations for the practise of external-beam radiotherapy and brachytherapy (Recorad), updated in September 2025. This technique uses threedimensional images of the target volumes and neighbouring organs obtained with a Computed Tomography (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 technique 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 being used increasingly frequently in France and is the reference technique for prostate and head and neck cancers. This technique involves irradiating a target volume through the continuous variation of several parameters during treatment: the shape and intensity of the beams, and the position and rotational speed of the linear accelerator around the target volume and, consequently, around the patient. Helical radiotherapy, or tomotherapy, enables radiation treatment to be delivered by combining the continuous rotation of an 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 highlylocalised 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 (whether cancerous or not) with sub-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. This technique demands great precision in defining the target volume to irradiate and uses specific identification techniques in order to localise the lesions with millimetric accuracy. The increase in doses per treatment session usually implies, with linear accelerators, the use of Flattening-Filter-Free (FFF) beams which allow the dose rate and therefore the dose per session to be increased. This therapeutic technique essentially uses three specific types of equipment, such as: ∙Gamma Knife®, which uses more than 190 cobalt-60 sources, that is to say more than 190 non-coplanar beams centred on the tumour. The movement of the table on which the patient is positioned enables the desired dose to be delivered to the entire tumour with great precision. ∙CyberKnife® is a miniaturised linear accelerator mounted on a robotic arm, providing nearly 2,000 non-coplanar beam entry points around the patient. This machine also allows tumour position tracking during irradiation. ∙Multi-purpose linear accelerators equipped with additional collimation means (mini-collimators, localisers that can produce mini-beams), ensuring appropriate mechanical precision and equipped with a table with 6 degrees of freedom (allowing noncoplanar treatments and better positioning, among other things). A new mono-energy radiotherapy accelerator, a self-shielded gyroscopic platform called “ZAP-X®” (ZAP Surgical, 3 MV, FFF mode) was authorised in March 2023 for use in France for stereotactic intracranial radiotherapy and radiosurgery (see points 1.2.2 and 1.3.2). Contact therapy or contact radiotherapy is an external-beam radiotherapy technique. The treatments are delivered by specific devices using low-energy photon beams with the radiation source placed in contact with the lesion to irradiate (superficial lesions such as skin cancers, endocavitary lesions such as cancer of the rectum, sometimes in contact with the surgical field after removing the tumour, as might be the case with cancer of the pancreas or liver, etc.). Intraoperative electron radiotherapy is based on applying a beam of electrons (energy up to 12 MeV) directly to the surgical field using mobile electron accelerators featuring the “CE” marking and with built-in shielding to allow them to be used directly in the operating theatre. They allow optimal irradiation of the tumour (dose in a single very high fraction) while preserving the surrounding healthy tissues to the maximum extent possible. This technique is used primarily as a complement to secondary external-beam radiotherapy for treating non-removable tumours (sarcomas, pancreas, etc.). 198 ASNR Report on the state of nuclear safety and radiation protection in France in 2025
RkJQdWJsaXNoZXIy NjQ0NzU=