Abstract # 2484 Four-Dimensional Megavoltage CT Imaging with a Helical Tomotherapy System

Presenter: Mahan, Stephen

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MVCT images were acquired using a degraded megavoltage fan-beam with a nominal accelerating potential of 2.5 MV. A single slice detector acquired images at the rate of one slice per 5 seconds. Time dependant imaging data was collected axially with the couch stationary for each slice. The detector data was over-sampled to capture sufficient angles of the MVCT beam in different phases of respiration. The data corresponding to each projection was re-ordered in the raw sinogram based on a measured respiration cycle. The re-binned data was reconstructed for multiple phases of the respiration cycle. This processes was then repeated over a range of slices by stepping the couch into the bore by a fixed slice thickness. By over-sampling the image data, a 4D representation can be extracted based upon aforementioned phase matching. For proof of principle, 4D image reconstruction was performed using MVCT imaging of a battery-powered motion phantom that consisted of a motor driving an off-center mounted disk. The resulting motion was a wobbling disk that traced an ellipse with the surface of the edge of the disk.

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