COMP-19. WATER-CONTENT BASED ELECTRIC PROPERTY TOMOGRAPHY (wEPT) FOR MODELLING DELIVERY OF TUMOR TREATING FIELDS TO THE BRAIN

Abstract

Understanding how Tumor Treating Fields (TTFields) distribute in the brain is important for optimizing delivery. The distribution depends on the electric properties (EPs) of the brain, which are heterogeneous. Therefore, there is a need for methods that map electric properties within tissue with high spatial resolution. Water content based EP tomography (wEPT) utilizes the ratio of two T1w to map tissue water content, and EPs. wEPT has been applied to map EPs at 128 MHz. This study examines the suitability of wEPT to map EPs in the brain at 100–1000 kHz (TTFields frequency range). MATERIALS AND A model connecting T1 images, Water content (WC) and EPs in the 100–1000 kHz range was created using tissue samples derived from bovine brains and aporcine CSF sample. For each sample, T1w images were acquired and WC and EPs measured. Curve fitting yielded models connecting Ir, WC and EPs. Next, wEPT was applied to map water content and EPs in tumor-bearing rat brains. EPs and WC were measured on 6 samples excised from each brain. The measured values were compared to the WC and EPs in the regions of the wEPT map corresponding to the sample. Water content estimated using wEPT agreed well with measurements on excised sample. A connection between EPs estimated with wEPT and the measured values was found. However, in some samples, especially samples excised from the tumors, large differences between wEPT-derived EP values and measurements existed. wEPT maps WC in healthy and tumor brain tissues However, the relationship between WC and EPs within this frequency range is not clear. Further work is required to refine this relationship enabling a robust non-invasive method for mapping electrical properties within the brain, and better strategies for optimizing TTFields treatment.