Four-Dimensional Computed Tomography Scan Analysis of Tumor and Organ Motion at Varying Levels of Abdominal Compression During Stereotactic Treatment of Lung and Liver

Purpose: To investigate the effectiveness of different abdominal compression levels on tumor and organ motion during stereotactic body radiotherapy of lower lobe lung and liver tumors using four-dimensional (4D)-CT scan analysis. Methods and Materials: Three 4D-CT scans were acquired for 10 patients first using with no compression and then compared with two different levels of abdominal compression. The position of the tumor and various organs were defined at the peak inspiratory and expiratory phases and compared to determine the maximum motion. Results: Mean (±SD) medium compression force (MC) and high compression force (HC) were 47.6 ± 16.0 N and 90.7 ± 27.1 N, respectively. Mean overall tumor motion was 13.6 mm (2σ [2 sigma] 11.5-15.6), 8.3 mm (2σ 6.0-10.5), and 7.2 mm (2σ 5.4-9.0) for no compression, MC, and HC, respectively. A significant difference in the control of both superior-inferior (SI) and overall motion of tumors was seen with the application of MC and HC when compared with no compression (p < 0.0001 for both). High compression force improved SI and overall tumor motion compared with MC, but this was only significant for SI motion (p = 0.04 and p = 0.06). Significant control of organ motion was only seen in the pancreas (p = 0.01). Conclusions: Four-dimensional CT shows significant control of both lower lobe lung and liver tumors using abdominal compression. High levels of compression improve SI tumor motion when compared with MC.