Effect of CT pitch on the GTV delineation of solitary pulmonary lesion

Objective: To explore the effect of pitch in three-dimensional computed tomography (3DCT) on the gross tumor volume (GTV) and spatial position of solitary pulmonary lesion (SPL), and to evaluate the feasibility of high-pitch 3DCT simulation for SPL. Methods: Twenty-two patients with peripheral lung cancer or metastatic SPL were divided into groups A and B according to the tumor location. All patients underwent spiral CT scans at different pitches (pitch_CON = 0.938, pitch_S = 0.438, and pitch_B = 1.188) during free breathing. All GTVs were delineated by the same radiation oncologist using the same contouring protocol. GTV_CON generated at pitch_CON, GTVs generated at pitches, and GTV_B generated at pitch_B were compared in terms of volume and geometric position, and GTVs and GTV_B were registered to GTV_CON gained at the conventional pitch. The Friedman M and Wilcoxon rank-rum test were used for comparison. Results: The volumes of GTV_CON, GTV_S,and GTV_B were 11.58 ± 16.42 cm³, 11.63 ± 17.73 cm³, and 12.09 ± 17.46 cm³, respectively (P = 0.11). There were no significant differences in the centroid position in x, y, and z directions between GTV_CON, GTV_S, and GTV_B (P_x = 0.33, P_y = 0.81, P_z = 0.39). The same result was found in group B (P_x = 0.92, P_y = 0.05, P_z = 0.37). The matching index (MI) between GTV_S and GTV_CON was related to the tumor location, so was the MI between GTV_B and GTV_CON. Conclusions: The pitch in 3DCT simulation has no significant effect on the GTV and spatial position of SPL. Increasing CT pitch appropriately can improve the scanning speed and shorten the duration of 3DCT simulation, so high-pitch 3DCT simulation is feasible for SPL. (authors)