Irreversible Electroporation: Treatment Effect Is Susceptible to Local Environment and Tissue Properties

Abstract

).q RSNA, 2013 Purpose:To study the effects of the surrounding electrical microenvironment and local tissue parameters on the electrical parameters and outcome of irreversible electroporation (IRE) ablation in porcine muscle, kidney, and liver tissue. Materials and Methods:Animal Care and Use Committee approval was obtained, and National Institutes of Health guidelines were followed. IRE ablation (n = 90) was applied in muscle (n = 44), kidney (n = 28), and liver (n = 18) tissue in 18 pigs. Two electrodes with tip exposure of 1.5-2 cm were used at varying voltages (1500-3000 V), pulse repetitions (n = 70-100), pulse length (70-100 µsec), and electrode spacing (1.5-2 cm). In muscle tissue, electrodes were placed exactly parallel, in plane, or perpendicular to paraspinal muscle fibers; in kidney tissue, in the cortex or adjacent to the renal medulla; and in liver tissue, with and without metallic or plastic plates placed 1-2 cm from electrodes. Ablation zones were determined at gross pathologic (90-120 minutes after IRE) and immunohistopathologic examination (6 hours after) for apoptosis and heat-shock protein markers. Multivariate analysis of variance with multiple comparisons and/or paired t tests and regression analysis were used for analysis. Results:Mean (6 standard deviation) ablation zones in muscle were 6.2 cm 6 0.3 3 4.2 cm 6 0.3 for parallel electrodes and 4.2 cm 6 0.8 3 3.0 cm 6 0.5 for in-plane application. Perpendicular orientation resulted in a cross-shaped zone. Orientation significantly affected IRE current applied (28.5-31.7A for parallel, 29.5-39.7A for perpendicular; P = .003). For kidney cortex, ovoid zones of 1.5 cm 6 0.1 3 0.5 cm 6 0.0 to 2.5 cm 6 0.1 3 1.3 cm 6 0.1 were seen. Placement of electrodes less than 5 mm from the medullary pyramids resulted in treatment effect arcing into the collecting system. For liver tissue, symmetric 2.7 cm 6 0.2 3 1.4 cm 6 0.3 coagulation areas were seen without the metallic plate but asymmetric coagulation was seen with the metallic plate. Conclusion:IRE treatment zones are sensitive to varying electrical conductivity in tissues. Electrode location, orientation, and heterogeneities in local environment must be considered in planning ablation treatment.q RSNA, 2013 Supplemental material: http://radiology.rsna.org/lookup /suppl

Safety and Feasibility of Irreversible Electroporation (IRE) in Patients with Locally Advanced Pancreatic Cancer: Results of a Prospective Study

“…It has been clearly demonstrated that the effectiveness of LEDC is highly associated with the distribution of the electric field in the tissue (with the contributing variables including voltage, distance between the electrodes and depth of electrodes insertion) required to reach the optimal electrode configuration and tumor coverage [3,10,36,38,39,40,41]. Irreversible electroporation aims to completely extirpate the tumor or, at least, to dramatically modify the neoplastic microenvironment without damaging the surrounding tissues or vessels.…”

A prospective Phase 2a pilot study investigating focal percutaneous irreversible electroporation (IRE) ablation by NanoKnife in patients with localised renal cell carcinoma (RCC) with delayed interval tumour resection (IRENE trial)

“…IRE may be reversible or irreversible, depending on the voltage applied and the peripheral decrease in field strength (edge area), whereby however only the irreversible region leads to visible tissue ablation [5]. One of the shortcomings of IRE today is the absence of dedicated, clinically validated protocols to be used in different tissue environments and for different tumour biologies [39,40]. In addition, no technical endpoint has yet been described that reliably predicts successful ablation of a tumour during the course of the intervention procedure [1,39].…”

“…Previous investigations on renal IRE were exclusively experimental or safety-oriented [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. A complete histological analysis is still required to assess the completeness of tumour ablation and the nephron-sparing potential of IRE in RCC.…”

Irreversible Electroporation of the Femoral Neurovascular Bundle: Imaging and Histologic Evaluation in a Swine Model

“…The clamp harboring the electrodes was also held at an angle with respect to the long axis of the nerve, in contrast to the perpendicular orientation in our study. These differences in local tissue environment and electrode orientation might increase the actual electric potential delivered to the nerves (14,15). We used ultrasound guidance during electrode insertion to avoid puncturing the nerve and to ensure that the neurovascular bundle was positioned perpendicularly at the midpoint of the paired electrodes.…”