Mapping patterns of metastatic lymph nodes for postoperative radiotherapy in thoracic esophageal squamous cell carcinoma: a recommendation for clinical target volume definition

Background: The clinical target volume (CTV) for postoperative radiotherapy for thoracic esophageal squamous cell carcinoma (TESCC) needs to be defined. The study aim was to map metastatic lymph nodes (LNMs) in a computed tomography (CT)-based atlas and delineate the postoperative radiotherapy target area. Methods: Sixty-nine TESCC patients with first recurrent regional LNMs after esophagectomy were included. The LNM epicenters were registered onto corresponding anatomic axial CT images of a standard patient in the treatment position, with reference to the surrounding vascular and bony structures. The LNM sites were based on lymph node map of esophageal cancer, AJCC 8th. The lymph metastasis risk for different segments of thoracic esophagus was assessed. Results: One hundred and seventy-nine LNMs were mapped onto standard axial CT images. The upper-middle mediastinum region (station 1 to 8 M) contained 97% of metastases in the upper segment of thoracic esophagus, 90% in the middle segment, and 66% in the lower one. Advanced pathological stage (>==IIIB) might be a predictive factor for upper abdominal region (UAR) relapse in lower TESCC. Lower cervical para-tracheal LNMs were within a 4.3-cm bilaterally expanded area from the midline of the body and a 2.2-cm expanded area from the anterior of vertebral body, from the superior border of the C7, to the inferior border of the first thoracic vertebra. Conclusion: A modified target from the upper border of C7 to the lower border of caudal margin of the inferior pulmonary vein level could cover the high-risk area of TESCC underwent postoperative radiotherapy. UAR seems to be an elective irradiation target for lower TESCC at pathological IIIB stage and higher.