Towards UWB microwave hyperthermia for brain cancer treatment

Licentiate thesis, 2021

Despite numerous clinical trials demonstrating that microwave hyperthermia is a powerful adjuvant modality in the treatment of cancers, there have been few instances where this method has been applied to brain tumors. The reason is a combination of anatomical and physiological factors in this site that require an extra degree of accuracy and control in the thermal dose delivery which current systems are not able to provide. All clinical applicators available today are in fact based on a single-frequency technology. In terms of treatment planning options, the use of a single frequency is limiting as the size of the focal spot cannot be modified to accommodate the specific tumor volume and location. The introduction of UWB systems opens up an opportunity to overcome these limitations, as they convey the possibility to adapt the focal spot and to use multiple operating frequencies to reduce the power deposition in healthy tissues.

In this thesis, we explore whether the current treatment planning methods can be meaningfully translated to the UWB setting and propose new solutions for UWB microwave hyperthermia. We analyze the most commonly used cost-functions for treatment planning optimization and discuss their suitability for use with UWB systems. Then, we propose a novel cost-function specifically tailored for UWB optimization (HCQ). To solve for the HCQ, we further describe a novel, time-reversal based, iterative scheme for the rapid and efficient optimization of UWB treatment plans. We show that the combined use of these techniques results in treatment plans that better exploit the benefits of UWB systems, yielding increased tumor coverage and lower peak temperatures outside the target. Next, we investigate the design possibilities of UWB applicators and introduce a fast E-field approximation scheme. The method can be used for the global optimization of the array parameters with respect to the multiple objectives and requirements of hyperthermia treatments. Together, the proposed solutions represent a step forward in the implementation of patient-specific hyperthermia treatments, increasing their accuracy and precision. The results suggest that UWB microwave hyperthermia for brain cancer treatment is feasible, and motivate the efforts for further development of UWB applicators and systems.