Comparison of simulation-based treatment planning with imaging and pathology outcomes for percutaneous CT-guided irreversible electroporation of the porcine pancreas: a pilot study

Irreversible electroporation for the management of pancreatic cancer: Current data and future directions

Pancreatic cancer is currently the seventh leading cause of cancer death (4.5% of all cancer deaths) while 80%-90% of the patients suffer from unresectable disease at the time of diagnosis. Prognosis remains poor, with a mean survival up to 15 mo following systemic chemotherapy. Loco-regional thermal ablative techniques are rarely implemented due to the increased risk of thermal injury to the adjacent structures, which can lead to severe adverse events. Irreversible electroporation, a promising novel non-thermal ablative modality, has been recently introduced in clinical practice for the management of inoperable pancreatic cancer as a safer and more effective loco-regional treatment option. Experimental and initial clinical data are optimistic. This review will focus on the basic principles of IRE technology, currently available data, and future directions.

Irreversible Electroporation (IRE) in Locally Advanced Pancreatic Cancer: A Review of Current Clinical Outcomes, Mechanism of Action and Opportunities for Synergistic Therapy

Locally advanced pancreatic cancer (LAPC) accounts for 30% of patients with pancreatic cancer. Irreversible electroporation (IRE) is a novel cancer treatment that may improve survival and quality of life in LAPC. This narrative review will provide a perspective on the clinical experience of pancreas IRE therapy, explore the evidence for the mode of action, assess treatment complications, and propose strategies for augmenting IRE response. A systematic search was performed using PubMed regarding the clinical use and safety profile of IRE on pancreatic cancer, post-IRE sequential histological changes, associated immune response, and synergistic therapies. Animal data demonstrate that IRE induces both apoptosis and necrosis followed by fibrosis. Major complications may result from IRE; procedure related mortality is up to 2%, with an average morbidity as high as 36%. Nevertheless, prospective and retrospective studies suggest that IRE treatment may increase median overall survival of LAPC to as much as 30 months and provide preliminary data justifying the well-designed trials currently underway, comparing IRE to the standard of care treatment. The mechanism of action of IRE remains unknown, and there is a lack of data on treatment variables and efficiency in humans. There is emerging data suggesting that IRE can be augmented with synergistic therapies such as immunotherapy.

Multi-Tissue Analysis on the Impact of Electroporation on Electrical and Thermal Properties

OBJECTIVE

Tissue electroporation is achieved by applying a series of electric pulses to destabilize cell membranes within the target tissue. The treatment volume is dictated by the electric field distribution, which depends on the pulse parameters and tissue type and can be readily predicted using numerical methods. These models require the relevant tissue properties to be known beforehand. This study aims to quantify electrical and thermal properties for three different tissue types relevant to current clinical electroporation.

METHODS

Pancreatic, brain, and liver tissue were harvested from pigs, then treated with IRE pulses in a parallel-plate configuration. Resulting current and temperature readings were used to calculate the conductivity and its temperature dependence for each tissue type. Finally, a computational model was constructed to examine the impact of differences between tissue types.

RESULTS

Baseline conductivity values (mean 0.11, 0.14, and 0.12 S/m) and temperature coefficients of conductivity (mean 2.0, 2.3, and 1.2 % per degree Celsius) were calculated for pancreas, brain, and liver, respectively. The accompanying computational models suggest field distribution and thermal damage volumes are dependent on tissue type.

CONCLUSION

The three tissue types show similar electrical and thermal responses to IRE, though brain tissue exhibits the greatest differences. The results also show that tissue type plays a role in the expected ablation and thermal damage volumes.

SIGNIFICANCE

The conductivity and its changes due to heating are expected to have a marked impact on the ablation volume. Incorporating these tissue properties aids in the prediction and optimization of electroporation-based therapies.

EView: An electric field visualization web platform for electroporation-based therapies

BACKGROUND AND OBJECTIVES

Electroporation is the phenomenon by which cell membrane permeability to ions and macromolecules is increased when the cell is briefly exposed to high electric fields. In electroporation-based treatments, such exposure is typically performed by delivering high voltage pulses across needle electrodes in tissue. For a given tissue and pulsing protocol, an electric field magnitude threshold exists that must be overreached for treatment efficacy. However, it is hard to preoperatively infer the treatment volume because the electric field distribution intricately depends on the electrodes' positioning and length, the applied voltage, and the electric conductivity of the treated tissues. For illustrating such dependencies, we have created EView (https://eview.upf.edu), a web platform that estimates the electric field distribution for arbitrary needle electrode locations and orientations and overlays it on 3D medical images.

