Interfractional reproducibility in pancreatic position based on four-dimensional computed tomography.

Abstract

To assess the interfractional positional variation of the pancreas using four-dimensional computed tomography (4D-CT) and to determine the suitable phase of respiration for dose delivery methods to account for pancreatic tumor motion. Fifteen patients with pancreatic cancer were enrolled in this study. For each patient, 4D-CT scans were performed at CT simulation and three times during the course of treatment. Regions of interest were set to the intrapancreatic bile ducts as a surrogate for pancreatic position. The centroids of the regions of interest were calculated at end-inhalation and end-exhalation of the respiration phase. The ranges of respiratory motion and interfractional positional variation were evaluated in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions. The medians of respiratory motion were 1.1 mm (range, 0.0-9.8 mm), 1.5 mm (range, 0.0-7.0 mm), and 5.0 mm (range, 0.0-12.5 mm) in the LR, AP, and SI directions, respectively. The means ± SDs of the interfractional positional variation at end-inhalation were 0.9 ± 5.1 mm (range, -9.2 to 15.6 mm), -1.9 ± 3.9 mm (range, -12.8 to 6.4 mm), and -1.3 ± 6.9 mm (range, -15.0 to 13.7 mm) and those at end-exhalation were 0.0 ± 3.1 mm (range, -7.0 to 5.3 mm), -1.2 ± 3.9 mm (range, -11.2 to 6.7 mm), and 0.1 ± 3.2 mm (range, -9.9 to 5.1 mm) in the LR, AP, and SI directions, respectively. The SDs of the interfractional positional variation in the LR and SI directions were significantly larger at end-inhalation than at end-exhalation (LR, p < 0.001; SI, p < 0.001). The ranges of respiratory motion during the course of treatment and the interfractional positional variation were not negligible. The interfractional positional reproducibility was higher at end-exhalation than at end-inhalation under free breathing.