Comparison of the position and volume of esophagus between quiet end-inspiration and end-expiration three dimensional CT assisted with active breathing control and corresponding phases in four dimensional CT

Objective: To compare the position, volume and matching index (MI) of esophagus between quiet end-inspiration and end-expiration in three dimensional CT (3D-CT) assisted with active breathing control (ABC) and the corresponding phases in four dimensional CT (4D-CT). Methods: Eleven patients with peripheral lung cancer underwent 4D-CT simulation scan and 3D-CT simulation scans in end-inspiratory hold (CT_EIH) and end-expiratory hold (CT_EEH) in succession. The 0% phase was defined as end-inspiratory phase (CT₀), while the 50% phase was defined as end-expiratory phase (CT₅₀). The proximal, mid-, and distal thoracic esophagus were delineated separately on CT₀, CT₅₀, CT_EIH and CT_EEH images. The position, volume and MI of each segment esophagus between CT₀ and CT_EIH, CT₅₀ and CT_EEH were compared. Results: In the left-right (x) direction, the position differences in the proximal, mid-, and distal thoracic esophagus between CT₀ and CT_EIH were (-0.02±0.16) cm, (0.06±0.26) cm and (0.10±0.33) cm respectively, and in the anterior-posterior (y) direction, the position differences were (0.04±0.24) cm, (0.04±0.12) cm and (0.08±0.15) cm respectively, and the position differences in the same direction were not statistically significant. In the x direction, the position differences of the proximal, mid-, or distal thoracic esophagus between CT)₅₀ and CT_EEH were (-0.02±0.24) cm, (0.12±0.37) cm and (0.26±0.33) cm respectively, and in the y direction, the position differences were (0.03±0.21) cm, (0.04±0.17) cm and (0.14±0.18) cm respectively, and the position differences in x and y directions of proximal and mid-thoracic esophagus between CT₅₀ and CT_EEH were not statistically significant, while the position differences in x and y directions of distal thoracic esophagus between CT₅₀ and CT_EEH were both statistically significant (t = 0.025, 0.024, P < 0.05). The volumes of the proximal, mid- and distal thoracic esophagus were all larger in CT₀ and CT₅₀ than those in CT_EIH and CT_EEH, but without statistical differences. The MIs of the volumes of the proximal, mid- and distal thoracic esophagus between CT₀ and CT_EIH were (0.50±0.17), (0.50±0.19) and (0.56±0.08), respectively, and those between CT₅₀ and CT_EEH were (0.50±0.16), (0.47±0.14) and (0.51±0.15), respectively. The MI of each segment esophagus between CT₀ and CT_EIH was larger than that between CT₅₀ and CT_EEH, but without statistical differences. Conclusions: The influence of breathing modes on the centroid positions of the proximal, mid-thoracic normal esophagus were not significant and there were spatial mismatches for any segment esophagus between 3D-CT assisted with ABC and 4D-CT. (authors)