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Objective: To observe prospectively the effect of different clinical target volumes （CTVs） on prognosis in patients with thoracic esophageal squamous cell carcinoma （SCC）, and to analyze the prognostic factors. To evaluate the relationship between regional lymph node failures and the dose to regional nodal stations in patients with T1-4N0M0 esophageal squamous cell carcinoma （SCC） without intentional elective nodal irradiation （ENI）.Methods: From May 2006 to November 2009, 94 patients with thoracic esophageal SCC were included in this study. They were randomized into the elective nodal irradiation group （the elective group） and the involved nodal irradiation group （the involve group） respectively. All the patients received 3DCRT. There were 49 patients in the involve group. The GTV was defined as any visible tumor on the image. The CTV was defined as the GTV plus a 3-cm margin superior and inferior to the primary tumor and a 0.8-1.0 cm radial margin. The involved lymphatic region was also included in the CTV. The PTV was defined as the CTV plus a 1.0-cm longitudinal margin and a 0.5-cm radial margin. The PTV1 was defined as GTV plus a 1.5 cm margin superior and inferior to the primary tumor and a 0.8-1.0 cm radial margin, and also the involved lymphatic region. There were 45 patients in the elective group. GTV, PTV and PTV1 were defined the same as that in the involved nodal irradiation group. Besides the same margins outside the primary tumor as that in the involved group, the adjacent regional lymphatics was included in the CTV according to the different location of the primary tumor. The prescribed dose to PTV was 50 Gy in 5 weeks followed by 10 to 12Gy to PTV1. For 18 T1-4N0M0 patients treated with 3DCRT without ENI, regional lymph node regions were outlined respectively according to the different locations of the primary tumor. And the mean dose and the percentage of volume receiving more than 50 Gy （V50）, 40 Gy （V40）, and 30 Gy （V30） for each region were computed for each nodal region.Results: （1） The tumor response rates were 95.9% and 97.8% in elective group and involved group respectively. No statistical difference was found in the two groups （P=0.817）. （2） Prognostic factors affecting the survival rate: The 1-, 2-, and 3-year overall survival rates were 66.9%, 55.4%, 36.2% in the involved group and 68.6%, 48.4%, 35.5% in the elective group respectively. The median survival was 28 months and 24 months. No statistical difference was found in the two groups （P=0.961）. The 1-, 2-, and 3-year survival rates were 70.8%, 63.0%, 37.8% in the CT-T1+2 group and 84.6%, 62.5%, 44.3% in the CT-T3 group and 40.0%, 29.1%, 21.8% in the CT-T43 group respectively （P=0.000）. The 1-, 2-, and 3-year survival rates were 72.6%, 46.0%, 33.8% in the CT-N0 group and 65.1%, 55.0%, 40.5% in the CT-N1 group respectively. No statistical difference was found between the two groups （P=0.828）. The 1-, 2-, and 3-year survival rates were 78.3%, 63.4%, 41.5% in≤5cm group and 59.6%, 39.6%, 31.2% in > 5cm group respectively（P=0.040）. The patients were divided into two groups according to the median volume of 34.9cm3. The 1-, 2-, and 3-year survival rates were 87.0%, 72.4%, 52.8% in≤34.9cm3 group and 49.9%, 29.3%, 18.3% in >34.9cm 3 group respectively （P=0.000）. The 1-, 2-, and 3-year survival rates were 95.2%, 84.4%, 61.6% in CR group and 61.1%, 42.3%, 28.7% in PR+SD group respectively. （P=0.002）. In Cox multivariate analysis, GTV volume before radiotherapy and short-term efficacy were independent factors for the overall survival,while the CTV size had no effect on the overall survival. （3） Prognostic factors affecting locoregional control rate: The 1-, 2-, and 3-year locoregional control rate were 72.4%, 59.4%, 54.5% in the involved group and 69.5%, 58.4%, 46.0% in the elective group respectively. No statistical difference was found between the two groups （P=0.640）. The 1-, 2-, and 3-year locoregional control rates were 87.8%, 87.8%, 65.9% in the CT-T1+2 group and 75.1%, 63.8%, 54.3% in the CT-T3 group and 54.0%, 32.7%, 32.7% in the CT-T4 group respectively （P=0.002）. The 1-, 2-, and 3-year locoregional control rates were 75.7%, 59.7%, 41.0% in the CT-N0 group and 68.5%, 58.4%, 54.8% in the CT-N1 group respectively. No statistical difference was found between the two groups （P=0.877）. The 1-, 2-, and 3-year survival rates were 86.9%, 76.7%, 65.8% in≤34.9cm3 group and 52.4%, 37.3%, 29.8% in>34.9cm 3 group respectively （P=0.000）. In Cox multivariate analysis, GTV volume before radiotherapy was the independent factor for locoregional control rate. The CTV had no effect on the locoregional control rate. （4） Prognostic factors affecting progression-free survival rate: The 1-, 2-, and 3-year progression-free survival rates were 63.8%, 43.7%, 43.7% in the involved group and 64.8%, 45.7%, 40.6% in the elective group respectively. No statistical difference was found between the two groups （P=0.887）. （5） More than 50% patients with T1-4N0M0 in the involved group received a mean dose≥40 Gy to left supraclavicular area, right supraclavicular area, 2R, 2L, 4L, 5, 7, paraesophageal region; More than 50% patients received V30≥90% to left supraclavicular area, 2R, 2L, 4R, 4L, 5, 7, paraesophageal region. Significant differences in incidental irradiation dose for levels 2R, 2L, 4R, 7 were found with tumor Location. The GTV volume and GTV length had no effect on the incidental irradiation dose. （6） Toxicities during and after Radiotherapy: Grade II and higher radiation esophagitis was 32.7% and 42.2% in the involved group and in the elective group respectively （P=0.338）. The symptomatic radiation pneumonitis was 30.6% and 35.6% in the two groups respectively （P =0.464）. （7） The comparison of dosimetry: The V10、V20、V30 and the mean dose of the lungs in the elective group were higher than those in the involved group, and statistical difference was found in V10, V20 indicators between the two groups. The maximum dose, the minimum dose and the mean dose to the spinal cord were higher in the elective group than those in the involved group with a statistical difference between the two groups. （8） Patterns of failures: The total failure rate was 51.0% and 51.1% in the involved group and the elective group respectively. Locoregional failure alone was 34.7% and 37.8% respectively. Distant metastasis was 16.3% and 13.3% respectively. No significant difference was found between the two groups.Conclusion: （1） Conformal radiotherapy with elective nodal irradiation for thoracic esophageal SCC showed no significant advantage over the conformal radiotherapy with the involved nodal irradiation in overall survival, locoregional control and progression-free survival. （2） Conformal radiotherapy with elective nodal irradiation conferred a higher radiation esophagitis and pneumonitis compared to conformal radiotherapy with involved nodal irradiation. （3） Dose to lungs and spinal cord was higher with elective nodal irradiation than that with involved nodal irradiation. （4） Lower regional lymph node failures in patients with esophageal carcinoma treated with radiotherapy is related to the incidental dose to regional nodal stations without intentional elective nodal irradiation （ENI）. （5） Volume of GTV before radiotherapy and short-term efficacy were independent factors for overall survival, GTV volume before radiotherapy was the independent factor for locoregional control rate.
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