Sonographically guided microwave coagulation treatment of liver cancer: an experimental and clinical study

Laparoscopic ultrasound-guided microwave ablation of hepatocellular carcinoma in a dog

OBJECTIVE

The aim of the study was to describe laparoscopic ultrasound (LUS) to guide microwave ablation (MWA) of hepatocellular carcinoma (HCC) in a dog.

ANIMALS

A 13-year-old female spayed Husky.

STUDY DESIGN

Case report.

METHODS

The dog was referred for laparoscopic MWA of a caudate lobe HCC measuring 2.7 cm × 1.9 cm× 2.3 cm. Laparoscopic ultrasound was used to guide percutaneous placement of a MWA probe within the caudate lobe mass. LUS was used to determine the tumor margins for placement of the probe within the medial and lateral aspects as well as the center of the mass. Additionally, LUS allowed visualization of vessels within the tumor so they could be avoided during probe placement.

RESULTS

Safe ablation was accomplished, and the dog recovered uneventfully with no complications. Follow-up computed tomography (CT) 3- and 12-months postoperatively revealed complete ablation of the caudate lobe mass. However, progressive increase in size of the right medial lobe mass occurred. Right medial liver lobectomy was performed 13 months after MWA, with a histopathologic diagnosis of HCC. The dog was euthanized 777 days post MWA and 1445 days post initial left lateral lobectomy for HCC.

CONCLUSION

Laparoscopic ultrasound was useful in guiding complete and safe MWA of an HCC in this dog. Laparoscopic ultrasound should be considered when performing laparoscopic MWA of liver lesions in dogs.

Percutaneous ablative therapies for hepatocellular carcinoma in the caudate lobe of the liver: efficacy and outcome

OBJECTIVE

To assess the efficacy and outcomes of percutaneous ablative therapies for hepatocellular carcinoma (HCC) in the caudate lobe.

METHODS

Patients within Milan criteria, who underwent thermal ablation (RFA/MWA) for HCC were analyzed. Based on the inclusion-criteria, patients were categorized in two groups. Group-1 (caudate-lobe HCC) and Group-2 (non-caudate-lobe HCC). Both the groups were analyzed for technical success (TS), local tumor progression (LTP), disease-free survival (DFS), and overall survival (OS) were compared between both the groups. Predictive factors for LTP, DFS, or OS in the study cohort were analyzed using appropriate statistical analyses.

RESULTS

Twenty-one patients qualified to be in Group-1 while 130 patients fulfilled the criteria for Group-2. TS of 90.5 and 97.7% was seen after the first session of ablation for Group-1 and group-2 respectively, while a TS of 95.2% (Group-1) and 100% (Group-2) was achieved after second session. The right-intercostal-approach was used in 66.7% (n = 14) and the anterior-epigastric-approach was used in 33.3% (n = 7) of patients having caudate-lobe HCC. Procedure-related complications in both the groups were comparable. Although, statistically insignificant, LTP in the Group-1 (19.5%, n = 4) was twice that of non-caudate lobe HCC (8.5%, n = 11). The cumulative DFS rate was better in Group-2 while OS in both groups were comparable. Multivariate analysis showed: tumor size and ablative margin of 5 mm being independent predictors of LTP after percutaneous-ablation of caudate-lobe HCC.

CONCLUSION

Ablative therapies for HCC in caudate lobe is feasible and safe with comparable LTP and OS to non-caudate lobe HCC. Tumor size >2 cm and lack of 5 mm ablative margin are independent predictors of LTP.

ADVANCES IN KNOWLEDGE

1. Percutaneous ablation of caudate lobe HCC is feasible using anterior epigastric approach or right intercostal approach. 2. These approaches may allow a safe and effective ablation of caudate lobe HCC with results comparable to non-caudate HCC ablation.

Single-center analysis of percutaneous ablation in the treatment of hepatocellular carcinoma: long-term outcomes of a 7-year experience

PURPOSE

The objective of this study is to examine the safety and efficacy of ablative therapy for hepatocellular carcinoma (HCC).

METHODS

A retrospective review of 419 consecutive patients diagnosed with HCC, treated with percutaneous ablation at a tertiary academic medical center from June 2015 to June 2022, was conducted. Data evaluated included demographics, disease and tumor burden scores, and functional status. Procedural outcomes included procedural course, complication rates, biochemical and radiologic response, survival, and functional status.

RESULTS

A total of 419 patients, including 313 males (74.7%) and 106 females (25.3%) with a mean age of 63.8 ± 6.64 years, made up the study cohort. 120 patients (28.6%) presented with solitary lesions and 299 patients (71.4%) had multifocal involvement, with a mean tumor size of 2.3 ± 0.92 cm. A majority of the interventions performed were microwave ablations (n = 413, 98.3%), with 6 radiofrequency ablations (1.4%). Treatment response was radiographically assessed up to 6 months post-ablation and graded as complete response (96.2%), partial response (2.6%), stable disease (0%), and progressive disease (1.2%). 97 (23.2%) of the treated patients went on to receive liver transplant. The average progression-free survival in the study population was 24 months with a survival of 85.9% (n = 360), 67.8% (n = 284), and 63.2% (n = 265) at 1 year, 3 years, and 5 years respectively. Functional outcomes, as defined by ECOG scores, were maintained or improved in 383 patients (91.4%) and 349 patients (83.3%) at 6 months and 12 months respectively.

CONCLUSIONS

This large institutional experience demonstrated safety and efficacy of ablation therapies for treatment of HCC with promising tumor response rates and enduring clinical outcomes including prolonged survival and preserved functional status.

Liver cancer treatment with integration of laser emission and microwave irradiation with the aid of gold nanoparticles

This paper studies the effectiveness of the integration of microwave field irradiation and laser emission in liver cancer therapy with the aid of gold nanorods, in order to find out the influences of these combinational methods in tumor necrosis. Hepatocellular carcinoma is a kind of liver cancer that usually has a complicated structure, including both of superficial and deep sections. In current research, in deep regions of cancerous tissue, microwave antenna is utilized and in superficial regions, laser beams are irradiated. A Pulsed laser with heating time of 50 s and cooling time of 20 s is utilized for hyperthermia treatment. It should be mentioned that gold nanorods are injected into the tumorous region to enhance the treatment process and reduce the patient’s exposure time. Simulation results showed that at the first step, without any injection of gold nanoparticles, 0.17% of the tumor’s volume encountered necrosis, while at the next stage, after injection of gold nanorods, the necrosis rate increased to 35%, which demonstrates the efficiency of gold nanorods injection on the tumor treatments. Furthermore, the combinational applying of both microwave antenna and laser illumination can eradiate the tumor tissue completely.

