Defining the individual internal gross tumor volume of hepatocellular carcinoma using 4DCT and T2-weighted MRI images by deformable registration

Abstract

Background: To study the feasibility of defining the individual internal gross tumor volume (IGTV) of hepatocellular carcinoma (HCC) using four-dimensional computed tomography (4DCT) imaging and T2-weighted magnetic resonance imaging (T2-weighted MRI) by deformable registration (DR). Methods: Ten HCC patients who previously received radiotherapy treatment were selected for this study. The following simulation images were acquired sequentially: 4DCT in free breathing and T2-weighted MRI in deep-inspiration breath holding. All 4DCT images were sorted into ten phases according to breath cycle (CT 00 –CT 90 ). Gross tumor volumes (GTVs) were contoured on all CT images and the IGTV was obtained by merging the GTVs in each phase of 4DCT imaging. The GTV on the T2-weighted MRI image was deformably registered to each 4DCT phase image using MIM software version 6.5.6 and the results were labeled with DR subscript. The IGTV DR was obtained by merging the GTV DR on the 4DCT images. Statistical differences in the GTVs and between the IGTV and IGTV DR were assessed by a paired t-test. Results: The edge of most lesions could be definitively identified using T2-weighted MRI images, compared to 4DCT images. The Reg Reveal and Reg Refine were used to minimize the DR error manually within 1 mm. The GTVs after DR on 4DCT different phase imaging increased by an average of 8.18% (P DR increased by an average of 9.67%, compared to that of IGTV (P Conclusions: The use of 4DCT imaging alone has the potential risk of missing a partial volume of HCC. However, T2-weighted MRI images can carry more information than 4DCT image. As such, the combination of 4DCT and T2-weighted MRI images using the DR technique may improve accuracy in the delineation of HCC.