Multiple-electrode radiofrequency ablation of in vivo porcine liver: comparative studies of consecutive monopolar, switching monopolar versus multipolar modes

Stereotactic ablation: A game changer?

For both primary and metastatic liver cancer, thermal ablation represents an interesting alternative to surgery. However, except for a small fraction of patients, conventional ultrasound- and CT-guided single-probe approaches have not achieved oncologic outcomes comparable with surgery. In this overview, we describe our stereotactic ablation workflow and discuss the short- and long-term results of stereotactic radiofrequency ablation (SRFA) and stereotactic microwave ablation (SMWA) for the treatment of primary and secondary liver tumours. The advantages of this method are discussed together with a summary of the existing stereotactic techniques for thermal ablation and the clinical data that support them. Stereotactic ablation is based on an optical navigation system and a specialized aiming tool. The workflow includes advanced three-dimensional planning, precise needle/probe placements according to the plan and intraoperative image fusion to check the needle positions and the ablation margins. Stereotactic ablation offers all the advantages of a minimally invasive procedure while producing oncological results comparable with surgery. The number of locally treatable liver cancers may be significantly expanded with these cutting-edge instruments and methods. We firmly believe that it can become a cornerstone in the treatment of liver cancers.

Interventional oncology in breast cancer

Breast cancer (BC) is the most common cancer and one of the most important causes of death in women. Surgery is the standard therapy for breast cancer and in the last decades evolved towards a more conservative approach, with lumpectomy, followed by radiation therapy, the most common option. Unfortunately, up to 40% of women affected by BC will develop metastases and will receive systemic therapy, which improves survival and quality of life. Interventional oncology (IO), thanks to the improvement in technology and clinical experience, is gaining an important role in the field of breast cancer, both in treating the primary tumour and also in metastasis in well-selected cases. Percutaneous thermal ablation and more recently cryoablation are reported to achieve promising results in the radical treatment of small breast cancer, with optimal cosmetic outcome and a very high safety profile. Percutaneous ablation as well as intra-arterial therapies, such as chemoembolization and radioembolization, might also be indicated in metastatic BC patients. In advanced stage disease, breast cancer liver metastases (BCLM) represent the main factor affecting the overall survival. Metastatic breast disease is a systemic disease, with tumour deposits potentially spread into different organs and tissues for which systemic therapy is the standard approach. Local therapies for liver metastases might have an important role in improving survival and quality of life in well-selected patients. Clinical and technical indications with their limitations, results and potential complications in local IO treatment for BCLM, will be also described.

Efficacy and safety of single- and multiple-antenna microwave ablation for the treatment of hepatocellular carcinoma and liver metastases: A systematic review and network meta-analysis

BACKGROUND

There is a myriad of microwave ablation (MWA) systems used in clinical settings worldwide for the management of liver cancer that offer a variety of features and capabilities. However, an analysis on which features and capabilities result in the most favorable efficacy and safety results has never been completed due to a lack of head-to-head comparisons. The aim of this study is to compare single-antenna and multiple-antenna MWA using radiofrequency ablation (RFA) as a common comparator in the treatment of very-early, early hepatocellular carcinoma (HCC) and ≤5 cm liver metastases.

METHODS

This network meta-analysis was performed according to PRISMA guidelines. PubMed, Cochrane, and Web of Science databases were searched for comparative studies. Complete ablation (CA) rate, local tumor progression-free (LTPF) rate, overall survival (OS), and major complication rate were assessed. Subgroup analyses were further performed based on synchronous or asynchronous MWA generators and tumor size (<2 cm or ≥2 cm).

RESULTS

Twenty-one studies (3424 patients), including 3 randomized controlled trials (RCTs) and 18 observational studies, met eligibility criteria. For CA, LTPF and major complications, as compared to single-antenna MWA, multiple-antenna MWA had relative risks (RRs) of 1.051 (95% CI: 0.987-1.138), 1.099 (95% CI: 0.991-1.246), and 0.605 (95% CI: 0.193-1.628), respectively. For 1-year and 3-year OS, as compared to single-antenna MWA, multiple-antenna MWA had odds ratios (ORs) of 0.9803 (95% CI: 0.6772-1.449) and 1.046 (95% CI: 0.615-1.851), respectively. Subgroup analysis found synchronized multi-antenna MWA was associated with significantly better LTPF by 22% (RR: 1.22, 95% CI 1.068, 1.421), and 21.4% (RR: 1.214, 95% CI 1.035, 1.449) compared with single-antenna MWA, and asynchronous multiple-antenna MWA, respectively, with more evident differences in larger tumors (≥2 cm).

CONCLUSION

Multi-antenna and single-antenna MWA showed similar effectiveness for local treatment of liver tumors, but synchronous multi-antenna MWA exhibited better LTPF compared to other MWA approaches, particularly for larger liver tumors (≥2 cm). Large-scale RCTs should be further conducted.

Comparison of procedure-related complications between percutaneous cryoablation and radiofrequency ablation for treating periductal hepatocellular carcinoma

PURPOSE

This study aimed to evaluate the incidence and severity of biliary complications after treating periductal hepatocellular carcinomas (HCCs) using either cryoablation (CA) or radiofrequency ablation (RFA) and assess independent risk factors for biliary complications after treatment.

MATERIALS AND METHODS

Between July 2008 and August 2018, 949 patients with treatment-naïve HCCs underwent either RFA or CA in our institution. Of these, patients with multiple HCCs, tumors equal to or larger than 3 cm or smaller than 1 cm, and tumors with non-periductal locations were excluded. Finally, 31 patients and 25 patients were included in the RFA group and the CA group, respectively. The incidence and severity of biliary complications were compared between the RFA and CA groups. The risk factors for biliary complications were assessed using univariable and multivariable logistic regression analyses using the following variables: age, sex, tumor size, Child-Pugh score, tumor location (peripheral duct versus central duct), ablation method (RFA versus CA), the number of applicators, ablation time, and ablation volume.

RESULTS

The incidence and severity of biliary complications were significantly higher in the RFA group than in the CA group (p = 0.007 and p = 0.002, respectively). In univariable and multivariable analyses, the ablation method was an independent risk factor for biliary complications (p = 0.004 and 0.013, respectively).

CONCLUSIONS

The incidence and severity of biliary complications after treating HCCs abutting the bile duct are lower in CA than RFA, demonstrating that CA is safer than RFA for ablating small periductal HCCs.

