ASN Report 2017

272 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 09  - Medical uses of ionising radiation This resolution details in particular the rules for the ventilation of nuclear medicine unit premises and the rooms accommodating patients receiving, for example, treatment for thyroid cancer with iodine-131. Guide No. 32 detailing certain aspects of this resolution was published by ASN in May 2017 ( www.asn.fr ). Furthermore, the facilities equipped with a CT scanner coupled with a gamma camera or a PET camera must comply with the provisions of ASN resolution 2017-DC-0591 of 13th June 2017 (see chapter 3). 3. External-beam radiotherapy and brachytherapy 3.1 Description of the techniques Alongside surgery and chemotherapy, radiotherapy is one of the key techniques employed to treat cancerous tumours. Some 200,000 patients 5 are treated each year, which represents nearly 4 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 treatment is either produced by an electric generator or emitted by radionuclides in the form of a sealed source. There are thus two ways of delivering the radiation: external-beam radiotherapy, where the source of radiation produced by a particle accelerator or radioactive sources (Gamma knife ® for example) is external to the patient, and brachytherapy, where the source is placed in direct contact with the patient, within or as close as possible to the area to treat. One hundred and seventy-two radiotherapy centres hold an ASN license, half with public status and half in private practice. The pool of external-beam radiotherapy facilities comprises 476 treatment devices, of which 461 are conventional linear accelerators (Radiotherapy observatory, INCa 2016). Seven hundred and fifty radiation oncologists were listed in the directory of the French Society for Radiation Oncology (SFRO) in 2016. Lastly, 63 radiotherapy centres hold an ASN license to perform brachytherapy treatments. 3.2. The various external-beam radiotherapy techniques 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. 5 . 204,471 persons with cancer were treated by radiotherapy in 2015: 113,384 in the public sector and 91,087 in the private sector. www.e-cancer. fr/Professionnels-de-sante/Les-chiffres-du-cancer-en-France/Activite- hospitaliere#toc-radioth-rapie 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 megaelectronvolts (MeV) and delivering dose-rates that can vary from 2 to 6 grays per minute (Gy)/min, although some latest-generation linear accelerators can deliver much higher dose-rates of up to 25 Gy/min (in the case of photon beams). 3.2.1 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. 3.2.2 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 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