Conductivity Rise During Irreversible Electroporation: True Permeabilization or Heat?

Change in tissue resistance after irreversible electroporation in liver tumors as an indicator of treatment success - A multi-center analysis with long term follow-up

INTRODUCTION

A nationwide multicenter study was performed to examine whether there is a correlation between decrease in tissue resistance and time to local tumor recurrence after irreversible electroporation (IRE) in patients with hepatocellular carcinoma (HCC) and colorectal cancer liver metastases (CRCLM).

METHODS

All patients treated with IRE for liver tumors in Sweden from 2011 until 2018 were included. Patient characteristics and recurrence patterns were obtained from medical records and radiological imaging. All procedural data from the IRE hardware at the three hospitals performing IRE were retrieved. The resistance during each pulse and the change during each treatment were calculated. The electrode pair with the smallest decrease in tissue resistance was used and compared with the time to LTP.

RESULTS

149 patients with 206 tumors were treated. Exclusion due to missing and inaccurate data resulted in 124 patients with 170 tumors for the analyses. In a multivariable Cox regression model, a smaller decrease in tissue resistance and larger tumor size were associated with shorter time to local tumor recurrence for CRCLM, but not for HCC.

CONCLUSION

There was an association between a decrease in tissue resistance and time to local tumor recurrence for CRCLM. The decrease in resistance, in combination with a rise in current, may be the parameters the interventionist should use during IRE to decide if the treatment is successful.

Temperature Distribution on Classical Two Needles IRE Setup Versus a Single Needle Prototype

OBJECTIVES

Irreversible Electroporation (IRE) is a non-thermal minimally invasive cancer therapy used in the treatment of liver tumors. However, the therapy entails an electrical current flux which can be high enough to cause a noticeable temperature increase. Therefore, the analysis of the heat distribution is important: during any IRE treatment, the target area is intended to be treated with non-thermal effects, where existing thermal effects should not damage nearby sensitive structures. This article aims to compare the established two parallel needles electrode setup, used by FDA-approved electroporation delivering devices, to a single needle, multiple electrode prototype design.

METHODS

Levels and distributions of the temperature at different distances from the applicators during an IRE liver treatment were investigated. The prototype results were collated with already published in-vivo data. All electrode configurations were analyzed numerically in COMSOL Multiphysics for different pulse protocols.

RESULTS

The extension of coagulation necrosis predicted by the model matched available in-vivo data. While the maximum average temperature during pulsation was higher for the prototype (74 °C) than for the two-needle IRE setup (57 °C), the thickness of the coagulation necrosis around the conductive electrodes was in the same range for both configurations. However, the location differed completely: the necrosis engendered by the prototype was located inside the tumor, while the two-needle IRE setup created necrosis outside the tumor, potentially closer to sensitive structures.

CONCLUSION

The results highlighted the importance of heat distribution analysis for the design of new IRE needles as well as for IRE treatment planning. Proper analysis ensures that the non-thermal effects are maximized while minimizing any potential thermal damage to surrounding sensitive structures.

Musa acuminata as electroporation model

Electrochemotherapy (ECT) and Irreversible electroporation (IRE) are cancer treatments based on electric field distribution in tissues. Solanum tuberosum (potato tissue) phantom is known to mimic changes in the electrical conductivity that occur in animal tissues during electroporation (EP). Electric field distribution is assessed through enzymatic staining. However, the 24-h wait for this assessment could slow agile response scenarios. We developed and validated the Musa acuminata (cavendish banana) conductivity model, which quickly evaluates EP by tissue staining. We investigated the frequency response of the tissue using impedance spectroscopy analysis, conductivity changes, and enzymatic staining. We optimized three usual EP models: adapted Gompertz, smoothed Heaviside, and the sigmoid or logistic function. We found dielectric parameters in banana tissue similar to those in potato (electrical conductivity of 0.035 S/m and relative permittivity of 4.1×104). The coefficients of determination R2 were 99.94% (Gompertz), 99.85% (Heaviside), and 99.58% (sigmoid). The sigmoid and Heaviside functions described the calibration and validation electric currents with 95% confidence. We observed the electroporated areas in bananas 3h30m after EP. Staining was significant after 450 V/cm. The conductivity model of Musa acuminata suits treatment planning, hardware development, and training scenarios. Banana phantom supports the 3Rs practice and is a reliable alternative for potato in EP studies.

g. Scholten GA, Stommel MWJ, Fütterer JJ, Verdaasdonk RM. 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.

PIRET-A Platform for Treatment Planning in Electroporation-Based Therapies

Tissue electroporation is the basis of several therapies. Electroporation is performed by briefly exposing tissues to high electric fields. It is generally accepted that electroporation is effective where an electric field magnitude threshold is overreached. However, it is difficult to preoperatively estimate the field distribution because it is highly dependent on anatomy and treatment parameters.

OBJECTIVE

We developed PIRET, a platform to predict the treatment volume in electroporation-based therapies.

