Abstract 4871: Comparative analysis of tumor treating fields using conventional versus alternative array placement for posterior fossa Glioblastoma
Authors: Lok Edwin , San Pyay , White Victoria , Wong Eric T. 
Published: August 2019

Abstract
Background: Tumor Treating Fields (TTFields) therapy is an approved treatment modality for glioblastoma. Optimal transducer array placement can be defined by anatomy-based finite element analysis (FEA), which helps to delineate electric field coverage of the tumor. The conventional array placement was designed to provide adequate electric field coverage for supratentorial glioblastomas. There is an alternative array placement configuration for infratentorial tumors, but the extent of coverage to posterior fossa glioblastoma is unknown.
Methods: Patient anatomy-based FEA models were created by segmenting MRI images — using the NewSegment algorithm from Statistical Paramedic Mapping 8 — into tissue “masks” utilizing ScanIP from Simpleware (Exeter, UK). The physical properties of each tissue type were first applied to these masks and then boundary conditions for physics modeling was set up within COMSOL Multiphysics (Burlington, MA). COMSOL generated electric field maps were compared for models using the conventional array placement configuration for supratentorial tumors versus the alternative array placement configuration for infratentorial tumors. Electric field-volume histograms (EVHs) and specific absorption rate-volume histograms (SARVHs) were constructed to numerically evaluate the relative and/or absolute magnitude volumetric differences between models.
Results: The alternative configuration consists of array placement at the vertex, the bi-occipital regions and the upper neck. The highest EAUC was found at the epidural space surrounding the spinal cord and scalp for both types of configurations, whereas the lowest was located at the tongue and orbits. Using the conventional configuration, the gross tumor volume (GTV) had an electric field area under the curve (EAUC) of 40.5 V/m, volume covered with electric field intensity of 150 V/m (VE150) of 0.01%, 95% electric field intensity (E95%) of 30.9 V/m, E50% of 41.1 V/m, and E20% of 46.6 V/m. The GTV also had a SARAUC of 4.0 W/kg, volume covered with SAR of 6 W/kg (VSAR6) of 0%, SAR95% of 0.6 W/kg, SAR50% of 0.7 W/kg, and SAR20% of 0.8 W/kg. The alternative configuration produced EAUC of 52.3 V/m, VE150 of 3.6%, E95% of 29.1 V/m, E50% of 44.7 V/m, and E20% of 58.1 V/m, as well as SARAUC of 0.9 W/kg, VSAR6 of 0.3%, SAR95% of 0.6 W/kg, SAR50% of 0.8 W/kg, and SAR20% of 0.9 W/kg.
Conclusions: The alternative array placement configuration provides a higher coverage of electric field (+29%) to the posterior fossa glioblastoma when compared to the conventional configuration.
Citation Format: Edwin Lok, Pyay San, Victoria White, Eric T. Wong. Comparative analysis of tumor treating fields using conventional versus alternative array placement for posterior fossa Glioblastoma [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 4871.