title: FDTD simulations to assess the performance of CFMA-434 applicators for superficial hyperthermia.
abstract: BACKGROUND
  Contact flexible microstrip applicators (CFMA), operating at 434 MHz, are applied at the Academic Medical Center (AMC) for superficial hyperthermia (e.g. chest wall recurrences and melanoma). This paper investigates the performance of CFMA, evaluating the stability of the specific absorption rate (SAR) distribution, effective heating depth (EHD) and effective field size (EFS) under different conditions.
  
  
  METHODS
  Simulations were performed using finite differences and were compared to existing measurement data, performed using a rectangular phantom with a superficial fat-equivalent layer of 1 cm and filled with saline solution. The electrode plates of the applicators measure approximately 7 x 20, 29 x 21 and 20 x 29 cm(2). Bolus thickness varied between 1 and 2 cm. The impact of the presence of possible air layers between the rubber frame and the electrodes on the SAR distribution was investigated.
  
  
  RESULTS
  The EHD was approximately 1.4 cm and the EFS ranged between approximately 60 and approximately 300 cm(2), depending on the applicator type. Both measurements and simulations showed a split-up of the SAR focus with a 2 cm water bolus. The extent and location of air layers has a strong influence on the shape and size of the iso-SAR contours with a value higher than 50%, but the impact on EFS and EHD is limited.
  
  
  CONCLUSIONS
  Simulations, confirmed by measurements, showed that the presence of air between the rubber and the electrodes changes the iso-SAR contours, but the impact on the EFS and EHD is limited.
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. H.P.Kok@amc.uva.nl
authors: H Petra
authors: HP
authors: Kok
authors: Martijn
authors: M
authors: De Greef
authors: Davi
authors: D
authors: Correia
authors: Paul J Zum Vörde Sive
authors: PJ
authors: Vörding
authors: Gerard
authors: G
authors: Van Stam
authors: Edward A
authors: EA
authors: Gelvich
authors: Arjan
authors: A
authors: Bel
authors: Johannes
authors: J
authors: Crezee
mesh_terms: D000388:Air; D003198:Computer Simulation; D004566:Electrodes; D006801:Humans; D006979:Hyperthermia, Induced / Q000295:instrumentation*; D008962:Models, Theoretical; D019047:Phantoms, Imaging