Implementation of TG-351 Reference Dosimetry for a 6 MV Photon Beam in an MR-Guided Radiotherapy System

Abstract

Magnetic resonance guided radiation therapy (MRgRT) combines magnetic resonance imaging (MRI) and radiation therapy to enable the visualization of anatomy in real time during treatment. The presence of a magnetic field in MRgRT affects charged particle radiation and detector responses, necessitating changes to traditional reference dosimetry procedures. The American Association of Physicists in Medicine (AAPM) Task Group 351 (TG-351) provides a formalism for reference dosimetry in MRgRT. In this study, the TG 351 formalism is used to perform reference dosimetry for a 6 MV flattening filter-free (FFF) photon beam from a Viewray MRIdian MR-Linac radiation therapy system. Beam quality determination, magnetic field correction factors, and radial profile corrections for FFF beams are included in the calculation for absorbed dose to water. An overview is given for the experimental setup, geometry, and data processing. The procedures enable a framework for reference dosimetry in MRgRT environments.