title: Evaluation of current clinical target volume definitions for glioblastoma using cell-based dosimetry stochastic methods.
abstract: OBJECTIVE
  Determination of an optimal clinical target volume (CTV) is complex and remains uncertain. The aim of this study was to develop a glioblastoma multiforme (GBM) model to be used for evaluation of current CTV practices for external radiotherapy.
  
  
  METHODS
  The GBM model was structured as follows: (1) a Geant4 cellular model was developed to calculate the absorbed dose in individual cells represented by cubic voxels of 20 μm sides. The system was irradiated with opposing 6 MV X-ray beams. The beams encompassed planning target volumes corresponding to 2.0- and 2.5-cm CTV margins; (2) microscopic extension probability (MEP) models were developed using MATLAB(®) 2012a (MathWorks(®), Natick, MA), based on clinical studies reporting on GBM clonogenic spread; (3) the cellular dose distribution was convolved with the MEP models to evaluate cellular survival fractions (SFs) for both CTV margins.
  
  
  RESULTS
  A CTV margin of 2.5 cm, compared to a 2.0-cm CTV margin, resulted in a reduced total SF from 12.9% ± 0.9% to 3.6% ± 0.2%, 5.5% ± 0.4% to 1.2% ± 0.1% and 11.1% ± 0.7% to 3.0% ± 0.2% for circular, elliptical and irregular MEP distributions, respectively.
  
  
  CONCLUSIONS
  A Monte Carlo model was developed to quantitatively evaluate the impact of GBM CTV margins on total and penumbral SF. The results suggest that the reduction in total SF ranges from 3.5 to 5, when the CTV is extended by 0.5 cm.
  
  
  CONCLUSIONS
  The model provides a quantitative tool for evaluation of different CTV margins in terms of cell kill efficacy. Cellular platform of the tool allows future incorporation of cellular properties of GBM.
authors.affiliation: 1 Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA, Australia.|2 School of Chemistry & Physics, University of Adelaide, Adelaide, SA, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Moghaddasi
authors.affiliation: 2 School of Chemistry & Physics, University of Adelaide, Adelaide, SA, Australia.|3 School of Health Sciences, University of South Australia, Adelaide, SA, Australia.
authors.forename: E
authors.initials: E
authors.lastname: Bezak
authors.affiliation: 1 Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA, Australia.|2 School of Chemistry & Physics, University of Adelaide, Adelaide, SA, Australia.
authors.forename: W
authors.initials: W
authors.lastname: Harriss-Phillips
mesh_terms: D000465:Algorithms; D001932:Brain Neoplasms / Q000532:radiotherapy*; D005909:Glioblastoma / Q000532:radiotherapy*; D006801:Humans; D008962:Models, Theoretical; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D013269:Stochastic Processes