Absorption rate density (ARD) computation in microwave hyperthermia by the finite-difference time-domain method

A mathematical model has been developed, which is able to predict power distributions in biological tissues during microwave hyperthermia delivered by waveguide applicators. The numerical solution of Maxwell's equations was obtained by the finite-difference time-domain (FDTD) technique. Two improvements with respect to the standard implementation of FDTD were introduced: a separation between the source and load calculations (based on the Schelkunoff equivalence principle) and a simple routine that automatically recognises the steady state. Two commercially available applicators, a dual-ridged and a side-loaded waveguide, were modelled using their theoretical aperture fields. The absorption rate density (ARD) distributions delivered by these applicators were measured through phantom thermal dosimetry and compared with the patterns estimated by the stimulation.