Comparison of planning target volumes based on three-dimensional CT and four-dimensional CT simulation images of non-small-cell lung cancer / 中华放射医学与防护杂志

ABSTRACT

Objecttve To compare the positional and volumetric differences of planning target volumes(PTVs)based on axial three-dimensional CT(3D-CT)and four-dimensional CT(4D-CT)for the primary tumor of non-small cell lung cancer(NSCLC).Methods Sixteen NSCLC patients with lesions located in the upper lobe and 12 patients with lesions in middle and lower lobes,totally 28 patients, initially underwent three-dimensional CT scans followed by 4D-CT scans of the thorax under normal free breathing.PTVvector was defined on gross tumor volume (GTV) contoured on 3D-CT and its motion vector. The clinical target volumes(CTVs)were created by adding 7 mm to GTVs,then, internal target volume (ITVs)were produced by enlarging CTVs isotropically based on the individually measured amount of motion in the 4D-CT,lastly,PTVs were created by adding 3 mm setup margin to ITVs. PTV4D was defined on the fusion of CTVs on all phases of the 4D data.The CTV wag generated by adding7 mm to the GTV on each phase.then,PIVs were produced by fusing CTVs on 10 phases and adding 3 mm setup margin.The position of the target center,the volume of target and the degree of inclusion(DI)were compared reciprocally between the PTVvector and the PTV 4D The difference of the position,volume and degree of inclusion of the targets between PTVvecter and PTV4D were compared,and the relevance between the relative characters of the targets and the three-dimensional vector was analyzed based on the groups of the patients. Results The median of the 3 D motion vector for the lesions in the upper lobe was 2.8 mm, significantly lower than that for the lesions in the middle and lower lobe ( 7.0 mm, z = - 3. 485, P < 0. 05 ). In the upper lobe group there was only significant spatial difference between the PTVvector and PTV4D targets in the center coordinate at the x axe (z = -2. 010, P < 0. 05 ), while in the middle and lower lobes there was only significant spatial difference between the PTVvector and PTV4D targets in the center coordinates at the z axe (z = -2. 136,P <0.05). The median of ratio of PTV4D and PTVvector, of the upper lobe group was 0. 75, significantly higher than that of the middle and lower lobes group (0. 52, z = - 2. 949, P < 0. 05 ).A significant correlation was found for the motion vector and the ratio of PTV and PTV4D in both groups ( r = - 0. 638, - 0. 850, P < 0. 05 ). For all patients, the median of D[ of PTV4D in PTVvector was 66. 39% ,while the median of DI of PTVvector, in PTV4D was 99. 55% , both showed a positive significant correlation with the motion vector (r = -0. 814,0. 613 ,P < 0. 05). Conclusions PTV4D defined based on 4D-CT simulation images is obviously less than PTV defined based on 3D-CT simulation images. The ratio and DI of both targets are related with the three-dimensional motion vector of the tumor.