Objective To observe the curative effect,failure pattern and treatment-related toxicities of elective nodal irradiation (ENI) and involved field irradiation (IFI) in patients with thoracic esophageal squamous cell carcinoma treated with radical radiotherapy, and determine the reasonable target delineation of radiotherapy. Methods Using prospective randomized controlled design, a total of 86 patients with thoracic esophageal squamous cell carcinoma were randomly allocated to two groups:ENI group(n=39)and IFI group(n=47).Both groups received concurrent chemoradiotherapy.In ENI group,the high-risk lymphatic drainage area received prophylactic irradiation on the basis of IFI group.After the treatment, all patients were followed up for 3~33 months.The median follow-up period was 15 months.The short-term effective rate, one year survival rate, progression free survival rate and the local control rate of two groups were calculated. The survival curve was drawn by the Kaplan-Meier method,and the survival rate was compared using the Log-rank method.Meanwhile, the treatment failure pattern and incidence of adverse reactions were analyzed in the two groups. Results There was no significant difference in effective rate between ENI group and IFI group (92.3% vs. 95.7%,χ 2=0.460, P>0.05). The one-year survival rates were 66.7% and 68.1% for the two groups,respectively.The progression-free survival rates were 56.4% and 53.2% respectively.The local control rates were 92.3% and 87.5% respectively,with no statistical difference(P>0.05). The median survival time was 15 months at the end of the follow-up for group ENI and group IFI, and there was no significant difference in survival rate between two groups(Log-rank χ2=1.520,P=0.218).There were 35 cases with treatment failure in all 86 patients, of which 17 cases were in group ENI and 18 cases in group IFI. The regional failure rates were 35.9% and 27.7% in ENI and IFI groups respectively,distant metastasis rates were 20.5% and 14.9% respectively,in-field failure rates were 30.8% and 23.4% respectively, and out-of-field failure rates were 4.3% and 5.1% respectively, which showed no significant differences (P>0.05). There were no significant differences in side effects, the incidence of bone marrow suppression,gastrointestinal reactions,radiation esophagitis and radiation-induced lung injury between two groups (P>0.05). Conclusion ENI shows similar recent efficacy, failure patterns, adverse reactions and prognosis with IFI for thoracic esophageal squamous cell carcinoma patients receiving radical radiotherapy. So IFI treatment is recommended to minimize the exposure dosage of normal tissue.