Safety and efficacy of radiofrequency thermal ablation in advanced liver tumors

Survival improvement for patients with metastatic colorectal cancer over twenty years

Over the past two decades of successive clinical trials in metastatic colorectal cancer (CRC), the median overall survival of both control and experimental arms has steadily improved. However, the incremental change in survival for metastatic CRC patients not treated on trial has not yet been quantified. We performed a retrospective review of 1420 patients with de novo metastatic CRC who received their primary treatment at the University of Texas M.D. Anderson Cancer Center (UTMDACC) from 2004 through 2019. Median OS was roughly stable for patients diagnosed between 2004 and 2012 (22.6 months) but since has steadily improved for those diagnosed in 2013 to 2015 (28.8 months), and 2016 to 2019 (32.4 months). Likewise, 5-year survival rate has increased from 15.7% for patients diagnosed from 2004 to 2006 to 26% for those diagnosed from 2013 to 2015. Notably, survival improved for patients with BRAFV600E mutant as well as microsatellite unstable (MSI-H) tumors. Multivariate regression analysis identified surgical resection of liver metastasis (HR = 0.26, 95% CI, 0.19-0.37), use of immunotherapy (HR = 0.44, 95% CI, 0.29-0.67) and use of third line chemotherapy (regorafenib or trifluridine/tipiracil, HR = 0.74, 95% CI, 0.58-0.95), but not year of diagnosis (HR = 0.99, 95% CI, 0.98-1), as associated with better survival, suggesting that increased use of these therapies are the drivers of the observed improvement in survival.

A review on radiofrequency, microwave and high-intensity focused ultrasound ablations for hepatocellular carcinoma with cirrhosis

Importance

Hepatocellular carcinoma (HCC) is usually accompanied by liver cirrhosis, which makes treatment of this disease challenging. Liver transplantation theoretically provides an ultimate solution to the disease, but the maximal surgical stress and the scarcity of liver graft make this treatment option impossible for some patients. In an ideal situation, a treatment that is safe and effective should provide a better outcome for patients with the dilemma.

Objective

This article aims to give a comprehensive review of various types of loco-ablative treatment for HCC.

Evidence Review

Loco-ablative treatment bridges the gap between surgical resection and transarterial chemotherapy. Various types of ablative therapy have their unique ability, and evidence-based outcome analysis is the most important key to assisting clinicians to choose the most suitable treatment modality for their patients.

Findings

Radiofrequency ablation (RFA) has a relatively longer history and more evidence to support its effectiveness. Microwave ablation (MWA) is gaining momentum because of its shorter ablation time and consistent ablation zone. High-intensity focused ultrasound (HIFU) ablation is a relatively new technology that provides non-invasive treatment for patients with HCC. It has been carried out at centers of excellence and it is a safe and effective treatment option for selected patients with HCC and liver cirrhosis.

Conclusion and Relevance

Selective use of different loco-ablative therapies will enhance clinicians' treatment options for treatment of HCC.

Factors Associated With Local Tumor Control and Complications After Thermal Ablation of Colorectal Cancer Liver Metastases: A 15-year Retrospective Cohort Study

INTRODUCTION

The purpose of this study was to identify risk factors associated with local tumor progression-free survival (LTPFS) and complications after colorectal liver metastases (CLM) thermal ablation (TA).

PATIENTS AND METHODS

This retrospective analysis included 286 patients with 415 CLM undergoing TA (radiofrequency and microwave ablation) in 378 procedures from January 2003 to July 2017. Prior hepatic artery infusion (HAI), bevacizumab, pre-existing biliary dilatation, ablation modality, minimal ablation margin (MM), prior hepatectomy, CLM number, and size were analyzed as factors influencing complications and LTPFS. Statistical analysis included the Kaplan-Meier method, Cox proportional hazards model, competing risk analysis, univariate/multivariate logistic/exact logistic regressions, and the Fisher exact test. Complications were reported according to modified Society of Interventional Radiology guidelines.

RESULTS

The median follow-up was 31 months. There was no LTP for MM > 10 mm. Smaller tumor size, increased MM, and prior hepatectomy correlated with longer LTPFS. The major complications occurred following 28 (7%) of 378 procedures. There were no biliary complications in HAI-naive patients, versus 11% in HAI patients (P < .001), of which 7% were major. Biliary complications predictors in HAI patients included biliary dilatation, bevacizumab, and MM > 10 mm. In HAI patients, ablation with 6 to 10 mm and > 10 mm MM resulted in major biliary complication rates of 4% and 21% (P = .0011), with corresponding LTP rates of 24% and 0% (P = .0033). In HAI-naive patients, the LTP rates for 6 to 10 mm and > 10 mm MM were 27% and 0%, respectively.

CONCLUSIONS

No LTP was seen for MM > 10 mm. Biliary complications occurred only in HAI patients, especially in those with biliary dilatation, bevacizumab, and MM > 10 mm. In HAI patients, MM of 6 to 10 mm resulted in 76% local tumor control and 4% major biliary complications incidence.

Cardiac synchronization and arrhythmia during irreversible electroporation

BACKGROUND AND OBJECTIVES

Irreversible electroporation (IRE) is a nonthermal electrical tumor ablative strategy for unresectable tumors. IRE is relatively safe around critical structures but may induce cardiac arrhythmia when its delivery is not synchronized to the cardiac cycle. We performed a systematic literature review to determine rates of arrhythmia when IRE was utilized with or without cardiac synchronization.

METHODS

An online literature search was conducted with additional hand selection of articles. Data were extracted and pooled analyses were performed.

RESULTS

Twelve articles were included in analysis. IRE was performed for 481 patients; 46% hepatic tumors (n = 223), 36% pancreatic lesions (n = 168), and multiple other locations including prostate. Synchronization was performed on 422 patients. Arrhythmias were noted in 3.7% of cases (n = 18/481); cardiac synchronization: 1.2% (n = 5/422) vs unsynchronized: 22.0% (n = 13/59), P < .0001. These events occurred in every organ except the prostate.

CONCLUSIONS

IRE remains a potent technology for unresectable tumors, but arrhythmia is a clinical concern. This literature review confirms that cardiac gating should be used in all cases outside of prostate to prevent this potentially serious adverse event.