Comparisons between impedance-based and time-based switching bipolar radiofrequency ablation for the treatment of liver cancer

Switching bipolar radiofrequency ablation (bRFA) is a cancer treatment technique that activates multiple pairs of electrodes alternately based on a predefined criterion. Various criteria can be used to trigger the switch, such as time (ablation duration) and tissue impedance. In a recent study on time-based switching bRFA, it was determined that a shorter switch interval could produce better treatment outcome than when a longer switch interval was used, which reduces tissue charring and roll-off induced cooling. In this study, it was hypothesized that a more efficacious bRFA treatment can be attained by employing impedance-based switching. This is because ablation per pair can be maximized since there will be no interruption to RF energy delivery until roll-off occurs. This was investigated using a two-compartment 3D computational model. Results showed that impedance-based switching bRFA outperformed time-based switching when the switch interval of the latter is 100 s or higher. When compared to the time-based switching with switch interval of 50 s, the impedance-based model is inferior. It remains to be investigated whether the impedance-based protocol is better than the time-based protocol for a switch interval of 50 s due to the inverse relationship between ablation and treatment efficacies. It was suggested that the choice of impedance-based or time-based switching could ultimately be patient-dependent.

Switching monopolar radiofrequency ablation improves long-term outcomes of medium-sized hepatocellular carcinoma

OBJECTIVES

Radiofrequency ablation (RFA) of medium-sized (3-5 cm) hepatocellular carcinoma (HCC) is suboptimal. Switching monopolar RFA (SW-RFA) enlarges the ablative volume to better cover larger tumors. This study aims to compare the long-term outcomes of medium-sized HCC treated by either SW-RFA or single-monopolar RFA (S-RFA).

METHODS

We retrospectively reviewed 139 cases (147 medium-size HCC) between 2008 and 2014. Under propensity score matching, a total of 43 paired patients with medium-size HCC and balanced clinical variables treated by either SW-RFA or S-RFA were selected for comparison.

RESULTS

SW-RFA showed a higher rate of achieving an adequate safety margin (p = 0.002). After a mean follow-up period of 40.4 months, SW-RFA produced significantly lower global RFA failure rates (p < 0.001) and better overall survival (p = 0.005) compared to S-RFA. SW-RFA was independently associated with a decreased risk of global RFA failure (hazard ratio [HR]: 0.136, 95% confidence interval [CI]: 0.030-0.607, p = 0.009) and improved overall survival (HR: 0.337, 95% CI: 0.152-0.747, p = 0.007). By last follow-up, the SW-RFA group maintained a superior tumor-free rate (p = 0.010) and fewer progressions to Barcelona Clinic Liver Cancer stage C (p = 0.011). Major complication rates were comparable in both groups (SW-RFA: 2.3% vs. S-RFA: 4.7%, p = 1.000).

CONCLUSIONS

The switching multi-monopolar ablation technique could be beneficial for patients with medium-sized HCCs given sustained control of larger tumors with better overall survival.

KEY POINTS

• Switching monopolar ablation could provide a sustained local tumor control and better overall survival than single-monopolar ablation for the medium-sized hepatocellular carcinoma. • Compared to single-monopolar ablation, switching monopolar ablation could create a larger homogeneous coagulation volume by using a shorter total ablation time to achieve a higher rate of adequate safety margin for a medium-sized HCC. • Patients with medium-sized HCC can be maintained at a higher rate of tumor-free status and at a lower risk of progression into BCLC stage C in the follow-up period after ablation by switching monopolar than by single-monopolar ablation.

Switching Monopolar No-Touch Radiofrequency Ablation Using Octopus Electrodes for Small Hepatocellular Carcinoma: A Randomized Clinical Trial

INTRODUCTION

A switching monopolar no-touch radiofrequency ablation (RFA) technique is used for small hepatocellular carcinoma (HCC); however, there have not been any randomized clinical trials comparing this technique to the conventional RFA technique.

OBJECTIVE

This study aims to compare the results of two RFA techniques, and to comparatively identify more effective methods to reduce the progression of local tumors associated with small HCC (≤2.5 cm).

METHODS

This prospective randomized clinical trial (NCT03375281) recruited a total of 116 participants (M:F, 93:23; 68.3 ± 8.4 years) between October 2016 and September 2017. The primary outcome was the cumulative incidence of local tumor progression (LTP) after RFA. Secondary outcomes included technical success rate, technique efficacy, and RFA procedure characteristics. Kaplan-Meier analysis and the Cox proportional hazard regression model were used.

RESULTS

The mean follow-up period was 24.1 months. A sufficient ablative margin was more frequently achieved in the no-touch RFA group (57/60 = 95%) than in the conventional RFA group (50/64 = 78.1%) on immediate follow-up CT (p = 0.01). The cumulative incidence of LTP in the no-touch RFA group was significantly lower than that in the conventional RFA group (p = 0.02). In multivariable analysis, no-touch RFA was the only predictive factor for LTP (p = 0.04, hazard ratio = 0.2, 95% confidence interval = 0.04-0.94).

CONCLUSIONS

A switching monopolar no-touch RFA technique is a favorable treatment option and provides lower LTP after RFA compared with conventional RFA for small HCC.

Radiofrequency Ablation Using a Separable Clustered Electrode for the Treatment of Hepatocellular Carcinomas: A Randomized Controlled Trial of a Dual-Switching Monopolar Mode Versus a Single-Switching Monopolar Mode

OBJECTIVE

This study aimed to prospectively compare the efficacy, safety, and mid-term outcomes of dual-switching monopolar (DSM) radiofrequency ablation (RFA) to those of conventional single-switching monopolar (SSM) RFA in the treatment of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

This single-center, two-arm, parallel-group, randomized controlled study was approved by the Institutional Review Board. Written informed consent was obtained from all patients upon enrollment. A total of 80 patients with 94 HCC nodules were randomized into either the DSM-RFA group or SSM-RFA group in a 1:1 ratio, using a blocked randomization method (block size 2). The primary endpoint was the minimum diameter of the ablation zone per unit time. The secondary endpoints included other technical parameters, complication rate, technique efficacy, and 2-year clinical outcomes.