METHODS

The platform seamlessly integrates tools to build patient-specific models where the electric field is simulated to predict the treatment volume. Patient anatomy is segmented from medical images and 3D reconstruction aids in placing the electrodes and setting up treatment parameters.

RESULTS

Four canine patients that had been treated with high-frequency irreversible electroporation were retrospectively planned with PIRET and with a workflow commonly used in previous studies, which uses different general-purpose segmentation (3D Slicer) and modeling software (3Matic and COMSOL Multiphysics). PIRET outperformed the other workflow by 65 minutes (× 1.7 faster), thanks to the improved user experience during treatment setup and model building. Both approaches computed similarly accurate electric field distributions, with average Dice scores higher than 0.93.

CONCLUSION

A platform which integrates all the required tools for electroporation treatment planning is presented. Treatment plan can be performed rapidly with minimal user interaction in a stand-alone platform.

SIGNIFICANCE

This platform is, to the best of our knowledge, the most complete software for treatment planning of irreversible electroporation. It can potentially be used for other electroporation applications.

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.

Multimodal therapy with or without irreversible electroporation for unresectable locally advanced pancreatic adenocarcinoma: a systematic review and meta-analysis

BACKGROUND

Irreversible electroporation (IRE) is used as a locoregional treatment modality for patients with locally advanced pancreatic cancer (LAPC), but is non-curative and is associated with postoperative morbidity and mortality. We performed a systematic review and meta-analysis comparing survival outcomes of multimodal therapy with or without IRE.

METHODS

Separate searches were performed for multimodal therapy + IRE and multimodal therapy alone given the lack of comparative literature using PubMed, SCOPUS, and Cochrane Library in 3/2021. We determined overall survival (OS) and progression-free survival (PFS) from diagnosis and time of IRE. Treatment-related morbidity and mortality was determined.

RESULTS

Of 585 published articles, 48 met inclusion criteria for IRE (n = 27) and without IRE (n = 21) with data for 1420 (IRE) and 1348 (without IRE) patients. The 6/12/24 months OS with IRE was 99%/84%/28%. The 6/12/24 months OS without IRE was 99%/80%/12%. At 12 months from IRE, OS was 55% and PFS was 12%. The mean major complication and 90-day mortality rates for IRE were 17.95% and 2.65%.

CONCLUSION

Multimodal therapy alone is associated with similar OS to multimodal therapy + IRE in patients with LAPC. Most patients progress and nearly half die within 1 year of the IRE procedure. Given the lack of quality prospective data, IRE should remain experimental and be used with caution in LAPC.

Electrochemotherapy treatment safety under parallel needle deflection

Electrochemotherapy is a selective electrical-based cancer treatment. A thriving treatment depends on the local electric field generated by pairs of electrodes. Electrode damage as deflection can directly affect this treatment pillar, the distribution of the electric field. Mechanical deformations such as tip misshaping and needle deflection are reported with needle electrode reusing in veterinary electrochemotherapy. We performed in vitro and in silico experiments to evaluate potential problems with ESOPE type II electrode deflection and potential treatment pitfalls. We also investigated the extent to which the electric currents of the electroporation model can describe deflection failure by comparing in vitro with the in silico model of potato tuber (Solanum tuberosum). The in silico model was also performed with the tumor electroporation model, which is more conductive than the vegetal model. We do not recommend using deflected electrodes. We have found that a deflection of ± 2 mm is unsafe for treatment. Inward deflection can cause dangerous electrical current levels when treating a tumor and cannot be described with the in silico vegetal model. Outward deflection can cause blind spots in the electric field.

Feasibility and effectiveness of endoscopic irreversible electroporation for the upper gastrointestinal tract: an experimental animal study

Irreversible electroporation (IRE) is a local non-thermal ablative technique currently used to treat solid tumors. Here, we investigated the clinical potency and safety of IRE with an endoscope in the upper gastrointestinal tract. Pigs were electroporated with recently designed endoscopic IRE catheters in the esophagus, stomach, and duodenum. Two successive strategies were introduced to optimize the electrical energy for the digestive tract. First, each organ was electroporated and the energy upscaled to confirm the upper limit energy inducing improper tissue results, including bleeding and perforation. Excluding the unacceptable energy from the first step, consecutive electroporations were performed with stepwise reductions in energy to identify the energy that damaged each layer. Inceptive research into inappropriate electrical intensity contributed to extensive hemorrhage and bowel perforation for each tissue above a certain energy threshold. However, experiments performed below the precluded energy accompanying hematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays showed that damaged mucosal area and depth significantly decreased with decreased energy. Relevant histopathology showed infiltration of inflammatory cells with pyknotic nuclei at the electroporated lesion. This investigation demonstrated the possibility of endoscopic IRE in mucosal dysplasia or early malignant tumors of the hollow viscus.

