4D CT Imaging and Segmentation for Hepatocellular Carcinoma

The simulation and segmentation procedures had been described in our previous report^{3 (link)}. All patients were immobilized in the supine position using a vacuum cushion and underwent a free-breathing 4-dimensional (4D) CT scan (GE LightSpeed RT 16; GE Healthcare, Waukesha, WI, USA). A real-time position management respiratory gating system (Varian Medical Systems, Palo Alto, CA, USA) was used to record the patients’ breathing patterns. The CT slice thickness was set to 2.5 mm. An intravenous contrast agent was injected to improve the segmentation accuracy of the target and normal organs. The CT data were sorted into 10 CT series according to the respiratory phase using 4D imaging software (Advantage 4D version 4.2; GE Healthcare). Contouring was performed on the CT images at the end-expiratory phase using a radiotherapy treatment planning system (Eclipse version 13.6; Varian Medical Systems). The organs at risk included the whole liver, duodenum, stomach, and right/left kidneys. Two professional radiographers with experience in segmentation of abdominal structures of more than 500 patients per year delineated the training sets and two radiation oncologists with more than 10 years of experience in hepatocellular carcinoma treatment confirmed each structure.