Application Of 4-dimensional Computed Tomography And Magnetic Resonance-T2 Weighted Image By Deformable Registration For Guided Radiotherapy Of Primary Liver Cancer

Objective: To investigate the feasibility of defining the radiotherapy target of primary liver cancer and dose distribution of liver using four-dimensional computed tomography(4DCT)and T2-weighted magnetic resonance(MR-T2)deformable image registration.Methods : Ten patients with hepatocellular carcinoma(HCC)who first received radiotherapy were included in this study.The 4DCT in free breathing and MR-T2 in deep breathing were acquired sequentially.4DCT were sorted into ten series of CT images according to the respiratory phase.MIM software was used for deformable image registration.The accuracy of deformable image registration was assessed by the maximal displacements in three-dimensional directions of the portal vein and the celiac trunk and the degree of liver overlapping(P-LIVER).Gross tumor volume(GTV)was delineated on different series of CT images and the internal GTV(IGTV)was merged by ten GTVs on 4DCT images in each phase.The MR-T2 image was deformably registered to 4DCT images in each phase to acquire ten GTVDR.The IGTVDR was obtained by merging the ten GTVDR.The IGTV and IGTVDR were respectively deformed to the CT00 phase,the outer security boundaries were expanded respectively to obtain PTV and PTVDR,and the radiotherapy planning was designed on this phase image.The differences between different target volumes were compared by paired t-test.Results:The maximal displacements in three-dimensional directions of the portal vein were 0.3±0.8 mm along the x-axis,0.8±1.8 mm along the y-axis,and 0.5±1.5 mm along the z-axis.The maximal displacements in three-dimensional directions of the celiac trunk were 0.1±1.0 mm along the x-axis,0.7±1.2 mm along the y-axis,and 0.6±2.0 mm along the z-axis.Overlapping degree was 115.4±13.8%.The volumes of GTVs obtained from 4DCT images in each phase after DR increased by an average of 8.18%(P<0.05),and were consistent with those delineated on MR-T2 images.The IGTV after DR increased by an average of 9.67%(P<0.05).No statistically significant differences were found in dosimetric indices of PTVD2、D98、D50、D95 and CI、HI.The amounts of liver V5、V10、 V20、 V30、V40 and average dose(Dmean)were lower than those before deformation,and decreased by 5.92%、 8.17%、 8.04%、 12.15%、 9.98% and 9.56% respectively,and the difference was statistically significant.Conclusions:MRI image can show more information and have a higher contrast than CT image.MRI images should be combined with 4DCT images for delineating the GTV.It can better determine the scope and trajectory of the target and improve the delineation accuracy of HCC target.The resulting dose distribution can reduce the normal dose of the liver.