Optimizing microwave hyperthermia antenna systems

Doktorsavhandling, 2018

This thesis presents design and optimization of a microwave hyperthermia antenna
system for treatment of head and neck cancer as well as brain cancer. Hyperthermia
has shown the ability to enhance the performance of radiotherapy and
chemotherapy in many clinical trials. The incidence of increased tissue toxicity as
a result of high radiotherapy dose has made hyperthermia a safe complementing,
treatment enhancing method to use in combination with radiotherapy. Although
many clinical studies have shown the effectiveness of hyperthermia for treatment
of the head-and-neck (H&N) cancer, the presence of large vessels, tissue transitions
and critical tissues in the head and neck poses therapeutic challenges for
treatment of advanced tumors in this region. Late side-effects of conventional
therapies in treatment of brain tumors in children have been made hyperthermia
an attractive method. However, heating tumors in the brain is even more challenging
because of its high sensitivity, high thermal conductivity and high perfusion.
In this thesis microwave hyperthermia applicators are presented for efficient
heating of the H&N and brain tumors. For this purpose, an ultra-wideband antenna
has been designed, built and evaluated to act as the radiating element of microwave
hyperthermia applicators. The time reversal focusing technique is used to
target electromagnetic energy into the tumor. To obtain more accurate treatment
planning, the effect of frequency and virtual source positions, in the time-reversal
method, are studied for different tumor sizes and tumor positions. The optimal
detailed design of the applicator, such as the number of antennas and the antenna
positions are also investigated.
In the second part of the thesis, the focus is on the applicators for treatment of
the brain tumors in children. Helmet applicators are presented and the effect of the
number of antennas and the frequency are investigated on the performance of the
applicators for heating large and deep-seated brain tumors. Finally, the optimum
position of antennas in helmet applicators are found by performing optimization
on simplified and realistic models of the child head.