title: Optically guided intensity modulated radiotherapy.
abstract: OBJECTIVE
  Previously, we reported on development of an optically guided system for 3D conformal intracranial radiotherapy using multiple noncoplanar fixed fields. In this paper we report on the extension of our system for stereotactic fractionated radiotherapy to include intensity modulated static ports.
  
  
  METHODS
  A 3D treatment plan with maximum beam separation is developed in the stereotactic space established by an optically guided system. Gantry angles are chosen such that each beam has a unique entrance and exit pathway, avoids the critical structures, and has a minimal beam's eye view projection. Once, a satisfactory treatment plan is found using this geometric approach an inverse treatment plan is developed using the beam portals established previously. The purpose of adding inverse planing is two fold, on the one hand it allows further reduction of margins around the PTV, while on the other hand it affords the possibility of conformal avoidance of critical structures that are close to or abut the PTV.
  
  
  RESULTS
  The use of the optically guided system in conjunction with intensity modulated noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit smaller 90, 70, and 50% of prescription dose isodose volumes, improved PITV ratios, comparable or improved EUD, smaller NTD(mean) for the critical structures, and an inhomogeneity index that is within generally accepted limits.
  
  
  CONCLUSIONS
  Because optically guided technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, the planning target volume needs to be corrected only for the limitations of image resolution. Intensity modulated static beam radiotherapy planning then provides the user the ability to further reduce margins on the PTV and to conform very closely to this smaller target volume, and enhances the normal tissue sparing, and high degree of conformality possible with 3D conformal radiotherapy. In addition, since optically guided technology affords improved patient localization and online monitoring of patient position during treatment delivery it allows for safe and efficient delivery of intensity modulated radiotherapy.
authors.affiliation: Department of Human Oncology, University of Wisconsin, K4/B100 Clinical Science Center, 600 Highland Avenue, Madison, WI 53792, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Tomé
authors.forename: S L
authors.initials: SL
authors.lastname: Meeks
authors.forename: T R
authors.initials: TR
authors.lastname: McNutt
authors.forename: J M
authors.initials: JM
authors.lastname: Buatti
authors.forename: F J
authors.initials: FJ
authors.lastname: Bova
authors.forename: W A
authors.initials: WA
authors.lastname: Friedman
authors.forename: M
authors.initials: M
authors.lastname: Mehta
mesh_terms: D000465:Algorithms; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy; D055095:Optics and Photonics; D019047:Phantoms, Imaging; D011834:Radiation Monitoring; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000379:methods*