Study on the installation and implementation of linear accelerators coupled to a nuclear magnetic resonance system in radiotherapy (IRM-linac). Report from the IRSN/SFPM working group

In the frame of the marketing of new radiation therapy devices coupling a linear electron accelerator to a magnetic resonance imaging system (MR-linac), the French Nuclear Safety Authority referred to the IRSN in order to achieve a state of the art for this technology and to identify the points of vigilance regarding the impact of the presence of a magnetic field on the operation of a radiation therapy service, the control of the dose delivered and the specificities of patient care work-flow. The study was conducted by relying on the expertise of the French Society of Medical Physics by establishing a working group (WG) lead by the IRSN. The WG has performed auditions (MR-linac manufacturers, first French center installing a machine, national metrology laboratory, medical physicists), tours of facilities, discussions with manufacturers and analysis of their documentation, a review of recent scientific literature, which evolves very quickly, and the drafting of this report. The numerous observations and recommendations concern the impact of the magnetic field on the accelerators of the neighbouring rooms, the impact of the quality of the MRI images on the quality of the treatment, the impact of the magnetic field on the measurements of the beam characteristics (commissioning and quality control), in particular on the beam calibration, the impact of the magnetic field on the dose distribution in the patient and the performance expected (recipe and quality control) for the treatment planning system, the independent control of the dose (second calculation and in vivo dosimetry), and finally the impact of the use of a MR linac on the organization of a radiation therapy service and on human resources, in particular the training of professionals, the adaptive radiotherapy specific organization and the risk management regarding electromagnetic fields. (authors)