SU‐CC‐ValA‐01: Automatic Comparison Between Reference and On Board Digital Tomosynthesis for Target Localization
Purpose: Digital tomosynthesis (DTS) is a method for reconstructing 3D images from cone‐beam projection data acquired with limited angulation (e.g., 40°) of an x‐ray source, and is much faster and lower dose than full cone‐beam CT (CBCT). We previously developed a method for generating reference DTS images from a planning CT for registration with actual on‐board DTS images. This study examines the accuracy of 3D‐3D registration of reference and on‐board DTS images to assess the potential of DTS for image‐guided radiation therapy (IGRT). Method and Materials: We simulated the online positioning of an anthropomorphic chest phantom with 6 noncoplanar reference BBs attached. Planning CT data of the phantom were acquired with a G.E. Lightspeed RT scanner. On‐board CBCT projection data were acquired with a Varian 21EX Clinac, equipped with a kV on‐board imager. On‐board DTS images were reconstructed from a subset of the CBCT projection data (81 projections, 44°). True alignment of planning and on‐board image data was achieved according to a 3D point‐based registration of the 6 reference BBs in the CT and CBCT images. Single‐axis rotations up to +/− 10° and 3‐axis translations up to +/− 10 mm were simulated in the planning CT, prior to the generation of reference DTS images. A 67.5mm × 162.5mm × 20.8mm region of interest surrounding the spinal cord was extracted for registration. Mutual information‐based 3D‐3D registration of reference and on‐board DTS images was performed, and residual registration error was recorded. Results: Registration errors are within 0.7mm and 0.1 degree in all cases. The average registration error was 30% less for translations along the dimension of tomographic motion than for the other two dimensions. Conclusions: 3D‐3D rigid‐body registration of reference and on‐board DTS images is highly accurate, suggesting that DTS may be an effective IGRT technique. Partially supported by a Varian research grant. © 2006, American Association of Physicists in Medicine. All rights reserved.
Ren, L; Godfrey, D; wu, J; Yan, H; Yin, F
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