Liver metastases

Liver metastases are commonly detected in a range of malignancies including colorectal cancer (CRC), pancreatic cancer, melanoma, lung cancer and breast cancer, although CRC is the most common primary cancer that metastasizes to the liver. Interactions between tumour cells and the tumour microenvironment play an important part in the engraftment, survival and progression of the metastases. Various cells including liver sinusoidal endothelial cells, Kupffer cells, hepatic stellate cells, parenchymal hepatocytes, dendritic cells, resident natural killer cells as well as other immune cells such as monocytes, macrophages and neutrophils are implicated in promoting and sustaining metastases in the liver. Four key phases (microvascular, pre-angiogenic, angiogenic and growth phases) have been identified in the process of liver metastasis. Imaging modalities such as ultrasonography, CT, MRI and PET scans are typically used for the diagnosis of liver metastases. Surgical resection remains the main potentially curative treatment among patients with resectable liver metastases. The role of liver transplantation in the management of liver metastasis remains controversial. Systemic therapies, newer biologic agents (for example, bevacizumab and cetuximab) and immunotherapeutic agents have revolutionized the treatment options for liver metastases. Moving forward, incorporation of genetic tests can provide more accurate information to guide clinical decision-making and predict prognosis among patients with liver metastases.

Electrochemotherapy Using Doxorubicin and Nanosecond Electric Field Pulses: A Pilot in Vivo Study

Pulsed electric field (PEF) is frequently used for intertumoral drug delivery resulting in a well-known anticancer treatment-electrochemotherapy. However, electrochemotherapy is associated with microsecond range of electrical pulses, while nanosecond range electrochemotherapy is almost non-existent. In this work, we analyzed the feasibility of nanosecond range pulse bursts for successful doxorubicin-based electrochemotherapy in vivo. The conventional microsecond (1.4 kV/cm × 100 µs × 8) procedure was compared to the nanosecond (3.5 kV/cm × 800 ns × 250) non-thermal PEF-based treatment. As a model, Sp2/0 tumors were developed. Additionally, basic current and voltage measurements were performed to detect the characteristic conductivity-dependent patterns and to serve as an indicator of successful tumor permeabilization both in the nano and microsecond pulse range. It was shown that nano-electrochemotherapy can be the logical evolution of the currently established European Standard Operating Procedures for Electrochemotherapy (ESOPE) protocols, offering better energy control and equivalent treatment efficacy.

Irreversible Electroporation for Locally Advanced Pancreatic Cancer

Several minimally invasive image guided tumor ablation techniques have been added to the treatment spectrum for locally advanced pancreatic cancer (LAPC). Irreversible electroporation (IRE) might have a significant additive value in the management of this difficult-to-treat disease. As opposed to thermal ablative techniques, IRE induces cell death by the delivery of high-voltage electrical pulses. The electrical energy disrupts the cellular membrane integrity, causes loss of cellular homeostasis and ultimately results in cell death. The extracellular matrix of connective tissue in surrounding delicate structures such as bile ducts, bowel wall, and larger blood vessels is spared. The preservation of these structures makes IRE attractive for the treatment of pancreatic cancers that are unresectable due to their anatomical location (ie, LAPC and local recurrence after surgical resection). In addition to its cytoreductive abilities, evidence is emerging on IRE's capability to induce systemic immunomodulation through active in vivo vaccination against pancreatic cancer cells. These effects in combination with immunotherapy may offer a new treatment paradigm for tumors with low immunogenic potential like pancreatic ductal adenocarcinoma (PDAC). This review discusses several practical and technical issues of IRE for LAPC: clinical evaluation, indications, patient preparations, procedural steps, imaging characteristics, clinical results, and "tricks of the trade" used to improve the safety and efficacy of the treatment. Future directions such as the combination of IRE with immunotherapy will be shortly addressed.

Electronic Emulator of Biological Tissue as an Electrical Load during Electroporation

Electroporation is an emerging technology, with great potential in many different medical and biotechnological applications, food engineering and biomass processing. Large variations of biological load characteristics, however, represent a great challenge in electroporator design, which results in different solutions. Because a clinical electroporator is a medical device, it must comply with medical device regulative and standards. However, none of the existing standards directly address the operation or electroporator’s performance requirements. In order to evaluate clinical, laboratory and prototype electroporation devices during the development process, or to evaluate their final performance considering at least from the perspective of output pulse parameters, we present a case study on the design of an electronic emulator of biological tissue as an electrical load during electroporation. The proposed electronic load emulator is a proof of concept, which enables constant and sustainable testing and unbiased comparison of different electroporators’ operations. We developed an analog electrical circuit that has equivalent impedance to the beef liver tissue in combination with needle electrodes, during high voltage pulse delivery and/or electroporation. Current and voltage measurements during electroporation of beef liver tissue ex vivo, were analyzed and parametrized to define the analog circuit equation. An equivalent circuit was simulated, built and validated. The proposed concept of an electronic load emulator can be used for “classical” electroporator (i.e., not nanosecond) performance evaluation and comparison of their operation. Additionally, it facilitates standard implementation regarding the testing protocol and enables quality assurance.