Abstract: Objective To compare the difference of dosimetric results in IMRT plans with 5-field for thoracic middle esophageal carcinoma.Methods Eight patients with thoracic middle esophageal carcinoma were involved in this study.Three IMRT plans with 5-field were designed for each patient.Plan IMRT1 included one anterior oblique field of patient left and two pairs of parallel-opposed fields.One pair of parallel-opposed fields were antero-posterior and postero-anterior(AP-PA).Another pair of f parallel-opposed fields were anterior oblique of patient right and posterior oblique of patient left which required to avoid the spinal cord.The fields of plan IMRT2 were equispaced,including 0°,72°,144°,216°and 288°.The fields of plan IMRT3 were optimized,including 0°,50°,150°,210°and 310°.Evaluation parameters included:mean dose(Dmean),homogeneity index(HI)and conformity index(CI)of PTV;V5,V10,V20 and V30 of total lung;V30,V40 and Dmean of heart;Dmax to the spinal cord.The aim of IMRT was follows:prescribed dose of 6000cGy/30Fx to 95% of PTV and 100% GTV.V20 of total lung ≤28%.The doses of heart were not limited.Dmax to the spinal cord were between 4200cGy~4300cGy.Results Significant differences of Dmean,HI and CI of PTV were obtained among the three plans(P＜0.05).All of the three evaluation parameters values in plan IMRT2 were higher than plan IMRT3.Plan IMRT3 were higher than plan IMRT1.But there were no significant difference of HI values between plan IMRT3 and plan IMRT2(P＞0.05).Significant differences of V5 and V30 of total lung were obtained among the three plans(P＜0.05).V5 values in plan IMRT2 were higher than plan IMRT1,and plan IMRT1 were higher than plan IMRT3.But there were no significant difference of V5 values between plan IMRT1 and plan IMRT3(P＞0.05).Among the three plans,V30 values in plan IMRT2 were the lowest one;plan IMRT1 were the second one,and plan IMRT3 were the highest one.There were significant difference of V30 values in plan IMRT2 and plan IMRT3(P＜0.05).There were no significant differences of V10,V20 and Dmean of total lung,cord Dmax.V30,V40 and Dmean of heart were among the three plans(P＞0.05).Conclusions Plan IMRT3 with angle optimized radiation fields improved CI of PTV,compared to IMRT1 in which parallel-opposed radiation fields were adopted.Plan IMRT3 had the advantage in reducing V5 of total lung and Dmean of PTV,compared to plan IMRT2 in which equispaced radiation fields were adopted.