Comparison of internal target volumes defined by three-dimensional, four-dimensional, and cone-beam computed tomography images of a motion phantom

BACKGROUND: To explore the variations of the gross tumor volume (GTV) from different three-dimensional computed tomography (3DCT) scan modes and the consistency of internal target volume (ITV) between different 3DCT, cone-beam computed tomography (CBCT) and four-dimensional computed tomography (4DCT) scan, a study using a motion phantom simulating sinusoidal movement was conducted. METHODS: For three 3DCT scan modes: the GTV was contoured, and ITV(I) was generated on the basis of GTV with a 10-mm margin while ITV(II) and ITV(III) with a 0-mm margin on the motion direction. ITV(CBCT) and ITV(MIP) were contoured on the images of CBCT and maximum-intensity projection (MIP) reconstructed 4DCT images. The centroid position shifts of ITVs were analyzed. The volume consistency between ITV(I), ITV(II), ITV(III) and ITV(MIP) were evaluated by calculating the Dice similarity coefficient (Dsc) and the value of Δ Volume (ΔV). Furthermore, the 3DCT and CBCT images from 12 NSCLC patients were retrospectively collected, then the Dsc and ΔV were calculated. RESULTS: The mean ± standard deviation of centroid position of ITV(I), ITV(II) and ITV(III) were 2.3±4.7, 2.6±4.0, and 1.0±1.4 mm, respectively. The mean ± standard deviation of Dsc between ITV(I), ITV(II), ITV(III) and ITV(MIP) were 0.78±0.77, 0.86±0.1, and 0.94±0.05, respectively. The ΔV of ITV(I), ITV(II), ITV(III) were 29.67%, 17.22%, and 6.46%, respectively. The ITV from CBCT showed a deduction rate of 3.1–9.3% compared to 4DCT. For the patients, the mean Dsc andΔV between ITV(I) and ITV(CBCT) were 0.50 and 60.76%. CONCLUSIONS: The GTV acquired from 3DCT scan mode I possessed great deviation of centroid position and target volume. ITV on the basis of this GTV was significantly larger than ITV(MIP). A good similarity was showed between ITV(III) and ITV(MIP), 4DCT is still a golden standard for the ITV delineation, but in the absence of 4DCT, image from 3DCT scan mode III and KV-CBCT may be considered for ITV delineation with caution.