Model-based optimal planning of hepatic radiofrequency ablation

This article presents a model-based pre-treatment optimal planning framework for hepatic tumour radiofrequency (RF) ablation. Conventional hepatic radiofrequency (RF) ablation methods rely on pre-specified input voltage and treatment length based on the tumour size. Using these experimentally obtained pre-specified treatment parameters in RF ablation is not optimal to achieve the expected level of cell death and usually results in more healthy tissue damage than desired. In this study we present a pre-treatment planning framework that provides tools to control the levels of both the healthy tissue preservation and tumour cell death. Over the geometry of tumour and surrounding tissue, we formulate the RF ablation planning as a constrained optimization problem. With specific constraints over the temperature profile (TP) in pre-determined areas of the target geometry, we consider two different cost functions based on the history of the TP and Arrhenius index (AI) of the target location, respectively. We optimally compute the input voltage variation to minimize the damage to the healthy tissue while ensuring a complete cell death in the tumour and immediate area covering the tumour. As an example, we use a simulation of a 1D symmetric target geometry mimicking the application of single electrode RF probe. Results demonstrate that compared to the conventional methods both cost functions improve the healthy tissue preservation.

Radiofrequency ablation for liver metastases in patients with gastric cancer as an alternative to hepatic resection

Background

The purpose of this retrospective study was to determine whether RFA could provide an alternative treatment modality for selected patients who are not candidates for hepatic resection.

Methods

A total of 18 consecutive patients with liver metastases alone from gastric cancer treated with radiofrequency ablation (RFA, n = 11) or hepatic resection (HR, n = 7) at Seoul St. Mary’s Hospital, Korea, between January 2000 and September 2014, were enrolled.

Results

The median OS and DFS in the RFA group were 40.5 ± 22.3 and 10.3 ± 1.07 months, respectively. There was no significant difference between the RFA and HR groups in terms of baseline characteristics except for performance status. Mean survival and DFS times of all patients were 60.1 ± 9.4 and 40.9 ± 10.2 months, respectively. Mean OS times in the HR and RFA groups were 67.5 ± 15.4 and 51.1 ± 9.8 months (P = 0.671), respectively, and the mean DFS time in the HR group (74.1 ± 14.2 months) was longer than that in the RFA group (26.9 ± 9.2 months), but the difference was not significant (P = 0.076).

Conclusions

In patients who are not candidates for surgical treatment, RFA may be an alternative to HR.

Evaluation of hepatocellular carcinoma tumor vascularity using contrast-enhanced ultrasonography as a predictor for local recurrence following radiofrequency ablation

PURPOSE

The purpose of this study was to evaluate whether the hypervascularity of hepatocellular carcinomas (HCCs) on contrast-enhanced ultrasonography (CEUS) prior to radiofrequency ablation (RFA) is a significant risk factor for local recurrence after RFA.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Overall, 208 patients (mean age, 71.7 years; range, 50-87 years; 137 men, 71 women) with 282 HCCs treated with RFA were analyzed retrospectively. The mean maximum tumor diameter was 15.7mm. We compared the abilities of CEUS and contrast-enhanced computed tomography (CECT) to detect hypervascularity in HCCs. We then classified the HCCs into two groups according to the arterial-phase CEUS findings: a "hypervascular group" with whole or partial hypervascular areas within the lesions compared with the surrounding liver parenchyma, and a "non-hypervascular group" with isovascular or hypovascular areas within the lesions. We assessed the cumulative rate of local recurrence after RFA, and we also evaluated the risk factors for local recurrence using a univariate analysis.

RESULTS

The detection rate for hypervascular HCCs was significantly higher using CEUS (78%, 221/282) than that using CECT (66%, 186/282) (P<0.001). Using the CEUS findings, the cumulative rate of local recurrence was significantly higher in the hypervascular group (41.2%, 56/221) than in the non-hypervascular group (18.4%, 6/61) (P=0.007). A univariate analysis revealed that hypervascularity on CEUS was an independent risk factor for local recurrence (P=0.010).

CONCLUSION

Hypervascularity in HCCs as observed using CEUS is a significant risk factor for local recurrence after RFA.

Pre-treatment estimation of future remnant liver function using gadoxetic acid MRI in patients with HCC

BACKGROUND & AIMS

This study aimed to determine whether the predicted remnant liver function on dynamic hepatocyte-specific contrast media-enhanced magnetic resonance (DHCE-MR) imaging correlates with the results of the indocyanin green retention test (ICG R₁₅) after hepatic resection or radiofrequency ablation (RFA).

METHODS

This prospective multicenter study was approved by the Institutional Review Boards of each hospital. Informed consents were obtained from all. DHCE-MRI and ICG R₁₅ were performed in 57 patients scheduled to undergo hepatectomy or RFA for hepatocellular carcinoma, once before treatment and repeated on post-treatment day 3. In nine donors and three recipients, DHCE-MRI and ICG R₁₅ were performed only preoperatively. The predicted remnant liver function (HEFml) was estimated using the hepatic extraction fraction (HEF) multiplied by the remnant liver volume, and compared with post-treatment ICG R₁₅. Intra-individual heterogeneity of HEF was assessed using pooled coefficients of variation (CV) among hepatic segments. Finally, development of post-treatment hepatic failure was assessed according to the 50-50 criteria on post-treatment day 5.

RESULTS

Predicted remnant HEFml showed a negative correlation with post-treatment ICG R₁₅ (r=-0.45, p=0.001), whereas liver volume did not (p>0.05). There were significant correlations between pre-treatment HEFml and pre-treatment ICG R₁₅ (r=-0.33, p=0.006) and between post-treatment HEFml and post-treatment ICG R₁₅ (r=-0.54, p<0.001). Pooled CV among segmental HEFs was 12.6%. No patients showed post-treatment liver failure on post-treatment day 5.

CONCLUSIONS

DHCE-MRI using Gd-EOB-DTPA was able to provide both global and segmental liver function information, and post-treatment remnant liver function predicted on pre-treatment DHCE-MRI showed a significant negative correlation with post-treatment ICG R₁₅.

LAY SUMMARY

Post-treatment liver function could be predicted at pre-treatment DHCE-MRI. Liver function was heterogeneous among the liver segments. Liver anatomy, disease extent, and underlying liver function can be assessed in one DHCE-MRI examination.

CLINICAL TRIAL NUMBER

ClinicalTrials.gov number, NCT01490203.

Three-dimensional quantitative assessment of ablation margins based on registration of pre- and post-procedural MRI and distance map

PURPOSE

Contrast-enhanced MR images are widely used to confirm the adequacy of ablation margin after liver ablation for early prediction of local recurrence. However, quantitative assessment of the ablation margin by comparing pre- and post-procedural images remains challenging. We developed and tested a novel method for three-dimensional quantitative assessment of ablation margin based on non-rigid image registration and 3D distance map.

