Interfractional diaphragmatic position variation according to stomach volume change during respiratory-gated radiotherapy for hepatocellular carcinoma.

Abstract

We evaluated the correlation between stomach volume change and interfractional baseline shifts of the diaphragm in image-guided radiotherapy (IGRT) for hepatocellular carcinoma (HCC). Twenty-four patients with HCC underwent ten fractions of IGRT, and a total of 240 cone beam computed tomography (CBCT) and on-board imager (OBI) kV image sets were acquired. These image sets were retrospectively analyzed. Baseline shifts of the diaphragm relative to bone and stomach volume change ratios were evaluated using four-dimensional simulation CT, kV image, and CBCT images. Associations between baseline shifts and patient physiologic factors were investigated. The average baseline shift of the diaphragm in the superior-inferior (SI) direction was 1.5mm (standard deviation 4.6mm), which was higher than the shift in other directions (0.7, 2.0mm and 0.9, 2.6mm in right-left (RL) and anterior-posterior (AP) directions, respectively). Interfractional baseline shifts of the diaphragm in the SI and AP directions were positively correlated with the stomach volume change ratio (Pearson's r: 0.416 and 0.302, p-value: <0.001 and <0.001, respectively). The interfractional baseline shifts of the diaphragm in the SI and AP directions correlated well with stomach volume changes. Efforts to maintain a constant stomach volume before the simulation and each treatment, such as fasting, may reduce interfractional baseline shifts of liver tumors.