Percutaneous microwave ablation applications for liver tumors: recommendations for COVID-19 patients

Microwave ablation (MWA) is an alternative locoregional therapy to surgical resection of solid tumors in the treatment of malignancies, and is widely used for hepatic tumors. It has a slightly higher overall survival (OS) rate compared to external beam radiation therapy (EBRT), and proton beam therapy (PBT), and better long-term recurrence-free OS rate compared to radiofrequency ablation (RFA). In this paper, current commercial devices, most recent noncommercial designs, and the principles behind them alongside the recently reported developments and issues of MWA are reviewed. The paper also provides microscopic insights on effects of microwave irradiation in the body. Our review shows that MWA is a safe and effective, minimally invasive method with high ablation completion rates. However, for large tumors, the completion rates slightly decrease, and recurrences increase. Thus, for large tumors we suggest using a cooled shaft antenna or multiple antenna placements. Comparisons of the two common ablation frequencies 915 MHz and 2.45 GHz have shown inconsistent results due to non-identical conditions. This review suggests that 915 MHz devices are more effective for ablating large tumors and the theory behind MWA effects corroborates this proposition. However, for small tumors or tumors adjacent to vital organs, 2.45 GHz is suggested due to its more localized ablation zone. Among the antenna designs, the double-slot antenna with a metallic choke seems to be more effective by localizing the radiation around the tip of the antenna, while also preventing backward radiation towards the skin. The review also pertains to the use of MWA in COVID-19 patients and risk factors associated with the disease. MWA should be considered for COVID-19 patients with hepatic tumors as a fast treatment with a short recovery time. As liver injury is also a risk due to COVID-19, it is recommended to apply liver function tests to monitor abnormal levels in alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, and other liver function indicators.

Histological Correlation for Radiofrequency and Microwave Ablation in the Local Control of Hepatocellular Carcinoma (HCC) before Liver Transplantation: A Comprehensive Review

Simple Summary

Liver cancer is a growing problem around the world. Drugs for liver cancer have limited effect, there are not enough donors for liver transplants and many patients are not candidates for surgery to remove the tumor. In many of these cases, hyperthermia can destroy the tumor in situ with minimally invasive methods such as radiofrequency or microwave ablation. In this paper we review the literature evaluating success rates for complete ablation as judged by actual examination of treated tumors that were removed when patients received a liver transplant. While notable successes can be achieved with ablation, the published studies indicate both that complete treatment is not as common as thought and that imaging methods such as computed tomography and magnetic resonance scans do not completely identify residual cancer. There is therefore an important opportunity for improvement in the treatment of this disease.

Abstract

Radiofrequency ablation (RFA) and microwave ablation (MWA) are the most widely studied and applied ablation techniques for treating primary and secondary liver tumors. These techniques are considered curative for small hepatic tumors, with post-ablation outcomes most commonly assessed by an imaging follow up. However, there is increasing evidence of a discrepancy between radiological and pathological findings when ablated lesions are evaluated following liver resection or liver transplantation. A comprehensive review of the available literature reporting the complete pathological response (cPR) following RFA and MWA was performed to estimate the success rate and identify the factors associated with treatment failure. Following RFA, cPR is reported in 26–96% of tumors compared to 57–95% with MWA. Larger tumor size and vessels larger than 3 mm adjacent to the treated tumor are the most important factors identified by previous studies associated with viable residual tumors after RFA. Correlating post-ablation radiological studies with pathological findings shows that computed tomography (CT) and magnetic resonance imaging (MRI) have low sensitivity but high specificity for detecting residual viable or recurrent hepatocellular carcinoma (HCC) tumors. There are promising recent reports combining multiprobe ablation techniques with three-dimensional treatment planning software and stereotactic-aiming instrumentation to achieve more than 90% cPR in both small and large HCC tumors. In conclusion, the reported success for achieving cPR in HCC following RFA and MWA is highly variable in different studies and decreases with increasing lesion size and unfavorable tumor characteristics. Very few studies have reported a high rate of cPR. As these studies are single-center and retrospective, they need to be further validated and reproduced in other clinical settings.

Prognosis of microwave ablation for hepatocellular carcinoma: does age make a difference?

Objective: Hepatocellular carcinoma (HCC) is a notable threat to the longevity of elderly people. However, there is no trial to study the prognosis of these elderly patients after microwave ablation (MWA) treatment. This study investigated whether elderly patients with HCC benefit from MWA similar to younger patients.Materials and methods: Patients who underwent ultrasound-guided percutaneous MWA were included and divided into four age groups and the prognosis was compared. The senior group (Group S, ≥75 years) was then compared with the younger group (Group Y, <75 years) after a 1:1 propensity score matching was applied. The prognostic outcomes were evaluated and Cox analysis was performed to determine the factors associated with survival.Results: The four age groups showed a statistically different distribution in terms of sex, size of liver nodules, and the Charlson comorbidity index. Although Group S had a higher Charlson comorbidity index, no significant differences were found between Group S and Group Y in the rates of complete ablation and major complications as well as overall survival and progression-free survival after matching. Cox analysis demonstrated that the size of tumors and Child Pugh grade rather than age or Charlson comorbidity index were significant prognostic factors for overall survival.Conclusion: The elderly patients with HCC, even though associated with more comorbidities, may achieve acceptable prognostic outcomes following MWA, which are not worse than their younger counterparts.

Risk factors of haemoglobinuria after microwave ablation of liver tumours

AIM

To explore the risk factors predicting haemoglobinuria after ultrasound-guided percutaneous microwave ablation (MWA) of liver tumours and discuss the treatments and outcomes.

MATERIALS AND METHODS

The present study comprised 2,829 patients admitted for liver tumours treated with MWA from Jan 2011 to April 2017. Ethics committee approval was waived and informed consent for treatment procedures were obtained from the patients. Haemoglobinuria after MWA was found in 149 patients. The influence of 19 risk factors was assessed. Binary logistic regression and receiver operating characteristic (ROC) curve analysis were used for statistical analysis. The treatments and outcomes of patients with haemoglobinuria were summarised.

RESULTS

By univariate analysis, histopathology, liver cirrhosis, MWA volume, MWA energy, and MWA duration were significant risk factors. By multivariate analysis and ROC curve, MWA energy, duration, and volume were identified as predictors of haemoglobinuria after MWA. Drug treatments including kidney protection, adequate hydration, alkalisation of urine, and diuresis were administrated to the patients with haemoglobinuria. One patient progressed to acute kidney injury (AKI) while others had good clinical outcomes.

CONCLUSION

Haemoglobinuria is a controllable side effect after MWA of liver tumours, which is related to high MWA energy, long MWA duration, and great MWA volume. It usually caused few side effects on renal function with correct treatment.

Comparison of microwave ablation and hepatic resection for hepatocellular carcinoma: a meta-analysis

BACKGROUND AND AIMS

Hepatic resection (HRN) and microwave ablation (MWA) have significant advantages in treating hepatocellular carcinoma; however, it remains unclear which way produces better outcomes. This meta-analysis of cohort studies compared the treatments in terms of effectiveness and safety.

METHODS

Six electronic databases (PubMed, Medline, EMBASE, Web of Science, EBSCO, and The Cochrane Library) were retrieved for studies comparing MWA and HRN. The meta-analysis was conducted based on statement of preferred reporting items for systematic reviews and meta-analyses.

