RTRB-23SENSITIVITY ANALYSIS OF PERMITTIVITY AND CONDUCTIVITY ON ALTERNATING ELECTRIC FIELDS THERAPY FOR RECURRENT GLIOBLASTOMA

Abstract

BACKGROUND: The NovoTTF Therapy device uses two pairs of arrays to deliver frequency-tuned alternating electric fields at 200 kHz to treat recurrent glioblastoma. Although its efficacy is equivalent to chemotherapies, the precise distribution of the electric fields within the brain remains poorly understood. METHODS: We performed computerized simulation to determine the electric field distribution inside a patient's brain with a right parietal recurrent glioblastoma, using co-registered post-gadolinium T1-weighted, T2 and MP RAGE MRI images together with pre-specified relative permittivity and conductivity values for each of the cerebral structures. RESULTS: We found higher field strength at the scalp surface, ventricular horns and the medial surface of the tumor. Because the mass density and charges may vary among tumors, particularly when there is variation on the cystic make-up of the necrotic tumor, we performed a sensitivity analysis to investigate the relative contribution of permittivity and conductivity parameters to changes in the electric field distribution. Within the solid portion of the gross tumor volume (GTV), we found no variation in electric field strength from changes in permittivity from 0.001-10,000, mean electric field strength from 81.156 to 78.854 V/m, but marked variation from changes in conductivity from 0.001-100 S/m, mean electric field strength from 131.22 to 1.1463 V/cm. Within the necrotic core of the GTV, we also found no variation in electric field strength from changes in permittivity from 0.001-10,000, mean electric field strength from 39.456 to 40.180 V/m, but again marked variation from changes in conductivity from 0.001-100 S/m, mean electric field strength from 43.074 to 7.2933 V/cm. CONCLUSIONS: The results indicate that conductivity of the tumor plays a greater role than permittivity in the electric field distribution from NovoTTF Therapy.