P04.37 The dielectric properties of malignant glioma tissue

Abstract

Background

Recently, tumor treating fields (TTFields) have been established as an effective new approach for the treatment of newly diagnosed GBM. One of the most crucial parameters defining the treatment efficacy of TTFields is the electric field intensity. Essentially, the higher the electric field intensity, the higher the tumor cell killing that can be achieved by TTFields. The electric properties of the normal intracranial compartments (cerebrospinal fluid, blood, white and grey mater) are well established, allowing the prediction of the electric field distribution by finite element mesh modelling. In contrast, there is no data available about the electric properties of tumor tissue, which leads to a lack of information regarding the electric field intensity within the tumor. In this study we will determine the dieclectric properties of malignant glioma by analyzing resected tissue following a fast acquisition protocol. To account for the intratumoral heterogeneity, different regions of the tumor will be sampled and analyzed separately.

Material and Methods

Twenty patients with high grade glioma currently being recruited. Tissue probes are acquired from the infiltration zone, vital tumor area, and perinecrotic compartment identified intraoperatively using neuronavigation, intraoperative ultrasound and fluorescence guidance. From each region, five tissue probes are sampled. Immediately after acquisition, the tissue is immediately to avoid artifacts by temperature change, change of fluid composition as well as post resection ischemia. A cylindrical fragment is dissected from each tissue sample and is placed into a cylindrical cell with a known diameter. Two parallel electrodes are placed on both sides of the sample and the thickness of the tissue is measured using a micrometer. The impedance is recorded at frequencies 20Hz-1MHz using a software specificly developed for this study, which controls the LCR meter (Keysight Technologies, Santa Rosa, USA). The measured impedance is then translated into dielectric properties of the sample (conductivity and relative permittivity) based on the parallel plate model, the recorded complex impedance and the geometry of the samples. Each tissue probe will be fixed, H&E stained and histologically analyzed for tumor cell count and specific tissue features (infiltration into normal brain, vital tumor area, necrosis).

Results

The study has received a positive vote from the Ethical Board of the University Regensburg Medical Center. The first patients are being recruited, the actual results will be evaluated and presented during the meeting.