title: Technical Note: Evaluation of the systematic accuracy of a frameless, multiple image modality guided, linear accelerator based stereotactic radiosurgery system.
abstract: OBJECTIVE
  To evaluate the total systematic accuracy of a frameless, image guided stereotactic radiosurgery system.
  
  
  METHODS
  The localization accuracy and intermodality difference was determined by delivering radiation to an end-to-end prototype phantom, in which the targets were localized using optical surface monitoring system (OSMS), electromagnetic beacon-based tracking (Calypso®), cone-beam CT, "snap-shot" planar x-ray imaging, and a robotic couch. Six IMRT plans with jaw tracking and a flattening filter free beam were used to study the dosimetric accuracy for intracranial and spinal stereotactic radiosurgery treatment.
  
  
  RESULTS
  End-to-end localization accuracy of the system evaluated with the end-to-end phantom was 0.5 ± 0.2 mm with a maximum deviation of 0.9 mm over 90 measurements (including jaw, MLC, and cone measurements for both auto and manual fusion) for single isocenter, single target treatment, 0.6 ± 0.4 mm for multitarget treatment with shared isocenter. Residual setup errors were within 0.1 mm for OSMS, and 0.3 mm for Calypso. Dosimetric evaluation based on absolute film dosimetry showed greater than 90% pass rate for all cases using a gamma criteria of 3%/1 mm.
  
  
  CONCLUSIONS
  The authors' experience demonstrates that the localization accuracy of the frameless image-guided system is comparable to robotic or invasive frame based radiosurgery systems.
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: N
authors.initials: N
authors.lastname: Wen
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: K C
authors.initials: KC
authors.lastname: Snyder
authors.affiliation: Varian Medical System, Täfernstrasse 7, Dättwil AG 5405, Switzerland.
authors.forename: S G
authors.initials: SG
authors.lastname: Scheib
authors.affiliation: Varian Medical System, Täfernstrasse 7, Dättwil AG 5405, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Schmelzer
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: Y
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: M S
authors.initials: MS
authors.lastname: Siddiqui
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, 2799 West Brand Boulevard, Detroit, Michigan 48202.
authors.forename: I J
authors.initials: IJ
authors.lastname: Chetty
mesh_terms: D002138:Calibration; D004867:Equipment Design; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods*; D012371:Robotics