The goal of this clinical research study is to learn if the results of a positron emission tomography/computed tomography (PET/CT) scan done 10-14 days after beginning chemotherapy and radiation (chemoradiation) can predict how a patient with cancer of the esophagus will respond to chemoradiation. Researchers also want to learn if biomarkers (substances in the body associated with cancer) found in tumor tissue can predict response to chemoradiation.