RESULTS

Nine studies met the inclusion criteria, with a total of 1,480 patients. The overall meta-analysis demonstrated no significant difference in overall survival between the MWA group and the HRN group (HR =0.98, 95% CI =0.76-1.26, P=0.878). There was no difference in disease-free survival between the MWA group and the HRN group (HR =1.16, 95% CI =0.79-1.71, P=0.442). Meanwhile, the meta-analysis demonstrated that MWA was associated with shorter operation time (standardized mean difference [SMD] =-1.37, 95% CI =-1.92 to -0.81, P=0.000), less amount of blood loss in operation (SWD =-1.19, 95% CI =-1.76 to -0.61, P=0.000), and less complications (OR =0.22, 95% CI =0.12-0.40, P=0.000) than HRN.

CONCLUSION

In conclusion, our meta-analysis suggests that MWA may be superior to HRN as it is as effective as HRN in terms of overall survival, disease-free survival, tumor recurrence, and is associated with shorter operation time, less amount of blood loss, and fewer complications.

Percutaneous thermal ablation for primary hepatocellular carcinoma: A systematic review and meta-analysis

BACKGROUND AND AIM

Percutaneous thermal ablation using radiofrequency ablation (RFA) and microwave ablation (MWA) are both widely available curative treatments for hepatocellular carcinoma. Despite significant advances, it remains unclear which modality results in better outcomes. This meta-analysis of randomized controlled trials (RCT) and observational studies was undertaken to compare the techniques in terms of effectiveness and safety.

METHODS

Electronic reference databases (Medline, EMBASE and Cochrane Central) were searched between January 1980 and May 2014 for human studies comparing RFA and MWA. The primary outcome was the risk of local tumor progression (LTP). Secondary outcomes were complete ablation (CA), overall survival, and major adverse events (AE). The ORs were combined across studies using the random-effects model.

RESULTS

Ten studies (two prospective and eight retrospective) were included, and the overall LTP rate was 13.6% (176/1298). There was no difference in LTP rates between RFA and MWA [OR (95% CI): 1.01(0.67-1.50), P = 0.9]. The CA rate, 1- and 3-year overall survival and major AE were similar between the two modalities (P > 0.05 for all). In subgroup analysis, there was no difference in LTP rates according to study quality, but LTP rates were lower with MWA for treatment of larger tumors [1.88(1.10-3.23), P = 0.02]. There was no significant publication bias or inter-study heterogeneity (I(2) < 50% and P > 0.1) observed in any of the measured outcomes.

CONCLUSION

Overall, both RFA and MWA are equally effective and safe, but MWA may be more effective compared to RFA in preventing LTP when treating larger tumors. Well-designed, larger, multicentre RCTs are required to confirm these findings.

Trimodal Therapy: Combining Hyperthermia with Repurposed Bexarotene and Ultrasound for Treating Liver Cancer

Repurposing of existing cancer drugs to overcome their physical limitations, such as insolubility, represents an attractive strategy to achieve enhanced therapeutic efficacy and broaden the range of clinical applications. Such an approach also promises to offer substantial cost savings in drug development efforts. Here we repurposed FDA-approved topical agent bexarotene (Targretin), currently in limited use for cutaneous manifestations of T-cell lymphomas, and re-engineer it for use in solid tumor applications by forming self-assembling nanobubbles. Physico-chemical characterization studies of the novel prodrug nanobubbles demonstrated their stability, enhanced target cell internalization capability, and highly controlled release profile in response to application of focused ultrasound energy. Using an in vitro model of hepatocellular carcinoma and an in vivo large animal model of liver ablation, we demonstrate the effectiveness of bexarotene prodrug nanobubbles when used in conjunction with catheter-based ultrasound, thereby highlighting the therapeutic promise of this trimodal approach.

Effects of combining transarterial chemoembolization with percutaneous microwave coagulation therapy for hepatocellular carcinoma abutting the diaphragm

OBJECTIVE

This study aims to explore the clinical effectiveness of a combination therapy of transarterial chemoembolization (TACE) and percutaneous microwave coagulation therapy (PMCT) in treating hepatocellular carcinoma (HCC) abutting the diaphragm.

MATERIAL AND METHODS

Six cases with HCC were treated with TACE followed by PMCT one month later with the aid of artificial pneumothorax.

RESULTS

CT/MRI revealed complete necrosis in the tumor lesions and the treated tumor margins (≥ 5 mm). Serum alpha-fetoprotein (AFP) levels markedly declined in patients who originally had higher serum AFP levels. Postoperative complications such as fever, mild hepatic dysfunction and pleural effusion were alleviated within a short period of time. All patients were closely monitored through follow-up; all patients survived, except for one patient who received a liver transplantation.

CONCLUSIONS

As lesions are either invisible or poorly visible in sonography, determining an effective treatment for HCC abutting the diaphragm remains a particular challenge. TACE and PMCT combined therapy with the aid of artificial pneumothorax proved to be an available treatment option.

Safety assessment and therapeutic efficacy of percutaneous microwave ablation therapy combined with percutaneous ethanol injection for hepatocellular carcinoma adjacent to the gallbladder

OBJECTIVE

This study sought to evaluate the safety and efficacy of ultrasound-guided (US-guided) percutaneous microwave (MW) ablation combined with percutaneous ethanol injection (PEI) to treat liver tumours adjacent to the gallbladder.

MATERIALS AND METHODS

A total of 136 patients with hepatocellular carcinoma (HCC) adjacent to the gallbladder, who underwent ultra-sonographically-guided percutaneous MW ablation, which was combined with PEI in 132 patients, were retrospectively assessed. The patient population characteristics, tumour features, local tumour progression and treatment were compared and analysed. The safety and efficacy of the therapy were assessed by clinical data and imaging in follow-up examinations.

RESULTS

All patients were completely treated with two sessions; 120 patients underwent one session, 16 patients underwent two sessions. The primary technique was effective in 95.6% of the cases, according to the computed tomography (CT) or magnetic resonance imaging (MRI) in the one-month follow-up (132 of 138 sessions). PEI and other therapies were performed in the patients who had been incompletely treated (all six patients underwent PEI, and some underwent other therapies, including one transcatheter arterial chemoembolisation (TACE), one liver transplantation and two liver resections). There was a median follow-up period of 30.1 months and a range of 4 to 68 months. None of the patients had major complications. There were no treatment-related deaths. Twenty-six patients died of primary disease progression that was not directly attributable to MW ablation (19.1%, 26/136). Local tumour progression was noted in five patients (3.7%, 5/136), who had completely ablated tumours at follow-up. The patients with locally progressing tumours underwent additional therapy (three patients underwent PEI, one patient TACE, and one liver resection).

CONCLUSION

Ultrasound-guided percutaneous MW ablation, in combination with percutaneous ethanol injection and thermal monitoring, is a safe and effective treatment for HCC adjacent to the gallbladder.

Ablative technologies for hepatocellular, cholangiocarcinoma, and metastatic colorectal cancer of the liver

A wide array of ablation technologies, in addition to the progressive sophistication of imaging technologies and percutaneous, laparoscopic, and open surgical techniques, have allowed us to expand treatment options for patients with liver tumors. In this article, technical considerations of chemical and thermal ablations and their application in hepatic oncology are reviewed.

