Multicentric characterisation of lateral beam profiles generated by 6FFF beam of three 0.35 T MR-linac systems.

Background: The physical characterisation of FFF-beam profiles in the presence of a magnetic field requires a new standardization procedure and formulation.

Purpose: The aim of this multicentric experience is to propose new normalisation factors to allow for the calculation of standard parameters typical of flattened beams, such as dosimetric field size and penumbra, for a 6 MV FFF beam from an MR-linac.

Methods: The measurements were carried out on three ViewRay-MRIdiansystems.