METHODS

Our method was tested with pre- and post-procedural MR images acquired in 21 patients who underwent image-guided percutaneous liver ablation. The two images were co-registered using non-rigid intensity-based registration. After the tumor and ablation volumes were segmented, target volume coverage, percent of tumor coverage, and Dice similarity coefficient were calculated as metrics representing overall adequacy of ablation. In addition, 3D distance map around the tumor was computed and superimposed on the ablation volume to identify the area with insufficient margins. For patients with local recurrences, the follow-up images were registered to the post-procedural image. Three-dimensional minimum distance between the recurrence and the areas with insufficient margins was quantified.

RESULTS

The percent tumor coverage for all nonrecurrent cases was 100 %. Five cases had tumor recurrences, and the 3D distance map revealed insufficient tumor coverage or a 0-mm margin. It also showed that two recurrences were remote to the insufficient margin.

CONCLUSIONS

Non-rigid registration and 3D distance map allow us to quantitatively evaluate the adequacy of the ablation margin after percutaneous liver ablation. The method may be useful to predict local recurrences immediately following ablation procedure.

Radiofrequency ablation versus transarterial chemoembolization for unresectable solitary hepatocellular carcinomas sized 5-8 cm

OBJECTIVES

This retrospective review was conducted to compare the efficacy of radiofrequency ablation (RFA) with that of transarterial chemoembolization (TACE) in treating large (5-8 cm) unresectable solitary hepatocellular carcinomas (HCCs).

METHODS

Patients with large unresectable solitary HCCs primarily treated by RFA or TACE were reviewed. The primary endpoint was overall survival. Secondary endpoints were tumour response, time to disease progression, and treatment-related morbidity and mortality.

RESULTS

There were 15 patients in the RFA group. Of these, 12 achieved complete ablation, one had ablation site recurrence, and five developed complications. Median disease-free survival in this group was 13.0 months (range: 2.8-38.0 months). The TACE group included 26 patients, of whom four obtained a partial response, none achieved a complete response, and five developed complications. The median time to disease progression in this group was 8.0 months (range: 1.0-68.0 months). There were no hospital deaths in this series. Median survival was 39.8 months in the RFA group and 19.8 months in the TACE group (P = 0.257). Rates of 1-, 2- and 5-year survival were 93.3%, 86.2% and 20.9%, respectively, in the RFA group and 73.1%, 40.6% and 18.3%, respectively, in the TACE group.

CONCLUSIONS

Both RFA and TACE are feasible treatments for large unresectable solitary HCCs. Both modes show comparable rates of complications and longterm survival, but RFA achieves better initial tumour control and results in better short-term survival.

Various complications of percutaneous radiofrequency ablation for hepatic tumors: radiologic findings and technical tips

Radiofrequency ablation is a safe and effective treatment for primary and secondary liver malignancies and has a low complication rate; however, there are various radiofrequency ablation-related complications which can occur from the thorax to the pelvis. Although most of these complications are usually minor and self-limited, they may become fatal if diagnosis and treatment are delayed. It is important for radiologists performing radiofrequency ablation to have a perspective regarding the possible radiofrequency ablation-related complications and their risk factors as well as the radiologic findings for their timely detection and increase of the treatment efficacy, and thereby encouraging the use of the radiofrequency ablation technique. This article illustrates the various imaging features of common and rare radiofrequency ablation-related complications as well as offers technical tips in order to avoid these complications.

Liver-directed therapies in metastatic colorectal cancer

Colorectal cancer (CRC) is a major health concern in the United States (US) with over 140,000 new cases diagnosed in 2012. The most common site for CRC metastases is the liver. Hepatic resection is the treatment of choice for colorectal liver metastases (CLM), with a 5-year survival rate ranging from 35% to 58%. Unfortunately, only about 20% of patients are eligible for resection. There are a number of options for extending resection to more advanced patients including systemic chemotherapy, portal vein embolization (PVE), two stage hepatectomy, ablation and hepatic artery infusion (HAI). There are few phase III trials comparing these treatment modalities, and choosing the right treatment is patient dependent. Treating hepatic metastases requires a multidisciplinary approach and knowledge of all treatment options as there continues to be advances in management of CLM. If a patient can undergo a treatment modality in order to increase their potential for future resection this should be the primary goal. If the patient is still deemed unresectable then treatments that lengthen disease-free and overall-survival should be pursued. These include chemotherapy, ablation, HAI, chemoembolization, radioembolization (RE) and stereotactic radiotherapy.

Clinical scenarios associated with local recurrence after laparoscopic radiofrequency thermal ablation of colorectal liver metastases

BACKGROUND

Over the last decade, radiofrequency thermal ablation (RFA) has been incorporated into the treatment algorithm of patients with unresectable colorectal liver metastases (CLM). For this population, the local recurrence (LR) rate is a key parameter used to assess the success of RFA. LR is defined as development of new tumor abutting and/or in 1 cm of an ablation zone. The aim of this study is to correlate LR with other hepatic or extrahepatic recurrence and patient survival.

METHODS

Between 2000 and 2011, 252 patients with CLM underwent laparoscopic RFA of 883 lesions. These patients were followed under a prospective protocol with quarterly liver computed tomography and blood work, including carcinoembryonic antigen levels quarterly for the first 2 years and then biannually. Clinical scenarios associated with LR were identified and categorized as being "isolated LR," "LR associated with new liver disease," or "LR associated with systemic disease." Demographic, clinical, and survival data were assessed using analysis of variance, Chi-square test, and univariate and multivariate Kaplan-Meier analysis.

RESULTS

One hundred eighteen patients (47%) developed LR after their initial laparoscopic RFA. These were 85 men (72%) and 33 women (28%), with a mean age of 70 ± 8 years. For this cohort, the mean of number of lesions was 3.1 ± 0.2 cm (range, 1-11) and dominant tumor size 2.9 ± 0.1 cm (range, 0.7-6.5) at the time of initial RFA. The LR rate per lesion was 29%. Of the patients who developed treatment failure at the RFA site, this was an isolated LR in 31 (26%) patients, associated with new liver disease in 51 (43%) and systemic metastases in 36 patients (31%). When patients with different clinical scenarios associated with LR were compared, no clinical predictors were identified to differentiate these subgroups. At a median follow up of 30 months (range, 3-113), the Kaplan-Meier median overall survival (OS) for patients with and without LR were 28 vs 31 months, respectively (P = .103). The OS for patients whose LR was isolated, associated with new liver and systemic recurrences was 39, 26, and 22 months, respectively (P = .009).

