Optimization of wet radiofrequency ablation using a perfused-cooled electrode: a comparative study in ex vivo bovine livers

Thyroid-dedicated internally-cooled wet electrode for benign thyroid nodules: experimental and clinical study

BACKGROUND

To assess the effects of radiofrequency ablation (RFA) using an internally-cooled wet (ICW) electrode in ex vivo bovine liver and evaluate the feasibility of the ICW electrode for benign thyroid nodules.

METHODS

We developed an 18-gauge ICW electrode with a microhole at the distal tip for tissue infusion of chilled (0 - 4 °C) isotonic saline (rate = 1.5 ml/min). RFA using ICW and IC electrodes were performed in bovine livers (40 pairs, 1-cm active tip, 50 W, 1-min). We compared the morphological characteristics of ablation zones and presence of carbonization. Twenty patients with benign thyroid nodules larger than 5 ml were prospectively enrolled in a clinical study and underwent ultrasound-guided RFA with ICW electrodes. Ultrasound examinations, laboratory data, and symptom and cosmetic scores were evaluated preprocedure and 1 and 6 months after the procedure.

RESULTS

In the ex vivo study, the ICW achieved significantly larger ablation zones than the IC (p<.001). In the clinical study, ICW electrodes were tolerable in all patients. At last follow-up, nodule volume had decreased from 15.6 ± 12.1 ml to 4.1 ± 4.3 ml (p<.001), and the mean volume reduction ratio (VRR) was 73.3 ± 13.7% at 6.0 months follow-up. Cosmetic and symptom scores were reduced from 3.52 ± 1.03 to 2.65 ± 0.88 and 3.10 ± 2.17 to 0.85 ± 0.99 (both p<.001), respectively. After RFA, thyroid function was well preserved in all patients, and mean thyroglobulin level decreased from 36.6 ± 52.1 ng/ml to 26.9 ± 62.2 ng/ml. One patient experienced a temporary voice change that recovered within a week.

CONCLUSIONS

We developed a thyroid-dedicated ICW electrode that we showed to be feasible and effective in patients with benign thyroid nodules.

Comparison of ablation performance between dual internally cooled wet tip and conventional dual internally cooled tip radiofrequency electrodes: an experimental study in ex vivo bovine liver

OBJECTIVE

To evaluate the performance of dual internally cooled wet tip (ICWT) radiofrequency electrodes in comparison to dual internally cooled tip (ICT) electrodes.

METHODS

Twenty ablation zones were created for each type of electrodes. Planned procedure time was 6 min. Diameters of the ablation zone along the x-, y-, and z-axes (Dx, Dy, and Dz), ablation zone sphericity, quantitative sphericity measurement, and ablation volume were measured and compared between the two electrode types. Circularity of the ablation zone on the surface with x- and z- axes (zx plane) and amount of energy applied were also compared.

RESULTS

Dx and Dz were significantly longer with ICWT than those with ICT (Dx: 3.0 vs. 2.8 cm, p = .018; and Dz: 2.7 vs. 2.3 cm, p < .001, respectively). Dy was not significantly different (3.0 vs. 2.9 cm, p = .220). Moreover, 85% (17/20) and 30% (6/20) of ablation zones from ICWT and ICT were spherical (p = .001), respectively. Quantitative measurement showed that ICWT was more spherical compared to ICT (0.962 vs. 0.881, p = .001). The ablation volume was also significantly higher with ICWT (11.55 vs. 9.45 cm3, p = .003). The ablation zone on the zx plane was more circular with ICWT (0.907 vs. 0.883, p = .028). The amount of energy applied was significantly bigger with ICWT (18508 vs. 16998 WS, p = .003).

CONCLUSION

Dual ICWT electrodes were better able to create more spherical and larger ablation zones than dual ICT electrodes.

Radiofrequency ablation using internally cooled wet electrodes in bipolar mode for the treatment of recurrent hepatocellular carcinoma after locoregional treatment: A randomized prospective comparative study

Objective

This study aimed to compare the efficacy between bipolar radiofrequency ablation (RFA), using twin internally cooled wet (TICW) electrodes, and switching monopolar RFA, using separable clustered (SC) electrodes, in the treatment of recurrent hepatocellular carcinoma (HCC) after locoregional treatment.

Materials and methods

In this single-center, two-arm, parallel-group, randomized controlled study, we performed a 1:1 random allocation on eligible patients with recurrent HCC after locoregional treatment, to receive TICW-RFA or SC-RFA. The primary endpoint was the minimum diameter of the ablation zone per unit ablation time. Secondary endpoints included other technical parameters, complication rate, technical success and technique efficacy, and clinical outcomes.

