title: Noninvasive referencing of intraocular tumors for external beam radiation therapy using optical coherence tomography: a proof of concept.
abstract: OBJECTIVE
  External beam radiation therapy is currently considered the most common treatment modality for intraocular tumors. Localization of the tumor and efficient compensation of tumor misalignment with respect to the radiation beam are crucial. According to the state of the art procedure, localization of the target volume is indirectly performed by the invasive surgical implantation of radiopaque clips or is limited to positioning the head using stereoscopic radiographies. This work represents a proof-of-concept for direct and noninvasive tumor referencing based on anterior eye topography acquired using optical coherence tomography (OCT).
  
  
  METHODS
  A prototype of a head-mounted device has been developed for automatic monitoring of tumor position and orientation in the isocentric reference frame for LINAC based treatment of intraocular tumors. Noninvasive tumor referencing is performed with six degrees of freedom based on anterior eye topography acquired using OCT and registration of a statistical eye model. The proposed prototype was tested based on enucleated pig eyes and registration accuracy was measured by comparison of the resulting transformation with tilt and torsion angles manually induced using a custom-made test bench.
  
  
  RESULTS
  Validation based on 12 enucleated pig eyes revealed an overall average registration error of 0.26 ± 0.08° in 87 ± 0.7 ms for tilting and 0.52 ± 0.03° in 94 ± 1.4 ms for torsion. Furthermore, dependency of sampling density on mean registration error was quantitatively assessed.
  
  
  CONCLUSIONS
  The tumor referencing method presented in combination with the statistical eye model introduced in the past has the potential to enable noninvasive treatment and may improve quality, efficacy, and flexibility of external beam radiotherapy of intraocular tumors.
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Bern 3010, Switzerland.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Rüegsegger
authors.affiliation: Berne University of Applied Sciences, HuCE OptoLab, 2501, Switzerland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Geiser
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Bern 3010, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Steiner
authors.affiliation: Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern 3010, Switzerland.
authors.forename: Alessia
authors.initials: A
authors.lastname: Pica
authors.affiliation: Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern 3010, Switzerland.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Aebersold
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Bern 3010, Switzerland.
authors.forename: Jens H
authors.initials: JH
authors.lastname: Kowal
mesh_terms: D000818:Animals; D002138:Calibration; D004867:Equipment Design; D005123:Eye / Q000473:pathology*; D015353:Eye Enucleation; D005134:Eye Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D008954:Models, Biological; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods*; D013552:Swine; D041623:Tomography, Optical Coherence / Q000295:instrumentation / Q000379:methods*