CONCLUSION

This study shows that, although the presence of LR does not negatively impact on survival, the pattern of recurrent disease does. LR after RFA for CLM is most often associated with new liver and systemic recurrences, reflecting the aggressive biology of cancer in patients channeled to this treatment modality.

Efficacy and safety of percutaneous microwave coagulation therapy followed by 125I seed brachytherapy for VX2 hepatic tumors in a rabbit model

The aim of this study was to evaluate the efficacy and safety of percutaneous microwave coagulation therapy (PMCT) followed by ¹²⁵I seed brachytherapy for VX2 liver cancer in rabbits. Eighty New Zealand rabbits were injected with suspensions of VX2 tumor cells to create an animal model. The rabbits were randomly divided into 4 groups (n=20); the control, PMCT, ¹²⁵I seed brachytherapy and combination groups. Group A was treated with PMCT at 40 W for 120 sec, group B was treated with ¹²⁵I seed brachytherapy and group C was treated with PMCT followed by ¹²⁵I seed brachytherapy. Group D were not treated and served as the control group. At 21 days after treatment, the rabbits were sacrificed for pathological assessment. The complete tumor necrosis rate was 19 out of 20 tumors (95%) in group C, 6 (30%) in group A, 0 (0%) in group B and 0 (0%) in the control group. The complete tumor necrosis rate was observed to be significantly different between groups C and A, and between groups C and B (P<0.01). No intraheptic metastasis occurred in group C, compared with an incidence of 7 (35%) in group A, 2 (10%) in group B and 20 (100%) in the control group. Between groups C and A, and between groups C and D, the intraheptic metastasis rate was statistically significant (P<0.01). PMCT followed by ¹²⁵I seed brachytherapy increased the rate of carcinoma necrosis and decreased carcinoma metastasis in the VX2 rabbit model. This combined treatment is a safe, effective and minimally invasive therapeutic option for liver cancer.

Clinical evaluation of a new technique to monitor return electrode skin temperature during radiofrequency ablation

PURPOSE

Return electrode burns occur occasionally in cardiac radiofrequency ablation and more frequently in tumor radiofrequency ablation. A return electrode incorporating a thermochromic liquid crystal (TLC) layer, which changes color with temperature, has been shown in sheep studies to accurately indicate underlying skin temperature. We aimed to validate the accuracy of TLC-coated return electrodes in indicating skin temperature in the clinical setting of cardiac radiofrequency ablation.

METHODS AND RESULTS

The top layer of a standard return electrode was replaced with TLC. Fluoro-optic thermometer (FOT) probes were laid on the skin side of the return electrode, which was then placed on the left lateral mid-thigh of 18 patients (mean age = 61 ± 12 years, 12 men) undergoing cardiac radiofrequency ablation. Return electrode photographs were taken when FOT temperature exceeded 35 °C. TLC color changes, observed in 11 patients, were converted to temperature and compared with FOT temperature. TLC temperature correlated well with FOT temperature (Pearson's coefficient = 0.97 ± 0.03). Bland-Altman analysis showed good agreement (mean temperature difference = -0.04 ± 0.08 °C, upper limit of agreement = 0.11 ± 0.005 °C, lower limit of agreement = -0.19 ± 0.005 °C). The maximum FOT temperature recorded was 39.6 °C. There was no thermal injury at the return electrode site on any patients, when assessed immediately after and the day following the procedure.

CONCLUSION

TLC-coated return electrodes accurately indicate underlying skin temperature in cardiac radiofrequency ablation and may help prevent burns. This technology might be essential in high energy radiofrequency ablation.

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.

Clinical applications of radio-frequency ablation in liver metastasis of colorectal cancer

PURPOSE

The aim of this study is to evaluate long-term survival and prognostic factors for radio-frequency ablation (RFA) in colorectal liver metastases.

METHODS

We retrospectively reviewed 35 colorectal liver metastases patients who underwent RFA between 2004 and 2008. We analyzed survival after RFA and prognostic factors for survival.

RESULTS

Of the 35 patients, 23 patients were male and 12 were female. Their mean age was 62.40 ± 12.52 years. Mean overall survival was 38.8 ± 4.6 months, and mean progression free survival was 19.9 ± 3.4 months. Three- and 5-year overall survival rates were 42.7 ± 0.1% and 26.0 ± 0.1%, respectively. Three- and 5-year progression-free survival rates were 19.6 ± 0.1% and 4.9 ± 0.04%, respectively. Overall survival and progression-free survival were significantly improved in male and in patients with carcinoembryonic antigen (CEA) ≤ 100 ng/mL, carbohydrate antigen (CA) 19-9 ≤ 100 ng/mL, absence of extrahepatic disease, and a unilobar hepatic lesion. In addition, progression-free survival was improved in patients with a solitary hepatic lesion. On the multivariate analysis, significant survival factors were the absence of extrahepatic disease and the presence of a unilobar hepatic lesion.

CONCLUSION

RFA for colorectal liver metastases is an effective treatment option in male patients and in patients with CEA or CA19-9 ≤ 100, absence of extrahepatic disease, a solitary hepatic lesion, and a unilobar hepatic lesion.

Pringle maneuver exacerbates systemic inflammatory response and multiple-organ injury induced by extended liver radiofrequency ablation

AIM

To assess the systemic inflammatory response (SIR) and the multi-organ damage after large-volume liver radiofrequency ablation (RFA) with or without concurrent Pringle maneuver.

METHODS

Wistar rats were subjected to 30% liver RFA (group RFA), liver RFA under 30-min Pringle maneuver (group RFA + P), Pringle only (group P) or sham operation (group S). Serum levels of interleukin-1α (IL-1α), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), serum biochemical profile, multiple-organ pathology and the activity of nuclear factor-κB (NF-κB) in the liver were assessed post-operatively.

RESULTS

The levels of IL-6 and TNF-α were increased from 1h up to 1w and 6h, respectively, in both RFA groups, while IL-6 was only mildly increased at 3 h in group P. IL-6 was higher in group RFA + P compared to group RFA. Serum biochemical profile was altered more intensely in group RFA + P compared to RFA. There was tissue injury in the non-ablated liver portion as well as in adjacent and remote organs with lesions being more severe in group RFA + P. At 1 h, NF-κB was equally activated in all study groups.

