Effect of irreversible electroporation parameters and the presence of a metal stent on the electric field line pattern

Abstract

The final ablation zone created with irreversible electroporation (IRE) depends on the size, shape and strength of the electric field that is influenced by several parameters. A profound understanding of the effect of IRE parameter alterations on the electric field are a prerequisite for a safe and effective treatment. Here, we demonstrate a semolina in castor oil model that enables visualization of the static electric field developed by a high-voltage generator between two needle-electrodes. We intuitively visualize the variation in electric field line pattern for selected IRE parameters; active needle length, inter-needle distance, applied voltage and presence of a nearby metal stent, by cameras in three dimensions. The observations were compared to and supported by two-dimensional numerical simulations of the electric field. Our semolina model visualizes the disturbance of the electric field by a metal stent, potentially leading to an incomplete tumour ablation between the needles. The reduction in electric field strength and the area at risk for incomplete tumour ablation are confirmed by the numerical simulations. The semolina model provides insight in the fundamental physics of the electric field, the effect of alterations in IRE parameter combinations and presence of a metal stent within the ablation zone. Irreversible electroporation (IRE) is theoretically a non-thermal ablation technique, which makes it especially suitable for ablation of tumours near vital structures, such as locally advanced pancreatic tumours 1-3. IRE uses a high-voltage external electric field and electric pulses of microsecond duration to change the transmembrane potential of tumour cells, resulting in permanent permeabilization of the cell membrane 4-6. Membrane permeabilization disturbs the cell's mechanisms to maintain homeostasis, finally leading to cell death via a necrotic pathway presumably or apoptosis 4,7-9. Tumour cells are ablated while the extracellular matrix, collagen and elastic fibres, such as blood vessels and bile ducts remain intact 9,10. Biliary drainage is frequently required in patients with pancreatic tumours. The use of a metal stent is usually preferred because of fewer stent-related complications (e.g. cholangitis) and less stent dislocations compared to plastic stents 11,12. It is currently unknown whether IRE can be safely and effectively applied in patients with a metal stent in situ close to the ablation site. Detrimental effects of a metal object on IRE outcomes have been suggested in literature. In a case report, severe complications have been described after IRE treatment in the proximity of a metal stent, potentially caused by unintended thermal effects 13. A retrospective clinical study demonstrated that IRE near small metal surgical clips (< 1 cm to tumour margin or needle electrodes) resulted in distortion of the electric field and inadequate coverage of the tumour, a less effective cell death and reduced treatment efficacy 14. The presence of a metal clip was also significantly related to local ...

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