MR based electric properties imaging for hyperthermia treatment planning and MR safety purposes

Abstract

Many randomized clinical studies have shown that the therapeutic effect of radiotherapy and chemotherapy is significantly enhanced when used in combination with hyperthermia (tumor heating in the range of 41-45 ℃). To generate spatially focussed heating in the deep seated tumors (e.g. cervical, bladder, prostate tumors), RF phased antenna-array systems are used. Prior to treatment, electromagnetic simulation is employed to compute the optimal antenna settings, a procedure known as Hyperthermia Treatment Planning. The electromagnetic field interactions between the system and the patient are governed by the electric tissue properties. Therefore, an accurate patient dielectric model is essential for optimal hyperthermia. This research was initiated to acquire electric tissue properties in living conditions (in vivo) by Magnetic Resonance Imaging (MRI) because the values reported in the literature show large variations for normal tissue. Furthermore, the tumor electric properties are scarcely reported in the literature. In this thesis electric tissue properties of 20 cervical cancer patients were acquired by an MR based method known as the Electric Properties Tomography (EPT). The results showed that in vivo values are higher than commonly used (Ch.3&4). The impact of the acquired electric properties on hyperthermia were investigated in five patient models, showing a significant impact in particular cases (Ch.5). Furthermore, a novel method is introduced in this thesis based on Contrast Source Inversion (CSI-EPT) and a great performance was shown for reconstruction of properties of small structures and at tissue boundaries (Ch.6). Finally, the potential of CSI-EPT was shown for MR safety purposes (Ch.7)