CONCLUSIONS

Extended liver RFA causes SIR and multi-organ injury, which are exacerbated when a concurrent Pringle maneuver is applied.

Radiofrequency ablation of neuroendocrine hepatic metastasis

Neuroendocrine cancer commonly metastasizes to the liver and often presents as unresectable disease. Liver resection or debulking most of the tumor provides a survival advantage for patients. Whether used alone or in combination with resection, radiofrequency ablation provides a unique tool to destroy metastases to the liver and spare hepatic parenchyma. Although randomized trials are lacking, retrospective series provide promising data to consider radiofrequency ablation in the management of hepatic neuroendocrine metastases.

Ablative therapies for colorectal liver metastases

Ablative therapies remain a useful adjunct in the multidisciplinary treatment of patients with colorectal liver metastases not amenable to hepatic resection. This review summarizes the rationale, underlying mechanisms, techniques, complications, and outcomes of current and emerging ablative modalities.

Biloma formation after radiofrequency ablation of hepatocellular carcinoma: incidence, imaging features, and clinical significance

OBJECTIVE

The objective of our study was to evaluate the frequency, morphologic patterns, temporal changes, and clinical significance of biloma after radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Between April 1999 and May 2008, 2,630 patients with HCC underwent a total of 3,284 sessions of RFA at our institution. We retrospectively reviewed all CT scans obtained before and after RFA in all patients. The frequency, morphologic patterns, temporal changes, and clinical course of biloma were studied at the thermal ablation zone after RFA.

RESULTS

A total of 109 bilomas (3.3%, 109/3,284) developed after RFA in 104 patients in our series. The bilomas developed from 0 to 526 days (mean, 64 days) after RFA, and the mean follow-up period was 469 days (range, 0-2,703 days). The most common morphologic type of biloma was a crescent shape (42.2%). The mean size of the bilomas at initial presentation was 3.8 cm (range, 1.7-11 cm), and the mean size of the bilomas on the last follow-up CT scan was 2.8 cm (range, 0-6.3 cm). Fifty-three (48.6%) of the 109 bilomas resolved during follow-up at a mean interval of 286 days. In one patient, the biloma was considered a major complication because percutaneous drainage was required to manage the biloma with infection (0.9%, 1/109). No patient died of a biloma.

CONCLUSION

The development of a biloma after percutaneous RFA in patients with HCC was not rare. However, in most cases they were a minor complication of no clinical significance.

Changes in interleukin-1β and 6 after hepatic microwave tissue ablation compared with radiofrequency, cryotherapy and surgical resections

BACKGROUND

Cytokine changes after microwave tissue ablation (MTA) were compared with hepatic resection, cryotherapy (CRYO), and radiofrequency ablation (RFA). Cytokine production was measured at various ablation volumes for each modality and correlated with the transitional inflammatory zone produced by the ablation techniques.

METHODS

Live rats underwent MTA, surgical resection, CRYO or RFA of 15%, 33%, or 66% of the total hepatic volume. Serum samples were collected preoperatively and at 1, 3, 6, 24, and 48 hours after surgery and analyzed for pro-inflammatory cytokines interleukin (IL)-1β and IL-6.

RESULTS

Significantly higher levels of both cytokines were present after CRYO and RFA compared with MTA, hepatic resection, or controls (P < .001). All animals survived except those undergoing RFA or CRYO of 66% of the hepatic volume, which died within 6 hours. Transitional zones produced after RFA were larger than those after CRYO or MTA, but no correlation was present with the amount of cytokines.

CONCLUSIONS

Large-volume MTA is associated with a significant decreased cytokine response and is well tolerated compared with RFA and CRYO.

Laparoscopic ultrasound with radiofrequency ablation of hepatic tumors in cirrhotic patients

BACKGROUND

The optimal treatment for hepatocellular carcinoma (HCC) is surgical resection. However, only a small percentage of patients are operative candidates due to associated liver cirrhosis. Recent advances in laparoscopic ultrasound and laparoscopy have greatly improved the accuracy in detecting intrahepatic tumor nodules, many of which were missed by preoperative imaging modality.

OBJECTIVE

The aim of this work was for an evaluation of the safety and efficacy of laparoscopic radiofrequency ablation (RFA) guided with laparoscopic ultrasound in detecting and treatment of liver tumors in patient with liver cirrhosis.

METHODS

Seventy-two patients with liver tumors (58 HCC, 9 metastatic adencarcinoma, 2 neoendocrine metastasis, 3 other metastasis) were submitted to laparoscopic RFA under laparoscopic ultrasound guidance. Forty-four patients (61.1%) were classified Child A and 28 patients (38.9%) Child B. Patients with large tumor (>6 cm), portal vein thrombosis, or Child C class were excluded from the study.

RESULTS

Laparoscopic RFA was completed in all patients without any conversion rate. Laparoscopic ultrasound identified 19 new malignant lesions (18.4%), in comparison with the result of preoperative imaging. A total of 103 hepatic focal lesions were treated by RFA (45 patients had 1 lesion, 23 patients had 2 lesions, and 4 patients had 3 lesions). There was no mortality. Morbidity occurred in 4 patients (5.5%): 2 patients had liver abscesses, 1 patient had pleural effusion, and 1 patient had postoperative bleeding necessitating blood transfusion and surgery. After a mean follow-up of 14.3 +/- 11.6 months, a complete response with 100% necrosis was achieved in 93 of 103 lesions (90.3%). Three lesions (2.9%) showed local recurrences, 5 lesions (4.8%) showed remote recurrences, and 2 lesions (1.9%) showed both local and remote recurrences.

CONCLUSIONS

Laparoscopic RFA guided with laparoscopic ultrasound is an excellent use of existing technology in the improvement of safety and efficacy of detection and treatment of intrahepatic tumors in patients with liver cirrhosis.

Improvement of long-term survival of colorectal cancer in Japanese-Americans of Hawaii from 1990 to 2001

BACKGROUND

To compare the long-term survival of colorectal cancer (CRC) during two 6-year periods using patients with similar characteristics of the same ethnicity in Hawaii.

METHODS

A retrospective review of Japanese-American patients in Hawaii with CRC surgically resected and followed more than 5 years in a single institution. Patients were divided into two groups by date that patients had surgery: Group 1; 1990-1995, and Group 2; 1996-2001 (introduction of newer chemotherapy, aggressive surgery for liver metastases including radiofrequency thermal ablation).