Hepatic toxicology following single and multiple exposure of engineered nanomaterials utilising a novel primary human 3D liver microtissue model

Background

The liver has a crucial role in metabolic homeostasis as well as being the principal detoxification centre of the body, removing xenobiotics and waste products which could potentially include some nanomaterials (NM). With the ever increasing public and occupational exposure associated with accumulative production of nanomaterials, there is an urgent need to consider the possibility of detrimental health consequences of engineered NM exposure. It has been shown that exposure via inhalation, intratracheal instillation or ingestion can result in NM translocation to the liver. Traditional in vitro or ex vivo hepatic nanotoxicology models are often limiting and/or troublesome (i.e. reduced metabolism enzymes, lacking important cell populations, unstable with very high variability, etc.).

Methods

In order to rectify these issues and for the very first time we have utilised a 3D human liver microtissue model to investigate the toxicological effects associated with a single or multiple exposure of a panel of engineered NMs (Ag, ZnO, MWCNT and a positively charged TiO₂).

Results

Here we demonstrate that the repeated exposure of the NMs is more damaging to the liver tissue as in comparison to a single exposure with the adverse effects more significant following treatment with the Ag and ZnO as compared with the TiO₂ and MWCNT NMs (in terms of cytotoxicity, cytokine secretion, lipid peroxidation and genotoxicity).

Conclusions

Overall, this study demonstrates that the human microtissue model utilised herein is an excellent candidate for replacement of traditional in vitro single cell hepatic models and further progression of liver nanotoxicology.

Toxicological effect of engineered nanomaterials on the liver

The liver has a crucial role in metabolic homeostasis, as it is responsible for the storage, synthesis, metabolism and redistribution of carbohydrates, fats and vitamins, and numerous essential proteins. It is also the principal detoxification centre of the body, removing xenobiotics and waste products by metabolism or biliary excretion. An increasing number of studies have shown that some nanomaterials (NMs) are capable of distributing from the site of exposure (e.g. lungs, gut) to a number of secondary organs, including the liver. As a secondary exposure site the liver has been shown to preferentially accumulate NMs (>90% of translocated NMs compared with other organs), and alongside the kidneys may be responsible for the clearance of NMs from the blood. Research into the toxicity posed by NMs to the liver is expanding due to the realization that NMs accumulate in this organ following exposure via a variety of routes (e.g. ingestion, injection and inhalation). Thus it is critical to consider what advances have been made in the investigation of NM hepatotoxicity, as well as appraising the quality of the information available and gaps in the knowledge that still exist. The overall aim of this review is to outline what data are available in the literature for the toxicity elicited by NMs to the liver in order to establish a weight of evidence approach (for risk assessors) to inform on the potential hazards posed by NMs to the liver.

Microwave ablation of benign thyroid nodules

ABSTRACT: 

Microwave ablation (MWA) has become increasingly popular as a minimally invasive treatment for benign and malignant tumors of the liver, lung and kidney. Recently, two studies have attempted to apply the technique to debulk benign thyroid nodules and gained positive results. MWA of benign nodules demonstrated significant volume reductions, while solving nodule-related clinical problems. This article reviews the basic physics, therapeutic indications, patient preparation, devices, procedures, clinical results and complications of thyroid MWA.

Clinical outcome of ultrasound-guided percutaneous microwave ablation on colorectal liver metastases

The present study aimed to assess the feasibility, safety and efficiency of ultrasound-guided percutaneous microwave ablation (MWA) on liver metastases from colon or rectal cancer. Patients who received MWA therapy for liver metastases from colon or rectal cancer between June 2009 and May 2012 were enrolled in the study. Follow-up data was collected from the patients in order to statistically analyze the adverse effects, concurrent disease and survival status. Of the total 115 patients, 62 presented with colon cancer and 53 with rectal cancer. A total of 78 patients were male and 37 were female. The patient age ranged between 30 and 86 years [mean ± standard deviation (SD), 59.46±11.79 years]. The number of overall ablation lesions was 165, and the diameter of the lesions ranged between 1.3 and 5.0 cm (mean ± SD, 3.10±1.05 cm). Subsequent to treatment, the mean (± SD) hospitalization time was 4.69±2.08 days (range, 2-10 days). The median follow-up time was 28 months (range, 12-48 months) and 5 patients were lost to follow-up. The pain grade was recorded between the 4th and 6th degree following treatment in 23 patients. The body temperatures of 35 patients reached >38°C, with the longest time at this temperature recorded as 5 days. Following treatment, 5 patients presented with pleural effusion and required thoracocentesis and drainage. Following ablation, the rate of local progression was 11.82%. The recurrence rates were 27.8, 48.4 and 59.3% and the cumulative survival rates were 98.1, 87.1 and 78.7% in years 1, 2 and 3 post-treatment, respectively. A total of 14 patients succumbed. No significant differences were observed in the liver metastases of colorectal cancer with regard to gender, age, number of lesions, lesion size and pathological differentiation (P>0.05). Also, no significant difference was observed in the recurrence or cumulative survival rates for years 1, 2 and 3 years post-treatment (P>0.05). In conclusion, ultrasound-guided percutaneous MWA is a safe and competent way to treat inoperable colorectal liver metastases.

Comparison of ablation zones among different tissues using 2450-MHz cooled-shaft microwave antenna: results in ex vivo porcine models

Background

For complete tumor ablation in different tissues, it is necessary to investigate the exact coagulation zone of microwave ablation in different tissues. The aim of this study was to compare the extent of microwave ablation zone in muscle, liver and adipose tissue in ex vivo porcine models and assess the shape of microwave coagulation zone among these tissues.

Materials and Methods

Microwave ablations were performed in ex vivo porcine muscle, liver and adipose tissue using 2450-MHz cooled-shaft microwave antenna. The content of water, fat and protein in these three tissues was determined. Two power increments (40 and 80 W) and five time increments (1, 3, 5, 7, and 10 minutes) were used in this study. Diameters and shapes of the ablation zones were assessed on gross specimens.

Results

The average percentages of water, fat and protein in these three tissues were significantly different (P < 0.001), respectively. The long-axis and short-axis diameters among these three tissues at each time-power combination were not significantly different (P > 0.05). The coagulation zones were all elliptical in muscle, liver and adipose tissue. When microwave ablation was performed in the tissue containing both muscle and adipose tissue, the coagulation zone was also elliptical. Regardless of the output power, the ellipticity index (EI) value of 1 minute treatment duration was higher than that of 10 minutes treatment duration (P < 0.05). Furthermore, the EI value did not decrease significantly when the treatment duration was more than 5 minutes (P > 0.05).

Conclusion

The extent of microwave ablation zones was not significantly different among completely different tissues. Microwave ablations with ≥ 5 minutes time duration can induce coagulation zones with clinical desirable shape. Future clinical studies are still required to determine the role of microwave ablation in different tissues.

A dual-slot microwave antenna for more spherical ablation zones: ex vivo and in vivo validation

PURPOSE

To compare the performance of a microwave antenna design with two annular slots to that of a monopole antenna design in creating a more spherical ablation zone.