RESULTS

Significantly higher ablation energy per unit time was delivered to the DSM-RFA group than to the SSM-RFA group (1.7 ± 0.2 kcal/min vs. 1.2 ± 0.3 kcal/min; p < 0.001). However, no significant differences were observed between the two groups for the analyzed variables, including primary endpoint, regarding size of the ablation zone and ablation time. Major complication rates were 4.9% in the DSM-RFA group and 2.6% in the SSM-RFA group (p = 1.000). The 2-year local tumor progression (LTP) rates of the HCC nodules treated using DSM-RFA and SSM-RFA were 8.5% and 4.7%, respectively (p = 0.316). The 2-year LTP-free survival rates of patients in the DSM-RFA and SSM-RFA groups were 90.0% and 94.4%, respectively (p = 0.331), and the 2-year recurrence-free survival rates were 54.9% and 75.7%, respectively (p = 0.265).

CONCLUSION

Although DSM-RFA using a separable clustered electrode delivers higher ablation energy than SSM-RFA, its effectiveness failed to show superiority over SSM-RFA in the treatment of HCC.

Percutaneous Radiofrequency Ablation With a Multiple-Electrode Switching System for Medium-Sized Hepatocellular Carcinomas

Objective

This study aimed to retrospectively evaluate the safety and short-term therapeutic efficacy of radiofrequency ablation (RFA) with a multiple-electrode switching system (MESS) to treat medium-sized (3.1–5.0 cm) hepatocellular carcinomas (HCCs).

Summary of Background Data

Conventional monopolar RFA is limited in achieving local control for tumors larger than 3 cm. Therefore, MESS-RFA was developed, and it can create a sufficiently large ablation volume, including the target tumor and a 5- to 10-mm safety margin in medium-sized tumors.

Methods

We performed a total of 168 RFAs with a MESS for 166 patients. The patients were treated under ultrasonographic guidance by a percutaneous switching system RFA with a multichannel RF generator and 2 or 3 internally cooled electrodes. Technical effectiveness, local progression, and remote recurrence of HCC were determined.

Results

For the 166 isolated HCC tumors, the complete ablation rate of MESS-RFA was 98.79% (164 of 166). Mean ablation time per procedure was 12.33 ± 3.01 minutes; mean ablation diameter was 5.79 ± 0.61 cm. The complication rate was 2.41%. During follow-up (averaging 16.54 months), local tumor progression occurred in 15 of 166 patients (9.03%) with technical effectiveness, whereas new HCCs were detected in 40 of 166 patients (24.09%). Multivariate analyses revealed that local tumor progression was only associated with serum α-fetoprotein levels above 100 ng/mL as a risk factor.

Conclusion

MESS-RFA for achieving sufficient ablation volume is safe and efficient. This method also showed relatively successful therapeutic effectiveness on short-term follow-up in the treatment of medium-sized HCCs.

Local Treatment of Breast Cancer Liver Metastasis

Breast cancer represents a leading cause of death worldwide. Despite the advances in systemic therapies, the prognosis for patients with breast cancer liver metastasis (BCLM) remains poor. Especially in case of failure or cessation of systemic treatments, surgical resection for BCLMs has been considered as the treatment standard despite a lack of robust evidence of benefit. However, due to the extent and location of disease and physical condition, the number of patients with BCLM who are eligible for surgery is limited. Palliative locoregional treatments of liver metastases (LM) include transarterial embolization (TAE), transarterial chemoembolization (TACE), and selective internal radiotherapy (SIRT). Percutaneous thermal ablation methods, such as radiofrequency ablation (RFA) and microwave ablation (MWA), are considered potentially curative local treatment options. They are less invasive, less expensive and have fewer contraindications and complication rates than surgery. Because conventional ultrasound- and computed tomography-guided single-probe thermal ablation is limited by tumor size, multi-probe stereotactic radiofrequency ablation (SRFA) with intraoperative image fusion for immediate, reliable judgment has been developed in order to treat large and multiple tumors within one session. This review focuses on the different minimally invasive local and locoregional treatment options for BCLM and attempts to describe their current and future role in the multidisciplinary treatment setting.

Hepatocellular carcinoma abutting large vessels: comparison of four percutaneous ablation systems

PURPOSE

To compare overall local tumour progression (OLTP), defined as the failure of primary ablation or local tumour progression, with single applicator monopolar radiofrequency ablation (RFA), microwave ablation (MWA), cluster-RFA and multi-bipolar radiofrequency (mbpRFA) in the treatment of hepatocellular carcinoma (HCC) ≤ 5 cm abutting large vessels (≥3 mm).

MATERIALS AND METHODS

This multicenter, retrospective, per-nodule study was performed from 2007 to 2015. The study was approved by the ethics review board, and informed consent was waived. A total of 160/914 HCC nodules treated by thermal ablation and abutting large vessels (40 per treatment group) treated by monopolar RFA, MWA, cluster-RFA or mbpRFA were matched for tumour size, alpha-feto-protein level and vessel size. OLTP rates were compared by the log-rank test and the multivariate Cox model after matching.

RESULTS

No differences were observed in tumour size, vessel size or alpha-feto-protein levels among the three groups (p = 1). The cumulative 4-year OLTP rates following monopolar RFA, cluster-RFA, multi-bipolar RFA and MWA were 50.5%, 16.3%, 16.3% and 44.2%, respectively (p = 0.036). On multivariate Cox regression, vessel size ≥10 mm, monopolar RFA and MWA were independent risk factors of OLTP compared to cluster-RFA or mbpRFA.

CONCLUSION

Multi-applicator RFA provides better local tumour control in HCC abutting large vessels than single-applicator techniques (monopolar RFA or MWA).

Comparison of switching bipolar ablation with multiple cooled wet electrodes and switching monopolar ablation with separable clustered electrode in treatment of small hepatocellular carcinoma: A randomized controlled trial

OBJECTIVE

A randomized controlled trial was conducted to prospectively compare the therapeutic effectiveness of switching bipolar (SB) radiofrequency ablation (RFA) using cooled-wet electrodes and switching monopolar (SM) RFA using separable clustered (SC) electrodes in patients with hepatocellular carcinomas (HCCs).

MATERIALS AND METHODS

This prospective study was approved by our Institutional Review Board. Between April 2014 and January 2015, sixty-nine patients with 74 HCCs were randomly treated with RFA using either internally cooled-wet (ICW) electrodes in SB mode (SB-RFA, n = 36) or SC electrodes in SM mode (SM-RFA, n = 38). Technical parameters including the number of ablations, ablation time, volume, energy delivery, and complications were evaluated. Thereafter, 1-year and 2-year local tumor progression (LTP) free survival rates were compared between the two groups using the Kaplan-Meier method.