METHODS

A client-server approach has been implemented to let the user set the electrode configuration easily on the web browser, whereas the simulation is computed on a dedicated server. By means of the finite element method, the electric field is solved in a 3D volume. For the sake of simplicity, only a homogeneous tissue is modeled, assuming the same properties for healthy and pathologic tissues. The non-linear dependence of tissue conductivity on the electric field due to the electroporation effect is modeled. The implemented model has been validated against a state of the art finite element solver, and the server has undergone a heavy load test to ensure reliability and to report execution times.

RESULTS

The electric field is rapidly computed for any electrode and tissue configuration, and alternative setups can be easily compared. The platform provides the same results as the state of the art finite element solver (Dice = 98.3 ± 0.4%). During the high load test, the server remained responsive. Simulations are computed in less than 2 min for simple cases consisting of two electrodes and take up to 40 min for complex scenarios consisting of 6 electrodes.

CONCLUSIONS

With this free platform we provide expert and non-expert electroporation users a way to rapidly model the electric field distribution for arbitrary electrode configurations.

Irreversible Electroporation of the Pancreas

Irreversible electroporation (IRE) is a relatively recent method of ablation. In contrast to many ablation devices that use thermal methods to induce cell death, IRE employs the use of an electric field to cause irreversible permeability of the cell membrane, thus inducing apoptosis. Since its use in the pancreas was first described in 2012, IRE has become established as part of the armamentarium of ablation devices currently available. The crucial advantage of IRE compared with other devices employing thermal ablation is the safety around vital structures such as vessels and ducts. This is especially important in the pancreas due to the close proximity of multiple major vascular structures, biliary ducts, and adjacent gastrointestinal organs. This article will explore the current evidence regarding the use of IRE in the pancreas.

Irreversible electroporation of pancreatic adenocarcinoma: a primer for the radiologist

Irreversible electroporation (IRE) is increasingly used for the ablation of unresectable locally advanced pancreatic adenocarcinoma. Unlike other ablation technologies that cannot be safely used around critical vasculature or ducts for risk of thermal damage, IRE uses high-voltage pulses to disrupt cellular membranes. This causes cell death by apoptosis and inflammation. IRE has been deployed by both open and percutaneous approaches. Generator parameters are the same for both approaches, and settings are pancreas specific. Variations in settings, probe placement, and probe exposure can result in thermal damage or reversible electroporation and resultant treatment failure, morbidity, or mortality. When used properly, IRE appears to improve overall survival and local recurrence, but does not influence the rate of distant recurrence. However, studies of both open and percutaneous approaches have been relatively small, non-controlled, and without appropriate comparisons. It is challenging for the radiologist to interpret treatment effects after IRE because of a dearth of guiding literature and pathologic correlates. This primer describes technical aspects, pathology correlates, post-IRE imaging, and outcomes for percutaneous and open approaches.

Irreversible Electroporation for Locally Advanced Pancreatic Cancer: Where Do We Stand in 2017?

Pancreatic adenocarcinoma has a very poor prognosis. Complete surgical resection remains the only current curative treatment. Locally advanced pancreatic cancers are considered as unresectable because of involvement of celiac and/or mesenteric vessels. Irreversible electroporation has recently been introduced to induce permanent cell death by apoptosis. Irreversible electroporation is a nonthermal cell-destruction technique that was claimed to allow destruction of cancerous cells with less damage to surrounding supporting connective tissues with collagenic structure (such as nearby blood vessels, biliary ducts, and nerves) than other types of treatment. Applications on pancreatic adenocarcinoma seem promising, and this article is an up-to-date review of the first results.

Irreversible electroporation for the ablation of pancreatic malignancies: A patient-specific methodology

BACKGROUND AND OBJECTIVES

Irreversible Electroporation (IRE) is a focal ablation technique highly attractive to surgical oncologists due to its non-thermal nature that allows for eradication of unresectable tumors in a minimally invasive procedure. In this study, our group sought to address the challenge of predicting the ablation volume with IRE for pancreatic procedures.

