title: A comprehensive evaluation of treatment accuracy, including end-to-end tests and clinical data, applied to intracranial stereotactic radiotherapy.
abstract: OBJECTIVE
  A methodology is presented to quantify the uncertainty associated with linear accelerator-based frameless intracranial stereotactic radiotherapy (SRT) combining end-to-end phantom tests and clinical data.
  
  
  METHODS
  The following steps of the SRT chain were analysed: planning computed tomography (CT) and magnetic resonance (MR) scans registration, target volume delineation, CT and cone beam CT (CBCT) registration and intrafraction-patient displacement. The overall accuracy was established with an end-to-end test. The measured uncertainties were combined, deriving the total systematic (ΣT) and random (σT) error components, to estimate the GTV-PTV margin.
  
  
  RESULTS
  The uncertainty in the MR-CT registration was on average 0.40mm (averaged over AP, CC and LR directions). Rotational variations were smaller than 0.5° in all directions. Interobser variation in GTV delineation was on average 0.29mm. The uncertainty in the CBCT-CT registration was on average 0.15mm. Again, rotational variations were smaller than 0.5° in all directions. The systematic and random intrafraction displacement errors were on average 0.55mm and 0.45mm, respectively. The systematic and random positional errors from the end-to-end test were on average 0.49mm and 0.53mm, respectively. Combining these uncertainties resulted in an average ΣT=0.9mm and σT=0.7mm and an average GTV-PTV margin of 2.8mm.
  
  
  CONCLUSIONS
  This comprehensive methodology including end-to-end tests enabled a GTV-PTV margin calculation considering all sources of uncertainties. This generic method can also be used for other treatment sites.
authors.affiliation: Department of Radiation Oncology (MAASTRO), University Medical Centre Maastricht, The Netherlands. Electronic address: e.seravalli@umcutrecht.nl.
authors.forename: E
authors.initials: E
authors.lastname: Seravalli
authors.affiliation: Department of Radiation Oncology, Catharina Hospital, Eindhoven, The Netherlands.
authors.forename: P M A
authors.initials: PM
authors.lastname: van Haaren
authors.affiliation: Department of Radiation Oncology, Catharina Hospital, Eindhoven, The Netherlands.
authors.forename: P P
authors.initials: PP
authors.lastname: van der Toorn
authors.affiliation: Department of Radiation Oncology, Catharina Hospital, Eindhoven, The Netherlands.
authors.forename: C W
authors.initials: CW
authors.lastname: Hurkmans
mesh_terms: D054893:Cone-Beam Computed Tomography; D006801:Humans; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D014057:Tomography, X-Ray Computed; D035501:Uncertainty
keywords: Clinical margin; End-to-end test; Intracranial stereotactic radiotherapy; Treatment accuracy