title: Collapsed cone dose calculations for heterogeneous tissues in brachytherapy using primary and scatter separation source data.
abstract: OBJECTIVE
  Brachytherapy is a form of radiation therapy using sealed radiation sources inserted within or in the vicinity of the tumor of, e.g., gynecological, prostate or head- and neck cancers. Accurate dose calculation is a crucial part of the treatment planning. Several reviews have called for clinical software with model-based algorithms that better take into account the effects of patient individual distribution of tissues, source-channel and shielding attenuation than the commonly employed TG-43 formalism which simply map homogeneous water dose distributions onto the patient. In this paper we give a comprehensive and thorough derivation of such an algorithm based on collapsed cone point-kernel superposition, and describe details of its implementation into a commercial treatment planning system for clinical use.
  
  
  METHODS
  A brachytherapy version of the collapsed-cone algorithm using analytical raytraces of the primary photon radiation followed by successive scattering dose calculation for once- and multiply scattered photons is described in detail, including derivation of the corresponding set of recursive equations for energy transport along cone axes/transport lines and the coupling to clinical source modeling. Specific implementation issues for setting up of the calculation grid, handling of intravoxel gradients and voxels partly containing non-patient applicator material are given.
  
  
  RESULTS
  Sample runs for two clinical cases are shown, one being a gynecological application with a tungsten-shielded applicator and one a breast implant. These two cases demonstrate the impact of improved dose calculation versus TG-43 formalism.
  
  
  CONCLUSIONS
  Use of model-based dose calculation algorithms for brachytherapy taking the three-dimensional treatment geometry into account increases the dosimetric accuracy in planning and follow up of treatments. The comprehensive description and derivations provided gives a rigid background for further clinical, educational and research applications.
authors.affiliation: Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Akademiska Sjukhuset, SE-75185 Uppsala, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Ahnesjö
authors.affiliation: Elekta Brachytherapy, 3905 TH Veenendaal, The Netherlands.
authors.forename: Bob
authors.initials: B
authors.lastname: van Veelen
authors.affiliation: Radiation Physics, Department of Medical and Health Sciences (IMH), Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden; Department of Medical Physics, Section for Radiotherapy Physics and Engineering, Karolinska University Hospital, SE-171 76 Stockholm, Sweden. Electronic address: asa.carlsson.tedgren@liu.se.
authors.forename: Åsa Carlsson
authors.initials: ÅC
authors.lastname: Tedgren
mesh_terms: D000465:Algorithms; D001918:Brachytherapy; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009010:Monte Carlo Method
keywords: Advanced collapsed cone engine; Brachytherapy; Model-based dose calculation; Point kernel superposition; Radiotherapy treatment planning