Objective:To compare the clinical factors and physical parameters between 3-fields and 4-field 3-dimensional con-formal radiotherapy(3DCRT)for mid-thoracic or upper-thoracic esophageal carcinoma.Methods:Patients with mid-thoracic or upper-thoracic esophageal carcinoma were chosen at random and treated with 3DCRT.Contouring and treatment planning were performed with VARIAN Eclipse treatment planning system(TPS).The target volume was determined according to guidelines from ICRU Report No.50.The three-beams treating plan and the four-beams treating plan were performed and a 8mm isotropic mar-gin was added for the planning target volume(PTV)in beam setting.The different plans were evaluated with dose volume histograms(DVH)in terms of dose coverage of PTV and protection of organs at risk(OAR).The prescribed dose was 60 Gy/30 F to the PTV.Results:There was no significant difference in the dose coverage to PTV and the explored dose to spinal cord with the two model of 3DCRT.When the three-beams treating plan was compared with four-beams treating plan

lungs V20 and V30 were significantly better

and at the same time lungs V5 was higher.Conclusions:3-fields 3DCRT is better than 4-fields 3DCRT with lower lungs V20 and V30 so as to prevent acute radial injury of lungs in radiotherapy of mid-thoracic or upper-thoracic esophageal carcinoma.