RESEARCH ARTICLE Efficient energy localization for hybrid wideband hyperthermia treatment system Nizam Uddin | Ibrahim Elshafiey Electrical Engineering Department, King Saud University, Riyadh, Saudi Arabia Correspondence Nizam Uddin, Electrical Engineering Department, King Saud University, Riyadh, Saudi Arabia. Email: enizamuddin@ksu.edu.sa Funding information King Abdul-Aziz City for Science and Technology (KACST), General Administration for Research Grants Grant/Award Number: AT 35-210. Abstract This article presents efficient energy localization approach for hybrid wideband sys- tem for hyperthermia treatment of cancer based on a transmission line (TL). A heterogeneous head phantom is built by incorporating frequency dependent tissue properties of head layers considering both electromagnetic and ultrasound treatment. Effective medium properties are derived and used to compensate signal phase and magnitude values based on TL model. The obtained field map results emphasize the feasibility of the developed approach to obtain system parameters that enhance energy localization and eradicate hotspots. KEYWORDS energy localization, hyperthermia treatment, SAR, transmission line model, wideband system 1 | INTRODUCTION Hyperthermia has emerged as a promising modality for cancer therapy. During hyperthermia treatment (HT), the temperature of the malignant tissues is raised to 408C-458C using either EM or ultrasound (US) energy. 1 When used in adjunct with radiotherapy and chemotherapy, HT can increase the efficacy of therapeutic plans. 2–6 The increase of temperature during hyperthermia is correlated to the specific absorption rate (SAR), which depends upon various factors including tissue properties, the number of heating sources, the biological inter- action of EM or US energy with human tissue, the size and location of tumor and the frequency of operation. 7 One of the main challenges in clinical hyperthermia is to heat deep-seated tumor without damaging the surrounding healthy tissue. Math- ematically, it requires SAR optimization to meet this challenge. Several techniques have been reported in recent research regarding SAR optimization in EM hyperthermia systems, including beamforming, 8 time reversal, 9 fixed-time topology, 10 inverse multiphysics strategy, 11 genetic algorithms, 12–19 eigenvalue-based optimization, 20 projection algorithm, 21 and particle swarm optimization. 22 When compared with EM fields, acoustic energy propagates with reduced speed and shorter wavelength values can be useful to target small-sized tumors with deep penetration. EM fields on other hand have wide wavefront and are capable of targeting larger areas. US fields also face a problem in noninvasive transcranial energy delivery compared with EM fields because of the high US impedance of skull-bone. 23 This research aims to enhance energy localization at the tumor site. System degrees of freedom are increased by assuming multiport excitation, hybrid energy and wideband operating system. Parameter optimization is based on simple transmission-line TL model. Cascaded TLs are used to repre- sent signal delay in different tissues. Effective permittivity values of the mediums are estimated by comparing results of the simplified TL model with results of 3D energy interac- tion model. A technique is also developed to nullify the phase aberrations for the case of US hyperthermia caused by the skull-bone layer. To investigate the feasibility of wideband HT, a numeri- cal head phantom model of radius 10 cm is built using CST microwave studio. 24 This cylindrical phantom is composed of tissue representing brain enclosed by 0.5-cm thickness of skull. A tumor of radius 2.5 cm is located at x 5 3 cm, y 5 4 cm and z 5 0 cm as shown in Figure 1A,B. Eight energy applicator ports surround the phantom. The amplitude and phase of the signal at excitation port is depicted in Figure 1C,D respectively. To ensure minimum reflections at the boundaries, open boundary conditions are selected for this Int J RF Microw Comput Aided Eng. 2018;e21238. https://doi.org/10.1002/mmce.21238 wileyonlinelibrary.com/journal/mmce V C 2018 Wiley Periodicals, Inc. | 1 of 13 Received: 3 August 2017 | Revised: 31 December 2017 | Accepted: 31 December 2017 DOI: 10.1002/mmce.21238