[A Survey of Dosimetry in the Magnetic Field of MR-Linacs].

In recent years, MR-Linac, a radiotherapy linear accelerator (linac) equipped with magnetic resonance (MR) imaging, has been deployed in clinical facilities across Japan. Because of the magnetic field of MR-Linac, which can affect the dose distributions and dose response of ionization chambers, conventional reference dosimetry for absorbed dose to water using an ionization chamber becomes impractical. Consequently, the magnetic field effect should be considered in the reference dosimetry for MR-Linac. Although numerous studies have delved into this matter and several magnetic field correction methods have been proposed to extend the conventional formalism, a practical protocol for reference dosimetry for MR-Linac remains elusive.The purpose of this review are as follows: (i) to summarize and evaluate literature and existing datasets as well as identify any gaps that highlight areas for the future research on this topic; (ii) to elucidate dosimetric challenges associated with ionization chamber dosimetry in magnetic fields; and (iii) to propose a formalism for reference dosimetry for MR-Linac based on available literature and datasets. This review focuses on studies based on commercially available MR-Linacs and datasets, specifically tailored for reference-class cylindrical ion chambers.