title: (125)I liquid in an intracranial balloon: TG-43 formalism for an extended source.
abstract: OBJECTIVE
  To present a calculation formalism for spherical homogeneous liquid brachytherapy sources and to analyze the difficulties encountered in numerical integration over non-spherical source volumes.
  
  
  METHODS
  TG-43 formalism provides a general definition of the geometric factor for distributed source distributions. Here the geometric factor and dose for a spherical source are computed for an (125)I balloon. The errors in numerical summation of dose from point sources are assessed by computing ratios of the geometric factors of point-source and extended-source voxel volumes.
  
  
  RESULTS
  This sphere calculation agrees well with measured dose values, showing maximum and average differences of 4.8% and 0.5% at the balloon surface. Numerical integration gives errors greater than 1% within five voxel radii of a voxel source.
  
  
  CONCLUSIONS
  A new spherical dose calculation technique is proposed for brachytherapy treatment planning systems. Numerical integration over point source voxels is not accurate near the balloon surface.
authors.affiliation: Department of Radiation Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA. desobry@xrt.upenn.edu
authors.forename: Gregory E
authors.initials: GE
authors.lastname: Desobry
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D007457:Iodine Radioisotopes; D011879:Radiotherapy Dosage
chemical_list: D007457:Iodine Radioisotopes