Finite Element Analysis Modeling of TTFields in Brain Metastasis According to Various Types of Cerebral Edema

Objective: To determine differences in Tumor treating Fields (TTFields) intensity for vasogenic, interstitial and cytotoxic edemas. Background: TTFields are being investigated as treatment for brain metastasis. Although vasogenic edema is the predominant type of cerebral edema, other forms of edema might arise within the brain and they may alter TTFields. Design/Methods: MRI DICOM images were obtained for auto-segmentation using SPM8 and MATLAB. Masks of various tissues within the head were generated in ScanIP from Simpleware and further corrections/delineation of the patient’s edema and gross tumor volume (GTV) were performed by the physician. Edema mask was given an electric conductivity value equivalent to Plasma (0.71S/m) for vasogenic edema, CSF (2.0S/m) for interstitial edema, and Gray Matter (0.14S/m) for cytotoxic edema, respectively. The electric conductivity for tumor remained the same at 0.25S/m. Finite element analysis (FEA) simulation was done in COMSOL Multiphysics and electric field, specific absorption rate and current density distribution plots were generated. Results: The physics modeling showed that the vasogenic edema had E75%=8.8 V/m, E50%=26.1 V/m and E25%=33.6/m, while interstitial edema had E75%=4.3 V/m, E50%=8.5 V/m and E25%=23.3/m, and cytotoxic edema had E75%=27.8 V/m, E50%=42.4V/m and E25%=59.0/m. GTV associated with interstitial edema hadE75%=7.1 V/m, E50%=21.9 V/m and E25%=25.3V/m, while GTV associated with cytotoxic edema had E75%=23.9 V/m, E50%=30.1 V/m and E25%=35.6/m, and GTV associated with vasogenic edema had E75%=22.7 V/m, E50%=28.6 V/m and E25%=33.9/m. Conclusions: The electric field coverage at the GTV was highest when the tumor was surrounded by cytotoxic edema. Vasogenic edema was associated with lowerfields coverage and interstitial edema was associated with the lowest electric field coverage at the GTV. Disclosure: Dr. Pisati has nothing to disclose. Dr. San has nothing to disclose. Dr. Lok has nothing to disclose. Dr. Wong has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Advance Medical, Merck, and Novocure. Dr. Wong has received research support from Novocure.