Application Of 4D-CT In Mapping Lung Tumor Target Areas

Objective:Systematically analyze the impact of target related factors on the measurement of lung tumor motion based on four-dimensional computed tomography（4D-CT）,and identify the characteristics of tumor motion in different subgroups.Internal target volume（ITV）of 10 respiratory phases collected by 4D-CT were selected as reference to compare the same tumor target based on Maximum Intensity Projection,MIP),Average Intensity Projection（AIP）,T₀CT and T₅₀CT to determine which contour method is more efficient for different tumor locations.Methods:A total of 135 patients with lung tumor who underwent routine 3D-CT scanning and 4D-CT scanning in the First Affiliated Hospital of Bengbu Medical College from October 2019 to January 2022 were selected.After scanning,use a post processing workstation to perform image reconstruction,divide the entire respiratory cycle of 4D-CT into 10 phases(T₀,T₁₀,T₂₀…T₉₀)on average,and reconstruct MIP and AIP images.The doctor performed GTV delineation on 10 phases of 4D-CT,recording the displacement and volume changes of the patient’s centroid and boundary along the left and right directions,head and foot directions,and front and back directions during a respiratory cycle,and analyzing the factors that affect these changes.Divide the lungs into 9 points and elaborate on the range of motion at different target locations.Fusing target regions delineated in 10 temporal phases to obtain IGTV₁₀;IGTV_MIP,IGTV_AIP,and IGTV₂ are obtained based on maximum intensity projection（MIP）,average intensity projection（AIP）,and T₀ and T₅₀ temporal image delineation of 4D-CT.Compare the difference between the above target area delineation methods from volume and centroid displacement.Results:1.The volume of the 10 phases of GTV is the closest to the average volume at T₅₀（P<0.05）.The mean motion amplitude of the GTV centroid in the left and right directions,the head and foot directions,and the front and rear directions were 1.76±1.12 mm,3.09±3.37 mm,2.15±1.58 mm,and 4.78±3.08 mm,respectively.The mean motion amplitude of the GTV boundary in the left and right directions,the head and foot directions,and the front and rear directions were 3.57±2.14mm,5.45±2.85mm,4.02±1.99mm,and 8.04±3.52mm,respectively.The displacement amplitude of the center point of GTV in the head and foot directions is the largest,which is greater than that in the front and rear directions（P<0.05）and left and right directions（P<0.05）;The displacement of each boundary of GTV in the head and foot directions is also the largest,larger than that in the front and rear directions （P<0.05）,and the left and right directions（P<0.05）,with a statistically significant difference.2.By analyzing the distribution of tumor motion amplitude in the left and right directions,it can be found that the tumors with larger motion amplitude are inner lower,outer middle,inner middle,and inner upper.The tumors with a larger range of motion in the head and foot direction are in the lower middle,inner lower,outer lower,and middle.The tumors with greater amplitude of movement in the anterior-posterior direction are inner lower,inner middle,middle,and outer middle.The tumors with larger motion amplitude in the three-dimensional motion vector direction are inner lower,inner middle,outer lower,and outer middle.3.There were statistically significant differences in GTV displacement in the left and right directions,head and foot directions,and three-dimensional motion vectors between adjacent locations（P<0.05）.The movement of GTV adjacent to the heart in the left and right directions was greater than that adjacent to the chest wall and isolated lesions（P<0.05）;The GTV adjacent to the diaphragm was larger in the head-foot direction than in the heart（P<0.05）;The GTV adjacent to the diaphragm had the greatest change in the anteroposterior direction（P>0.05）;The three-dimensional motion vector of solitary lesions was the largest,larger than that of lesions adjacent to the heart and chest wall（P<0.05）;The volume change of GTV adjacent to the heart was greater than that of diaphragm,chest wall,and isolated lesions（P<0.05）.There was no significant correlation between GTV volume and mobility（P>0.05）.4.The ratios of IGTV_MIP,IGTV_AIP,and IGTV₂ to IGTV₁₀ in the upper lobe group were 1.00,0.98,and 0.99,respectively（P=0.143,0.000,0.000）,and the ratios of IGTV_MIP to IGTV₁₀ in the middle and lower lobe group were 0.99,0.96,and 0.98, respectively（P=0.603,0.000,0.000）.There was no statistically significant difference in the mutual inclusion degree between IGTV₁₀ and IGTV_MIP in the upper lobe group（P>0.05）,but there was a statistically significant difference in the mutual inclusion degree between IGTV₁₀ and IGTV_MIP,IGTV_AIP,and IGTV₂ in the middle and lower lobe group（P<0.05）.Conclusion:1.Patients with lung tumors have the most obvious movement in the head and foot directions.Dividing the lung into nine parts can provide a more detailed explanation of the movement characteristics of different parts.The application of 4D-CT can provide a better summary of tumor displacement at different locations for target area expansion.The location and adjacent structure of the lesion have a significant impact on displacement and volume changes in each direction.2.The 10 temporal fused images contain significantly greater motion information than AIP images and T₀+T₅₀temporal fused images,but are close to MIP images.When using MIP images to delineate the target area,it is also necessary to consider the location of the tumor.