title: The selection of portal aperture using interactively displayed Beam's Eye Sections.
abstract: Portal apertures are often defined by wax-pencil lines drawn on simulator films. The simulator-film images suffer degradation due to X ray absorption and scatter in tissues proximal to and distal to the intended target volume. We describe a method for avoiding the degradation by using a 3-D dataset to produce high-contrast section images with a user-defined orientation. The calculation of these Beam's Eye Section (BES) images requires a set of medium-to high-resolution transverse section data (the 3-D dataset), as well as a medium- to high-performance computer workstation. These CT-like section images, providing more contrast and detail than a projection (that is, a simulator or Digitally Reconstructed Radiograph [DRR]) image, should allow for more accurate selection of portal apertures. The BES image plane is oriented perpendicular to the central axis of a user-selected beam. Once the user has created a beam, the system allows the user to step along that beam with a new BES image produced at each step. Contours manually drawn on these BES images are ultimately projected onto a DRR image. The outermost segments of these sometimes crisscrossing contours (the union of all projected areas) accurately defines the portal aperture needed to encompass the target at all levels.
authors.affiliation: Department of Radiation Oncology and Nuclear Medicine, Hahnemann University, Philadelphia, PA 19102-1192.
authors.forename: M S
authors.initials: MS
authors.lastname: Weinhous
authors.forename: Z
authors.initials: Z
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Holman
mesh_terms: D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed