The frequency dependent FDTD method for multi-frequency results in microwave hyperthermia treatment simulation

Abstract

Among the techniques for speeding up the optimal parameter achievement processes in hyperthermia treatment planning, pulse excitation in the FDTD, (finite-difference time-domain) method plays an important role because it provides multi-frequency results with a single run of the code. The introduction of the frequency dependent FDTD ((FD)2TD) method has also recently provided a means to accurately deal with dispersive tissues on the condition that they have a first-order permittivity. A multi-relaxation (FD)2TD approach which can improve the match between actual and simulated tissue permittivities is presented. A comparison of ordinary FDTD, triple-relaxation (FD)2TD and analytical results in a muscle cylinder struck by a TM plane wave demonstrates the errors caused in the early multi-frequency approaches by using average permittivity values. An example of the calculation of absorption rate density (ARD) distributions in a patient specific model of a head/neck tumour managed by a waveguide applicator is reported. Some secondary refinements of the method, such as the use of dispersive absorbing boundary conditions and a field-equivalence theorem for separating applicator from tissue calculations, are also discussed.