Analysis about Synchronization of Respiration-induced Motion at Duodenum, Stomach, and Lymph Node Regions for Primary tumor in Pancreatic Cancer Using 4-Dimensional Computed Tomography

Abstract

In radiotherapy for pancreatic cancer, movement of the primary tumor is important. However, if organs at risk and lymph node regions move apart from the primary lesion due to breathing, evaluation of the dose distribution may not be reflected. Therefore, we investigated the synchronization of respiration-induced motion at the primary tumor, organs at risk and lymph node regions for the primary tumor. Four-dimensional (4D) computed tomography images and 3-dimensional (3D) computed tomography images at the inhale and exhale phases were acquired under the condition of shallow free breathing in 9 patients with pancreatic cancer. The primary tumor (PT), duodenum (DU), stomach (ST), celiac node region (CT), and superior mesenteric artery node region (SMA) were contoured in the images at the 3D exhale phase. Then contouring of those images was adapted to 4D images of each phase using deformable image registration. With reference to the 50% phase (exhale phase), the excursion of respiration-induced motion of the PT, DU, ST, CT and SMA at each phase was measured. To investigate the synchronization of respiration-induced motion of other contouring for the PT, we evaluated the changes in distances of the DU, ST, CT, and SMA in the positional relationship with the PT. The mean maximum excursions were 2.0, 3.2, and 9.0 mm in the left-right, anterior-posterior, and superior-inferior directions, respectively. The mean maximum 3D excursions at the PT, DU, ST, CT, and SMA were 9.5, 9.8, 10.1, 5.1, and 7.5 mm, respectively. At the 50% phase, the mean distances of the DU, ST, CT, and SMA from PT were 38, 70, 30, and 26 mm, respectively. At 0% and 90% phases (inhale phase), mean distance changes in the positional relationship with the PT were 0.3 and 0.7, -2.5 and -2.4, 1.7 and 1.3, and 0.4 and 0.1 mm in the DU, ST, CT, and SMA, respectively. At 20% and 70% phases, those with PT were 0.5 and 0.2, -0.9 and -0.3, 0.4 and 0.4, and 0.2 and -0.1 mm in the DU, ST, CT, and SMA, respectively. Our results showed a tendency for respiration-induced motion of the DU, ST, CT, and SMA for the PT. The DU and SMA moved synchronously with the PT due to respiration.