gms | German Medical Science

Objective: 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. The electric properties of the normal intracranial compartments are well established, however, there is no data available about the electric properties of tumor tissue. In this study we determined the dieclectric properties of malignant glioma compared to other 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: Thirty-two patients with tumors of different histology and malignancy grade have been recruited [low grade glioma (n=7), glioblastoma (GBM; n=7); meningioma (n=12) and brain metastases (n=6)]. Tissue probes were acquired from the vital and perinecrotic compartment if present. From each region, five tissue probes were sampled. Immediately after acquisition, a tissue fragment was dissected from each 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. 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: 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 values compared to the solid tumor compartment. Also, we found significant intratumoral heterogeneity in tumors of one specific histological class.

Conclusion: The dielectric properties of intracranial tumors depend 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.