ESTRO 2021 Abstract Book

S621

ESTRO 2021

Conclusion No quantity could be identified as superior. More experimental data with smaller statistical uncertainties are needed to determine the best input parameter for phenomenological RBE models for protons. Alternatively, it might be the case that for protons, many of the various beam quality quantities might correlate to such a high degree that the corresponding RBE predictions become only marginally different, thereby making the choice of beam quality quantity almost inconsequential. This question will be resolved in the future when more RBE data are available.

Poster discussions: Poster discussion 11: Quality assessment of complex techniques

PD-0788 First results from the national network for quality assurance of MR images in RT in Denmark S.W. Hasler 1,2 , J.F. Kallehauge 3,4 , R.H. Hansen 5 , C.M. Nilsson 6 , D.T. Arp 7 , H.D. Nissen 8 , J.M. Edmund 9,10 , F. Mahmood 1,2 1 Odense University Hospital, Laboratory of Radiation Physics, Department of Oncology, Odense, Denmark; 2 University of Southern Denmark, Department of Clinical Research, Odense, Denmark; 3 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 4 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark; 5 Copenhagen University Hospital, Section for Radiation Therapy, Department of Oncology, Center for Cancer and Organ Diseases, Copenhagen, Denmark; 6 Zealand University Hospital, Radiation Therapy Department, Næstved, Denmark; 7 Aalborg University Hospital, Department of Medical Physics, Department of Oncology, Aalborg, Denmark; 8 Vejle Hospital, Department of Medical Physics, Vejle, Denmark; 9 Herlev and Gentofte Hospital, Radiotherapy Research Unit, Department of Oncology, Herlev, Denmark; 10 University of Copenhagen, Niels Bohr Institute, Copenhagen, Denmark Purpose or Objective It is known that MRI is not as geometric accurate as CT. In MRI-guided RT this can have implications for the accuracy of dose delivery. MRI is now available in all RT facilities in Denmark and to monitor image quality, a national network for quality assurance of MR images in RT in Denmark (NIMBUS) was founded in 2018. The aim of the network is to improve quality by performing and sharing measurements and knowledge across all centers in Denmark and in particular to secure image quality in national clinical trials. By identifying baseline