1 Contact Author: bbh5108@psu.edu A DEPLOYABLE MULTI-TINE ENDOSCOPIC RADIOFREQUENCY ABLATION ELECTRODE: SIMULATION VALIDATION IN A THERMOCHROMIC TISSUE PHANTOM Bradley Hanks 1 , Fariha Azhar, Mary Frecker Pennsylvania State University University Park, PA, USA Ryan Clement, Jenna Greaser, Kevin Snook Actuated Medical Inc. Bellefonte, PA, USA ABSTRACT Endoscopic radiofrequency ablation has gained interest for treating abdominal tumors. The radiofrequency ablation electrode geometry largely determines the size and shape of the ablation zone. Mismatch between the ablation zone and tumor shapes leads to reoccurrence of the cancer. Recently, work has been published regarding a novel deployable multi-tine electrode for endoscopic radiofrequency ablation. The prior work developed a thermal ablation model to predict the ablation zone surrounding an electrode and a systematic optimization of the electrode shape to treat a specific tumor shape. The purpose of this work is to validate the thermal ablation model through experiments in a tissue phantom that changes color at ablation temperatures. The experiments highlight the importance of thermal tissue damage in finite element modeling. Thermal induced changes in tissue properties, if not accounted for in finite element modeling, can lead to significant overprediction of the expected ablation zone surrounding an electrode. Keywords: Radiofrequency ablation, endoscopic ultrasound, finite element modeling 1 INTRODUCTION Radiofrequency ablation (RFA) is a method of cancer treatment that involves inserting an electrode into a tumor and applying an alternating current, developing an intense electric field in the surrounding tissue [1–3]. The alternating current causes ions and charged molecules to oscillate, generating frictional heating and ablation of surrounding tissue [1]. The ablation zone depends on electrode geometry, often resulting in a shape mismatch between the ablation zone and tumor geometry, leaving portions of tumor intact [4–6]. A variety of laparoscopic electrodes have been designed to target specific tumor shapes and locations [1,7]. However, there are upper abdominal locations inaccessible to laparoscopic procedures. Endoscopic Ultrasound (EUS)-guided techniques are often employed to biopsy and treat tumors, providing minimally invasive access to upper abdominal tumors. Recently, EUS- guided RFA has been explored for treating upper abdominal tumors [8–11]. Currently, there are two commercial EUS-guided RFA electrodes: Habib EUS-RFA catheter (Emcision Ltd, London) [12–14] and the cyrotherm probe (ERBE, Elektromedizin GmbH, Tübingen, Germany) [15–17]. The Habib electrode is a simple device (essentially a single wire) that may be inserted into the tumor. The cryotherm probe (cylindrical profile like Habib electrode) employs a complex combination treatment of cryoablation and RFA. As previously stated, the RFA electrode geometry plays a major role in the size and shape of the ablation zone. With commercial EUS electrodes, the slender cylindrical electrode shape results in ablation zones that are typically ellipsoidal with limited breadth. Tumors, on the other hand, are typically spherical, meaning that there is a mismatch between the necrosis zone and treatment region. Because of the mismatch, multiple insertions are required to reposition the electrode and overlap a series of ablations to fully treat a tumor [13,14]. In our previous work, the design optimization of a deployable multi-tine EUS electrode has been explored using a finite element thermal ablation model (TAM) to predict the ablation zone [18]. A formal optimization procedure was developed to tailor the shape of the electrode, matching the ablation zone and tumor geometries. Using the finite element models, the percentage of the tumor ablated increased from 25% for a commercial electrode to 71-87% for an optimized deployable multi-tine electrode [18]. The primary focus of this paper is the validation of the TAM in predicting the ablation zone surrounding the electrode. Section 2 is a summary of the deployable multi-tine electrode design, TAM, phantom tissue experimental setup, and analysis methods. In Section 3, the results of the phantom tissue experiments are reported. Section 4 contains a discussion of the results and comparison to the computational model as well as limitations of the approach. Finally, in section 5 the major conclusions and future work are summarized. 1 Copyright © 2019 ASME Proceedings of the 2019 Design of Medical Devices Conference DMD2019 April 15, 16-18, 2019, Minneapolis, MN, USA DMD2019-3214 Downloaded from https://asmedigitalcollection.asme.org/BIOMED/proceedings-pdf/DMD2019/41037/V001T06A001/5171277/v001t06a001-dmd2019-3214.pdf by guest on 02 July 2020