RESULTS

In the SB-RFA group, less number of ablations were required (1.72±0.70 vs. 2.31±1.37, P = 0.039), the ablation time was shorter (10.9±3.9 vs.14.3±5.0 min, p = 0.004), and energy delivery was smaller (13.1±6.3 vs.23.4±12.8 kcal, p<0.001) compared to SM-RFA. Ablation volume was not significantly different between SB-RFA and SM-RFA groups (61.8±24.3 vs.54.9±23.7 cm3, p = 0.229). Technical failure occurred in one patient in the SM-RFA group, and major complications occurred in one patient in each group. The 1-year and 2-year LTP free survival rates were 93.9% and 84.3% in the SB-RFA group and 94.4% and 88.4% in the SM-RFA group (p = 0.687).

CONCLUSION

Both SB-RFA using ICW electrodes and SM-RFA using SC electrodes provided comparable LTP free survival rates although SB-RFA required less ablations and shorter ablation time.

No-touch radiofrequency ablation using multiple electrodes: An in vivo comparison study of switching monopolar versus switching bipolar modes in porcine livers

Objective

To evaluate the in vivo technical feasibility, efficiency, and safety of switching bipolar (SB) and switching monopolar (SM) radiofrequency ablation (RFA) as a no-touch ablation technique in the porcine liver.

Materials and methods

The animal care and use committee approved this animal study and 16 pigs were used in two independent experiments. In the first experiment, RFA was performed on 2-cm tumor mimickers in the liver using a no-touch technique in the SM mode (2 groups, SM1: 10 minutes, n = 10; SM2: 15 minutes, n = 10) and SB-mode (1 group, SB: 10 minutes, n = 10). The technical success with sufficient safety margins, creation of confluent necrosis, ablation size, and distance between the electrode and ablation zone margin (DEM), were compared between groups. In the second experiment, thermal injury to the adjacent anatomic organs was compared between SM-RFA (15 minutes, n = 13) and SB-RFA modes (10 minutes, n = 13).

Results

The rates of the technical success and the creation of confluent necrosis were higher in the SB group than in the SM1 groups (100% vs. 60% and 90% vs. 40%, both p < 0.05). The ablation volume in the SM2 group was significantly larger than that in the SB group (59.2±18.7 cm³ vs. 39.8±9.7 cm^3,p < 0.05), and the DEM in the SM2 group was also larger than that in the SB group (1.39±0.21 cm vs. 1.07±0.10 cm, p < 0.05). In the second experiment, the incidence of thermal injury to the adjacent organs and tissues in the SB group (23.1%, 3/13) was significantly lower than that in the SM group (69.2%, 8/13) (p = 0.021).

Conclusion

SB-RFA was more advantageous for a no-touch technique for liver tumors, showing the potential of a better safety profile than SM-RFA.

No-Touch Radiofrequency Ablation: A Comparison of Switching Bipolar and Switching Monopolar Ablation in Ex Vivo Bovine Liver

OBJECTIVE

To evaluate the feasibility, efficiency, and safety of no-touch switching bipolar (SB) and switching monopolar (SM) radiofrequency ablation (RFA) using ex vivo bovine livers.

MATERIALS AND METHODS

A pork loin cube was inserted as a tumor mimicker in the bovine liver block; RFA was performed using the no-touch technique in the SM (group A1; 10 minutes, n = 10, group A2; 15 minutes, n = 10) and SB (group B; 10 minutes, n = 10) modes. The groups were compared based on the creation of confluent necrosis with sufficient safety margins, the dimensions, and distance between the electrode and ablation zone margin (DEM). To evaluate safety, small bowel loops were placed above the liver surface and 30 additional ablations were performed in the same groups.

RESULTS

Confluent necroses with sufficient safety margins were created in all specimens. SM RFA created significantly larger volumes of ablation compared to SB RFA (all p < 0.001). The DEM of group B was significantly lower than those of groups A1 and A2 (all p < 0.001). Although thermal injury to the small bowel was noted in 90%, 100%, and 30% of the cases in groups A1, A2, and B, respectively, full depth injury was noted only in 60% of group A2 cases.

CONCLUSION

The no-touch RFA technique is feasible in both the SB and SM modes; however, SB RFA appears to be more advantageous compared to SM RFA in the creation of an ablation zone while avoiding the unnecessary creation of an adjacent parenchymal ablation zone or adjacent small bowel injuries.

Comparison of no-touch multi-bipolar vs. monopolar radiofrequency ablation for small HCC

BACKGROUND & AIMS

The primary aim of this study was to compare the rate of global radiofrequency ablation (RFA) failure between monopolar RFA (MonoRFA) vs. no-touch multi-bipolar RFA (NTmbpRFA) for small hepatocellular carcinoma (HCC) ⩽5cm in cirrhotic patients.

METHODS

A total of 362 cirrhotic patients were included retrospectively across four French centres (181 per treatment group). Global RFA failure (primary RFA failure or local tumour progression) was analysed using the Kaplan-Meier method after coarsened exact matching. Cox regression models were used to identify factors associated with global RFA failure and overall survival (OS).

RESULTS

Patients were well matched according to tumour size (⩽30/>30mm); tumour number (one/several); tumour location (subcapsular and near large vessel); serum AFP (<10; 10-100; >100ng/ml); Child-Pugh score (A/B) and platelet count (</⩾100G/L), p=1 for all. One case of perioperative mortality was observed in the NTmbpRFA group and the rate of major complications was 7.2% in both groups (p=1). The cumulative rates of global RFA failure at 1, 3 and 5years were respectively 13.3%, 31% and 36.7% for MonoRFA vs. 0.02%, 7.9% and 9.2% for NTmbpRFA, p<0.001. Monopolar RFA, tumour size >30mm and HCC near large vessel were independent factors associated with global RFA failure. Five-year OS was 37.2% following MonoRFA vs. 46.4% following NTmbpRFA p=0.378.

CONCLUSIONS

This large multicentre case-matched study showed that NTmbpRFA provided better primary RFA success and sustained local tumour response without increasing severe complications rates, for HCC ⩽5cm.

LAY SUMMARY

Using no-touch multi-bipolar radiofrequency ablation for hepatocellular carcinoma ⩽5cm provide a better sustained local tumour control compared to monopolar radiofrequency ablation.

