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Objective To clear and definite the predictive value of low dose volume of lung on acute radiation pneumonitis(RP) in patients with middle and lower thoracic esophageal cancer. Methods Two hundred and five patients with middle and lower thoracic esophageal cancer treated with radiotherapy were followed up. The clinical factors and treatment parameters were analyzed by univariate and multivariate analysis. Indexes of low dose volume of lung were evaluated. Results The acute RP with ≥grade 2 were observed in 60 patients(29.27%, 60/205). The incidence of grade 2, 3 and 4 were 23.41%(48/205), 4.88%(10/205) and 0.98%(2/205), respectively. Univariate analysis showed that the X-ray length of esophagus cancer lesion,the maximum transverse diameter of GTV, GTV length, radiation fields, MLD, GTV volume, PTV volume and lung V5-V15 all had significant relationship with ≥grade 2 acute RP. Multivariate analysis showed that radiation fields, MLD and Lung V5 were the independent risk factors for ≥grade 2 acute RP. ROC curves showed that the efficiency value to predict RP for V5 values was 51.17%. Conclusion The low dose volume of V5 is effective in predicting ≥grade 2 acute RP in patients with middle and lower thoracic esophageal cancer. We recommend that it should be attached importance in the radiotherapy plan for middle and lower esophageal cancer in the future and the effective value should be ≤51.17%.