Abstract
This study presents a method for fast and low-cost X-ray beam quality checks of magnetic resonance-guided radiotherapy (MRgRT) linacs using the on-board megavoltage imager (MVI). On four linacs from two clinics, beam quality was varied (quantified by ionization chamber measurements) and correlated with MVI-measured beam flatness. Both inter-linac consistency and long-term repeatability were demonstrated. The model developed for MVI-based beam quality checks was assessed in clinical practice and can be implemented on any linac of the same type for use in daily, automated dosimetry checks.