Comparative study of overall and stratified measurement of internal margin expansion of esophageal cancer based on four-dimensional computed tomography

Objective: To evaluate the difference of esophageal cancer internal margin expansion measured by contouring the overall or stratified GTVs parallel to the top, bottom and center level of adjacent vertebra based on 4DCT. Methods: Based on T1 phase of 4DCT scanned for 13 patients with esophageal cancer, an radiation oncologist contoured the gross tumor volumes of 10 respiratory phases in treatment planning system, the center coordinates of target volumes were recorded. Then according to the top, bottom and center level of adjacent vertebra, target volumes on multiple CT slices of 10 respiratory phases were contoured, the center coordinates (x, y) and maximum diameters of GTVs were recorded. Internal margins of multiple esophageal cancer layers contoured according to the adjacent vertebra were calculated by the formula: IM = x(y)T1-T10 - x(y)T1 ± (dT1-T10 - dT1), then the maximum IM of the same direction were filtered. The relationship of three dimensional movement of esophageal cancer and the difference of internal margin expansion measured by the whole or layers of esophageal cancer were analyzed. Results: The motion range of the whole esophageal cancer was 1.32 mm in left-right (x-axis) direction, 1.09 mm in anterior-posterior (y-axis) direction, and 2.92 mm in cranial-caudal (z-axis) direction. It was similar in x and y directions (t = 1.21, P = 0.251), but different in x and z directions (t = - 3.38, P = 0.005), and different in y and z directions (t = - 4.02, P = 0.002). There were significant relationship between motion range in x and y directions (r = 0.597, P = 0.040), in x and z directions (r = 0.662, P = 0.019) and in y and z directions (r = 0.723, P = 0.008). The mean movement of whole esophageal cancer in left, right,anterior and posterior was - 0.38, 0.94, - 0.62 and 0.47 mm, respectively; the mean maximum movement of esophageal cancer layers according to adjacent vertebra level was - 1.83, 2.21, - 1.85 and 2.02 mm ,respectively. There were significant differences of internal margin expansion by overall or stratified measurement of esophageal cancer in left , right , anterior and posterior dimensions (t = 5.15, - 4.58, 3.50, - 7.56, P = 0.000, 0.001, 0.004, 0.000). Conclusions: There was significant relationship between motion range in thee dimensions, internal margin expansion measured by the overall esophageal cancer was less than that by stratified measurement. (authors)