METHODS

In compliance with HIPAA and hospital IRB approval, we established a pre-treatment planning methodology for IRE procedures in pancreas, which optimized treatment protocols for individual cases of locally advanced pancreatic cancer (LAPC). A new method for confirming treatment plans through intraoperative monitoring of tissue resistance was also proved feasible in three patients.

RESULTS

Results from computational models showed good correlation with experimental data available in the literature. By implementing the proposed resistance measurement system 210 ± 26.1 (mean ± standard deviation) fewer pulses were delivered per electrode-pair.

CONCLUSION

The proposed physics-based pre-treatment plan through finite element analysis and system for actively monitoring resistance changes can be paired to significantly reduce ablation times and risk of thermal effects during IRE procedures for LAPC.

Time-Dependent Impact of Irreversible Electroporation on Pancreas, Liver, Blood Vessels and Nerves: A Systematic Review of Experimental Studies

Introduction

Irreversible electroporation (IRE) is a novel ablation technique in the treatment of unresectable cancer. The non-thermal mechanism is thought to cause mostly apoptosis compared to necrosis in thermal techniques. Both in experimental and clinical studies, a waiting time between ablation and tissue or imaging analysis to allow for cell death through apoptosis, is often reported. However, the dynamics of the IRE effect over time remain unknown. Therefore, this study aims to summarize these effects in relation to the time between treatment and evaluation.

Methods

A systematic search was performed in Pubmed, Embase and the Cochrane Library for original articles using IRE on pancreas, liver or surrounding structures in animal or human studies. Data on pathology and time between IRE and evaluation were extracted.

Results

Of 2602 screened studies, 36 could be included, regarding IRE in liver (n = 24), pancreas (n = 4), blood vessels (n = 4) and nerves (n = 4) in over 440 animals (pig, rat, goat and rabbit). No eligible human studies were found. In liver and pancreas, the first signs of apoptosis and haemorrhage were observed 1–2 hours after treatment, and remained visible until 24 hours in liver and 7 days in pancreas after which the damaged tissue was replaced by fibrosis. In solitary blood vessels, the tunica media, intima and lumen remained unchanged for 24 hours. After 7 days, inflammation, fibrosis and loss of smooth muscle cells were demonstrated, which persisted until 35 days. In nerves, the median time until demonstrable histological changes was 7 days.

Conclusions

Tissue damage after IRE is a dynamic process with remarkable time differences between tissues in animals. Whereas pancreas and liver showed the first damages after 1–2 hours, this took 24 hours in blood vessels and 7 days in nerves.

Optimizing Irreversible Electroporation Ablation with a Bipolar Electrode

PURPOSE

To optimize single-insertion bipolar irreversible electroporation (IRE) by characterizing effects of electric parameters and controlling tissue electric properties in a porcine model.

MATERIALS AND METHODS

Single-insertion electrode bipolar IRE was performed in 28 in vivo pig livers (78 ablations). First, effects of voltage (2,700-3,000 V), number of pulses, repeated cycles (1-6 cycles), and pulse width (70-100 µs) were studied. Next, electric conductivity was altered by instillation of hypertonic and hypotonic fluids. Finally, effects of thermal stabilization were assessed using internal electrode cooling. Treatment effect was evaluated 2-3 hours after IRE. Dimensions were compared and subjected to statistical analysis.

RESULTS

Delivering 3,000 V at 70 µs for a single 90-pulse cycle yielded 3.8 cm ± 0.4 × 2.0 cm ± 0.3 of ablation. Applying 6 cycles of energy increased ablation to 4.5 cm ± 0.4 × 2.6 cm ± 0.3 (P < .001). Further increasing pulse lengths to 100 µs (6 cycles) increased ablation to 5.0 cm ± 0.4 × 2.9 cm ± 0.3 (P < .001) but resulted in electric spikes and system crashes in 40%-50% of cases. Increasing tissue electric conductivity via hypertonic solution instillation in surrounding tissues increased frequency of generator crashes, whereas continuous instillation of distilled water eliminated this arcing phenomenon but reduced ablation to 2.3 cm ± 0.1. Controlled instillation of distilled water when electric arcing was suspected from audible popping produced ablations of 5.3 cm ± 0.6 × 3.1 cm ±0.3 without crashes. Finally, 3.1 cm ± 0.1 short-axis ablation was achieved without system crashes with internal electrode perfusion at 37°C versus 2.3 cm ± 0.1 with 4°C-10°C perfusion (P < .001).

