Geometrical differences in gross target volumes between 3DCT and 4DCT imaging in radiotherapy for non-small-cell lung cancer

摘要

A total of 28 patients with peripheral NSCLC underwent 4DCT simulation for treatment planning between September 2009 and July 2010 in Shandong Cancer Hospital and Institute. Pathology demonstrated adenocarcinoma in 21 patients, squamous cell carcinoma in 6 patients, and adenosquamous carcinoma in 1 patient. The patients included 19 men and 9 women, and had a median age of 60 (range, 39–80). The T stage, according to the TNM classification of AJCC (7th edn, 2009), was classified as T1 in 17 patients, T2 in 7 patients and T3 in 4 patients. The patients were divided in two groups: those with lesions located in the upper lobe (16 patients) belonging to Group A, while those with lesions located in the middle lobe (3 patients) or in the lower lobe (9 patients) were combined to make up Group B. All patients provided written informed consent prior to treatment planning. Vacuum bags were used to immobilize all patients in the supine position with arms raised above the head. For each person, an axial 3DCT scan of the thoracic region was performed, followed by a 4DCT scan during uncoached free breathing on a 16-slice CT scanner (Philips Brilliance Bores CT). For 3DCT scanning, each scan (360° rotation) took 1 s to acquire, followed by a 1.8 s dead time, with a 2.4-cm coverage. The whole axial 3DCT scanning procedure for the thoracic region took about 30 s. The 4D acquisition protocol has been described in our previous study [17]. The 4DCT images were sorted into 10 bins according to the phase of the breathing signal, with 0% corresponding to end-inhalation and 50% corresponding to end-exhalation. Both the 3DCT and 4DCT images were reconstructed using a thickness of 3 mm, and then transferred to the Eclipse treatment planning system (Varian Eclipse 8.6). GTVs were manually delineated on the 10 phases of the 4DCT images and the 3DCT image by a radiation oncologist using the lung window setting (window width: 1600 HU and window level: –600 HU) [18]. ‘Partial volume effect' and ‘partial projection effect for moving objects' on 3DCT and 4DCT manifest as blurring of object boundaries. The entire blurred extent of the tumor was delineated as the GTV. Because the 3DCT images and the 4DCT images for a given person were produced during the same imaging session, Eclipse considers the images as being registered with each other. Firstly, GTV-0%, GTV-20% and GTV-70% derived from end-inspiration (0% phase), mid-expiration (20% phase) and mid-inspiration (70% phase) images were copied onto the end-expiration (50% phase) image (Fig. 1), then, the IGTV-10, encompassing all of these 4DCT-based GTVs, was produced on the end-expiration image by merging the 10 GTVs derived from all phases of 4DCT; lastly, the GTV-3D, derived from 3DCT, was copied onto the end-expiration image. Volume, position, matching index (MI) and degree of inclusion (DI) between the 4D volumes (GTV-0%, GTV-20%, GTV-50%, GTV-70% and IGTV-10) and the 3D volume (GTV-3D) were compared, respectively. The position for each tumor was expressed using the x (left-right, LR), y (anterior-posterior, AP) and z (cranial-caudal, CC) coordinates of the center of mass for each bin for 4DCT. Then, the intra-fractional motion range of the center of mass in each coordinate was obtained. The 3D motion vector of the center of mass was calculated according to the formula as follows: Statistical analysis was performed using the SPSS software package (SPSS 16.0 for Windows). A one-way ANOVA test was used to determine the variations in the centroid shifts and the MIs of GTV-3D and GTV-0%, GTV-3D and GTV-20%, GTV-3D and GTV-50%, and GTV-3D and GTV-70%. The paired t-test was used to determine paired data variables. The wilcoxon test was performed to test data for Group A and Group B variables. We used the Pearson correlation test to analyze for associations between GTV motion vectors and continuous variables (e.g. size, MI and DI). Values of P 0.05 were regarded as significant for all the tests. The mean of the average size of GTVs from 10 phases for all patient were 7.96 ± 10.59 cm3 (range, 0.32–37.08 cm3). The mean of the standard deviation (SD) of GTVs from 10 phases for all patients was 0.51 ± 0.75 cm3 (range, 0.02–3.4 cm3). The mean coefficient of variation (SD/Mean) of GTVs was 8.76% ± 6.47% (range, 1.94–23.73%). Figure 3 illustrates the tumor motion in the LR, AP, CC and 3D directions for each patient. The mean tumor motion amplitudes were 1.6 ± 1.0 mm, 2.1 ± 1.1 mm, 4.0 ± 3.9 mm and 5.2 ± 3.5 mm in the LR, AP, CC and 3D directions, respectively. The tumor motion in the LR, AP and CC directions were 1.4 ± 0.8 mm, 1.8 ± 1.0 mm and 1.8 ± 1.8 mm for Group A, and 1.8 ± 1.3 mm, 2.5 ± 1.1 mm and 6.9 ± 4.0 mm for Group B, respectively. The mean 3D motion vector was 3.2 ± 1.7 mm for Group A, and 8.0 ± 3.5 mm for Group B, with a significant statistical difference (z = 0.667, P 0.001). Table 1 shows the centroid shifts in the LR, AP, CC and 3D