Respiratory motion is a major concern in radiotherapy (RT) in liver cancer patients. Probability-based treatment planning is an evolving approach for tumor motion management. A major hurdle of this approach is that the dosimetric error is tightly linked to the reproducibility of the tumor motion probability density function (PDF). Previous studies in lung used single-slice dynamic MRI for PDF reproducibility evaluation that could only captured the 2D respiratory motion restricted by the MRI acquisition speed. Moreover, inter-subject and inter-fractional variability of time evolved PDF might be underestimated by using just two fractions. In this study, we aim to investigate the inter-fractional and inter-subject abdominal motion PDF and its reproducibility using an ultrafast volumetric 4D- MRI.