MATERIALS AND METHODS

Animal care and use committee approval was obtained before in vivo experiments were performed. Microwave ablation zones were created by using dual-slot and monopole control antennas for 2, 5, and 10 minutes at 50 and 100 W in ex vivo bovine livers. Dual-slot and monopole antennas were then used to create ablation zones at 100 W for 5 minutes in in vivo porcine livers, which also underwent intraprocedural imaging. Ablation diameter, length, and aspect ratio (diameter ÷ length) were measured at gross pathologic examination and compared at each combination of power and time by using the paired Student t test. A P value less than .05 was considered to indicate a significant difference. Aspect ratios closer to 1 reflected a more spherical ablation zone.

RESULTS

The dual-slot antenna created ablation zones with a higher aspect ratio at 50 W for 2 minutes (0.75 vs 0.53, P = .003) and 5 minutes (0.82 vs 0.63, P = .053) than did the monopole antenna in ex vivo liver tissue, although the difference was only significant at 2 minutes. At 100 W, the dual-slot antenna had a significantly higher aspect ratio at 2 minutes (0.52 vs 0.42, P = .002). In vivo studies showed significantly higher aspect ratios at 100 W for 5 minutes (0.63 vs 0.53, respectively, P = .029). Intraprocedural imaging confirmed this characterization, showing higher rates of ablation zone growth and heating primarily at the early stages of the ablation procedure when the dual-slot antenna was used.

CONCLUSION

The dual-slot microwave antenna created a more spherical ablation zone than did the monopole antenna both in vivo and ex vivo liver tissue. Greater control over power delivery can potentially extend the advantages of the dual-slot antenna design to higher power and longer treatment times.

Multiple applicator hepatic ablation with interstitial ultrasound devices: theoretical and experimental investigation

PURPOSE

To evaluate multiple applicator implant configurations of interstitial ultrasound devices for large volume ablation of liver tumors.

METHODS

A 3D bioacoustic-thermal model using the finite element method was implemented to assess multiple applicator implant configurations for thermal ablation with interstitial ultrasound energy. Interstitial applicators consist of linear arrays of up to four 10 mm-long tubular ultrasound transducers, each under separate and dynamic power control, enclosed within a water-cooled delivery catheter (2.4 mm OD). The authors considered parallel implants with two and three applicators (clustered configuration), spaced 2-3 cm apart, to simulate open surgical placement. In addition, the authors considered two applicator implants with applicators converging and diverging at angles of ∼20°, 30°, and 45° to simulate percutaneous placement. Heating experiments (10-15 min) were performed and compared against simulations employing the same experimental parameters. To estimate the performance of parallel, multiple applicator configurations in an in vivo setting, simulations were performed taking into account a range of blood perfusion levels (0, 5, 12, and 15 kg m(-3) s(-1)) that may occur in tumors of varying vascularity. The impact of tailoring the power supplied to individual transducer elements along the length of applicators is explored for applicators inserted in non-parallel (converging and diverging) configurations. Thermal dose (t(43) > 240 min) and temperature thresholds (T > 52 °C) were used to define the ablation zones, with dynamic changes to tissue acoustic and thermal properties incorporated within the model.

RESULTS

Experiments in ex vivo bovine liver yielded ablation zones ranging between 4.0-5.6 cm × 3.2-4.9 cm, in cross section. Ablation zone dimensions predicted by simulations with similar parameters to the experiments were in close agreement (within 5 mm). Simulations of in vivo heating showed that 15 min heating and interapplicator spacing less than 3 cm are required to obtain contiguous, complete ablation zones. The ability to create complete ablation zone profiles for nonparallel implants was illustrated by tailoring applied power levels along the length of applicators.

CONCLUSIONS

Parallel implants consisting of three interstitial ultrasound applicators in a triangular configuration yield complete ablation zones measuring up to 6.2 cm × 5.7 cm after 15 min heating. At larger interapplicator spacing, the level of blood perfusion in the tumor may yield indentations along the periphery of the ablation zone. Tailoring applied power along the length of the applicator can accommodate for nonparallel implants, without compromising safety.

Ultrasound-guided characterization of interstitial ablated tissue using RF time series: feasibility study

This paper presents the results of a feasibility study to demonstrate the application of ultrasound RF time series imaging to accurately differentiate ablated and nonablated tissue. For 12 ex vivo and two in situ tissue samples, RF ultrasound signals are acquired prior to, and following, high-intensity ultrasound ablation. Spatial and temporal features of these signals are used to characterize ablated and nonablated tissue in a supervised-learning framework. In cross-validation evaluation, a subset of four features extracted from RF time series produce a classification accuracy of 84.5%, an area under ROC curve of 0.91 for ex vivo data, and an accuracy of 85% for in situ data. Ultrasound RF time series is a promising approach for characterizing ablated tissue.

Microwave ablation treatment of liver cancer with a 2,450-MHz cooled-shaft antenna: pilot study on safety and efficacy

To evaluate efficacy of microwave ablation in a primary clinical study, sixty patients (44 men, 16 women; mean age 53 years) with 96, 1-8 cm (mean 3.20 ± 0.17 cm) liver cancers were treated with 2,450-MHz internally cooled-shaft antenna. Complete ablation (CA) and local tumor progression (LTP) rates as well as complications were determined. CA rates in small (<3.0 cm), intermediate (3.1-5.0 cm) and large (5.1-8.0 cm) liver cancers were 96.4% (54/56), 92.3% (24/26) and 78.6% (11/14), respectively. During a mean follow-up period of 17.17 ∓ 6.52 months, LTP occurred in five (5.21%) treated cases. There was no significant difference in the CA and LTP rates between the HCC and liver metastasis patient subgroups (P<0.05). Microwave ablation provides a reliable, efficient, and safe technique to perform hepatic tumor ablation.

Percutaneous microwave ablation for liver cancer adjacent to the diaphragm

PURPOSE

The aim of the study was to prospectively evaluate the safety and effectiveness of percutaneous microwave (MW) ablation for liver cancer adjacent to the diaphragm.

MATERIALS AND METHODS

From May 2005 to June 2008, 89 patients with 96 hepatic lesions adjacent to the diaphragm (the shortest distance from the lesion margin to the diaphragm less than 5 mm), who underwent ultrasound (US)-guided percutaneous MW ablation, were included in the study group. A total of 100 patients with 127 hepatic lesions not adjacent to the diaphragm (the shortest distance from the lesion to the diaphragm and the first or second branch of the hepatic vessels more than 10 mm), who underwent US-guided percutaneous MW ablation, were included in the control group. During the ablation the temperature of marginal ablation tissue proximal to the diaphragm was monitored and controlled at 50°-60°C for more than 10 min in the study group. We compared the results of ablation between the two groups.

RESULTS

A total of 91 of 96 tumours (94.8%) in the study group and 123 of 127 tumours (96.9%) in the control group achieved complete ablation (P > 0.05). Local tumour progression was found in 18 of 96 tumours (18.8%) in the study group and 21 of 127 tumours (16.5%) in the control group during follow-up after MW ablation (P > 0.05). No major complications occurred in either group.