CONCLUSIONS

Bipolar IRE ablation zones can be increased with repetitive high voltage and greater pulse widths accompanied by either judicious instillation of hypotonic fluids or internal electrode perfusion to minimize unwanted electric arcing.

Comparison of ablation defect on MR imaging with computer simulation estimated treatment zone following irreversible electroporation of patient prostate

To determine whether patient specific numerical simulations of irreversible electroporation (IRE) of the prostate correlates with the treatment effect seen on follow-up MR imaging. Computer models were created using intra-operative US images, post-treatment follow-up MR images and clinical data from six patients receiving IRE. Isoelectric contours drawn using simulation results were compared with MR imaging to estimate the energy threshold separating treated and untreated tissue. Simulation estimates of injury to the neurovascular bundle and rectum were compared with clinical follow-up and patient reported outcomes. At the electric field strength of 700 V/cm, simulation estimated electric field distribution was not different from the ablation defect seen on follow-up MR imaging (p = 0.43). Simulation predicted cross sectional area of treatment (mean 532.33 ± 142.32 mm(2)) corresponded well with the treatment zone seen on MR imaging (mean 540.16 ± 237.13 mm(2)). Simulation results did not suggest injury to the rectum or neurovascular bundle, matching clinical follow-up at 3 months. Computer simulation estimated zone of irreversible electroporation in the prostate at 700 V/cm was comparable to measurements made on follow-up MR imaging. Numerical simulation may aid treatment planning for irreversible electroporation of the prostate in patients.

Irreversible electroporation and the pancreas: What we know and where we are going?

Pancreatic adenocarcinoma continues to have a poor prognosis with 1 and 5 years survival rates of 27% and 6% respectively. The gold standard of treatment is resection, however, only approximately 10% of patients present with resectable disease. Approximately 40% of patients present with disease that is too locally advanced to resect. There is great interest in improving outcomes in this patient population and ablation techniques have been investigated as a potential solution. Unfortunately early investigations into thermal ablation techniques, particularly radiofrequency ablation, resulted in unacceptably high morbidity rates. Irreversible electroporation (IRE) has been introduced and is promising as it does not rely on thermal energy and has shown an ability to leave structural cells such as blood vessels and bile ducts intact during animal studies. IRE also does not suffer from heat sink effect, a concern given the large number of blood vessels surrounding the pancreas. IRE showed significant promise during preclinical animal trials and as such has moved on to clinical testing. There are as of yet only a few studies which look at the applications of IRE within humans in the setting of pancreatic adenocarcinoma. This paper reviews the basic principles, techniques, and current clinical data available on IRE.

Safety and feasibility of Irreversible Electroporation (IRE) in patients with locally advanced pancreatic cancer: results of a prospective study

PURPOSE

To evaluate the safety of the NanoKnife Low Energy Direct Current (LEDC) System (Irreversible Electroporation, IRE) in order to treat patients with unresectable pancreatic adenocarcinoma.

METHODS

Prospective, nonrandomized, single-center clinical evaluation of ten patients with a cytohystological diagnosis of unresectable locally advanced pancreatic cancer (LAPC) that was no further responsive to standard treatments. The primary outcome was the rate of procedure-related abdominal complications. The secondary endpoints included the evaluation of the short-term efficacy of IRE through the evaluation of tumor reduction at imaging and biological tumor response as shown by CA 19-9, clinical assessments and patient quality of life.

RESULTS

Ten patients (5 males, 5 females) were enrolled, with a median age of 66 and median tumor size of 30 mm. All patients were treated successfully with a median procedure time of 79.5 min. Two procedure-related complications were described in one patient (10%): a pancreatic abscess with a pancreoduodenal fistula. Three patients had early progression of disease: one patient developed pulmonary metastases 30 days post-IRE and two patients had liver metastases 60 days after the procedure. We registered an overall survival of 7.5 months (range: 2.9-15.9).

CONCLUSIONS

IRE is a safe procedure in patients with LAPC and may represent a new technological option in the treatment and multimodality management of this disease.