Observation of different tumor motion magnitude within liver and estimate of internal motion margins in postoperative patients with hepatocellular carcinoma

Aims To assess motion magnitude in different parts of the liver through surgical clips in postoperative patients with hepatocellular carcinoma and to examine the correlation between the clip and diaphragm motion. Methods Four-dimensional computed tomography images from 30 liver cancer patients under thermoplastic mask immobilization were selected for this study. Three to seven surgical clips were placed in the resection cavity of each patient. The liver volume on computed tomography image was divided into the right upper (RU), right middle (RM), right lower (RL), hilar, and left lobes. Agreement between the clip and diaphragm motion was assessed by calculating intraclass correlation coefficient, and Bland-Altman analysis (Diff). Furthermore, population-based and patient-specific margins for internal motion were evaluated. Results The clips located in the RU lobe showed the largest motion, (7.5±1.6) mm, which was significantly more than in the RM lobe (5.7±2.8 mm, p=0.019), RL lobe (4.8±3.3 mm, p=0.017), and hilar lobe (4.7±2.7 mm, p<0.001) in the cranial-caudal direction. The mean intraclass correlation coefficient values between the clip and diaphragm motion were 0.915, 0.735, 0.678, 0.670, and the mean Diff values between them were 0.1±0.8 mm, 2.3±1.4 mm, 3.1±2.0 mm, 2.4±1.5 mm, when clips were located in the RU lobe, RM lobe, RL lobe, and hilar lobe, respectively. The clip and diaphragm motions had high concordance when clips were located in the RU lobe. Internal margin can be reduced from 5 mm in the cranial-caudal direction based on patient population average and to 3 mm based on patient-specific margins. Conclusions The motion magnitude of clips varied significantly depending on their location within the liver. The diaphragm was a more appropriate surrogate for tumor located in the RU lobe than for other lobes.