SU‐FF‐J‐57: Digital Tomosynthesis for Verification of Radiation Therapy Positioning: Preliminary Results From a Kilovoltage On‐Board Imaging System
Purpose: This study introduces a new radiation therapy target localization technique using online digital tomosynthesis (DTS), a method for reconstructing 3‐D slices from 2‐D projection data acquired with limited source motion. By separating the visualization of overlapping structure, DTS is expected to improve the visualization of anatomy compared with 2‐D planar radiographic imaging techniques, and may therefore yield more accurate target localization during radiation therapy set‐up. Method and Materials: We simulated treatment planning and setup of an anthropomorphic chest phantom. A treatment isocenter was marked in CT images. The phantom was then aligned for treatment on a Varian 21EX equipped with an on‐board‐imager (OBI), attached to the gantry orthogonal to the megavoltage treatment axis. Once aligned, 2‐D image projections were acquired over 200 degrees and coronal and sagittal DTS planes were reconstructed through the treatment isocenter from projection sub‐sets spanning 40°. Comparison of DTS images with corresponding planes from the CT data, as well as lateral and postero‐anterior (PA) planar radiographs, yielded estimations of set‐up error. Results: Sagittal and coronal DTS slices improved the visibility of anatomy when compared with planar radiograph equivalents, improving estimation of the set‐up error. Registration of sagittal and coronal DTS reconstructions with corresponding planes through the isocenter in the CT data was found to be feasible for estimating set‐up error. Preliminary determination of the set‐up accuracy of our clinical procedure was determined to be within 1mm for the phantom study presented here. Conclusion: Tomosynthesis has been demonstrated on a commercially available medical accelerator, and may be practical for improving patient set‐up when full cone‐beam‐CT is not required. DTS significantly improves the visibility of soft‐tissue detail that is obscured by overlying anatomy in radiographs and portal images. Additional benefits include a reduction in dose, acquisition and reconstruction time, and easier data handling compared with full cone‐beam‐CT. © 2005, American Association of Physicists in Medicine. All rights reserved.
Godfrey, D; Oldham, M; Dobbins, J; Yin, F
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