title: Intraoperative localization of tantalum markers for proton beam radiation of choroidal melanoma by an opto-electronic navigation system: a novel technique.
abstract: OBJECTIVE
  External beam proton radiation therapy has been used since 1975 to treat choroidal melanoma. For tumor location determination during proton radiation treatment, surgical tantalum clips are registered with image data. This report introduces the intraoperative application of an opto-electronic navigation system to determine with high precision the position of the tantalum markers and their spatial relationship to the tumor and anatomical landmarks. The application of the technique in the first 4 patients is described.
  
  
  METHODS
  A navigated reference base was attached noninvasively to the eye, and a navigated pointer device was used to record the spatial position of the tantalum markers, the tumor, and anatomical landmarks. Measurement accuracy was assessed on ex vivo porcine eye specimen by repetitive recording of the tantalum marker positions. The method was applied intraoperatively on 4 patients undergoing routine tantalum clip surgery. The spatial position information delivered by the navigation system was compared to the geometric data generated by the EYEPLAN software.
  
  
  RESULTS
  In the ex vivo experiments, the maximum repetition error was 0.34 mm. For the intraoperative application, the root mean square error of paired-points matching of the marker positions from the navigation system and from the EYEPLAN software was 0.701-1.25 mm.
  
  
  CONCLUSIONS
  Navigation systems are a feasible tool for accurate localization of tantalum markers and anatomic landmarks. They can provide additional geometric information, and therefore have the potential to increase the reliability and accuracy of external beam proton radiation therapy for choroidal melanoma.
authors.affiliation: Department of Ophthalmology, University Hospital Zurich, Frauenklinikstrasse 24, 8091 Zurich, Switzerland. christoph.amstutz@usz.ch
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Amstutz
authors.forename: Nikolaos E
authors.initials: NE
authors.lastname: Bechrakis
authors.forename: Michael H
authors.initials: MH
authors.lastname: Foerster
authors.forename: Jens
authors.initials: J
authors.lastname: Heufelder
authors.forename: Jens H
authors.initials: JH
authors.lastname: Kowal
mesh_terms: D000818:Animals; D002830:Choroid Neoplasms / Q000532:radiotherapy*; D057918:Fiducial Markers; D006801:Humans; D008545:Melanoma / Q000532:radiotherapy*; D059351:Organ Sparing Treatments / Q000295:instrumentation / Q000379:methods; D010865:Pilot Projects; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D058998:Remote Sensing Technology / Q000295:instrumentation / Q000379:methods*; D012590:Sclera; D013552:Swine; D013635:Tantalum; D014604:Uveal Neoplasms / Q000532:radiotherapy*; D000098943:Uveal Melanoma
chemical_list: D013635:Tantalum