Results

Enrolled patients were randomly assigned to the TICW-RFA group (n = 40) or SC-RFA group (n = 37). The two groups did not show significant differences in the primary endpoint, the minimum diameter of the ablation zone per unit ablation time was 2.71 ± 0.98 mm/min and 2.61 ± 0.96 mm/min in the TICW-RFA and SC-RFA groups, respectively (p = 0.577). Total RF energy delivery (11.75 ± 9.04 kcal vs. 22.61 ± 12.98 kcal, p < 0.001) and energy delivery per unit time (0.81 ± 0.49 kcal/min vs. 1.45 ± 0.42 kcal/min, p < 0.001) of the TICW-RFA group were less than those of the SC-RFA group. No procedure-related death or major complications occurred. Technical success was achieved in all patients in both groups, and technique efficacy rates were 100% (46/46) in the TICW-RFA group and 95.0% (38/40) in the SC-RFA group (p = 0.213). The 1-year and 2-year cumulative LTP rates were 11.8% and 24.2%, respectively, in the TICW-RFA group, and 8.6% and 18.1%, respectively, in the SC-RFA group (p = 0.661).

Conclusion

In this single-center randomized controlled study from a Korean tertiary referral hospital, TICW-RFA demonstrated similar therapeutic efficacy and safety profile for recurrent HCC after locoregional treatment compared with SC-RFA.

Trial registration

ClinicalTrials.gov (NCT03806218)

Characterization of the ablation zones produced by three commercially available systems from a single vendor for radiofrequency thermoablation in an ex vivo swine liver model

Background

Radiofrequency Ablation (RFA) is rarely performed in veterinary medicine. A rationale exists for its use in selected cases of canine liver tumours. RFA induces ablation zones of variable size and geometry depending on the technique used and on the impedance of the targeted organ.

Objectives

(a) to describe the geometry and reproducibility of the ablation zones produced by three commercially available systems from a single company, using isolated swine liver parenchyma as a model for future veterinary applications in vivo; (b) to study the effects of local saline perfusion into the ablated parenchyma through the electrode tip and of single versus double passage of the electrode on size, geometry and reproducibility of the ablation zones produced.

Methods

Size, and geometry of ablation zones reproduced in six livers with one cooled and perfused (saline) and two cooled and non‐perfused systems, after single or double passage (n = 6/condition), were assessed macroscopically on digitalized images by a blinded operator. Longitudinal and transverse diameters, equivalent diameter, estimated volume and roundness index were measured. Reproducibility was assessed as coefficient of variation.

Results and Conclusions

Ablation zone reproducibility was higher when expressed in terms of ablation zone diameters than estimated volume. Local saline perfusion of the parenchyma through the electrode tip during RFA increased the ablation zone longitudinal diameter. Ablation zone estimated volume increased with saline perfusion only when double passage was performed. These data may provide useful information for those clinicians who intend to include RFA as an additive tool in veterinary interventional radiology.

Percutaneous radiofrequency ablation using internally cooled wet electrodes for the treatment of hepatocellular carcinoma

OBJECTIVE

The objective of our study was to evaluate the efficacy and safety of percutaneous radiofrequency ablation (RFA) using internally cooled wet electrodes in patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

From March 2008 to October 2010, 122 patients with 129 HCCs (mean size, 2.2 ± 0.6 [SD] cm; range, 0.7-4 cm) were treated with RFA using internally cooled wet electrodes. Primary technical effectiveness, the frequency of major complications, and local tumor progression rates were evaluated.

RESULTS

Two patients (2%) had major complications (liver abscess, significant pleural effusion) after RFA. When evaluated 1 month after RFA, the primary technical effectiveness rate was 99%. The 1- and 2-year local tumor progression rates were 8% and 12%, respectively. Additionally, there was no difference in effectiveness and complication rates between patients with subcapsular HCC and those with nonsubcapsular HCC.

CONCLUSION

Percutaneous RFA using internally cooled wet electrodes is safe and provides successful local tumor control in patients with HCC. The safety and effectiveness of RFA using internally cooled wet electrodes are comparable to those reported in the literature using conventional RFA electrodes and are similar for nonsubcapsular and subcapsular tumors.

Radiofrequency ablation using a new type of internally cooled electrode with an adjustable active tip: an experimental study in ex vivo bovine and in vivo porcine livers

PURPOSE

The aims of this study were to evaluate the performance of radiofrequency (RF) ablation using a new type of internally cooled RF electrode with an adjustable active tip in an ex vivo bovine liver model and to determine if adjustment of the active tip length makes a significant difference in the size of ablation zone in an in vivo porcine liver model.