Switching Monopolar Radiofrequency Ablation Using a Separable Cluster Electrode in Patients with Hepatocellular Carcinoma: A Prospective Study

OBJECTIVE

This study was conducted to evaluate the outcomes of multi-channel switching RFA using a separable cluster electrode in patients with HCC.

METHODS

From November 2011 to July 2013, 79 patients with 98 HCCs < 5 cm were enrolled and treated with RFA using a multi-channel switching radiofrequency system and a separable cluster electrode under the guidance of a real-time fusion imaging system. The primary and secondary endpoints were the 3-year local tumor progression (LTP) rate and recurrence-free survival (RFS) rate, respectively. For post hoc analyses, LTP, RFS, and major complication rates were retrospectively compared with a historical control group treated with RFA using the same radiofrequency system but with multiple internally-cooled electrodes.

RESULTS

The technique success rate of the 98 tumors was 100%. Cumulative 1-year, 2-year, and 3-year LTP rates were 3.4%, 6.9%, and 12.4%, respectively. For patient-level data, cumulative 1-year, 2-year, and 3-year RFS rates were 83.9%, 68.6%, and 45.4%, respectively. On post hoc analyses, none of the baseline characteristics showed a significant difference between the separable cluster electrode and multiple internally-cooled electrodes group. Cumulative LTP and RFS rates of the two groups also showed no significant difference (p = 0.401 and p = 0.881, respectively). Finally, major complication rates of the separable cluster electrode group (5.0%, 4/79) and multiple internally-cooled electrodes group (5.9%, 4/74) were also comparable (p = 1.000).

CONCLUSION

Switching monopolar RFA using a separable cluster electrode is a feasible and efficient technique for the treatment of HCCs smaller than 5 cm, providing comparable local tumor control to multiple internally-cooled electrodes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02745483.

The Effectiveness of Multiple Electrode Radiofrequency Ablation in Patients with Hepatocellular Carcinoma with Lesions More than 3 cm in Size and Barcelona Clinic Liver Cancer Stage A to B2

Outcomes of hepatocellular carcinoma (HCC) lesions >3.0 cm in size including Barcelona Clinic Liver Cancer (BCLC) stage B after radiofrequency ablation (RFA) with a single electrode remain unsatisfactory. This study aimed to investigate the outcomes of RFA with multiple electrodes (ME-RFA) for HCC tumors 3.1-7.0 cm in size and BCLC stage B. This retrospective study included 70 consecutive patients with 58 medium- (3.1-5.0 cm) and 17 large- (5.1-7.0 cm) sized HCCs after ME-RFA using a controller. Outcomes in terms of complete response, primary technique effectiveness, local tumor progression, and overall survival were investigated. After 1-4 applications of ME-RFA, the rates of complete response and PTE in medium-sized tumors were 79.3% and 91.4%, respectively, and in large tumors were 76.5% and 94.1%, respectively. Overall, the major complication rate was 5.7%. After a median 21-month follow-up period, both two- and three-year estimated overall survival rates were above 80%. There were no significant differences in overall survival and local tumor progression rates between medium- and large-size tumors and among BCLC stages A, B1 and B2. A complete response to ME-RFA was the only significant factor associated with improved survival (p=0.008). In conclusion, ME-RFA can effectively treat 3.1-7.0-cm sized HCCs with a comparable outcome between medium- and large-size tumors and among BCLA stages A to B2.

Thermal tumor ablation in clinical use

Although a surgical procedure is performed by visual inspection with histopathological assessment of the excised tumor and margins, percutaneous and noninvasive thermal ablation is performed strictly with the aid of imaging. Applicator guidance into the target zone, treatment monitoring and verification, and clinical follow-up rely on effective imaging. Detailed discussion of imaging is beyond the scope of this article, but the influence of imaging on the choice of thermal ablation or procedural approach will be discussed as needed. More information on imaging for interventional therapies can be found in other articles in this issue of IEEE Pulse.

Recent Advances in Tumor Ablation for Hepatocellular Carcinoma

Image-guided tumor ablation for early stage hepatocellular carcinoma (HCC) is an accepted non-surgical treatment that provides excellent local tumor control and favorable survival benefit. This review summarizes the recent advances in tumor ablation for HCC. Diagnostic imaging and molecular biology of HCC has recently undergone marked improvements. Second-generation ultrasonography (US) contrast agents, new computed tomography (CT) techniques, and liver-specific contrast agents for magnetic resonance imaging (MRI) have enabled the early detection of smaller and inconspicuous HCC lesions. Various imaging-guidance tools that incorporate imaging-fusion between real-time US and CT/MRI, that are now common for percutaneous tumor ablation, have increased operator confidence in the accurate targeting of technically difficult tumors. In addition to radiofrequency ablation (RFA), various therapeutic modalities including microwave ablation, irreversible electroporation, and high-intensity focused ultrasound ablation have attracted attention as alternative energy sources for effective locoregional treatment of HCC. In addition, combined treatment with RFA and chemoembolization or molecular agents may be able to overcome the limitation of advanced or large tumors. Finally, understanding of the biological mechanisms and advances in therapy associated with tumor ablation will be important for successful tumor control. All these advances in tumor ablation for HCC will result in significant improvement in the prognosis of HCC patients. In this review, we primarily focus on recent advances in molecular tumor biology, diagnosis, imaging-guidance tools, and therapeutic modalities, and refer to the current status and future perspectives for tumor ablation for HCC.

Microwave Ablation: Comparison of Simultaneous and Sequential Activation of Multiple Antennas in Liver Model Systems

PURPOSE

To compare microwave ablation zones created by using sequential or simultaneous power delivery in ex vivo and in vivo liver tissue.

MATERIALS AND METHODS

All procedures were approved by the institutional animal care and use committee. Microwave ablations were performed in both ex vivo and in vivo liver models with a 2.45-GHz system capable of powering up to three antennas simultaneously. Two- and three-antenna arrays were evaluated in each model. Sequential and simultaneous ablations were created by delivering power (50 W ex vivo, 65 W in vivo) for 5 minutes per antenna (10 and 15 minutes total ablation time for sequential ablations, 5 minutes for simultaneous ablations). Thirty-two ablations were performed in ex vivo bovine livers (eight per group) and 28 in the livers of eight swine in vivo (seven per group). Ablation zone size and circularity metrics were determined from ablations excised postmortem. Mixed effects modeling was used to evaluate the influence of power delivery, number of antennas, and tissue type.

