Dosimetric study of a respiratory gating technique based on four-dimensional computed tomography in non-small-cell lung cancer

This study sought to compare the differences in target volumes and dose distributions to the targets and organs at risk (OARs) between a four-dimensional computed tomography (4DCT)-based respiratory-gated intensity-modulated radiation therapy (IMRT) plan (Plan(EOE)) and a three-dimensional CT (3DCT)-based IMRT plan (Plan(3D)) in patients with non-small-cell lung cancer (NSCLC). For 17 patients with Stages I–III NSCLC, both 4DCT data and conventional 3DCT data were obtained. The Plan(3D) and Plan(EOE) were designed based on 3DCT data and 4DCT data, respectively. The displacements of the gross tumor volume (GTV) centroid were 0.13 ± 0.09 cm, 0.15 ± 0.1 cm, and 0.27 ± 0.27 cm in the right–left, anterior–posterior, and superior–inferior directions, respectively. The volume of the GTV(EOE) was 3.05 ± 5.17 cm(3) larger than that of the GTV(3D). The volume of the PTV(3D) was 72.82 ± 48.65 cm(3) larger than that of the PTV(EOE). There was no significant difference between the PTV(3D) and PTV(EOE) for V55.8, V60, V66 and the homogeneity index. The PTV(3D) had a lower target conformity index than the PTV(EOE) (P = 0.036). Plan(EOE) had a significantly lower lung V10, V20, V30, V40 and mean lung dose (MLD) than Plan(3D). For the heart, Plan(EOE) had a significantly lower V(30) and mean dose. In conclusion, 4DCT is an appropriate method for assessing the displacement of the GTV centroid in three dimensions. Plan(EOE) has smaller PTVs and a decreased dose and volume for the normal lung and heart, as compared with Plan(3D).