Numerical and experimental methods for further development of deep-body hyperthermia

The therapy of deep-seated pelvic tumors can be considerably improved, if in addition to radiotherapy, chemotherapy, and surgery, the deep-body hyperthermia (HT) is applied. This therapy is based on constructive E-field interference generated inside a circular phased array HT applicator at frequencies between 70 and 120 MHz. Such treatments are limited by tissue inhomogeneities and require careful planning. Different numerical methods based on integral equations, finite elements and finite differences were developed and verified in phantoms and patients. This quality assurance contains experimental verification of calculated antenna parameters, distributions of E-field, SAR and temperature. Further numerical studies have shown that the therapy efficiency can be increased when full 3-D instead of conventional transversal 2-D phase control is applied. However, a simple axial segmentation of existing 2-D HT applicators results in short radiators of reduced efficiency (mismatch, low effective height, coupling between channels). Another important precondition for further development of deep-body HT is a non-invasive monitoring of temperature in patients using magnetic resonance (MR) methods. Therefore, an interaction-free combination of HT applicator and MR tomograph is necessary. This MR compatibility means reduction of metal amounts and cross dimensions, avoidance of loops and large surfaces as well as an absolute ban of ferromagnetic materials. To solve these problems, a novel MR compatible 3-D phased array applicator for deep-body HT has been developed in a systematic way. This development from a simple antenna structure to a complex 3-D phased array was carried out by means of numerical electromagnetic modeling accompanied by measurements