Abstract 1413: Using conventional imaging to predict water content and electrical properties at 200 kHz in brain and GBM tumor tissues: a feasibility study in three TTFields patients
Authors: Wenger Cornelia , Hershkovich Hadas Sara , Brami Catherine Tempel , Giladi Moshe , Bomzon Zeev 
Published: August 2019

Introduction

Tumor Treating Fields (TTFields) are approved for the treatment of Glioblastoma (GBM). The efficacy of TTFields increases with field intensity at the tumor which depends on its highly heterogeneous electrical properties (EPs) distribution. Thus, an imaging technique, preferably with conventional sequences, rapid acquisition and fast processing, that is able to assess the EPs non-invasively might be of high interest for patient-specific TTFields treatment planning.

An approach termed water content electrical properties tomography (wEPT), estimates the EPs of brain tissue at 128 MHz from water content (WC) maps which are created with two spin echo sequences resembling a T1w and a PD image. Recently we performed experiments in tumor-bearing rats suggesting that wEPT could be adapted to map EPs in the brain at 200 kHz. Here we tested the feasibility of applying wEPT to map EPs at 200 kHz in GBM patients.

Methods

Analysis was performed for three patients that participated in the EF-14 trial. The image ratio was calculated as pixel-by-pixel division of T1 and PD images. The WC maps were estimated with a transfer function and two separate equations were used to calculate the maps of the electrical conductivity σ and the relative permittivity ϵr at 200 kHz. The table summarizes the median values in 5 tissues of normalized T1 and PD signals and the wEPT-estimations of WC, σ, and ϵr at 200 kHz.

Results

median valuesT1normPDnormWC[%]σ[S/m]ϵr[-]white matterPatient 10,230,5876%0,112575Patient 20,180,3276%0,112462Patient 30,240,3574%0,102191gray matterPatient 10,200,6083%0,222923Patient 20,160,3381%0,172799Patient 30,220,3881%0,172919necrosisPatient 10,230,8689%0,472495Patient 20,120,3298%1,431381Patient 30,240,4484%0,242988enhancing tumorPatient 10,370,8371%0,091546Patient 20,170,3581%0,172961Patient 30,230,4285%0,262932non-enhancing tumorPatient 10,230,7385%0,262979Patient 20,180,3678%0,142769

Conclusions

We adapted the wEPT approach to map WC and EPs at 200 kHz in three GBM patients. In healthy brain tissues the estimations are consistent with literature and also among patients, contrary to the highly variable tumor. This fast approach only needing conventional MRI holds some promise for patient-specific TTFields treatment planning. Yet the mapping of tumor tissues needs to be validated further, possibly including EP measurements of excised tumor samples and generally a higher number of patients analyzed.

Citation Format: Cornelia Wenger, Hadas Sara Hershkovich, Catherine Tempel Brami, Moshe Giladi, Zeev Bomzon. Using conventional imaging to predict water content and electrical properties at 200 kHz in brain and GBM tumor tissues: a feasibility study in three TTFields patients [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 1413.