RESULTS

On average, ablations created by using the simultaneous power delivery technique were larger than those with the sequential technique (P < .05). Simultaneous ablations were also more circular than sequential ablations (P = .0001). Larger and more circular ablations were achieved with three antennas compared with two antennas (P < .05). Ablations were generally smaller in vivo compared with ex vivo.

CONCLUSION

The use of multiple antennas and simultaneous power delivery creates larger, more confluent ablations with greater temperatures than those created with sequential power delivery.

Radiofrequency ablation for treatment of hypersplenism: A feasible therapeutic option

We present a case of a patient with hypersplenism secondary to portal hypertension due to hepato-splenic schistosomiasis, which was accompanied by severe and refractory thrombocytopenia. We performed spleen ablation and measured the total spleen and ablated volumes with contrast-enhanced computed tomography and volumetry. No major complications occurred, thrombocytopenia was resolved, and platelet levels remained stable, which allowed for early treatment of the patient’s underlying disease. Previous work has shown that splenic radiofrequency ablation is an attractive alternative treatment for hypersplenism induced by liver cirrhosis. We aimed to contribute to the currently sparse literature evaluating the role of radiofrequency ablation (RFA) in the management of hypersplenism. We conclude that splenic RFA appears to be a viable and promising option for the treatment of hypersplenism.

Moving-shot versus fixed electrode techniques for radiofrequency ablation: comparison in an ex-vivo bovine liver tissue model

Objective

To compare the ablation characteristics of the moving-shot technique (MST) and the fixed electrode technique (FET) for radiofrequency (RF) ablation in an ex-vivo bovine liver tissue model.

Materials and Methods

We performed RF ablation using FET in 110 bovine liver blocks using 11 different ablation times ranging from 5 seconds to 5 minutes (10 blocks per each time duration). Ten bovine liver blocks at each ablation time of 1- or 2-minute, were ablated with MST, which treated conceptual ablation units by moving the electrode tip. We evaluated the ablation volume obtained with FET across ablation time lengths. The results of FET and MST performed with the same ablation time lengths, i.e., 1- and 2-minute ablation time were also compared.

Results

The ablation volume achieved with FET gradually increased with increasing ablation time; however, the pair-wise statistical comparison between 2 neighboring ablation time lengths was not significant after 30 seconds. MST with either 1- or 2-minute ablation time achieved larger ablation volumes (1.1 ± 0.2 mL vs. 2.7 ± 0.3 mL, p < 0.001; and 1.4 ± 0.2 mL vs. 5.6 ± 0.4 mL, p < 0.001, respectively), longer true RF times (46.7 ± 4.6 seconds vs. 60 seconds, p < 0.001; and 64.8 ± 4.6 seconds vs. 120 seconds, p < 0.001, respectively), fewer numbers of RF cut-offs (1.6 ± 0.5 vs. 0, p < 0.001; and 5.5 ± 0.5 vs. 0, p < 0.001, respectively), and greater energy deposition (2050.16 ± 209.2 J vs. 2677.76 ± 83.68 J, p < 0.001; and 2970.64 ± 376.56 J vs. 5564.72 ± 5439.2 J, p < 0.001, respectively), than FET.

Conclusion

The MST can achieve a larger ablation volume by preventing RF cut-off, compared with the FET in an ex-vivo bovine liver model.

Laser ablation for small hepatocellular carcinoma: State of the art and future perspectives

During the last two decades, various local thermal ablative techniques for the treatment of unresectable hepatocellular carcinoma (HCC) have been developed. According to internationally endorsed guidelines, percutaneous thermal ablation is the mainstay of treatment in patients with small HCC who are not candidates for surgical resection or transplantation. Laser ablation (LA) represents one of currently available loco-ablative techniques. In this article, the general principles, technique, image guidance, and patient selection are reported. Primary effectiveness, long-term outcome, and complications are also discussed. A review of published data suggests that LA is equivalent to the more popular and widespread radiofrequency ablation in both local tumor control and long-term outcome in the percutaneous treatment of early HCC. In addition, the LA technique using multiple thin laser fibres allows improved ablative effectiveness in HCCs greater than 3 cm. Reference centres should be equipped with all the available techniques so as to be able to use the best and the most suitable procedure for each type of lesion for each patient.

Tumor ablation: common modalities and general practices

Tumor ablation is a minimally invasive technique that is commonly used in the treatment of tumors of the liver, kidney, bone, and lung. During tumor ablation, thermal energy is used to heat or cool tissue to cytotoxic levels (less than -40°C or more than 60°C). An additional technique is being developed that targets the permeability of the cell membrane and is ostensibly nonthermal. Within the classification of tumor ablation, there are several modalities used worldwide: radiofrequency, microwave, laser, high-intensity focused ultrasound, cryoablation, and irreversible electroporation. Each technique, although similar in purpose, has specific and optimal indications. This review serves to discuss general principles and technique, reviews each modality, and discusses modality selection.

Monopolar radiofrequency ablation using a dual-switching system and a separable clustered electrode: evaluation of the in vivo efficiency

OBJECTIVE

To determine the in vivo efficiency of monopolar radiofrequency ablation (RFA) using a dual-switching (DS) system and a separable clustered (SC) electrode to create coagulation in swine liver.

MATERIALS AND METHODS

Thirty-three ablation zones were created in nine pigs using a DS system and an SC electrode in the switching monopolar mode. The pigs were divided into two groups for two experiments: 1) preliminary experiments (n = 3) to identify the optimal inter-electrode distances (IEDs) for dual-switching monopolar (DSM)-RFA, and 2) main experiments (n = 6) to compare the in vivo efficiency of DSM-RFA with that of a single-switching monopolar (SSM)-RFA. RF energy was alternatively applied to one of the three electrodes (SSM-RFA) or concurrently applied to a pair of electrodes (DSM-RFA) for 12 minutes in in vivo porcine livers. The delivered RFA energy and the shapes and dimensions of the coagulation areas were compared between the two groups.

RESULTS

No pig died during RFA. The ideal IEDs for creating round or oval coagulation area using the DSM-RFA were 2.0 and 2.5 cm. DSM-RFA allowed more efficient RF energy delivery than SSM-RFA at the given time (23.0 ± 4.0 kcal vs. 16.92 ± 2.0 kcal, respectively; p = 0.0005). DSM-RFA created a significantly larger coagulation volume than SSM-RFA (40.4 ± 16.4 cm(3) vs. 20.8 ± 10.7 cm(3); p < 0.001). Both groups showed similar circularity of the ablation zones (p = 0.29).

