“…For treatment planning, the superior soft-tissue contrast of MRI can decrease organ delineation uncertainties (Schmidt and Payne 2015), whilst the dose-free nature of MRI enables multiple and extended acquisitions, accounting for cycleto-cycle breathing variations (Kauczor and Plathow 2006, Biederer et al 2010, Jaffray 2012. During treatment, the new generation of in-room MRI / X-ray treatment unit systems (Ménard and van der Heide 2014, Keall, Barton and Crozier 2014, Fallone 2014, Lagendijk et al 2014, Jaffray et al 2014, Mutic and Dempsey 2014 allows direct imaging and both inter-and intra-fraction treatment adaptation strategies (Bainbridge et al 2017a, Hunt et al 2018. The recent clinical application of hybrid MRI and treatment unit systems (Olsen, Green and Kashani 2014, Kashani and Olsen 2018 represents an important milestone in external beam radiotherapy, and this technology is expected to provide improved clinical outcomes and reduce toxicities as well as efficient workflows.…”