RESULTS

A total of 344 patients in Group 1 (median age 69.5 years) and 330 patients in Group 2 (median age 71.7 years) were included. There were no differences between two groups in gender, age, anatomic site, carcinoembryonic antigen, tumor size, histologic grade, and TNM stage distribution, including pT, pN, and pM status. Overall 5-year survival rate difference approached significance between two groups (Group 1: 73.2% vs. Group 2: 78.9%; p = 0.097). Particularly, there was significant difference in stage IV patients (Group 1; 8.7% vs. Group 2: 26.0%; p = 0.030) and histologic grade 3 (Group 1; 41.67% vs. Group 2: 67.73%; p = 0.032). Subgroup analyses showed significant difference (p < 0.05) for more advanced cancers (larger tumor, node positive, metastatic disease, poorly differentiated cancer).

CONCLUSIONS

In this study of patients with the same ethnicity, the better survival outcome in latter (Group 2) patients suggests improvement of treatment, especially for patients with more advanced and metastatic cancer (stage IV).

Metastasectomy for stage IV colorectal cancer

Metastatic colorectal cancer traditionally has been considered incurable. Over the past 3 decades, however, resection of low-volume hepatic disease has been recognized as beneficial in some cases. More recently, resection of isolated pulmonary metastases has been shown to offer long-term survival in carefully selected patients. Resection of metastases to more unusual sites (ovary, brain, peritoneal cavity) is more controversial; nevertheless, retrospective data suggest that a few patients may be cured with resection of these tumors. In this article, we review the history and current status of metastasectomy in stage IV colorectal cancer.

Thermoablation of colorectal liver metastasis

Thermoablation is a local therapy that is effective in in situ destruction of colorectal liver metastasis while preserving surrounding normal liver tissue. It is less invasive compared to surgery, easy to use, and can be repeated. The therapy provides local control of unresectable disease and is an alternative therapy for small resectable lesions in patients with insufficient hepatic reserve after resection or coexistent comorbid conditions. It can artificially increase the resection margin thus increasing the number of patient candidate for resection. When used in conjunction with liver resection it clears the liver of multiple lesions that are surgically inaccessible or unresectable. Main limitations of the treatment are local recurrence of the disease, treatment-related complications, and questionable impact on patient. Outcome of therapy can be improved when used as part of multimodality treatment.

Myoglobinuria after laparoscopic radiofrequency ablation of liver tumors

BACKGROUND

There are scant data in the literature about myoglobinuria after radiofrequency ablation (RFA) of liver tumors. The aim of this study is to analyze the incidence and identify the risk factors involved in this complication after RFA.

PATIENTS AND METHODS

An initial case of myoglobinuria and acute kidney injury (AKI) during laparoscopic liver RFA after 10 years of the liver ablation program led to the design of this study. Prospective data were collected on 41 consecutive patients undergoing laparoscopic RFA at our institution over a 9-month period. Urine myoglobin, serum creatinine kinase, and serum creatinine levels were obtained preablation and postablation. Variables were compared between patients to identify possible risk factors that might be related to this rare complication. Data are expressed as mean +/- standard error of the mean.

RESULTS

Two patients were excluded from the study due to preoperative myoglobinuria of unknown etiology. Of the remaining 39 patients, three developed dark urine with significant myoglobinuria on postoperative day 1. Two of these patients had carcinoid liver metastases; the remaining patient had a metastatic colorectal lesion. The number of tumors ablated in these patients was 14, 11, and 3 vs. 2.4 +/- 0.4 in the rest of the patients. Cumulative tumor volume was larger in the group of patients that developed the complication vs. those who did not (127.9 +/- 59.5 vs. 48 +/- 3 cm(3)). Two grounding pads were used in the three patients that had a complication vs. four pads in the rest of the patients. Dark urine was identified promptly intraoperatively and treated aggressively. All of these patients required intensive care unit (ICU) admission and had a prolonged hospital stay. Marked elevation of transaminases and creatinine kinase as well as a drop in hematocrit and platelet count was observed in patients with myoglobinuria. In our retrospective review of 706 patients that underwent liver RFA in the past 10 years, we detected 27 patients (3.8%) with ten or more lesions (11.9 +/- 0.4). None of these patients had significant elevation of serum creatinine postoperatively. In the whole series of 706 patients, 22 (3.2%) were found to have elevated creatinine after liver RFA, with return to baseline in all but seven patients in follow-up.

CONCLUSION

Myoglobinuria after liver RFA is a rare but potentially devastating complication that may lead to AKI with significant morbidity and prolonged hospital stay. Patients with large tumor volumes requiring longer ablation times need to be monitored closely for the development of this complication. The fact that this was not observed in other patients with similar tumor characteristics suggests that individual patient-related factors might play an important role.

Long-term outcomes following hepatic resection and radiofrequency ablation of colorectal liver metastases

Recently some have called for randomized controlled trials comparing RFA to hepatic resection, particularly for patients with only a few small metastases. The objectives were to compare local recurrence and survival following RFA and hepatic resection for colorectal liver metastases. This was a retrospective review of open RFA and hepatic resection for colorectal liver metastases between January 1998 and May 2007. All patients who had RFA were considered to have unresectable disease. 58 patients had hepatic resection and 43 had RFA. A 5-year survival after resection was 43% compared to 23% after RFA. For patients with solitary lesions, a 5-year survival was 48% after resection and 15% after RFA. Sixty percent of patients suffered local recurrences after RFA compared to 7% after hepatic resection. RFA is inferior to resection. The results observed in this study support the consensus that RFA cannot be considered an equivalent procedure to hepatic resection.

Liver tumor ablation: percutaneous and open approaches

The global incidence of liver cancer is greater than a million cases a year. Surgical resection where applicable is still the standard of care for these patients. Various liver-directed regional therapies have been developed in an effort to treat the vast majority of unresectable liver tumors. This article reviews the principles behind various ablation therapies currently available for malignant liver tumors and their outcomes.

