Volumetric tracking tool using four-dimensional CT for image guided-radiation therapy.

To analyze lung vessel motion automatically, we developed computerized tracking software for multi-slice CT (MSCT) data. Here, we evaluated the tracking accuracy in images of healthy porcine lungs obtained by 256 multi-slice CT (256-MSCT). A domestic pig was scanned with 256-MSCT under free breathing conditions. The 256-MSCT provides 128-mm scan coverage with a 0.5-mm slice thickness in a single rotation (1.0 s/rot). Automatic tracking was performed by template matching, where volumes of interest (VOIs) can be identified by mouse click on all three principal orthogonal planes (axial, sagittal and coronal). The results were compared with those obtained by manual tracking. There was no significant difference between the results obtained with the computerized method and those with the manual method. The maximum tracking error was less than 1.4 mm in all directions. The computerized method allowed real-time tracking and significantly saved time in determining target displacement. The present method, 256-MSCT with a computerized tracking system, could quantify hysteresis-like behavior of lung vessels during respiration in 4DCT data. The quantitative information on the target trajectory is expected to be useful for clinical radiotherapy planning and IGRT to the lower lobe of the lung and liver area, which show large respiratory displacement.