title: Development of a phantom to validate high-dose-rate brachytherapy treatment planning systems with heterogeneous algorithms.
abstract: OBJECTIVE
  This work presents the development of a phantom to verify the treatment planning system (TPS) algorithms used for high-dose-rate (HDR) brachytherapy. It is designed to measure the relative dose in a heterogeneous media. The experimental details used, simulation methods, and comparisons with a commercial TPS are also provided.
  
  
  METHODS
  To simulate heterogeneous conditions, four materials were used: Virtual Water™ (VM), BR50/50™, cork, and aluminum. The materials were arranged in 11 heterogeneity configurations. Three dosimeters were used to measure the relative response from a HDR (192)Ir source: TLD-100™, Gafchromic(®) EBT3 film, and an Exradin™ A1SL ionization chamber. To compare the results from the experimental measurements, the various configurations were modeled in the penelope/penEasy Monte Carlo code. Images of each setup geometry were acquired from a CT scanner and imported into BrachyVision™ TPS software, which includes a grid-based Boltzmann solver Acuros™. The results of the measurements performed in the heterogeneous setups were normalized to the dose values measured in the homogeneous Virtual Water™ setup and the respective differences due to the heterogeneities were considered. Additionally, dose values calculated based on the American Association of Physicists in Medicine-Task Group 43 formalism were compared to dose values calculated with the Acuros™ algorithm in the phantom. Calculated doses were compared at the same points, where measurements have been performed.
  
  
  RESULTS
  Differences in the relative response as high as 11.5% were found from the homogeneous setup when the heterogeneous materials were inserted into the experimental phantom. The aluminum and cork materials produced larger differences than the plastic materials, with the BR50/50™ material producing results similar to the Virtual Water™ results. Our experimental methods agree with the penelope/penEasy simulations for most setups and dosimeters. The TPS relative differences with the Acuros™ algorithm were similar in both experimental and simulated setups. The discrepancy between the BrachyVision™, Acuros™, and TG-43 dose responses in the phantom described by this work exceeded 12% for certain setups.
  
  
  CONCLUSIONS
  The results derived from the phantom measurements show good agreement with the simulations and TPS calculations, using Acuros™ algorithm. Differences in the dose responses were evident in the experimental results when heterogeneous materials were introduced. These measurements prove the usefulness of the heterogeneous phantom for verification of HDR treatment planning systems based on model-based dose calculation algorithms.
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705 and Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
authors.forename: Eduardo S
authors.initials: ES
authors.lastname: Moura
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: John A
authors.initials: JA
authors.lastname: Micka
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Cliff G
authors.initials: CG
authors.lastname: Hammer
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Wesley S
authors.initials: WS
authors.lastname: Culberson
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Larry A
authors.initials: LA
authors.lastname: DeWerd
authors.affiliation: Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
authors.forename: Maria Elisa C M
authors.initials: ME
authors.lastname: Rostelato
authors.affiliation: Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Zeituni
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D003198:Computer Simulation; D004867:Equipment Design; D005373:Film Dosimetry; D006801:Humans; D007496:Iridium Radioisotopes; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D012984:Software; D013819:Thermoluminescent Dosimetry; D014867:Water
chemical_list: D007496:Iridium Radioisotopes; D014867:Water