title: Patient position reproducibility in fractionated stereotactically guided conformal radiotherapy using the BrainLab mask system.
abstract: OBJECTIVE
  Dedicated mask systems nowadays allow the use of stereotactic radiotherapy in fractionated regimes, therefore combining the advantages of high precision radiotherapy with the biological benefit of fractionation. Therefore the knowledge of institution specific isocenter accuracy is essential for decision-making about margins to be allowed to form the planning target volume.
  
  
  METHODS
  Measurements of isocenter deviations during fractionated treatments were performed in 33 patients using the simulator Simulix-xy (Oldelft) in connection with the BrainLab angiographic localizer-box as well as port-films. In both cases repeated images were overlaid by use of anatomical landmarks with a methodical accuracy in the order of 0.5 mm.
  
  
  RESULTS
  Both methods yield random isocenter deviations of less then 2 mm (standard deviation) in all three directions and no significant systematic deviations. These values are in the order of the accuracy of the method, obtained by comparison of two independent investigators, as well as they are comparable with the literature.
  
  
  CONCLUSIONS
  The accuracy of less than 2 mm indicates safety margins of 3-4 mm as sufficient for clinical routine to cover the target in 95.5% of all set-ups (2 SD).
authors.affiliation: Department of Radiotherapy and Radiooncology, Medical Faculty and University Clinic Carl Gustav Carus, Technical University Dresden, Germany alheit@rcs1.urz.tu-dresden.de
authors.forename: H
authors.initials: H
authors.lastname: Alheit
authors.forename: S
authors.initials: S
authors.lastname: Dornfeld
authors.forename: M
authors.initials: M
authors.lastname: Dawel
authors.forename: M
authors.initials: M
authors.lastname: Alheit
authors.forename: B
authors.initials: B
authors.lastname: Henzel
authors.forename: K
authors.initials: K
authors.lastname: Steckler
authors.forename: H
authors.initials: H
authors.lastname: Blank
authors.forename: P
authors.initials: P
authors.lastname: Geyer
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary / Q000601:surgery*; D002533:Cerebral Angiography; D019583:Dose Fractionation, Radiation; D005910:Glioma / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D006801:Humans; D008579:Meningioma / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D009442:Neurilemmoma / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D011187:Posture; D011785:Quality Assurance, Health Care; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D015203:Reproducibility of Results