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 radionuclide sources, in the form of sealed 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 risks 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 Presentation 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 dose-rate delivered by the sources used. Low Dose‑Rate (LDR) brachytherapy is carried out 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). 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 duration of the planned 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 ultra– sonography monitoring, and do not require hospitalisation in a room with radiation protection. The PDR technique, which uses source after loaders (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. 2.2.3 Radiation protection situation in brachytherapy ASN has licensed 59 brachytherapy centres, 50 of which use the HDR technique. ASN issued 19 licenses in 2021. The majority of these cases concerned the updating of an existing license (see Graph 3). The brachytherapy activity is stable. The INCa observatory has recorded 500 to 600 LDR treatments per year using iodine-125 seeds, 650 to 800 PDR treatments per year for gynaecological cancers, and about 3,000 HDR treatments per year. In the same way as for external-beam radiotherapy, the safety of brachytherapy treatments has been a priority area of ASN oversight since 2007, because of the intensity of the doses deliv– ered and, where applicable, the high dose rates. As brachytherapy is carried out within the radiotherapy departments, the inspection programme for the 2020‑2023 period is identical to that for external-beam radiotherapy, with a four-yearly frequency and checks similar to those applied in external-beam radiotherapy (see point 2.1.3.2). On account of the use of high activity sources, specific checks focus on medical staff training, such as knowledge of the action to take in the event of an emergency (source jam– ming), and the security of these sources (organisation in place for source management, appropriate measures to prevent unauthorised access to the sources, source inventory, protection against malicious acts and management of sensitive information). 16 inspections were carried out in 2021, representing slightly over a quarter of the licensed departments, and four of them were conducted remotely due to the Covid-19 pandemic. 2.2.3.1 Management of sources The brachytherapy sources are well managed. All the centres inspected record the tracking of source movements, transmit the source inventory to IRSN and store the sources waiting to be loaded or collected in a suitable place. 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. The organisational measures in place in 2021 enable the category of each source or batch of sources to be identified in all the inspected centres and in half the centres the personnel have been issued with the necessary authorisations to access the highactivity sealed sources. Furthermore, 66% of the inspected centres have put in place appropriate measures to prevent unauthorised access to these sources. ASN notes that the new requirements relative to protecting access to high-activity sources are being progressively deployed. 214 ASN Report on the state of nuclear safety and radiation protection in France in 2021 07 – MEDICAL USES OF IONISING RADIATIONS
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