title: Image guidance for precise conformal radiotherapy.
abstract: OBJECTIVE
  To review the state of the art in image-guided precision conformal radiotherapy and to describe how helical tomotherapy compares with the image-guided practices being developed for conventional radiotherapy.
  
  
  METHODS
  Image guidance is beginning to be the fundamental basis for radiotherapy planning, delivery, and verification. Radiotherapy planning requires more precision in the extension and localization of disease. When greater precision is not possible, conformal avoidance methodology may be indicated whereby the margin of disease extension is generous, except where sensitive normal tissues exist. Radiotherapy delivery requires better precision in the definition of treatment volume, on a daily basis if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided processes of helical tomotherapy that enable this goal are described.
  
  
  RESULTS
  Examples of the results of helical tomotherapy processes for image-guided intensity-modulated radiotherapy are presented. These processes include megavoltage CT acquisition, automated segmentation of CT images, dose reconstruction using the CT image set, deformable registration of CT images, and reoptimization.
  
  
  CONCLUSIONS
  Image-guided precision conformal radiotherapy can be used as a tool to treat the tumor yet spare critical structures. Helical tomotherapy has been designed from the ground up as an integrated image-guided intensity-modulated radiotherapy system and allows new verification processes based on megavoltage CT images to be implemented.
authors.affiliation: Department of Human Oncology, University of Wisconsin, Madison, WI, USA.
authors.forename: Thomas Rockwell
authors.initials: TR
authors.lastname: Mackie
authors.forename: Jeff
authors.initials: J
authors.lastname: Kapatoes
authors.forename: Ken
authors.initials: K
authors.lastname: Ruchala
authors.forename: Weiguo
authors.initials: W
authors.lastname: Lu
authors.forename: Chuan
authors.initials: C
authors.lastname: Wu
authors.forename: Gustavo
authors.initials: G
authors.lastname: Olivera
authors.forename: Lisa
authors.initials: L
authors.lastname: Forrest
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Tome
authors.forename: Jim
authors.initials: J
authors.lastname: Welsh
authors.forename: Robert
authors.initials: R
authors.lastname: Jeraj
authors.forename: Paul
authors.initials: P
authors.lastname: Harari
authors.forename: Paul
authors.initials: P
authors.lastname: Reckwerdt
authors.forename: Bhudatt
authors.initials: B
authors.lastname: Paliwal
authors.forename: Mark
authors.initials: M
authors.lastname: Ritter
authors.forename: Harry
authors.initials: H
authors.lastname: Keller
authors.forename: Jack
authors.initials: J
authors.lastname: Fowler
authors.forename: Minesh
authors.initials: M
authors.lastname: Mehta
mesh_terms: D000818:Animals; D004285:Dogs; D004867:Equipment Design; D006801:Humans; D009038:Motion; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D010315:Particle Accelerators / Q000295:instrumentation; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation; D014463:Ultrasonography