Motion and volume change of tumor tissue depending on patient position in liver cancer treatment with use of tomotherapy

The aim of this study was to determine the proper position for the radiation treatment of liver cancer by tomotherapy by comparing the changes in the target location and volume depending on the position (prone position and supine position). Among the patients diagnosed with hepatocellular carcinoma from January to December 2012, five patients who had a similar tumor size and location were selected as study subjects. An abdominal and chest motion control device (radiation therapy device) was used to guide free respiration while Body Fix was used to minimize the motion of the abdomen. 4DCT was conducted in both the supine and prone positions. After the CT image was obtained, the contour of the target was determined before Tomotherapy Planning System Ver. 4.2 (Tomotherapy, Inc. Madison, WI, USA) was used to complete a plan and analyze the motion of the target. A dose volume histogram was used to analyze the integral dose. When the radiation treatment was conducted in the prone position, the motion due to respiration was reduced more than in the supine position (SI direction: 1.7 mm, AP direction: 0.7 mm, and LR direction: 0.2 mm) and the target volume was also reduced (GTV: 11.7 cm3, CTV: 19.4 cm3, and PTV: 14.1 cm3). As a result, the dose in the PTV increased by 3.4% at the maximum, whereas the dose reduction was 27.8% (V50) for the normal tissue of a normal liver: 53% (V30) for the stomach, 75% (V25) for the right kidney, and 50% (V45) for the spinal cord. Therefore, the maximum dose was assigned to the tumor tissue and at the same time, the minimum dose was observed in the normal tissue, showing a high therapeutic ratio (TR). In liver cancer treatment using tomotherapy, motion of the target volume can be minimized when the patient is placed in the prone position, rather than in the supine position. In addition, the proper dose of radiation was assigned to the tumor tissue and the absorbed dose was lower in the normal tissue.