Evaluation of anatomical landmark position differences between respiration-gated MRI and four-dimensional CT for radiation therapy in patients with hepatocellular carcinoma

Objective: To measure the accuracy of position differences in anatomical landmarks in gated MRI and four-dimensional CT (4D-CT) fusion planning for radiation therapy in patients with hepatocellular carcinoma (HCC). Methods: From April to December 2009, gated MR and planning 4D-CT images were obtained from 53 inoperable HCC patients accrued to this study. Gated MRI and planning 4D-CT were conducted on the same day. Manual image fusions were performed by matching the vertebral bodies. Liver volumes and three specific anatomical landmarks (portal vein conjunction, superior mesenteric artery bifurcation, and other noticeable points) were contoured from each modality. The points chosen nearest the centre of the four landmark points were compared to measure the accuracy of fusion. Results: The average distance differences (+/- standard deviation) of four validation points were 5.1mm (+/- 4.6 mm), 5.6 mm (+/- 6.2 mm), 5.4 mm (+/- 4.5 mm) and 5.1 mm (+/- 4.8 mm). Patients who had ascites or pulmonary disease showed larger discrepancies. MRI-CT fusion discrepancy was significantly correlated with positive radiation response (p<0.05). Conclusions: Approximately 5-mm anatomical landmark positional differences in all directions were found between gated MRI and 4D-CT fusion planning for HCC patients; the gap was larger in patients with ascites or pulmonary disease. Advances in knowledge: There were discrepancies of approximately 5mm in gated MRI-CT fusion planning for HCC patients.