SUMMARY In radiotherapy, the inspections carried out by ASN in nearly one quarter of the radiotherapy units in 2022, considered alongside those carried out over the period 2018-2021, enabling all the departments to be covered, confirm that the safety fundamentals are in place: organisation of medical physics, equipment verifications, training in the radiation protection of patients, deployment of quality assurance procedures, recording and analysis of events. However, the analysis of the 2018-2022 period confirms that assessing the effectiveness of corrective actions is still the weak point of the ILS procedures and is struggling to become more widely adopted. Although the preliminary risk assessments are inadequately updated prior to an organisational or technical change or following the analysis of events, ASN view positively the voluntary development of peer review practices in medical physics, when new equipment is installed. ASN underlines that the buy-outs of centres are situations entailing considerable disruptions that lead to risks if the impact on the working activity of the professionals is not analysed and if these changes are not prepared for with all the teams. ASN also observes that the formalisation of the specific work tasks authorisation procedures, which have been mandatory since August 2021, is being deployed with differences between the professional categories. Finally, the occurrence of events such as patient identification errors, delineation of organs at risk and/or target organs, and once again calibration, still reveals organisational weaknesses and the need to regularly assess practices. ASN moreover observes a loss of memory of lessons learned from past ESRs and a steady reduction the number of ESRs reported to ASN since 2015. Although this can be partly attributed to greater treatment safety, a regression in the culture of reporting internal events is noticeable, with the events analysis committees meeting less frequently and conducting less detailed analyses. Furthermore, the occurrence of cyber attacks also underlines the new challenges facing radiotherapy professionals in a context of increasing digitisation of data. Finally, the new techniques and practices, which are constantly evolving, are not always sufficiently evaluated to allow an assessment of the long-term radiation induced effects (adaptive radiotherapy, hypofractionation, flash-radiotherapy, etc.). 2.2 Brachytherapy Brachytherapy can be used to treat cancerous tumours either specifically or as a complement to another treatment technique. This technique consists in placing sealed radionuclide sources either in contact with or inside the solid tumours to be treated. The main radionuclides used in brachytherapy are iridium-192 and iodine-125. Brachytherapy uses three techniques, which differ more specifically in the dose rate applied (details below) according to the indications. As with radiotherapy, the radiation protection risks are linked to the intensity of the dose delivered to the patient and, if applicable, the high dose rates and the mastery of the equipment. Furthermore, as high-activity sources are involved, the management of emergency situations in the event of source jamming, as illustrated by the feedback from events reported to ASN, and the security of the sources, constitute specific issues of brachytherapy. That is why the ASN checks focus on the management of source security in addition to those on external-beam radiotherapy. 2.2.1 Description of the techniques The radiation protection risks in brachytherapy, apart from the problem of managing sealed sources, depend on the dose rate associated with the technique, the method of delivering the radiation to the tumour (permanent or temporary implantation, or temporary application). The use where necessary of source afterloaders means that the medical personnel do not have to handle the sources and allows the patient to be treated without irradiating the personnel or interrupting the treatment when the sources are stored in the afterloader. On the other hand, it is necessary to make provision for accident situations associated with malfunctioning of the source afterloader and the high doserate delivered by the sources used. Low Dose‑Rate (LDR) brachytherapy is carried out at present using sealed sources of iodine-125 in the form of permanently implanted seeds, or caesium-137 applied temporarily. The dose rates are between 0.4 and 2 grays per hour (Gy/h). A new medical technique called “DaRT” (Diffusing alpha emitters Radiation Therapy) is currently being tested in a clinical investigation into the treatment of skin cancers. This technique consists in implanting sealed radium-224 sources which emit alpha particles in the tumour using an afterloader; the sources are left in the tumour for 15 to 20 days. Pulsed Dose‑Rate (PDR) brachytherapy delivers dose rates of between 2 and 12 Gy/h and uses sources of iridium-192 with a maximum activity of 18.5 gigabecquerels (GBq), which are applied with a specific source afterloader. It is based on the use of a single radioactive source which moves in steps, and stops in predetermined positions for predetermined times. The doses are delivered in sequences of 5 to 20 minutes, sometimes even 50 minutes, every hour for the entire duration of the treatment, hence the name pulsed dose-rate brachytherapy. High Dose‑Rate (HDR) brachytherapy is carried out using high-activity (about 370 GBq) sealed sources of iridium-192 or cobalt-60. The dose rates are higher than 12 Gy/h. The treatment is performed using an afterloader containing the source, and the treatments are delivered on an out-patient basis in one or more sessions lasting a few minutes, spread over several days. 2.2.2 Technical rules applicable to brachytherapy facilities The rules for radioactive source management in brachytherapy are comparable to those defined for all sealed sources, regardless of their use (see point 1.3.1). In cases where permanent implant techniques are used (LDR), the applications are carried out in the operating theatre with ultrasonography monitoring, and do not require hospitalisation in a room with radiation protection. The PDR technique, which uses source afterloaders (usually 18.5 GBq of iridium-192), necessitates hospitalisation of the patient for several days in a room with radiological protection appropriate for the maximum activity of the radioactive source used. Lastly, with the HDR sources, as the maximum activity used in the source afterloaders is high (370 GBq of iridium-192 or 91 GBq of cobalt-60), the irradiations can only be carried out in a room with a configuration comparable to that of an external-beam radiotherapy room in terms of collective protection because of the high dose level used. The Order of 29 November 2019 sets the obligations concerning the protection of ionising radiation sources and batches of radioactive sources of categories A, B, C and D against malicious acts. The requirements concerning the protection barriers and their resistance time for category A, B and C sources shall be enforceable as from 1 July 2022. ASN Report on the state of nuclear safety and radiation protection in France in 2022 219 • 07 • Medical uses of ionising radiation 07 01 08 13 AP 04 10 06 12 14 03 09 05 11 02
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