 The aim of study is to evaluate the benefit of adaptive radiation therapyART for esophageal cancer. 80 patients with locally advanced esophageal cancer will be treated with 3D-CRTthree dimensional conformal radiotherapy, 3D-CRTIMRTintensity modulated radiotherapy, IMRT, dividing to experimental group and control group 40 patients each. All patients are kVCTkilo-voltage computed tomography, kVCT scanned weeklythe fifth fraction in a week and CBCT cone beam computed tomography, CBCT scanned per fraction before treatment. Irradiated dose distribution of each patient is calculated using the CBCT images corrected with validated modelling and accumulate the volumetric dose for all PTVplanning target volume,PTV and OARsorgans at risk, OAR using deformable registration algorithm. For the experimental group, replan the treatment when the target volume is not covered by the prescribed dose or OARs is overdose beyond the action level to achieve an optimal dose distribution. Conversely, no action is taken in the control group and the original plan will be used for the full treatment course. Dosimetric parameters such as the ratio of target coverage, the mean dose of OARs, etc ,treatment toxicities such as radiation pneumonitis and esophagitis, PFSProgress Free Survival,PFSand OSOverall Survival, OSof the two groups will be analyzed and compared in the study. 