ASN Report 2018

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 (MRI, PET, 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 multi-leaf collimator. In its guide giving recommendations for the practice of external-beam radiotherapy and brachytherapy ( Recorad ) published in September 2016, the 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 (IMRT) 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 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 (VMAT®, RapidArc®) depending on the manufacturer, is achieved using isocentric linear accelerators equipped with this technological option. • Helical radiotherapy Helical radiotherapy, marketed under the name TomoTherapy®, or RadixactTM for the subsequent generation, 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. Thirty-two systems of this type were inventoried in France in 2017 (Radiotherapy Observatory, INCa 2017). 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 extra-cranial tumours. This therapeutic technique chiefly uses three specific types of equipment, such as: ∙ ∙ Gamma Knife®, which uses more than 190 sources of cobalt-60 whose emission is directed towards a single focal point (5 units in service); Breakdown of the number of external-beam radiotherapy facilities inspected by ASN in 2018 0 10 20 30 40 50 60 70 80 90 100 Strasbourg Division Paris Division Orléans Division Nantes Division Marseille Division Lyon Division Lille Division Dijon Division Châlons-en- Champagne Division Caen Division Bordeaux Division Authorised centres Accelerators Authorisations Diagram 5 ASN report on the state of nuclear safety and radiation protection in France in 2018  207 07 – MEDICAL USES OF IONISING RADIATION 07