Session: 17-01-01 Research Posters

Paper Number: 76819

Start Time: Thursday, 02:25 PM

76819 - Finite Element Models Guide Energy Delivery for Non-Contact Irreversible Electroporation in the Esophagus With Thermal Damage 

Introduction: Patients with esophageal cancer (ECa) remain at elevated risk of recurrence following initial treatment of their disease. Clinically used techniques such as esophagectomy, chemotherapy, and stenting are largely palliative and carry substantial risk of complications such as leakage, fistula, and infections. Ablation, or the application of non-ionizing energy for non-surgical destruction of tumors, is widely used in patients who are not eligible for other forms of treatment due to age or comorbidities.  Irreversible electroporation (IRE) is a recently developed ablation technique that uses high-voltage ultrashort electric pulses to kill cells and has been found to be safe for ablation adjacent to sensitive structures such as the esophagus. While IRE is considered to be a non-thermal form of ablation, there is potential for substantial temperature increase in the vicinity of the electrodes, which could be detrimental to the healthy esophagus. The ability to perform IRE using an endoscopic approach without thermal damage to healthy tissues is desirable and would support translation of the technique to treat patients with ECa. We report the use of finite element models to validate the novel concept of using a non-contact wet electrode to perform IRE, allowing mitigation of thermal damage to the tissue while providing an electrically conductive pathway.

Methods and Methods: A geometric model of a human esophagus (45mm diameter, 10mm thickness) with a tumor (15mm) obstructing the lumen along with peripheral visceral tissue (74mm thickness) was constructed using a computer aided modeling software (Autodesk Inventor) with dimensions and material properties derived from published data. The geometry was imported into Comsol Multiphysics for mesh generation and finite element analysis. Two configurations were tested, conventional IRE (conIRE) where the treatment electrode (20 mm length, 5mm diameter) was placed directly into the tumor, and wet electrode IRE (wIRE) where the electrode was placed adjacent to the tumor within the esophageal lumen containing chilled saline to provide a path for the conduction of current. The conIRE finite element model (FEM) consisted of 63,597 elements and the wIRE FEM consisted of 62,402 elements. Both scenarios were simulated for an IRE treatment performed with the following pulse parameters (3000V for 90 pulses, a pulse width of 100 µs, and an interpulse delay of 1s) delivered between the monopolar electrode in the esophagus and a distal ground placed on the skin surface surrounding the organ. Maxwell’s equations were used to determine the electric field distribution. Temperature increase from Joule heating was calculated and coupled with the Pennes Bioheat equation to account for metabolic heat flux. Potential for thermal injury was estimated using an adapted Arrhenius equation.

Results and Discussion: Simulations indicated the feasibility of depositing electrical energy into the tumor using the wIRE approach. An electric field strength of 750 V/cm was used to identify tissue expected to experience ablation. The volume of the tumor anticipated to undergo ablation for conIRE and wIRE was 67% and 37% respectively. The average and peak tumor temperature for conIRE was 38°C and 70°C, whereas for wIRE the average and peak tumor temperatures were 32°C and 54°C. wIRE approach did not cause thermal damage or ablation of the esophageal wall. conIRE treatment resulted in 50% of the esophageal wall adjacent to the tumor to undergo IRE and a considerable amount of the esophageal wall experienced thermal damage. The average and peak esophageal wall temperatures for conIRE was 34°C and 69°C, where the corresponding values for wIRE temperatures were 27°C and 37°C respectively.

Conclusion: FEM simulations suggest non-contact ablation of esophageal tumors using our wIRE approach to be feasible and can mitigate thermal damage to healthy esophagus that arises when placing the electrode directly in the tumor.

Presenting Author: Mary Chase Sheehan University of Massachusetts Amherst

Authors:

Mary Chase Sheehan University of Massachusetts Amherst
Govindarajan Srimathveeravalli University of Massachusetts Amherst