Development of a new hyperthermia application for treatment of head and neck tumors : a theoretical exploration

In this thesis a theoretical investigation to a new head and neck hyperthermia applicator is described. This project forms the first step towards the development of a head and neck hyperthermia treatment system. Hyperthermia is defined as a temperature elevation by several degrees (3-TC) above the normal physiological level. A hyperthermia cancer treatment aims to kill cancerous cells by deliberately increasing the tissue temperature. Because the vascularization is chaotic in certain regions of the carcinoma, an increase of 3-5°C is sufficient to kill the tumor cells. As a result, the temperature just needs a small increase, therefore not affecting healthy regions. Research in the temperature distribution has to be undertaken to determine whether a hyperthermia treatment, using heating with electromagnetic power, can be effective. This is achieved by calculating the power absorbtion in the target region from which information of the local temperature can be obtained. The setups are gradually changed towards a physically feasible setup, that represents an actual clinical setup. The calculations are done using a Finite Difference Time Domain (FDTD) code developed at TNO-FEL: FELFDTD. This code is adapted for calculation of power absorbtion distributions in a human body. The antenna characteristics, the influence of the boundary conditions and the influence of the implementation of the FDTD code on the power absorbtion values are visualized and discussed. The results of FEL-FDTD are compared with a FDTD based, commercial software using the same test setup, however to fully verify the results further research would be necessary. Results obtained by calculations, with the FEL-FDTD program on a human head model that is illuminated by electric field point sources or dipole antennae, indicate that a local rise in temperature can be achieved. The results obtained with hard sources compared to results with dipole antennae show a large variation, which indicates that additional calculations are needed to optimize the tuning. It is noted that further research is needed to calculate setups with the head model illuminated by dipoles that are embedded in water as a first step into a better modelling of the physical applicator setup.