CONCLUSIONS

Under strict temperature monitoring, percutaneous MW ablation is safe and can achieve a high complete ablation rate for the treatment of hepatic tumours adjacent to the diaphragm.

Ultrasound-guided microwave ablation for abdominal wall metastatic tumors: a preliminary study

AIM

To evaluate the feasibility, safety and efficacy of ultrasound-guided microwave (MW) ablation for abdominal wall metastatic tumors.

METHODS

From August 2007 to December 2010, a total of 11 patients with 23 abdominal wall nodules (diameter 2.59 cm ± 1.11 cm, range 1.3 cm to 5.0 cm) were treated with MW ablation. One antenna was inserted into the center of tumors less than 1.7 cm, and multiple antennae were inserted simultaneously into tumors 1.7 cm or larger. A 21 gauge thermocouple was inserted near important organs which required protection (such as bowel or gallbladder) for real-time temperature monitoring during MW ablation. Treatment outcome was observed by contrast-enhanced ultrasound and magnetic resonance imaging (MRI) [or computed tomography (CT)] during follow-up.

RESULTS

MW ablation was well tolerated by all patients. Six patients with 11 nodules had 1 thermocouple inserted near important organs for real-time temperature monitoring and the maximum temperature was 56 °C. Major complications included mild pain (54.5%), post-ablation fever (100%) and abdominal wall edema (25%). All 23 tumors (100%) in this group were completely ablated, and no residual tumor or local recurrence was observed at a median follow-up of 13 mo (range 1 to 32 mo). The ablation zone was well defined on contrast-enhanced imaging (contrast-enhanced CT, MRI and/or contrast-enhanced ultrasound) and gradually shrank with time.

CONCLUSION

Ultrasound-guided MW ablation may be a feasible, safe and effective treatment for abdominal wall metastatic tumors in selected patients.

In vitro assessment of engineered nanomaterials using a hepatocyte cell line: cytotoxicity, pro-inflammatory cytokines and functional markers

Effects on the liver C3A cell line treated with a panel of engineered nanomaterials (NMs) consisting of two zinc oxide particles (ZnO; coated 100 nm and uncoated 130 nm), two multi-walled carbon nanotubes (MWCNTs), one silver (Ag < 20 nm), one 7 nm anatase, two rutile TiO2 nanoparticles (10 and 94 nm) and two derivatives with positive and negative covalent functionalisation of the 10 nm rutile were evaluated. The silver particles elicited the greatest level of cytotoxicity (24 h LC50 - 2 µg/cm(2)). The silver was followed by the uncoated ZnO (24 h LC50 - 7.5 µg/cm(2)) and coated ZnO (24 h LC50 - 15 µg/cm(2)) particles with respect to cytotoxicity. The ZnO NMs were found to be about 50-60% soluble which could account for their toxicity. By contrast, the Ag was <1% soluble. The LC50 was not attained in the presence of any of the other engineered NMs (up to 80 µg/cm(2)). All NMs significantly increased IL-8 production. Meanwhile, no significant change in TNF-α, IL-6 or CRP was detected. Urea and albumin production were measured as indicators of hepatic function. These markers were only altered by the coated and uncoated ZnO, which significantly decreased albumin production.

Preinjected fluids do not benefit microwave ablation as those in radiofrequency ablation

RATIONALE AND OBJECTIVES

To detect whether the efficacy of microwave ablation (MWA) could be improved by preinjected fluids in an ex vivo porcine liver model.

MATERIALS AND METHODS

Ablations were performed for 12 minutes using energy output of impedance-based (power output gradually rose to 200W, maintained until increases in tissue impedance of 20 Ω, reduced to 10W, and switched on again 15 seconds later) in radiofrequency ablation (RFA) or 80 W in MWA. Before ablation, 5 mL of ethanol, distilled water, 0.9% NaCl solution, or 10% NaCl solution (n = 6 each) was injected into the targeted liver tissue. Ablations without fluid injection served as control. The ablation diameter, volume, shape index, and temperature were recorded and compared.

RESULTS

Preinjection of 0.9% or 10% NaCl solution resulted in larger coagulation volumes than that of the control group in RFA experiments (28.1 ± 2.9 cm(3), 45.3 ± 6.3 cm(3), 20.0 ± 2.5 cm(3), respectively; P < .05). Ethanol and distilled water had no impact on coagulation volumes in RFA. Preinjection of ethanol or 10% NaCl solution created smaller coagulation volumes than that of the control group in MWA experiments (34.3 ± 2.0 cm(3), 33.9 ± 4.1 cm(3), 58.0 ± 6.6 cm(3), respectively; P < .001). 0.9% NaCl solution and distilled water had no impact on coagulation volumes in MWA.

CONCLUSION

In an ex vivo porcine liver, preinjected fluids do not benefit microwave ablation as those in radiofrequency ablation.

Comparison of temperature curve and ablation zone between 915- and 2450-MHz cooled-shaft microwave antenna: results in ex vivo porcine livers

OBJECTIVE

To compare temperature curve and ablation zone between 915- and 2450-MHz cooled-shaft microwave antenna in ex vivo porcine livers.

MATERIALS AND METHODS

The 915- and 2450-MHz microwave ablation and thermal monitor system were used in this study. A total of 56 ablation zones and 280 temperature data were obtained in ex vivo porcine livers. The output powers were 50, 60, 70, and 80 W and the setting time was 600 s. The temperature curve of every temperature spot, the short- and long-axis diameters of the coagulation zones were recorded and measured.

RESULTS

At all four power output settings, the peak temperatures of every temperature spot had a tendency to increase accordingly as the MW output power was increased, and except for 5mm away from the antenna, the peak temperatures for the 915 MHz cooled-shaft antenna were significantly higher than those for the 2450 MHz cooled-shaft antenna (p<0.05). Meanwhile, the short- and long-axis diameters for the 915 MHz cooled-shaft antenna were significantly larger than those for the 2450 MHz cooled-shaft antenna (p<0.05).

CONCLUSION

The 915 MHz cooled-shaft antenna can yield a significantly larger ablation zone and achieve higher temperature in ablation zone than a 2450 MHz cooled-shaft antenna in ex vivo porcine livers.

Local thermal ablation of renal cell carcinoma

PURPOSE

With evolving local thermal ablation technology, the clinical application of thermal ablation has been actively investigated in the treatment for renal cell carcinoma. We review the evolution and current status of radiofrequency ablation and microwave ablation for renal cell carcinoma.

MATERIALS AND METHODS

All articles published in English on radiofrequency ablation or microwave ablation as a treatment for renal cell carcinoma were identified with a MEDLINE® and PubMed® search from 1990 to 2010.

RESULTS

Local thermal ablation has several advantages, including keeping more normal renal units, relatively simple operation, easy tolerance, fewer complications, a shorter hospitalization and convalescence period. Long-term data has determined radiofrequency ablation is responsible for poor surgical candidates with renal cell carcinoma, however, tumor size, location and shape might affect the efficacy of radiofrequency ablation. Microwave ablation can induce large ablation volumes and yield good local tumor control. Associated complications appear to be low.

