Quantification of accumulated dose and associated anatomical changes of esophagus using weekly Magnetic Resonance Imaging acquired during radiotherapy of locally advanced lung cancer

•MRI is suited for tracking volumetric changes/accumulating doses in the esophagus.•Introduced medial axis of esophagus to calculate inter-fraction positional uncertainty.•Planned and accumulated esophagus dose-volume parameter differences are significant.•Longitudinal expansion of esophagus may link to acute esophagitis.