Magnetic resonance imaging (MRI) with functional features of diffusion weighted imaging (DWI) are advancing imaging technologies that have potential to overcome limitations of conventional staging methods, radiation treatment planning and the assessment of tumor response in esophageal or esophagogastric cancer. This study aimed to explore the value of MRI for the prediction of tumor response to chemoradiotherapy and accurate target volume delineation as compared to CT simulation for patients with unresectable or potentially resectable esophageal or esophagogastric cancer undergoing chemoradiotherapy. The average CT texture features are also extracted before and during treatment to establish a model to predict the prognosis or side effects (e.g. radiation pneumonitis or esophagitis) of patients.