CONCLUSION

Dual-switching monopolar-radiofrequency ablation using an SC electrode is feasible and can create larger ablation zones than SSM-RFA as it allows more RF energy delivery at a given time.

Dual switching monopolar radiofrequency ablation using a separable clustered electrode: comparison with consecutive and switching monopolar modes in ex vivo bovine livers

Objective

To compare the in-vitro efficiency of dual-switching monopolar (DSM) radiofrequency ablation (RFA) using a separable clustered electrode (Octopus® electrodes) with consecutive monopolar (CM) and switching monopolar (SM) RFA techniques to create an ablative zone in the explanted bovine liver.

Materials and Methods

For DSM-RFA, we used a prototype, three-channel, dual generator RFA Unit and Octopus® electrodes with three, 17 gauge internally cooled electrodes. The RFA Unit allowed simultaneous radiofrequency (RF) energy delivery to two electrodes of the Octopus® electrodes as well as automatic switching among the three electrode pairs according to the impedance changes. RF energy was sequentially applied to one of the three electrodes for 24 minutes (group A; CM mode, n = 10) or alternatively applied for 12 minutes (group B; SM mode, n = 10) or concurrently applied to a pair of electrodes for 12 minutes (group C; DSM mode, n = 10) in explanted bovine livers. Changes in the impedance and current during RFA as well as the dimensions of the thermal ablative zones were compared among the three groups.

Results

The mean, delivered RF energy amounts in groups A, B, and C were 63.15 ± 8.6 kJ, 72.13 ± 5.4 kJ, and 106.08 ± 13.4 kJ, respectively (p < 0.001). The DSM mode created a significantly larger ablation volume than did the other modes, i.e., 68.1 ± 10.2 cm³ (group A), 92.0 ± 19.9 cm³ (group B), and 115.1 ± 14.0 cm³ (group C) (p < 0.001). The circularity in groups A, B, and C were 0.84 ± 0.06, 0.87 ± 0.04 and 0.90 ± 0.03, respectively (p = 0.03).

Conclusion

DSM-RFA using Octopus® electrodes can help create large ablative zones within a relatively short time.

Small- and medium-sized hepatocellular carcinomas: monopolar radiofrequency ablation with a multiple-electrode switching system-mid-term results

PURPOSE

To prospectively assess the safety and mid-term therapeutic effectiveness of monopolar radiofrequency (RF) ablation with a multiple-electrode switching system for treating small- and medium-sized (≤ 5 cm) hepatocellular carcinomas (HCCs).

MATERIALS AND METHODS

The institutional review board approved this prospective study, and all patients gave informed consent. From February 2009 to January 2010, 166 patients (110 men and 56 women; age range, 38-86 years; mean age, 62 years ± 10 [standard deviation]) with 166 HCCs less than or equal to 5 cm in diameter were treated with monopolar RF ablation with a multiple-electrode switching system. One of three experienced radiologists performed the RF ablation. Technique effectiveness, ablation volume and time, and major complications were evaluated by means of computed tomography (CT) immediately after RF ablation and at follow-up CT examinations at 1 month and then every 3 months after the procedure. The overall survival, disease-free survival, and local tumor progression-free survival rates were evaluated by using the Kaplan-Meier method.

RESULTS

The technique effectiveness rate determined 1 month after RF ablation was 99.4%. Mean ablation parameters were as follows: volume, 85 cm(3) ± 54; maximum diameter, 61 mm ± 13; and minimum diameter, 43 mm ± 11. The major complication rate was 4.8%. The 6-month and 1-, 2-, and 3-year local tumor progression rates were 2%, 6%, 10%, and 11%, respectively. The overall survival rates at 1, 2, and 3 years after RF ablation were 99%, 97%, and 96%, and corresponding local tumor progression-free survival rates were 94%, 90%, and 89%, respectively. The disease-free survival rates at 1, 2, and 3 years after RF ablation were 75%, 60%, and 54%, respectively.

CONCLUSION

Monopolar RF ablation with a multiple-electrode switching system in small- and medium-sized HCCs was safe and efficient, and it provided successful local tumor control and high local tumor progression-free survival rates because an adequate ablation volume was obtained.

Multiple-electrode radiofrequency ablations using Octopus® electrodes in an in vivo porcine liver model

OBJECTIVES

The objective of this study was to determine the in vivo efficacy of radiofrequency ablation (RFA) in porcine liver using Octopus® electrodes for creating a large coagulation compared with RFA using clustered electrodes.

METHODS

A total of 39 coagulations were created using a 200-W generator and clustered electrodes or Octopus electrodes during laparotomy in 19 pigs. Radiofrequency was applied to the livers using four protocols: (1) Group A-1, monopolar mode using a clustered electrode (n=11); (2) Group A-2, monopolar mode using an Octopus electrode (n=11); (3) Group B-1, consecutive monopolar mode using three, clustered electrodes (n=8); and (4) Group B-2, switching monopolar mode using two Octopus electrodes (n=9). The energy efficiency, shape, diameters (D) and volume (V) of the coagulation volume were compared in each of the two groups.

RESULTS

The mean maximum D and V of the coagulations in Group A-2 (4.7 cm and 33.1 cm(3), respectively) were significantly larger than those in Group A-1 (4.1 cm and 20.3 cm(3), respectively) (p<0.05). Furthermore, the mean minimum D, maximum D and V of the coagulations in Group B-2 were significantly larger than those in Group B-1, i.e. 5.3 vs 4.0 cm, 6.6 vs 4.9 cm and 66.9 vs 30.2 cm(3), respectively (p<0.05). The energy efficiencies were also significantly higher in Groups A-2 and B-2 than in Groups A-1 and B-1 (p<0.05).

CONCLUSION

The Octopus electrodes were more efficient for creating a large ablation zone than clustered electrodes, and the efficacy of RFA with Octopus electrodes can be amplified in the switching monopolar mode.

Percutaneous radiofrequency ablation with multiple electrodes for medium-sized hepatocellular carcinomas

Objective

To prospectively evaluate the safety and short-term therapeutic efficacy of switching monopolar radiofrequency ablation (RFA) with multiple electrodes to treat medium-sized (3.1-5.0 cm), hepatocellular carcinomas (HCC).

