title: Dosimetric properties and commissioning of cone-beam CT image beam line with a carbon target.
abstract: OBJECTIVE
  Accurate patient positioning before radiotherapy is often verified using advanced imaging techniques such as cone-beam computed tomography (CBCT). Even for dedicated imaging beam lines, the applied dose is not necessarily negligible with respect to the treatment dose and should be considered in the treatment plan.
  
  
  METHODS
  This study presents measurements of the beam properties of the Siemens kView (Siemens AG, Munich, Germany) image beam line (IBL) and the commissioning in the Philips Pinnacle(3) treatment planning system (TPS; Philips, Amsterdam, Netherlands).
  
  
  RESULTS
  The percent depth dose curve reaches its maximum at a depth of 10 mm, with a surface dose of 44 %. The IBL operates in flattening filter-free mode, showing the characteristic dose falloff from the central axis. Stability over several days to months is within less than 2 % dose deviation or 1 mm distance-to-agreement. Modelling of the IBL beam line was performed using the Pinnacle(3) automatic modelling routine, with absolute dosimetric verification and film measurements of the fluence distribution.
  
  
  CONCLUSIONS
  After commissioning of the IBL beam model, the dose from the imaging IBL CBCT can be calculated. Even if the absolute dose deposited is small, repeated imaging doses may sum up to significant amounts and can shift the position of the dose maximum by several centimetres.
authors.affiliation: Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum des Saarlandes, Kirrberger Str., Gebäude 6.5, 66421, Homburg/Saar, Germany. yvonne.dzierma@uks.eu
authors.forename: Y
authors.initials: Y
authors.lastname: Dzierma
authors.forename: F G
authors.initials: FG
authors.lastname: Nuesken
authors.forename: N P
authors.initials: NP
authors.lastname: Licht
authors.forename: C
authors.initials: C
authors.lastname: Ruebe
mesh_terms: D002244:Carbon; D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D005720:Gamma Rays; D006801:Humans; D056888:Patient Positioning / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D013819:Thermoluminescent Dosimetry
chemical_list: D002244:Carbon