CONCLUSIONS

Local ablative approaches seem to represent an attractive alternative to extirpative surgery for the treatment of small renal neoplasms in select patients. Potential developments include concepts to improve the accuracy and effectiveness of thermal ablation by improving the guiding, monitoring capabilities and detection capacity of multi-center lesions to provide at least equivalent cancer control to conventional surgery.

Feasible temperature of percutaneous microwave ablation of dog liver abutting the bowel

PURPOSE

This study used a dog model to determine the optimal temperature of percutaneous microwave ablation that causes complete necrosis of liver but not the adjacent bowel, supporting the use of this method to specifically and effectively treat liver tumour abutting the bowel.

MATERIALS AND METHODS

Ultrasound-guided percutaneous microwave ablation of liver abutting the bowel was performed on healthy adult dogs. Temperature of the ablation margin was monitored and controlled through inserted thermal monitoring needles. Dogs were divided into three groups and received microwave ablation at 75-95°C, 65-75°C, or 55-65°C. Imaging and histological examination were used to evaluate the damage of the bowel adjacent to the ablated liver.

RESULTS

Within one hour of treatment, the bowel adjacent to the ablated liver was seriously burned in the group receiving 75-95°C microwave ablation. Inflammation and congestion were found in the submucosa of the bowel in the group receiving 65-75°C microwave ablation. Minor inflammation was found in the mucosa of the bowel in the group receiving 55-65°C microwave ablation. Moreover, in the group receiving 55-65°C microwave ablation, ablated liver areas were covered with omenta, and histological examination revealed inflammatory reaction of the omenta 28 days after ablation.

CONCLUSIONS

Microwave ablation at 55-65°C for 6 min is preferred for ablation of liver tissue abutting the bowel in dogs. These findings may provide some valuable reference for percutaneous microwave ablation of human liver tumour adjacent to the bowel.

Minimally invasive image-guided therapy for inoperable hepatocellular carcinoma: What is the evidence today?

Hepatocellular carcinoma (HCC) is a primary malignant tumor of the liver that accounts for an important health problem worldwide. Only 10-15% of HCC patients are suitable candidates for hepatic resection and liver transplantation due to the advanced stage of the disease at time of diagnosis and shortage of donors. Therefore, several minimally invasive image-guided therapies for locoregional treatment have been developed. Tumor ablative techniques are either based on thermal tumor destruction, as in radiofrequency ablation, cryoablation, microwave ablation, laser ablation and high-intensity focused ultrasound, or chemical tumor destruction, as in percutaneous ethanol injection. Image-guided catheter-based techniques rely on intra-arterial delivery of embolic, chemoembolic or radioembolic agents. These minimally invasive image-guided therapies have revolutionized the management of inoperable HCC. This review provides a description of all minimally invasive image-guided therapies currently available, an up-to-date overview of the scientific evidence for their clinical use, and thoughts for future directions.

Microwave ablation: An experimental comparative study on internally cooled antenna versus non-internally cooled antenna in liver models

RATIONAL AND OBJECTIVES

Microwave ablation is an alternative therapy with high cost-effectiveness for liver malignancy. The authors designed this experiment to compare the effect of microwave ablation using a non-internally cooled (NIC) antenna with that using an internally cooled (IC) antenna in both an ex vivo and an in vivo liver models.

MATERIALS AND METHODS

Sixty-two microwave ablations were performed in ex vivo porcine and in vivo canine liver models (NIC antenna, 28 coagulations; IC antenna, 34 coagulations). Pair comparisons were executed in terms of the coagulation parameters, including short-axis diameter (SD), long-axis diameter (LD), and spherical ratio (SR, SD/LD). The distributions of tissue temperatures were compared in ex vivo ablation. During in vivo ablation, the temperatures of antenna shaft were measured and unintended tissue coagulation were observed and compared.

RESULTS

In both ex vivo and in vivo ablations, less charring areas were found around the IC antenna shaft. With a longer SD (P < .01) and a shorter LD (P < .01), the coagulations of IC antenna appeared to be more spherical than those of NIC antenna (P < .01). During ablations in vivo, the temperatures of NIC antennas shaft were up to 90 degrees C or even higher, which resulted in some unintended tissue coagulation, whereas the temperatures of IC antennas shaft were lower than 20 degrees C in all ablation processes without any unintended tissue coagulation (P < .01).

CONCLUSION

The IC antenna performed better than NIC antenna in microwave ablation for liver models and might be more suitable for therapy for liver malignancy in clinical practice.

Microwave ablation treatment of liver cancer with 2,450-MHz cooled-shaft antenna: an experimental and clinical study

PURPOSE

To evaluate effects of microwave ablation with a 2,450-MHz internally cooled-shaft antenna in animal experiments and in a clinical study.

METHODS

Microwave ablation was performed using a cooled-shaft antenna in eight in vivo (36 ablations) porcine livers. The coagulation diameters achieved in different microwave ablation parameter groups were compared. Sixty patients (44 men, 16 women; mean age 53 years) with 96, 1-8 cm (mean 3.20 +/- 0.17 cm) liver cancers were treated with the same microwave ablation technique. Complete ablation (CA), local tumor progression (LTP) rates and complications were determined.

RESULTS

In vivo livers, short axis diameter correlated with the coagulation duration in a sigmoidal curve fashion (60-W group R(2) = 0.76, 80-W group R(2) = 0.87), with a relative plateau achieved within 10 min for power settings of 60 or 80 W. Within 10 min in the 60 and 80-W groups, respectively, 89 and 85.76% of maximum short axis diameter were achieved. CA rates in small (3.0 cm), intermediate (3.1-5.0 cm) and large (5.1-8.0 cm) liver cancers were 96.43% (54/56), 92.31% (24/26) and 78.57% (11/14), respectively. During a mean follow-up period of 17.17 +/- 6.52 months, LTP occurred in five (5.21%) treated cancers. There was no significant difference in the CA and LTP rate between the HCC and liver metastasis patient subgroups (P > 0.05).

CONCLUSIONS

The short axis diameter enlargement has a relative plateau within 10 min by fixing power output to 60 or 80 W, using the 2,450-MHz internally cooled-shaft antenna in vivo porcine livers. Effective local tumor control was achieved during one microwave ablation session.

915MHz microwave ablation with implanted internal cooled-shaft antenna: initial experimental study in in vivo porcine livers

PURPOSE

To explore a preferred power output for further clinical application based on the ablated lesions induced by the four power outputs of 915 MHz microwave in experimental study of in vivo porcine livers.

MATERIALS AND METHODS

A KY 2000-915 microwave ablation system with an implanted 915 MHz internal cooled-shaft antenna was used in this study. A total of 24 ablations were performed in eight in vivo porcine livers. The energy was applied for 10 min at microwave output powers of 50 W, 60 W, 70 W, and 80 W. Long-axis and short-axis diameters of the coagulation zone were measured on all gross specimens.

