ASN Report 2020

2. External-beam radiotherapy 3. In 2019, 205,585 people with cancer were treated by radiotherapy in 4,284,242 sessions (source: INCa Observatory). 2.1  Description of the techniques Radiotherapy, along with surgery and chemotherapy, is one of the key techniques employed to treat cancerous tumours. More than 200,000 patients (3) are treated each year, which represents nearly 4.2 million radiation sessions. Radiotherapy uses ionising radiation to destroy malignant cells (and non-malignant cells in a small number of cases). The ionising radiation necessary for the treatments is produced by an electric generator or emitted by radionuclides in sealed sources. We distinguish external-beam radiotherapy, where the source of radiation (particle accelerator or a radioactive source such as Gamma Knife®) is external to the patient, from brachytherapy, where the source is placed as close as possible to the cancerous lesion. The installed base of external-beam radiotherapy facilities in 2020 comprises 536 particle accelerators installed in 174 radiotherapy centres subject to ASN licensing. The French Radiotherapy Observatory (source: National Cancer INstitute – INCa, 2019), lists 819 radiotherapists in 2019. The irradiation sessions are always preceded by preparation of a treatment plan which precisely defines the dose to be delivered, the target volume(s) to be treated, the volumes at risk to be protected, the irradiation beam setting and the estimated dose distribution (dosimetry) for each patient. Preparation of this plan, which aims to set conditions for achieving a high dose in the target volume while preserving surrounding healthy tissues, requires close cooperation between the radiation oncologist, the medical physicist and, when applicable, the dosimetrists. In the vast majority of treatments, irradiation is ensured using linear particle accelerators with an isocentric arm emitting beams of photons produced at a voltage varying from 4 to 25 megavolts (MV) or electrons with an energy level of between 4 and 25 mega- electronvolts (MeV) and delivering dose-rates that can vary from 2 to 6 grays per minute (Gy/min). It should be noted that some latest-generation linear accelerators can deliver much higher dose rates, of up to 25 Gy/min (in the case of photon beams). ASN issued 95 licenses in 2020. The majority of these cases concerned the updating of an existing license. 2.1.1 Three-dimensional conformal radiotherapy This technique 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.). During a three-dimensional conformal radiotherapy treatment, the shape of each beam is fixed and the dose delivered by each beam is uniform within the treatment field delimited by the multileaf collimator. In its guide giving recommendations for the practice of external- beam radiotherapy and brachytherapy (Recorad) published in September 2016, the French Society for Radiation Oncology (SFRO) considers that this irradiation technique is used as the basic technique by all the French centres for all patients receiving curative treatment. It has nevertheless been observed in the last few years that the proportion of treatments using this technique is giving way to intensity-modulated conformal radiotherapy. 2.1.2 Intensity-Modulated (conformal) Radiotherapy Intensity-Modulated (conformal) Radiotherapy (IMRT) is a technique that was developed in France in the early 2000’s. Unlike 3D conformal radiotherapy, the collimator leaves move during irradiation, enabling the intensity of the beams – and therefore the delivered dose – to be modulated during irradiation to better adapt to complex volumes and better protect the neighbouring organs at risk. Volumetric modulated arc therapy Following on from IMRT, volumetric modulated arc therapy is now being used more and more frequently in France. This technique consists in irradiating a target volume by continuous irradiation rotating around the patient. Several parameters can vary during the irradiation, including the shape of the multileaf collimator aperture, the dose-rate, the rotation speed of the arm or the orientation of the multileaf collimator. This technique, designated under different terms (Volumetric Modulated Arc Therapy – VMAT®, RapidArc®) depending on the manufacturer, is achieved using conventional isocentric linear accelerators equipped with this technological option. Helical radiotherapy 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 technique employed is similar to the principle of helical image acquisitions obtained with computed tomography. A photon beam, emitted at a voltage of 6 MV and a dose-rate of 8 Gy/min, shaped by a multileaf collimator enabling the intensity of the radiation to be modulated, allows the irradiation of large volumes of complex shape as well as extremely localised lesions, which may be in anatomically independent 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. In 2019, there were 42 devices of this type installed in France (source: Radiotherapy observatory, INCa 2019). 2.1.3 Stereotactic radiotherapy 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. In stereotactic radiotherapy treatments, 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 firstly requires great precision in defining the target volume to irradiate, and secondly that the treatment be as conformal as possible, that is to say that the irradiation beams follow the shape of the tumour as closely as possible. It was originally developed to treat surgically-inaccessible non- cancerous diseases in neurosurgery (artery or vein malformations, benign tumours) and uses specific positioning techniques to ensure very precise localisation of the lesion. It is used more and more frequently to treat cerebral metastases, but also for extracranial tumours. ASN Report on the state of nuclear safety and radiation protection in France in 2020 213 07 – MEDICAL USES OF IONISING RADIATION 07