Sequential activation of ground pads reduces skin heating during radiofrequency tumor ablation: in vivo porcine results

Skin burns below ground pads during monopolar RF ablation are increasingly prevalent, thereby hindering the development of higher power RF generators capable of creating larger tumor ablation zones in combination with multiple or new applicators. Our goal was to evaluate reduction in skin temperatures via additional ground pads in an in vivo porcine model. Three ground pads placed on the animal's abdomen were activated either simultaneously or sequentially, where activation timing was adjusted to equilibrate skin temperature below each pad. Thirteen RF ablations (n = 4 simultaneous at 300 W, n = 5 sequential at 300 W, and n = 4 sequential at 375 W) were performed for 12 min via two internally cooled cluster electrodes placed in the gluteus maximus of domestic swine. Temperature rise at each pad and burn degree as determined via histology were compared. Ablation zone size was determined via T2-weighted MRI. Maximum temperature rise was significantly higher with simultaneous activation than with either of the sequential activation group (21.4 degrees C versus 8.1 degrees C or 9.6 degrees C, p < 0.01). Ablation zone diameters during simultaneous (300 W) and sequential activations (300 and 375 W) were and 6.9 +/- 0.3, 5.6 +/- 0.3, and 7.5 +/- 0.6 cm, respectively. Sequential activation of multiple ground pads results in significantly lower skin temperatures and less severe burns, as measured by histological examination.

Radiofrequency ablation combined with KS-IL2 immunocytokine (EMD 273066) results in an enhanced antitumor effect against murine colon adenocarcinoma

PURPOSE

Radiofrequency ablation (RFA) is a common treatment modality for surgically unresectable tumors. However, there is a high rate of both local and systemic recurrence.

EXPERIMENTAL DESIGN

In this preclinical study, we sought to enhance the antitumor effect of RFA by combining it with huKS-IL2 immunocytokine [tumor-specific monoclonal antibody fused to interleukin-2 (IL2)] in mice bearing CT26-KS colon adenocarcinoma. Mice were treated with RFA, huKS-IL2 via intratumoral injection, or combination therapy.

RESULTS

Treatment of mice bearing s.c. tumors with RFA and huKS-IL2 resulted in significantly greater tumor growth suppression and enhanced survival compared with mice treated with RFA or huKS-IL2 alone. When subtherapeutic regimens of RFA or huKS-IL2 were used, tumors progressed in all treated mice. In contrast, the combination of RFA and immunocytokine resulted in complete tumor resolution in 50% of mice. Treatment of a tumor with RFA and intratumoral huKS-IL2 also showed antitumor effects against a distant untreated tumor. Tumor-free mice after treatment with RFA and huKS-IL2 showed immunologic memory based on their ability to reject subsequent challenges of CT26-KS and the more aggressive parental CT26 tumors. Flow cytometry analysis of tumor-reactive T cells from mice with complete tumor resolution showed that treatment with RFA and huKS-IL2 resulted in a greater proportion of cytokine-producing CD4 T cells and CD8 T cells compared with mice treated with RFA or huKS-IL2 alone.

CONCLUSIONS

These results show that the addition of huKS-IL2 to RFA significantly enhances the antitumor response in this murine model, resulting in complete tumor resolution and induction of immunologic memory.

Tolerance of radiofrequency ablation by patients of hepatocellular carcinoma

BACKGROUND

Radiofrequency ablation (RFA) is currently an effective method for ablation of hepatocellular carcinoma (HCC). Early reports have indicated that RFA is safe and virtually free from major complications. Unlike partial hepatectomy for HCC on patients with cirrhosis, there are no data on the safety limit of RFA. However, information is vital for selection of appropriate patients for the procedure. In this study, we analyzed results from use of RFA on HCC patients and determined the lower limit of liver function with which HCC patients can tolerate RFA.

METHOD

Preoperative variables of 310 patients who underwent RFA for HCC were analyzed to identify the risk factors in RFA intolerance in terms of morbidity associated with stress-induced complications.

RESULTS

Thirty-nine (12.6%) patients developed intolerance of RFA. Postoperative morbidity was mainly because of intractable ascites (n = 13), hyperbilirubinemia (n = 10), massive pleural effusion (n = 7), and other complications (n = 14). Multivariate analysis revealed that serum albumin level (P = 0.001), serum bilirubin level (P = 0.000), tumor number (P = 0.002), and RFA duration (P = 0.017) all played a role in this issue.

CONCLUSIONS

Simple data such as serum bilirubin, serum albumin level, and tumor number can be used to predict HCC patients' tolerance of RFA. Avoidance of excessive RFA time and careful monitoring of patients at risk are important means of reducing the postoperative morbidity rate.

Research progress of radiofrequency ablation in treating primary hepatocellular carcinoma

Radiofrequency ablation (RFA) is currently an effective treatment for primary hepatocellular carcinoma (PHC). Judicious case selection and appropriate approaches in combination with other anti-tumor therapies are essential to achieve a favorable outcome. RFA is as effective as open surgery in treating PHC smaller than 3 cm in diameter with less complications and mortalities, shorter admission period and fewer cost. In the future, RFA will play a more and more important role as part of multimodality therapy in treating PHC.

Laparoscopic radiofrequency ablation for hepatocellular carcinoma

Radiofrequency ablation (RFA) is one of the best curative treatments for hepatocellular carcinoma in selected patients, and this procedure can be applied either percutaneously or laparoscopically. Although the percutaneous approach is less invasive and is considered the first choice, RFA with laparoscopic guidance is highly recommended for patients with a relative contraindication for percutaneous RFA, such as lesions adjacent to the gastrointestinal tract, gallbladder, bile duct and heart. Recent advances in laparoscopic ultrasound have widened the indication for laparoscopic ablation. In the present paper, we review the indications, advantages, prognosis and safety of laparoscopic RFA for hepatocellular carcinoma.

Comparative study of resection and radiofrequency ablation in the treatment of solitary colorectal liver metastases

BACKGROUND

We compared outcomes in patients with solitary colorectal liver metastases treated by either hepatic resection (HR) or radiofrequency ablation (RFA).

METHODS

A retrospective analysis from a prospective database was performed on 67 consecutive patients with solitary colorectal liver metastases treated by either HR or RFA.

RESULTS

Forty-two patients underwent HR and 25 patients underwent RFA. The 5-year overall and local recurrence-free survival rates after HR (50.1% and 89.7%, respectively) were higher than after RFA (25.5% and 69.7%, respectively) (P = .0263 and .028, respectively). In small tumors less than 3 cm (n = 38), the 5-year survival rates between HR and RFA were similar, including overall (56.1% vs 55.4%, P = .451) and local recurrence-free (95.7% vs 85.6%, P = .304) survival rates. On multivariate analysis, tumor size, metastases treatment, and primary node status were significant prognostic factors.

