Research Papers

Optimization of an Endoscopic Radiofrequency Ablation Electrode

[+] Author and Article Information
Bradley Hanks

Department of Mechanical and
Nuclear Engineering,
Pennsylvania State University,
314 Leonhard Building,
University Park, PA 16802
e-mail: bbh5108@psu.edu

Mary Frecker

Fellow ASME
Department of Mechanical and
Nuclear Engineering,
Pennsylvania State University,
127 Reber Building,
University Park, PA 16802
e-mail: mxf36@engr.psu.edu

Matthew Moyer

Division of Gastroenterology and Hepatology,
Penn State Hershey Medical Center,
Penn State Cancer Institute,
Hershey, PA 17033
e-mail: mmoyer@hmc.psu.edu

1Corresponding author.

Manuscript received August 14, 2017; final manuscript received April 17, 2018; published online July 13, 2018. Assoc. Editor: Michael Eggen.

J. Med. Devices 12(3), 031002 (Jul 13, 2018) (11 pages) Paper No: MED-17-1286; doi: 10.1115/1.4040184 History: Received August 14, 2017; Revised April 17, 2018

Radiofrequency ablation (RFA) is an increasingly used, minimally invasive, cancer treatment modality for patients who are unwilling or unable to undergo a major resective surgery. There is a need for RFA electrodes that generate thermal ablation zones that closely match the geometry of typical tumors, especially for endoscopic ultrasound-guided (EUS) RFA. In this paper, the procedure for optimization of an RFA electrode is presented. First, a novel compliant electrode design is proposed. Next, a thermal ablation model is developed to predict the ablation zone produced by an RFA electrode in biological tissue. Then, a multi-objective genetic algorithm is used to optimize two cases of the electrode geometry to match the region of destructed tissue to a spherical tumor of a specified diameter. This optimization procedure is then applied to EUS-RFA ablation of pancreatic tissue. For a target 2.5 cm spherical tumor, the optimal design parameters of the compliant electrode design are found for two cases. Cases 1 and 2 optimal solutions filled 70.9% and 87.0% of the target volume as compared to only 25.1% for a standard straight electrode. The results of the optimization demonstrate how computational models combined with optimization can be used for systematic design of ablation electrodes. The optimization procedure may be applied to RFA of various tissue types for systematic design of electrodes for a specific target shape.

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Grahic Jump Location
Fig. 1

The electrode will be deployed into the tumor through an endoscopic needle whose tip has been positioned at the periphery of the tumor

Grahic Jump Location
Fig. 2

Two variations of the proposed electrode design are pictured in the stowed ((a) and (d)) and deployed ((b) and (e)) configurations. The design parameters for each are shown ((c) and(f)).

Grahic Jump Location
Fig. 3

General setup for the RFA model. Due to the symmetry of the electrode, the model was reduced to quarter symmetry to decrease computation time. The grounding pads regions are the top and bottom quarter circles as well as the exterior wall of the cylinder (not shown).

Grahic Jump Location
Fig. 4

Graphical description of the objective functions used for optimization

Grahic Jump Location
Fig. 5

Each design tested during the optimization is plotted in this figure according to its corresponding objective function values

Grahic Jump Location
Fig. 6

The side view of each optimal solution for cases 1 and 2 are shown in the figure above. The ablation zone is marked by the white isothermal contour (60 °C).

Grahic Jump Location
Fig. 8

Top and side views of the ablation zones for the straight electrode and optimal solutions of cases 1 and 2. The ablation zone is marked by the 60 °C isothermal surface and the circle represents the target zone.

Grahic Jump Location
Fig. 7

Each case 2 design simulated is plotted above according to its corresponding objective function values



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