Towards a microwave hyperthermia system for head and neck tumors

Licentiate thesis, 2016

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, made hyperthermia as a safe method in combination with radiotherapy to enhance the treatment outcome. Although many clinical studies have shown the effectiveness of hyperthermia for treatment of head-and-neck (H&N) cancer, presence of large vessels, tissue transitions and critical tissues in head and neck pose therapeutic challenges for treatment of advanced tumors in this region. Moreover the application of hyperthermia to deep seated tumors in H&N region requires suitable heating equipment which was not available until recently. In this thesis, an ultra wideband antenna has been designed, evaluated and built to act as the radiating element of microwave hyperthermia applicator. The time reversal focusing technique is used to target electromagnetic energy to the tumor. This focusing method is implemented by a 3D finite difference time domain based code for tumor models in head and neck. The single antenna element is a modified bow-tie antenna with wideband characteristic over 430-1000 MHz and small size. The antenna size has been reduced considerably by immersion in a conical shape water bolus, while maintaining the radiation characteristics in the presence of human phantom. The specific shape and size of water container, wideband matching network between coaxial port and feeding elements of the bow-tie and addition of low-permittivity dielectric material to the bow-tie radiating arms are the other influential factors on final performance of the antenna. The focusing ability of 3D time reversal technique was analyzed using tumor models in head and neck region of an anthropomorphic phantom. Two hyperthermia applicators were designed and used, one for the head and one for the neck. The 3D models of Head&Neck phantom together with phased array applicators were modeled in two electromagnetic solvers, CST microwave studio and an inhouse developed FDTD-based code. Keywords: microwave hyperthermia, time reversal, wideband antenna, treatment planning, head and neck tumors.