title: Overlap-guided fixed-patient support positioning optimization for cranial SRT.
abstract: OBJECTIVE
  To investigate potential dosimetric improvements through the optimization of fixed-couch rotational position in cranial cancer stereotactic treatments.
  
  
  METHODS
  Using previously delivered cranial stereotactic radiotherapy plans treated at the Nova Scotia Health Authority (NSHA), we have redesigned the treatment arrangement to find the optimal couch rotation positions based on the reduction of overlap between organs-at-risk of exposure (OARs) and target volume (PTV). Maintaining the gantry arrangements from the delivered treatment, the couch positions were determined based on a cost function analysis of accumulation of overlap score from an equation developed by Yang et al. and refined by MacDonald et al. The algorithm incorporates factors for radiation dose sensitivities of each OAR, depth of both OARs and target (PTV) volumes, and orthogonality of the 3D vector between OAR and PTV in the case of proximal OAR position.
  
  
  RESULTS
  The plan evaluation was conducted on 16 acoustic neuroma patients treated with stereotactic radiotherapy plans at the NSHA. Maximum and mean doses to the OARs were reduced by approximately 14.30% ± 2.86% and 19.25% ± 2.10%, respectively, with application of this optimization technique as compared to the delivered treatment plans. In addition, PTV conformity and homogeneity were improved with application of this optimization technique.
  
  
  CONCLUSIONS
  This variation of the existing delivery techniques with guidance from a PTV-OAR overlap cost function analysis technique can yield significant dosimetric improvements with no increase to delivery or planning time.
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
authors.forename: R Lee
authors.initials: RL
authors.lastname: MacDonald
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada.|Department of Medical Physics, Nova Scotia Health Authority, Halifax, NS, B3H 1V7, Canada.|Department of Radiation Oncology, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
authors.forename: James L
authors.initials: JL
authors.lastname: Robar
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada.|Department of Medical Physics, Nova Scotia Health Authority, Halifax, NS, B3H 1V7, Canada.|Department of Radiation Oncology, Dalhousie University, Halifax, NS, B3H 4R2, Canada.|Department of Radiology, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Thomas
mesh_terms: D006801:Humans; D058958:Organs at Risk / Q000528:radiation effects; D056888:Patient Positioning / Q000379:methods; D011874:Radiometry; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D012886:Skull / Q000528:radiation effects*
keywords: optimization; radiotherapy; stereotactic; trajectory