MATERIALS AND METHODS

We performed ex vivo experiments by producing 100 RF ablation zones in 40 extracted bovine livers using a new type of RF electrode that had an adjustable active tip (adjustable electrode) (n = 50) and a conventional internally cooled electrode (conventional electrode) (n = 50). We also performed an in vivo study with the induction of 30 RF ablation zones in ten living porcine livers using the adjustable electrode with 2 cm (n = 15) and 3 cm (n = 15) active tip adjustments. The size (three perpendicular diameters), volume and ratio of the two axes of the ablation zone were macroscopically evaluated and were compared.

RESULTS

For the ex vivo study using a 2 cm and 3 cm active tip, there was no significant difference in ablation performance between the use of conventional and adjustable electrodes. For the use of the conventional and adjustable electrodes with 2 cm active tip, respectively, the volume was 10.75 ± 3.43 cm(3) versus 10.64 ± 3.25 cm(3) and the ratio of the two axes was 1.24 ± 0.16 versus 1.30 ± 0.17; p > 0.05. For the use of the conventional and adjustable electrodes with 3 cm active tip, respectively, the volume was 21.17 ± 4.09 cm(3) versus 21.48 ± 3.51 cm(3) and the ratio of the two axes was 1.28 ± 0.12 versus 1.28 ± 0.07; p > 0.05. For the in vivo study using the adjustable electrode, the ablation volume with the 2 cm adjustment was significantly smaller as compared to the 3 cm adjustment (5.29 ± 2.22 cm(3) versus 13.44 ± 4.25 cm(3); p < 0.05) with no statistical difference for the ratio of the two axes (1.44 ± 0.22 versus 1.49 ± 0.24; p > 0.05).

CONCLUSION

Using a new type of internally cooled RF electrode, we could induce different volumes of the RF ablation zone by means of adjusting the length of the exposed active tip, where performance was similar to the use of a conventional internally cooled RF electrode.

CT findings after radiofrequency ablation in rabbit livers: comparison of internally cooled electrodes, perfusion electrodes, and internally cooled perfusion electrodes

PURPOSE

To compare the computed tomography (CT) findings of radiofrequency (RF) ablation of rabbit livers with the use of internally cooled electrodes, perfusion electrodes, and internally cooled perfusion (ICP) electrodes.

MATERIALS AND METHODS

RF ablation zones were created in 24 rabbit livers in vivo in three groups, each treated at 30 W for 30 minutes with an electrode with a 1-cm active portion: one group was treated with an internally cooled electrode (group A), one with a perfusion electrode (group B), and one with an ICP electrode (group C). In the latter two groups, 0.9% saline solution mixed with contrast medium (9:1 ratio) was infused at a rate of 1 mL/min. Immediate CT images were ascertained in all groups and follow-up CT was performed in the latter two groups. CT findings of the RF ablation zone and surrounding liver parenchyma were evaluated and compared among groups.

RESULTS

On immediate unenhanced CT, infused contrast medium was noted in the center of the ablation zone without extravasation. Marginal linear or tubular low densities of the RF ablation zone were noted only in groups B (n=4) and C (n=3). Liver infarction was more frequently noted in groups B (n=5) and C (n=7) than in group A (n=3). Periportal tracking was noted more frequently in groups B (n=7) and C (n=8) than in group A (n=1). Pericaval or perihepatic tracking was noted only in groups B (n=3) and C (n=3). Extensive portal venous gas was noted in one animal in group C.

CONCLUSIONS

On CT, RF ablation with the perfusion or ICP electrode seemed to show more severe surrounding parenchymal changes than RF ablation with an internally cooled electrode.

Experimental and Clinical Radiofrequency Ablation: Proposal for Standardized Description of Coagulation Size and Geometry

BACKGROUND

Radiofrequency (RF) ablation is used to obtain local control of unresectable tumors in liver, kidney, prostate, and other organs. Accurate data on expected size and geometry of coagulation zones are essential for physicians to prevent collateral damage and local tumor recurrence. The aim of this study was to develop a standardized terminology to describe the size and geometry of these zones for experimental and clinical RF.

METHODS

In a first step, the essential geometric parameters to accurately describe the coagulation zones and the spatial relationship between the coagulation zones and the electrodes were defined. In a second step, standard terms were assigned to each parameter.

