Explore the Radiotherapeutic Clinical Target Volume Delineation for Thoracic Esophageal Squamous Cell Carcinoma from the Pattern of Lymphatic Metastases

Introduction: Esophageal carcinoma is characterized by a high frequency of lymph node metastasis (LNM). It is difficult to accurately define the radiotherapeutic clinical target volume in patients with thoracic esophageal squamous cell carcinoma (ESCC), because the LNM rate and the included node level varied greatly among previous studies. This study aimed to determine which node level should be included for radiotherapy by analyzing LNM rate in thoracic ESCC patients. Methods: The clinicopathological factors related to LNM were analyzed using the chi(2) test. The sites with LNM rate higher than 15%, an empirical cutoff value, were considered as high-risk areas and were included in clinical target volume of thoracic ESCC patients for radiotherapy. Results: This study included 1893 thoracic ESCC patients treated at Shandong Cancer Hospital, Jinan, China. The rates of LNM in patients with upper thoracic tumors were 14.6% cervical, 29.3% upper mediastinal, 8.5% middle mediastinal, 9.8% lower mediastinal, and 7.3% abdominal, respectively. The rates of LNM in patients with middle thoracic tumors were 4.3%, 5.0%, 32.9%, 2.5%, and 14.9%, respectively. The rates of LNM in patients with lower thoracic tumors were 2%, 2.2% 15.4%, 38.1%, and 27.5%, respectively. Independent prognostic factors for LNM included length of tumor, histologic differentiation, and depth of tumor invasion (p < 0.001). Conclusions: Irradiation of the selective regional lymph node and the correlated lymphatic drainage regions should be performed according to the clinicopathological factors. For the large, deeply invasive longer tumors and poorly differentiated thoracic ESCC, the irradiation field should be enlarged appropriately.