Alternating-Frequency Microwave Hyperthermia: Preliminary Results

Microwave hyperthermia therapy for breast cancer supports chemotherapy and radiotherapy. The tumor temperature levels are increased using the heat energy emitted from the microwave sources, while the energy is optimized to minimally affect the non-cancerous regions. Introducing different frequency radiation can increase the energy-focusing sensitivity. However, a simultaneous multi-frequency radiation can be challenging when the power and phase requirements for the electromagnetic wave emitted for each frequency are different. This paper presents a frequency alteration approach. The optimized energy distributions for two frequencies were introduced in turns to the breast phantom after each other. The duration for each turn is optimized to obtain the best temperature focusing over the phantom. The alternating-frequency final temperature distribution has an 11.8% higher target-to-breast temperature ratio, $0.2{}^{\circ}\ \mathrm{C}$ lower healthy tissue temperature values and 11%-20% lower hotspot-to-target temperature ratio compared to the single-frequency results.

I. Introduction

The elevated temperature levels up to at the cancerous tissue increases the effectiveness of chemotherapy and radio-therapy provided that the healthy tissue levels are preserved. Microwave hyperthermia (MH) contributes with an external microwave heat source to the Pennes' bio-heat equation that changes the temperature stability [1]. The heat source, represented as the specific absorption rate (SAR), needs to be optimized to focus the energy to the tumor region.