Article
Dielectric properties of intracranial tumours
Dielektrische Eigenschaften von intrakraniellen Tumoren
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Published: | June 4, 2021 |
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Objective: Recently, tumor treating fields (TTFields) were established for the treatment of newly diagnosed glioblastoma (GBM). One of the most crucial parameters defining the treatment efficacy of TTFields is the electric field intensity, which depends on the dielectric properties of the 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 analyzed separately. In addition, sensitivity analyses for specific parameters (tissue hydration, temperature, and saline irrigation) were conducted.
Methods: A cohort of 130 patients with tumors of different histology and malignancy grade have been recruited (meningioma: n=36; brain metastases n=29; low grade glioma n=7; anaplastic glioma = 12; glioblastoma n=39; other= 7). Tissue samples were placed into a cylindrical cell with a known diameter. The impedance was recorded at frequencies 20Hz-1MHz using a software specifically developed for this study. The measured impedance was translated into dielectric properties of the sample (conductivity and relative permittivity) based on the parallel plate model. Each tissue probe was fixed and analyzed histologically. To assess the impact of tissue conditions on the measurements, probes were warmed to 35 degree Celsius, dehydrated or irrigated with 0.9% saline solution.
Results: We found significant differences between the conductivity of different types of tumors with meningiomas showing the lowest and GBM tissue exhibiting the highest conductivity values. Consistently, the perinecrotic areas of tumors displayed lower conductivity values compared to the solid tumor compartments. Also, we found a significant intratumoral heterogeneity within individual tumors. While tissue temperature had no detectable effects on the dielectric properties in GBM, saline irrigation tissue hydration significantly affected the results.
Conclusion: The dielectric properties of intracranial tumors appear to be depending on histological class and malignancy grade and show significant intratumoral heterogeneity. Dehydration and saline irrigation are important influencing factors. These results may allow a more precise modelling of electric field intensity distribution within the tumor.