Title: 4D dose reconstruction for scanned proton therapy using liver 4DCT-MRI Shortened running title: 4DCT-MRI for proton dose reconstruction (max 40 characters) Authors: MSc. Kinga Bernatowicz 1,2 , PhD Marta Peroni 2 , PhD Rosalind Perrin 2 , Prof Dr med Damian C. Weber 1,3 and Prof Dr Anthony J. Lomax 1,2 1 Department of Physics, ETH Zürich, 8092 Zürich, Switzerland 2 Proton Therapy Center, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 3 Department of Radiation Oncology, University Hospital of Zürich , 8092 Zürich , Switzerland Correspondence address : Kinga Bernatowicz, Paul Scherrer Institute, WBBA/007, 5232 Villigen PSI, Switzerland; Phone +41 56 310 50 16 Fax: +41 56 310 21 99; kinga.bernatowicz@psi.ch Acknowledgment: This work is supported by the SNF grant 320030-1493942-1. Authors would like to acknowledge MGH Boston for sharing liver 4DCT data. Many thanks to ETH Zurich and University Basel for collaboration on 4DMRI image acquisition and processing. Summary 4DCT-MRI can simulate many 4DCT data sets by combining patient CT with motion extracted from 4DMRI studies. 4DCT-MRI images have been generated using different motion extraction approaches and compared with 4DCT data of liver patients. This method extends the capabilities of motion modeling for accurate 4D dose calculations by accounting for realistic and variable motion patterns. 4DCT-MRI enables plan robustness studies to different motion conditions and 4D dose reconstruction of delivered plan for patient-specific QA. © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/