THE FREQUENCY-DEPENDENT FDTD METHOD FOR MULTIFREQUENCY RESULTS IN MICROWAVE HYPERTHERMIA TREATMENT SIMULATION

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. In this paper, 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.