The Effect of Partial Electrical Insulation of the Tip and Active Needle Length of Monopolar Irreversible Electroporation Electrodes on the Electric Field Line Pattern and Temperature Gradient to Improve Treatment Control.

Unintentional local temperature effects can occur during irreversible electroporation (IRE) treatment, especially near the electrodes, and most frequently near the tip. Partial electrical insulation of the IRE electrodes could possibly control these temperature effects. This study investigated and visualized the effect of partial electrical insulation applied to the IRE electrodes on the electric field line pattern and temperature gradient. Six designs of (partial) electrical insulation of the electrode tip and/or active needle length (ANL) of the original monopolar 19G IRE electrodes were investigated. A semolina in castor oil model was used to visualize the electric field line pattern in a high-voltage static electric field. An optical method to visualize a change in temperature gradient (color Schlieren) was used to image the temperature development in a polyacrylamide gel. Computational models were used to support the experimental findings. Around the electrode tip, the highest electric field line density and temperature gradient were present. The more insulation was applied to the electrodes, the higher the resistance. Tip and ANL insulation together reduced the active area of and around the electrodes, resulting in a visually enlarged area that showed a change in temperature gradient. Electrically insulating the electrode tip together with an adjustment in IRE parameter settings could potentially reduce the uncontrollable influence of the tip and may improve the predictability of the current pathway development.

The Influence of Irreversible Electroporation Parameters on the Size of the Ablation Zone and Thermal Effects: A Systematic Review.

Introduction: The aim of this study was to review the effect of irreversible electroporation parameter settings on the size of the ablation zone and the occurrence of thermal effects. This insight would help to optimize treatment protocols and effectively ablate a tumor while controlling the occurrence of thermal effects. Methods: Various individual studies report the influence of variation in electroporation parameters on the ablation zone size or occurrence of thermal effects. However, no connections have yet been established between these studies. With the aim of closing the gap in the understanding of and personalizing irreversible electroporation parameter settings, a systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A quality assessment was performed using an in-house developed grading tool based on components of commonly used grading domains. Data on the electroporation parameters voltage, number of electrodes, inter-electrode distance, active needle length, pulse length/number/protocol/frequency, and pulse interval were extracted. Ablation zone size and temperature data were grouped per parameter. Spearman correlation and linear regression were used to define the correlation with outcome measures. Results: A total of 7661 articles were screened, of which 18 preclinical studies (animal and phantom studies) met the inclusion criteria. These studies were graded as moderate (4/18) and low (14/18) quality. Only the applied voltage appeared to be a significant linear predictor of ablation zone size: length, surface, and volume. The pulse number was moderately but nonlinearly correlated with the ablation zone length. Thermal effects were more likely to occur for higher voltages (≥2000 V), higher number of electrodes, and increased active needle length. Conclusion: Firm conclusions are limited since studies that investigated and precisely reported the influence of electroporation parameters on the ablation zone size and thermal effects were scarce and mostly graded low quality. High-quality studies are needed to improve the predictability of the combined effect of variation in parameter combinations and optimize irreversible electroporation treatment protocols.

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

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.