Assessment of gross tumor volume motion and the influence factors during respiration for lung cancer using four-dimensional computed tomography

Objective: This study was to assess the three-dimensional gross tumor volume(GTV) motion of lung cancer caused by respiration using four-dimensional computed tomography (4DCT), and to analyze the influence factors. Methods: Four-DCT scans of 22 lung focuses in 21 patients with lung cancer were analyzed. The gross tumor volume was contoured in all 10 respiration phases of 4DCT scans. The changes in volume of GTV, the 3D motion of the centroid,boundary of GTV and the 3D spatial motion vectors were calculated and the influence factors were analyzed. Results: The average change in volume of GTV was + 14.3%(0.2%-42.5%)/-8.4% (0.4%-38.6%), the average movement amplitude of GTV centroid and GTV boundary were (0.18±0.12)cm, (0.20±0.16)cm, (0.53±0.59)cm and (0.42±0.23)cm, (0.41±0.22)cm, (0.57±0.70)cm in medio-lateral, vertro-dorsal, cranio-caudal (CC) direction, respectively. The CC movement was larger than other directions (Z=-2.12, P=0.034; Z:-2.10, P=0.035), and no significant difference was observed in 3D motion of GTV boundary (Z=-0.81, P=0.417; Z=-0.86, 0.391). The CC motion of GTV centroid in lower lobe was larger than that in upper lobe [(0.87±0.64) and (0.35±0.49)cm, (t=-2.12, P=0.047)], and no significant difference was found in other directions [(0.23±0.10) and (0.19±0.18)cm (t=-0.49, P=0.629), (0.21±0.13) and (0.17±0.11)cm (t=0.76, P=0.460)]. There was no correlation of the 3D movement and 3D spatial motion vector of GTV to the volume of GTV (r=-0.306, -0.062, -0.279, -0.300; P=0.189, 0.796, 0.234, 0.199). Conclusions: GTV motion of patients with lung cancer is individual, the CC movement is the moat obvious, using 4DCT to assess is comparatively accurate. The motion amplitude of lower lobe focuses is larger. No significant correlation of the GTV motion to the volume was observed. Larger sample study is needed to analyze the influence of adjacency to the GTV motion. (authors)