RESULTS

The shapes of the 915 MHz microwave ablation lesions were elliptical commonly. As the power increased, the long-axis and short-axis diameters of the coagulation zone had a tendency to rise. But the long-axis diameter of the ablated lesion at 50 W was not significantly smaller than that of the ablated lesion at 60 W (P>0.05) and there were no statistical differences in short-axis diameters of the ablated lesion among the three power outputs of 60 W, 70 W and 80 W (P>0.05). After 10 min irradiation of 60 W, the long-axis and short-axis diameters of the coagulation zone were 5.02±0.60 cm and 3.65±0.46 cm, respectively.

CONCLUSIONS

For decreasing the undesired damages of liver tissues along the shaft and the number of antenna in further clinically percutaneous microwave ablation treatment, the power of 60 W may be a preferred setting among the four power outputs used in present study.

Percutaneous microwave ablation or nephrectomy for VX-2 carcinoma in rabbit kidney

PURPOSE

We compared the effectiveness of percutaneous microwave ablation and radical nephrectomy for implanted VX-2 carcinoma in rabbit kidneys.

MATERIALS AND METHODS

VX-2 tumors were surgically implanted into the left lower pole parenchyma of 26 New Zealand White rabbit kidneys. At 12 days after implantation implanted rabbits were randomly assigned to 1 of 3 groups according to therapy type, including percutaneous microwave ablation, nephrectomy and no treatment. The anticancer effect and safety were compared among the groups. Histopathological changes in tumor tissue with time after microwave ablation were evaluated.

RESULTS

The survival rate in the percutaneous microwave ablation group was significantly higher than that in the no treatment group and showed no statistically significant difference compared with that in the nephrectomy group. Serum creatinine did not increase after microwave therapy but we noted a statistically significant serum creatinine increase in the nephrectomy group. Histological analysis revealed completely coagulative necrosis of the tumor in 10 of 12 rabbits (83.3%) after microwave ablation. Two rabbits died, including 1 of peritonitis in the nephrectomy group and 1 of intestinal fistula due to heat injury in the percutaneous microwave ablation group.

CONCLUSIONS

This study shows that percutaneous microwave ablation can achieve effects similar to those of radical nephrectomy. It caused no significant changes in renal function when treating implanted VX-2 renal tumors. Percutaneous microwave ablation has the potential of being a minimally invasive treatment for small renal tumors.

Phantom experimental study on microwave ablation with a water-cooled antenna

Microwave ablation therapy using a water-cooled antenna was studied experimentally in a phantom. The development of the heating pattern induced by the microwave antenna was determined from the thermocouple-measured temperature field, and the influence of the cooling water flow within the antenna on temperature distribution and heating pattern was investigated. The shape of the heating pattern was pear-like, and the enlarging rate of the heating pattern decreased with heating time. Because of strong cooling effect, the heating pattern in the region with Z < 0 (where Z = 0 represents the position of radiator, Z < 0 and Z > 0 represent the backward direction of the antenna with cooling water and forward direction without water, respectively) was smaller in diameter than that with Z > 0, and the heating pattern with Z < 0 was slightly reduced when the velocity of the cooling water increased. The highest ablative temperature occurred with Z > 0 decreasing. Finally, the specific absorption rate distribution was also determined and investigated analytically. The present results can be helpful in clinical ablation therapy practice and will be applicable to multiple applicators for surgical planning.

Thermal characteristics of microwave ablation in the vicinity of an arterial bifurcation

PURPOSE

The objective of this research was to reveal the thermal characteristics of microwave ablations in the vicinity of an arterial bifurcation.

METHODS

The temperature distribution after microwave heating of a liver-like material in the close proximity of an arterial bifurcation was simulated using the finite element method. Coupled fluid flow and solid heat transfer were taken into consideration and a three-dimensional analysis was performed. An experimentally determined SAR (specific absorption rate) generated by the absorption of microwaves in liver-like material was used in the analysis instead of utilizing electromagnetic calculations. Several different tests of time-controlled ablations with varying distances between the microwave antenna and the bifurcation were performed and detailed temperature distributions near the bifurcation were obtained.

RESULTS

The interaction between the recirculation flow in the bifurcation and the heat transfer in the surrounding tissue makes the temperature distribution near the bifurcation complicated. Most importantly, after a period of continuous heating with constant microwave output power, the maximum temperatures caused by the ablation did not always increase with the distance between the antenna and the bifurcation.

CONCLUSION

It can be concluded that inadequate ablations can be the result not only from a close proximity between the antenna and the blood vessel, but also from a complicated blood flow in large vessels whose structure causes recirculation flow.

Combined therapy with transcatheter arterial chemoembolization and percutaneous microwave coagulation for small hepatocellular carcinoma

AIM: To assess the efficacy of combined transcatheter arterial chemoembolization (TACE) and percutaneous microwave coagulation therapy (PMCT) for small hepatocellular carcinoma (HCC).

METHODS: Thirty-five patients with a total of 41 HCC nodules (≤ 3 cm in diameter) were treated with TACE followed by computed tomograghy (CT)-guided percutaneous microwave coagulation therapy (PMCT) within 1-3 wk.

RESULTS: By biopsies and enhanced CT scans, complete necrosis of the tumor and 3-5 mm of the surrounding non-cancerous area were observed in 34 foci. In seven foci, incomplete necrosis of the surrounding parenchyma was observed. Serum alpha-fetoprotein (AFP) levels returned to normal 10 d after treatment in 25 patients who originally had high serum AFP levels. The follow-up period was 6-31 mo, and all patients remained alive. One patient had a recurrence in the subsegments of the liver, and another patient had a recurrence near the original lesion.

CONCLUSION: Combined therapy with TACE and PMCT is a safe and effective treatment without severe complications for small HCC.

Percutaneous microwave ablation of liver cancer adjacent to the gastrointestinal tract

PURPOSE

The purpose of the study was to prospectively evaluate safety and effectiveness of percutaneous microwave ablation under temperature monitoring assisted with ethanol injection for liver cancer abutting gastrointestinal tract.

MATERIALS AND METHODS

One hundred seventy-nine hepatic tumors that underwent percutaneous microwave ablation with curative intention were included. Fifty-three lesions located less than 5 mm from gastrointestinal tract were in gastrointestinal group. One hundred twenty-six lesions located more than 5 mm from hepatic surface and first or second branch of hepatic vessels were in control group. The temperature of marginal ablation tissue proximal to gastrointestinal tract was monitored and controlled to fluctuating between 45 degrees C and 58 degrees C for more than 10 min for tumors in the gastrointestinal group. Ethanol (2-27 ml) was injected into marginal tissue in 33 of 53 lesions of the GI group.

RESULTS

Forty-seven of 53 tumors (88.7%) in the gastrointestinal group and 116 of 126 tumors (92.1%) in the control group achieved complete ablation (p > 0.05). There were neither immediate nor periprocedural complications in both groups. Tumor seeding happened in one of the gastrointestinal group and two of the control group. There was no delayed complication of bile ducts injury.

CONCLUSION

Under strict temperature monitoring, microwave ablation assisted with ethanol injection is safe and achieves a high complete ablation rate for hepatic tumors adjacent to gastrointestinal tract.