title: Comparing cone-beam CT intensity correction methods for dose recalculation in adaptive intensity-modulated photon and proton therapy for head and neck cancer.
abstract: BACKGROUND
  Adaptive intensity-modulated photon and proton radiotherapy (IMRT and IMPT) of head and neck (H&N) cancer requires frequent three-dimensional (3D) dose calculation. We compared two approaches for dose recalculation on the basis of intensity-corrected cone-beam (CB) x-ray computed tomography (CT) images.
  
  
  METHODS
  For nine H&N tumor patients, virtual CTs (vCT) were generated by deformable image registration of the planning CT (pCT) to the CBCT. The second intensity correction approach used population-based lookup tables for scaling CBCT intensities to the pCT HU range (CBCTLUT). IMRT and IMPT plans were generated with a commercial treatment planning system. Dose recalculations on vCT and CBCTLUT were analyzed using a (3%, 3 mm) gamma-index analysis and comparison of normal tissue and tumor dose/volume parameters. A replanning CT (rpCT) acquired within three days of the CBCT served as reference. Single field uniform dose (SFUD) proton plans were created and recalculated on vCT and CBCTLUT for proton range comparison.
  
  
  RESULTS
  Dose/volume parameters showed minor differences between rpCT, vCT and CBCTLUT in IMRT, but clinically relevant deviations between CBCTLUT and rpCT in the spinal cord for IMPT. Gamma-index pass-rates were found increased for vCT with respect to CBCTLUT in IMPT (by up to 21 percentage points) and IMRT (by up to 9 percentage points) for most cases. The SFUD-based proton range assessment showed improved agreement of vCT and rpCT, with 88-99% of the depth dose profiles in beam's eye view agreeing within 3 mm. For CBCTLUT, only 80-94% of the profiles fulfilled this criterion.
  
  
  CONCLUSIONS
  vCT and CBCTLUT are suitable options for dose recalculation in adaptive IMRT. In the scope of IMPT, the vCT approach is preferable.
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.|b Department of Medical Physics , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kurz
authors.affiliation: b Department of Medical Physics , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: George
authors.initials: G
authors.lastname: Dedes
authors.affiliation: b Department of Medical Physics , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Resch
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Reiner
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Ganswindt
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Reinoud
authors.initials: R
authors.lastname: Nijhuis
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Thieke
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
authors.affiliation: b Department of Medical Physics , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Katia
authors.initials: K
authors.lastname: Parodi
authors.affiliation: a Department of Radiation Oncology , Ludwig-Maximilians-University , Munich , Germany.|b Department of Medical Physics , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Landry
mesh_terms: D054893:Cone-Beam Computed Tomography; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*