title: Dosimetric accuracy of a deterministic radiation transport based 192Ir brachytherapy treatment planning system. Part II: Monte Carlo and experimental verification of a multiple source dwell position plan employing a shielded applicator.
abstract: OBJECTIVE
  The aim of this work is the dosimetric validation of a deterministic radiation transport based treatment planning system (BRACHYVISION v. 8.8, referred to as TPS in the following) for multiple 192Ir source dwell position brachytherapy applications employing a shielded applicator in homogeneous water geometries.
  
  
  METHODS
  TPS calculations for an irradiation plan employing seven VS2000 192Ir high dose rate (HDR) source dwell positions and a partially shielded applicator (GM11004380) were compared to corresponding Monte Carlo (MC) simulation results, as well as experimental results obtained using the VIP polymer gel-magnetic resonance imaging three-dimensional dosimetry method with a custom made phantom.
  
  
  RESULTS
  TPS and MC dose distributions were found in agreement which is mainly within +/- 2%. Considerable differences between TPS and MC results (greater than 2%) were observed at points in the penumbra of the shields (i.e., close to the edges of the "shielded" segment of the geometries). These differences were experimentally verified and therefore attributed to the TPS. Apart from these regions, experimental and TPS dose distributions were found in agreement within 2 mm distance to agreement and 5% dose difference criteria. As shown in this work, these results mark a significant improvement relative to dosimetry algorithms that disregard the presence of the shielded applicator since the use of the latter leads to dosimetry errors on the order of 20%-30% at the edge of the "unshielded" segment of the geometry and even 2%-6% at points corresponding to the potential location of the target volume in clinical applications using the applicator (points in the unshielded segment at short distances from the applicator).
  
  
  CONCLUSIONS
  Results of this work attest the capability of the TPS to accurately account for the scatter conditions and the increased attenuation involved in HDR brachytherapy applications employing multiple source dwell positions and partially shielded applicators.
authors.affiliation: Medical Physics Laboratory, Medical School, University of Athens, 75 Mikras Asias, 115 27 Athens, Greece. lpetrok@phys.uoa.gr
authors.forename: L
authors.initials: L
authors.lastname: Petrokokkinos
authors.forename: K
authors.initials: K
authors.lastname: Zourari
authors.forename: E
authors.initials: E
authors.lastname: Pantelis
authors.forename: A
authors.initials: A
authors.lastname: Moutsatsos
authors.forename: P
authors.initials: P
authors.lastname: Karaiskos
authors.forename: L
authors.initials: L
authors.lastname: Sakelliou
authors.forename: I
authors.initials: I
authors.lastname: Seimenis
authors.forename: E
authors.initials: E
authors.lastname: Georgiou
authors.forename: P
authors.initials: P
authors.lastname: Papagiannis
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D011835:Radiation Protection / Q000295:instrumentation*; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results
chemical_list: D007496:Iridium Radioisotopes