CONCLUSIONS

HR had better outcomes than RFA for recurrence and survival after treatment of solitary colorectal liver metastases. However, in tumors smaller than 3 cm, RFA can be recommended as an alternative treatment to patients who are not candidates for surgery because the liver metastases is poorly located anatomically, the functional hepatic reserve after a resection would be insufficient, the patient's comorbidity inhibits a major surgery, or extrahepatic metastases are present.

Seeding after radiofrequency ablation of hepatocellular carcinoma in patients with cirrhosis: a prospective study

BACKGROUND

Neoplastic seeding of hepatocellular carcinoma may arise after radiofrequency ablation.

AIMS

In order to clarify the real risk of seeding, we observed a prospective cohort of patients undergoing radiofrequency ablation.

METHODS

Ninety-three (22.9%) out of 406 consecutive patients with hepatocellular carcinoma superimposed to cirrhosis diagnosed at our Liver Unit (2000-2005) were selected for radiofrequency ablation according to the Barcelona 2000 EASL guidelines. Seventy-one patients were treated by a percutaneous approach and 22 at laparotomy. After radiofrequency ablation ultrasound scan was repeated every 3 months and spiral-computed tomography every 6 months.

RESULTS

Overall 145 sessions were performed in 93 patients: 113 (77.9%) by a percutaneous approach and 32 (22.1%) at laparotomy. The median follow-up was 23 months (range 1-60). Only 1 of the 71 patients (1.4%; 95% C.I. 0.25-7.56) treated percutaneously and none of the 22 (0%; 95% C.I. 0-14.8) treated at laparotomy showed neoplastic seeding.

CONCLUSION

In our experience the risk of seeding of hepatocellular carcinoma after radiofrequency ablation was small (1.1% per patient, 95% C.I. 0.19-5.84; 0.7% per procedure, 95% C.I. 0.12-3.80). A stringent selection of patients for radiofrequency ablation and retraction of the needle with a hot tip may have been instrumental in obtaining this low frequency.

Local recurrence after laparoscopic radiofrequency ablation of liver tumors: an analysis of 1032 tumors

BACKGROUND

The best measure of the technical success of radiofrequency ablation (RFA) is local recurrence (LR). The aim of this prospective study is to identify factors that predict LR.

METHODS

Three hundred thirty-five patients with 1032 unresectable liver tumors underwent laparoscopic RFA between November 1999 and August 2005. All lesions were assessed prospectively regarding tumor type, size, liver segment, blood vessel proximity, and central or peripheral location in the operating room and size of ablation zone at 1-week computed tomographic (CT) scans. Lesions that recurred in follow-up CT scans were identified prospectively. LR was categorized as contiguous or adjacent. Univariate Kaplan-Meier and Cox proportional hazard models were used for statistical analysis.

RESULTS

LR was identified 21.7% of tumors on CT scans with a mean follow-up of 17 months (median, 12 months; range, 3-68 months). This was contiguous in 70% and adjacent in 30%. LR rate per tumor was highest for colorectal metastasis (34%), followed by noncolorectal, nonneuroendocrine metastasis (22%), hepatocellular carcinoma (18%), and neuroendocrine metastasis (6%). By univariate analysis, tumor type and size, ablation margin, liver segmental location, blood vessel proximity, and type of ablation (first time vs. repeat) were found to affect LR. The Cox proportional hazard model identified tumor type, tumor size, ablation margin, and blood vessel proximity to be independent predictors of LR.

CONCLUSION

LR after RFA is predicted by certain tumor characteristics and technical factors. This information can be used intraoperatively to identify those tumors at a higher risk for failure.

Sequential activation of a segmented ground pad reduces skin heating during radiofrequency tumor ablation: optimization via computational models

Radiofrequency (RF) ablation has become an accepted treatment modality for unresectable tumors. The need for larger ablation zones has resulted in increased RF generator power. Skin burns due to ground pad heating are increasingly limiting further increases in generator power, and thus, ablation zone size. We investigated a method for reducing ground pad heating in which a commercial ground pad is segmented into multiple ground electrodes, with sequential activation of ground electrode subsets. We created finite-element method computer models of a commercial ground pad (14 x 23 cm) and compared normal operation of a standard pad to sequential activation of a segmented pad (two to five separate ground electrode segments). A constant current of 1 A was applied for 12 min in all simulations. Time periods during sequential activation simulations were adjusted to keep the leading edge temperatures at each ground electrode equal. The maximum temperature using standard activation of the commercial pad was 41.7 degrees C. For sequential activation of a segmented pad, the maximum temperature ranged from 39.3 degrees C (five segments) to 40.9 degrees C (two segments). Sequential activation of a segmented ground pad resulted in lower tissue temperatures. This method may reduce the incidence of ground pad burns and enable the use of higher power generators during RF tumor ablation.

Sequential activation of multiple grounding pads reduces skin heating during radiofrequency tumor ablation

PURPOSE

Radiofrequency (RF) tumor ablation has become an accepted treatment modality for tumors not amenable to surgery. Skin burns due to ground pad heating may become a limiting factor for further increase in ablation zone dimensions and generator power. We investigated a method were groups of ground pads are sequentially activated to reduce skin heating.

METHODS

We compared conventional operation (i.e. simultaneous connection of all pads) to sequentially switched activation of the pads where different pad combinations are active for periods of approximately 0.3 - 8 s. The timing during sequential activation was adjusted to keep the leading edge temperature equal between the pads. We created Finite Element Method computer models of three pads (5 x 5 cm, 1 cm apart) placed in line with the RF electrode on a human thigh to determine differences in tissue heating during simultaneous and sequential ground pad activation. We performed experiments with three ground pads (5 x 10 cm, 4 cm apart) placed on a tissue phantom (1.5 A, 12 min) and measured pad surface and leading edge temperatures.

RESULTS

Temperature rise below the leading edge for proximal, middle and distal ground pad in relation to active electrode location was 5.9 degrees C +/- 0.1 degrees C, 0.8 degrees C +/- 0.1 degrees C and 0.3 degrees C +/- 0.1 degrees C for conventional operation, and 3.3 degrees C +/- 0.1 degrees C, 3.4 degrees C +/- 0.2 degrees C and 3.4 degrees C +/- 0.2 degrees C for sequentially activated operation in the experiments (p < 0.001).

CONCLUSION

Sequential activation of multiple ground pads resulted in reduced maximum tissue temperature. This may reduce the incidence of ground pad burns and may allow higher power RF generators.