Multifrequency approach in hyperthermia treatment planning: Impact of frequency on SAR distribution in head and neck

Addition of hyperthermia to radiotherapy has been shown beneficial in management of many types of cancer [1], including Head and Neck tumors [2]. The objective of hyperthermia treatment is to raise the temperature in the tumor to a therapeutic level 40–44°C for typically 60 minutes to achieve cell death or render the cells more sensitive to ionizing radiation and chemical toxins. In our work, we aim to develop H&N applicator that is capable of modifying the focus size according to tumor position and volume. The system consists of a number of antennas placed around a patient, relying on a constructive wave interference to selectively heat the tumour. The spatial control of the foci spot and thus the quality of hyperthermia treatment can be controled by varying operational frequency in addition to amplitude and phase optimization. Due to different wavelengths, treatment associated hot spots often appear at different locations. In conjunction with cooling effect of the blood, the multi-frequency system have potential to achieve higher tumor temperature with ‘same’ constraints on hot spots. In this paper we investigated if combination of treatment plans utilizing sequential application of various frequencies is superior to the heating with single frequency settings.