To quantify motion based variation of the target volume of the primary tumor over the course of chemoradiotherapy in esophageal cancer patients, and to use this information to calculate appropriate PTV (planning target volume) margins according to the margins recipe for patients receiving trimodality (neoadjuvant chemoradiation and surgery) or definitive chemoradiation in order to personalize radiation treatment, resulting in either better target coverage or a reduction in normal tissue radiation exposure.