Abstract 4031: The dielectric properties of brain tumor tissue

Introduction: Recently, tumor treating fields (TTFields) have been established as for the treatment of newly diagnosed GBM1. One of the most crucial parameters defining the treatment efficacy of TTFields is the electric field intensity. The electric properties of the normal intracranial compartments are well established, allowing the prediction of the electric field distribution. In contrast, there is no data available about the electric properties of tumor tissue. In this study we determined the dieclectric properties of brain tumors by analyzing resected tissue following a fast acquisition protocol. To account for the intratumoral heterogeneity, different regions of the tumor were sampled and analyzed separately. Methods: A cohort of thirty patients with tumors of different histology and malignancy grade have been recruited (meningioma: n=11; brain metastases n=7; low grade glioma n=6; glioblastoma n=6). Tissue probes were acquired whenever possible from the vital tumor area, and perinecrotic compartment identified intraoperatively using neuronavigation, intraoperative ultrasound and fluorescence guidance. From each region, five tissue probes were sampled. After acquisition, the tissue was measured immediately to avoid artifacts induced by temperature change, differences of fluid composition as well as post resection ischemia. A fragment was dissected from each tissue sample and was placed into a cylindrical cell with a known diameter. Two parallel electrodes were placed on both sides of the sample and the thickness of the tissue was measured using a micrometer. The impedance was recorded at frequencies 20Hz-1MHz using a software specifically developed for this study, which controls the LCR meter (Keysight Technologies, Santa Rosa, USA). The measured impedance was 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 was fixed, H&E stained and histologically analyzed for tumor cell count and specific tissue features. Results: After receiving a positive ethics votum, the first 30 patients were recruited. As a reference, grey and white matter tissue samples from mouse brains were used. We found significant differences between the tumor entities with meningiomas showing the lowest and GBM tissue the highest conductivity values. Consistently, the perinecrotic areas displayed lower conductivity values compared to the solid tumor compartment. Also, we found a significant heterogeneity in the dielectric properties within one tumor. Conclusion: The dielectric properties of intracranial tumors appear to be depending on histological class and malignancy grade and show significant intratumoral heterogeneity. These results may allow a more precise modelling of electric field intensity distribution within the Tumor. Citation Format: Martin A. Proescholdt, Amer Haj, Christian Doenitz, Alexander Brawanski, Zeev Bomzon, Hadas Sara Hershkovich. The dielectric properties of brain tumor tissue [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4031.