Differences in displacement of the proximal and distal ends of mid-upper thoracic esophageal squamous cell carcinoma

In the present study, clips were used as markers to evaluate displacement differences between proximal and distal ends of esophageal tumors and to test whether their internal target volume (ITV) margins should be determined separately. A total of 23 patients with mid-upper thoracic esophageal squamous-cell carcinoma, a tumor length of ≤8 cm and an esophageal lumen suitable for endoscopic ultrasonography were recruited for the present study. Clips were implanted endoscopically at the proximal and distal ends of the esophageal tumor (upper and lower clips). In a further exploratory study on 16 of the patients, a third clip was placed at the distal esophagus 2 cm above the gastro-esophageal junction (GEJ) (cardiac clip). The clips were contoured for all 10 phases of the four-dimensional computed tomography and the maximum displacements of the clip centroids among different breathing phases in left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions were marked as x, y and z, respectively. The ITV margins that covered 95% of the LR, SI and AP motion were 2.89, 5.00 and 2.36 mm, respectively. Axial displacement (y) was greater than radial displacement (x, z; P<0.05). It was also revealed that LR(x), SI(y) and AP(z) displacement of cardiac clips was greater than that of upper or lower clips (P<0.05). Differences in the axial and radial displacement of the upper and lower clips indicated that axial and radial ITV margins should be determined separately. However, further study is required on patients in whom the distal tumor end is located in proximity to the GEJ.