Comparison of the Planning Target Volume Based on 3-dimensional CT and 4-dimensional CT Images of Thoracic Esophageal Cancer

Abstract

To compare the centroid position, volumetric differences and dice similarity coefficient (DSC) of planning target volume (PTV) based on three-dimensional CT (3DCT) and four-dimensional CT (4DCT) for the thoracic primary tumor of esophageal cancer. Forty-three patients with esophageal cancer underwent 3DCT and 4DCT simulation scans of the thorax during normal free breathing. The motion of primary tumors located in the proximal (group A), mid-(group B), and distal (group C) thoracic esophagus were obtained from the 4DCT scans. PTV3D was defined on 3DCT using the tumor motion measured by 4DCT scans; PTV4D was defined as the union of the target volume contoured on the 10 phases of 4DCT images. The differences in target centroid position, volume, DSC, and degree of inclusion (DI) between PTV3D and PTV4D were evaluated for tumors in different groups respectively. The mean centroid shifts between PTV3D and PTV4D in the three dimensional directions were less than 0.3 cm, for all the three groups. However, the target centroid shift was demonstrated significant difference in lateral direction for group C (Z = -2.355, p = 0.019). The median size ratio of PTV4D to PTV3D was 0.79 ± 0.07, 0.91 ± 0.25, and 0.70 ± 0.07 for group A, B and C. There was no significant correlation between the ratio of PTV4D to PTV3D and the target motion for the three groups. The DSC between the PTV4D and PTV3D were 0.87 ± 0.04, 0.88 ± 0.06, and 0.81 ± 0.03. The median DI of PTV3D in PTV4D was 0.78, 0.85, 0.69 for group A, B and C, and the median DI of PTV4D in PTV3D was 0.98, 0.97, and 0.99 for group A, B and C, respectively. The 3DCT-based PTV provides a good coverage of the 4DCT-based PTV, especially for middle esophageal tumors, but for proximal and distal esophageal tumors, PTV3D also encompasses relatively large normal tissues.