Esophageal motion characteristics in thoracic esophageal cancer: Impact of clinical stage T4 versus stages T1-T3

PURPOSE: The main purpose was to investigate the differences of the esophageal motion (EM) and the internal target volume (ITV) margins for the esophagus between clinical T1-T3 (cT1-T3) and cT4 cases, using 4-dimensional computed tomography. A secondary purpose was to assess the metastatic lymph nodal motion (NM) and the ITV margins for lymph nodes (LNs) using the datasets of patients with nodal involvement pathologically defined. METHODS AND MATERIALS: We analyzed patients with thoracic esophageal cancer consecutively treated with definitive chemoradiation, measuring the EM and the ITV margins in the left-right, anteroposterior, and superoinferior directions. All esophageal contours were divided at the carina. The EM and NM were measured from the displacement of the centroid point between 0% images (at the end of inhalation) and 50% images (at the end of exhalation). The ITV margins were defined as the maximum distance in each direction from the clinical target volume at the 4-dimensional computed tomography average images to the intersection of the clinical target volume at the 0% and 50% images of complete coverage in each patient. RESULTS: The EM below the carina in cT4 was significantly smaller than that in cT1-T2 in all directions (P < .01) and than that in cT3 in all directions (left-right: P = .03, anteroposterior and superoinferior: P < .01). The EM in the case of a cT4 tumor located below the carina was smaller than that in the case of cT4 tumor located above the carina. The NM of abdominal-LNs was much larger than that of cervicothoracic-LNs and the EM below the carina. These tendencies were similar in the ITV measurements. CONCLUSIONS: The EM and the ITV margins in cT4 were significantly smaller than those in cT1-T3. The NM and the ITV margins of abdominal LNs were much larger than those of cervicothoracic LNs and the esophagus. In clinical radiation therapy planning for esophageal cancer, we should take cT stage into consideration.