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 (CTEIH) and end-expiratory hold (CTEEH) 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,CTEIH and CTEEH images.The position,volume and MI of each segment esophagus between CT0 and CTEIH,CT50 and CTEEH were compared.Results In the left-right (x) direction,the position differences in the proximal,mid-,and distal thoracic esophagus between CT0and CTEIH 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 CT50 and CTEEH 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 CTEEH were not statistically significant,while the position differences in x and y directions of distal thoracic esophagus between CT50and CTEEH 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 CT0and CT50 than those in CTEIHand CTEEH,but without statistical differences.The MIs of the volumes of the proximal,mid-and distal thoracic esophagus between CT0 and CTEIH were (0.50 ± 0.17),(0.50 ± 0.19) and (0.56 ± 0.08),respectively,and those between CT50and CTEEH were (0.50 ±0.16),(0.47 ±0.14) and (0.51 ±0.15),respectively.The MI of each segment esophagus between CT0and CTEIHwas larger than that between CT50 and CTEEH,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.

Objective To analyze artifacts of gross tumor volume (GTV) and correlated factors in each phase images of four dimensional CT (4DCT) for peripheral lung cancer based on three dimensional CT (3DCT) assisted with active breathing control.Methods Nineteen patients with peripheral lung cancer underwent 3DCT (CTFB) and 4DCT simulation scans during free breathing and then underwent 3DCT simulation scans in end inspiration hold (CTEIH) and end expiration hold (CTEEH) assisted with active breathing control.The relative deviations (Devref) between the reference GTV (GTVref) and the GTVsdelineated based on CTFB (GTVFB) and all phases of 4DCT were calculated respectively.Correlations between GTVref and Devmax and between the tumor motion in the cranio-caudal (CC) direction and Devref were analyzed.Results The maximum median Devref of GTV was GTVFB with 17.83％,and the maximum median Devref of the GTV in all phases of 4DCT was GTV30 with 17.20％.A significant negative correlation was found between GTVEIH and Devmax (r =-0.691,P =0.001).The Devref was crrnelated with the tumor motion amplitude in the CC direction (r =0.323-0.617,P =0.005-0.150).The partial regression coefficient of influence of GTVref size and motion amplitude in the CC direction to the tumor Devmax were -0.500 and 0.583,P =0.002 and 0.001,respectively.Conclusions The GTV artifacts in different phase of 4DCT for the peripheral lung cancer were different to each other,and the influence of target displacement to artifacts was larger than that of target volume,so artifacts could be reduced by controlling breathing to reduce target displacement.