Materials and Methods

In this prospective study, 30 patients with single medium-sized HCCs (mean, 3.5 cm; range, 3.1-4.4 cm) were enrolled. The patients were treated under ultrasonographic guidance by percutaneous switching monopolar RFA with a multichannel RF generator and two or three internally cooled electrodes. Contrast-enhanced CT scans were obtained immediately after RFA, and the diameters and volume of the ablation zones were then measured. Follow-up CT scans were performed at the first month after ablation and every three months thereafter. Technical effectiveness, local progression and remote recurrence of HCCs were determined.

Results

There were no major immediate or periprocedural complications. However, there was one bile duct stricture during the follow-up period. Technical effectiveness was achieved in 29 of 30 patients (97%). The total ablation time of the procedures was 25.4 ± 8.9 minutes. The mean ablation volume was 73.8 ± 56.4 cm³ and the minimum diameter was 4.1 ± 7.3 cm. During the follow-up period (mean, 12.5 months), local tumor progression occurred in three of 29 patients (10%) with technical effectiveness, while new HCCs were detected in six of 29 patients (21%).

Conclusion

Switching monopolar RFA with multiple electrodes in order to achieve a sufficient ablation volume is safe and efficient. This method also showed relatively successful therapeutic effectiveness on short-term follow up for the treatment of medium-sized HCCs.

Principles of and advances in percutaneous ablation

Image-guided tumor ablation with both thermal and nonthermal sources has received substantial attention for the treatment of many focal malignancies. Increasing interest has been accompanied by continual advances in energy delivery, application technique, and therapeutic combinations with the intent to improve the efficacy and/or specificity of ablative therapies. This review outlines clinical percutaneous tumor ablation technology, detailing the science, devices, techniques, technical obstacles, current trends, and future goals in percutaneous tumor ablation. Methods such as chemical ablation, cryoablation, high-temperature ablation (radiofrequency, microwave, laser, and ultrasound), and irreversible electroporation will be discussed. Advances in technique will also be covered, including combination therapies, tissue property modulation, and the role of computer modeling for treatment optimization.

Radiofrequency ablation of hepatocellular carcinoma: pros and cons

Among locoregional treatments for hepatocellular carcinoma (HCC), radiofrequency ablation (RFA) has been accepted as the most popular alternative to curative transplantation or resection, and it shows an excellent local tumor control rate and acceptable morbidity. The benefits of RFA have been universally validated by the practice guidelines of international societies of hepatology. The main advantages of RFA include 1) it is minimally invasive with acceptable morbidity, 2) it enables excellent local tumor control, 3) it has promising long-term survival, and 4) it is a multimodal approach. Based on these pros, RFA will play an important role in managing the patient with early HCC (smaller than 3 cm with fewer than four tumors). The main limitations of current RFA technology in hepatic ablation include 1) limitation of ablation volume, 2) technically infeasible in some tumors due to conspicuity and dangerous location, and 3) the heat-sink effect. Many technical approaches have been introduced to overcome those limitations, including a novel guiding modality, use of artificial fluid or air, and combined treatment strategies. RFA will continue to play a role as a representative ablative modality in the management of HCC, even in the era of targeted agents.

Current status of radiofrequency ablation of hepatocellular carcinoma

Loco-regional treatments for hepatocellular carcinoma (HCC) are important alternatives to curative transplantation or resection. Among them, radiofrequency ablation (RFA) is accepted as the most popular technique showing excellent local tumor control and acceptable morbidity. The current role of RFA is well documented in the evidence-based practice guidelines of European Association of Study of Liver, American Association of Study of the Liver Disease and Japanese academic societies. Several randomized controlled trials have confirmed that RFA is superior to percutaneous ethanol injections in terms of local tumor control and survival. The overall survival after RFA is comparable to after surgical resection in a selected group of patients with smaller (< 3 cm) tumors. Currently, the clinical benefits of combined RFA with transarterial chemoembolization for intermediate stage HCC are increasingly being explored. Here we review the ongoing technical advancements of RFA and future potential.

Microwave tissue ablation: biophysics, technology, and applications

Microwave ablation is an emerging treatment option for many cancers, cardiac arrhythmias, and other medical conditions. During treatment, microwaves are applied directly to tissues to produce rapid temperature elevations sufficient to produce immediate coagulative necrosis. The engineering design criteria for each application differ, with individual consideration for factors such as desired ablation zone size, treatment duration, and procedural invasiveness. Recent technological developments in applicator cooling, power control, and system optimization for specific applications promise to increase the utilization of microwave ablation in the future. This article reviews the basic biophysics of microwave tissue heating, provides an overview of the design and operation of current equipment, and outlines areas for future research.

Radiofrequency ablation: simultaneous application of multiple electrodes via switching creates larger, more confluent ablations than sequential application in a large animal model

PURPOSE

To compare radiofrequency (RF) ablations created by using a sequential technique to those created simultaneously by using a switching algorithm in ex vivo and in vivo liver models.

MATERIALS AND METHODS

RF ablation was performed by using either sequential or switched application of three cooled electrodes in a 2-cm triangular array in ex vivo bovine liver (28 total ablations) and in vivo swine liver (12 total ablations) models. For sequential ablations, electrodes were powered for 12 minutes each with a 5-minute rest interval between activations to simulate electrode repositioning. Switched ablations were created by using a multiple-electrode switching system for 12 minutes. Temperatures were measured during ex vivo experiments at four points in the ablation zone. Ablation zones were measured for minimum and maximum diameter, cross-sectional area, and isoperimetric ratio. Mann-Whitney and Wilcoxon matched pairs tests were used to identify differences between groups.

RESULTS

The switched application created larger and more circular zones of ablation than did the sequential application, with mean (+/-standard deviation) ex vivo cross-sectional areas of 25.4 cm(2) +/- 5 .3 and 18.8 cm(2) +/- 6.6 (P = .001), respectively, and mean in vivo areas of 17.1 cm(2) +/- 5.1 and 13.2 cm(2) +/- 4.2 (P < .05). Higher temperatures and more rapid heating occurred with the switched application; switched treatments were 74% faster than sequential treatments (12 vs 46 minutes). In the sequential group, subsequent ablations grew progressively larger due to local ischemia.

CONCLUSIONS

Switched application of three electrodes creates larger, more confluent ablations in less time than sequential application. Thermal synergy and ablation-induced ischemia both substantially influence multiple-electrode ablations.