Radiation therapy is an important treatment tool for patients with esophageal cancer. Some clinical data show that PET-CT can guide radiation therapy, thus improving the accuracy of radiation therapy and reducing the damage to surrounding tissues. At present, radiotherapy used to treat esophageal cancer in China is mainly based on external radiation, and the scope of irradiation is determined according to the actual invasion range of tumor and the possible surrounding subclinical lesions and regional lymph node drainage area. However, pulmonary, tracheal, spinal cord and cardiovascular radiation complications after radiation therapy have become one of the most important factors for increased mortality in esophageal cancer. Therefore, the determination of radiotherapy target area is the most critical part of radiation therapy for esophageal cancer. If PET-CT all-in-one system is used, it becomes a new platform for radiotherapy simulation and localization through its outstanding advantage of close combination of functional and anatomical images. This is because although CT images can clearly show anatomical features, it is difficult to determine the margins of infiltrating tumors and distinguish local infiltration and inflammatory reactions of tumors, but if combined with PET images, it can reflect the function, blood flow and molecular metabolism information of tumors and normal tissues. It further improves the accuracy of target area outlining for esophageal cancer, so as to maximize the protection of surrounding normal tissues and organs while delivering high-dose irradiation to the tumor during radiotherapy.