Finite-difference-time-domain simulation of insulated monopole in brain tumor hyperthermia treatment

Abstract

Hyperthermia treatment has been used to treat brain tumor diseases where conventional surgical removal is invasive and poses threat to a patient. The treatment technique is to apply microwave energy which transforms into heat on the target tumour without overheating surrounding healthy tissue. The insulated monopole has proven to be suitable as an applicator in hyperthermia treatment whereby its thin slot form and small cross section area allows it to reach deep seated brain tumour. Nowadays, simulation is used to evaluate insulated monopole design. However, existing commercial simulators are difficult to learn and operate. In this study, a simple and user friendly finite-difference-time-domain (FDTD) based simulator written in MATLAB codes is developed for hyperthermia brain tumour treatment. Using the developed simulator, electric field, specific-absorption-rate (SAR) distribution and reflection coefficient of two designed insulated monopoles have been studied. The first designed insulated monopole is a simple insulated monopole with thin air gap. The second design is a multi-layer insulated monopole used to treat large deep-seated brain tumour. The resulting electric field and SAR distribution were compared and validated against analytical solutions and commercial simulator’s results, respectively. The simulator’s result was found to be more accurate with less reflection at the wave scatter boundary when complex frequency shifted perfectly matched layer (CFS-PML) absorbing boundary condition was used. And the optimal parameters of the absorbing boundary condition CFSPML in reducing computation cost were identified to be 10 layers with the degree of polynomial, m = 4.