Application of 4DCT and MRI image deformation registration in the determination of primary liver cancer radiotherapy target

Abstract

Objective To investigate the feasibility of defining the radiotherapy target of primary liver cancer 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 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). 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. Key words: Magnetic resonance imaging; Tomography, X-ray computed, four-dimensional; Deformable registration; Liver neoplasms/radiotherapy