SU‐FF‐J‐09: Limited‐Angle Imaging for Target Positioning Using Orthogonal Conebeam X‐Ray Systems

Purpose: To investigate limited‐angle imaging using orthogonal x‐ray systems, with regard to use for target positioning onboard external beam radiation therapy (EBRT) machines. Method and Materials: Image reconstruction was performed using projection data acquired with a single conebeam CT (CBCT) system for an anonymized head‐and‐neck patient onboard an EBRT machine. The original data set included 678 angles over 360°. Four subsets of this data were generated corresponding to the following angular ranges of the x‐ray tube: (i) Dual−40°: −110° to −70° plus −20° to 20°; (ii) Single−80°: −130° to −50°; (iii) Dual−80°: −130° to −50° plus −40° to 40°; (iv) all 360°. Images were reconstructed from each data set by an ordered‐subsets iterative statistical method (OSTR). Sagittal, coronal, and transverse slices were obtained from the reconstructed images and evaluated. This study design does not include the cross‐scatter that would occur between two orthogonally mounted CBCT systems. Results: Equal‐dose comparisons of Dual−40° and Single−80° images showed that the Dual−40° provided sufficient sharpness to position the target along all 3 dimensions. The Single−80° images did not provide adequate sharpness along the lateral direction. Equal‐time comparisons of Dual−80° and Single−80° images showed marked improvement in image quality in all 3 slices and all 3 dimensions. Conclusion: Dual−40° scans have approximately equal dose to Single−80° scans, allow positioning along all 3 dimensions, and require only half the imaging time. Reduced imaging time can reduce motion artifacts in the image and reduce probability of motion between imaging and treatment. Dual−80° scans have approximately twice the dose of Single−80° scans, but they provide much better image quality with no increase in scan time. Onboard limited‐angle imaging with dual orthogonal CBCT systems thus has advantages over limited‐angle imaging with a single CBCT system. © 2009, American Association of Physicists in Medicine. All rights reserved.

Duke Scholars

Author Lei Ren Radiation Oncology

Author Fang-Fang Yin Radiation Oncology