RESULTS

The proposed terms for single-electrode RF ablation include axial diameter, front margin, coagulation center, maximal and minimal radius, maximal and minimal transverse diameter, ellipticity index, and regularity index. In addition a subjective description of the general shape and regularity is recommended.

CONCLUSIONS

Adoption of the proposed standardized description method may help to fill in the many gaps in our current knowledge of the size and geometry of RF coagulation zones.

Radiofrequency Renal Ablation: In Vivo Comparison of Internally Cooled, Multitined Expandable and Internally Cooled Perfusion Electrodes

PURPOSE

To evaluate the in vivo efficiency of radiofrequency ablation using an internally cooled-perfusion (ICP) electrode for inducing coagulation necrosis compared with those of RFA using internally cooled or multitined expandable electrodes in porcine kidneys.

MATERIALS AND METHODS

Using a 200 W generator and internally cooled and ICP electrodes or a 150 W generator and a multitined expandable electrode, a total of 15 radiofrequency ablations were performed in the kidneys of nine pigs. After placement of an electrode in the lower pole of a kidney, one ablation zone was created using one of three different regimens: group A, radiofrequency ablation using an internally cooled electrode; group B, radiofrequency ablation using an ICP electrode with 14.6% NaCl solution instillation at 1 mL/minute; group C, radiofrequency ablation using a multitined expandable electrode. Three days after the procedures, contrast-enhanced CT scans were obtained to evaluate ablation region volumes, and kidneys were harvested for gross measurements. The three groups were compared with respect to technical parameters such as changes in impedance and current during radiofrequency ablation. The dimensions of thermal ablation zones created in the three groups were compared histologically.

RESULTS

In vivo study showed that ICP electrode allowed a greater energy delivery than internally cooled or multitined expandable electrode during radiofrequency ablation: 63.3 +/- 8.8 kJ in group A; 101 +/- 3.3 kJ in group B; and 61.8 +/- 12.5 kJ (P < .05). In vivo studies showed radiofrequency ablation using ICP electrode achieved larger mean coagulation volumes than radiofrequency ablation using the other electrodes: 12.0 +/- 3.9 cm(3) in group A; 30.5 +/- 7.6 cm(3) in group B; and 11.6 +/- 6.7 cm(3) in group C (P < .05). In addition, group B had a larger mean short-axis diameter of radiofrequency-induced coagulation necrosis than groups A or C: 2.6 +/- 0.5 cm in group A; 3.6 +/- 0.4 cm in group B; and 2.4 +/- 0.7 cm in group C (difference between groups B and C: P < .05).

CONCLUSIONS

Radiofrequency ablation using an ICP electrode showed better performance at creating coagulation necrosis than radiofrequency ablation using internally cooled or multitined expandable electrodes in this porcine renal model.

Radiofrequency ablation of the porcine liver in vivo: increased coagulation with an internally cooled perfusion electrode

RATIONALE AND OBJECTIVES

A major limitation of radiofrequency (RF) ablation is its inability to produce a large enough diameter of coagulation necrosis to encompass hepatic tumors with an appropriate ablative margin at a single RF application. We evaluated the in vivo efficiency of RF ablation (RFA) using an internally cooled perfusion (ICP) electrode with hypertonic saline infusion to induce coagulation necrosis compared with that of RFA using single needle electrode types.

MATERIALS AND METHODS

RF was applied to a porcine liver in monopolar mode using a 200 W generator and an internally cooled electrode (group A) or an ICP electrode (group B) at 200 W for 12 minutes or using a 60 W generator with a perfusion electrode at 40 W for 20 minutes (group C). In total, 36 (3 x 12) ablation zones were created using the three different regimens. In group B, 14.6% NaCl solution was infused at 1 mL/minute and in group C, 0.9% NaCl solution was infused at 1.5 mL/minute. The three groups were compared in terms of amount of delivered RF energy and dimensions and the coefficients of variation of the ablation zones.

RESULTS

The mean energies applied in the three groups were 52.3 +/- 10.3 kJ for group A, 115.4 +/- 10.5 kJ for group B, and 38.5 +/- 11.5 kJ for group C, respectively (P < .05). The mean ablation volumes in groups A, B and C were 13.1 +/- 4.7 cm3 in group A, 43.7 +/- 17.5 cm3 in group B, and 26.3 +/- 20.2 cm3 in group C, respectively (P < .05). In addition, the coefficients of variation of the volumes of the ablation zones in groups A, B, and C were 0.36, 0.4, and 0.78, respectively.

CONCLUSIONS

RFA using the ICP electrode showed better performance in terms of creating a larger ablation zone than RFA using an internally cooled or a perfusion electrode.