title: Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system.
abstract: OBJECTIVE
  VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking.
  
  
  METHODS
  To determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/tilt performance were measured.
  
  
  RESULTS
  The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E(90%)<0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E(90%) of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt.
  
  
  CONCLUSIONS
  In terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.
authors.affiliation: Radiotherapy Department, UZ Brussel, Vrije Universiteit Brussel, Laarbeeklaan 101, Brussels, Belgium. tom.depuydt@uzbrussel.be
authors.forename: Tom
authors.initials: T
authors.lastname: Depuydt
authors.forename: Dirk
authors.initials: D
authors.lastname: Verellen
authors.forename: Olivier
authors.initials: O
authors.lastname: Haas
authors.forename: Thierry
authors.initials: T
authors.lastname: Gevaert
authors.forename: Nadine
authors.initials: N
authors.lastname: Linthout
authors.forename: Michael
authors.initials: M
authors.lastname: Duchateau
authors.forename: Koen
authors.initials: K
authors.lastname: Tournel
authors.forename: Truus
authors.initials: T
authors.lastname: Reynders
authors.forename: Katrien
authors.initials: K
authors.lastname: Leysen
authors.forename: Mischa
authors.initials: M
authors.lastname: Hoogeman
authors.forename: Guy
authors.initials: G
authors.lastname: Storme
authors.forename: Mark
authors.initials: M
authors.lastname: De Ridder
mesh_terms: D003198:Computer Simulation; D006801:Humans; D009369:Neoplasms / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results