Comparison of microwave ablation and multipolar radiofrequency ablation, both using a pair of internally cooled interstitial applicators: results in ex vivo porcine livers

Efficacy and safety of computed tomography-guided microwave ablation with fine needle-assisted puncture positioning technique for hepatocellular carcinoma

BACKGROUND

In microwave ablation (MWA), although computed tomography (CT) scanning can overcome gas interference, it cannot achieve real-time localization. Therefore, the puncture technique is more important in CT-guided ablation.

AIM

To compare the fine needle-assisted puncture (FNP) positioning technique and the conventional puncture (CP) technique for the safety and efficacy of CT-guided MWA in treating hepatocellular carcinoma (HCC).

METHODS

This retrospective study included 124 patients with 166 tumor nodules from February 2018 and June 2021. Seventy patients received CT-guided MWA under the FNP technique (FNP group), and 54 patients received MWA under the CP technique (CP group). Intergroup comparisons were made regarding local tumor progression (LTP), recurrence-free survival (RFS), overall survival (OS), and complications. The influencing variables of LTP and RFS were analyzed through univariate and multivariate regressions.

RESULTS

The 1-, 2-, and 3-year cumulative incidences of LTP in the FNP group were significantly lower than those in the CP group (7.4%, 12.7%, 21.3% vs 13.7%, 32.9%, 36.4%; P = 0.038). The 1-, 2-, and 3-year RFS rates in the FNP group were significantly higher than those in the CP group (80.6%, 73.3%, 64.0% vs 83.3%, 39.4%, and 32.5%, respectively; P = 0.008). The FNP technique independently predicted LTP and RFS. Minor complications in the FNP group were lower than those in the CP group (P < 0.001). The difference in median OS was insignificant between the FNP and CP groups (P = 0.229).

CONCLUSION

The FNP technique used in CT-guided MWA may improve outcomes in terms of LTP, RFS, and procedure-related complications for HCC.

Numerical Simulation of Microwave Ablation in the Human Liver

Microwave thermal ablation was developed as an alternative to other forms of thermal ablation procedures. The objective of this study is to numerically model a microwave ablation probe operating at the 2.45 GHz level using the finite element and finite volume methods to provide a comprehensive and repeatable study within a human male approximately 25 to 30 years old. The three-dimensional physical model included a human liver along with the surrounding tissues and bones. Three different input powers (10, 20, and 30 watts) were studied, along with the effect of the probe’s internal coolant flow rate. One of the primary results from the numerical simulations was the extent of affected tissue from the microwave probe. The resulting time and temperature results were used to predict tissue damage using an injury integral method. The numerical approach was validated with available experimental data and was found to be within 6% of the average experimentally measured temperatures.

Techniques for Temperature Monitoring of Myocardial Tissue Undergoing Radiofrequency Ablation Treatments: An Overview

Cardiac radiofrequency ablation (RFA) has received substantial attention for the treatment of multiple arrhythmias. In this scenario, there is an ever-growing demand for monitoring the temperature trend inside the tissue as it may allow an accurate control of the treatment effects, with a consequent improvement of the clinical outcomes. There are many methods for monitoring temperature in tissues undergoing RFA, which can be divided into invasive and non-invasive. This paper aims to provide an overview of the currently available techniques for temperature detection in this clinical scenario. Firstly, we describe the heat generation during RFA, then we report the principle of work of the most popular thermometric techniques and their features. Finally, we introduce their main applications in the field of cardiac RFA to explore the applicability in clinical settings of each method.

CT-based quantification of short-term tissue shrinkage following hepatic microwave ablation in an in vivo porcine liver model

BACKGROUND

Microwave ablation (MWA) is a minimally invasive treatment option for solid tumors and belongs to the local ablative therapeutic techniques, based on thermal tissue coagulation. So far there are mainly ex vivo studies that describe tissue shrinkage during MWA.

PURPOSE

To characterize short-term volume changes of the ablated zone following hepatic MWA in an in vivo porcine liver model using contrast-enhanced computer tomography (CECT).

MATERIAL AND METHODS

We performed multiple hepatic MWA with constant energy parameters in healthy, narcotized and laparotomized domestic pigs. The volumes of the ablated areas were calculated from venous phase CT scans, immediately after the ablation and in short-term courses of up to 2 h after MWA.

RESULTS

In total, 19 thermally ablated areas in 10 porcine livers could be analyzed (n = 6 with two volume measurements during the measurement period and n = 13 with three measurements). Both groups showed a statistically significant but heterogeneous volume reduction of up to 12% (median 6%) of the ablated zones in CECT scans during the measurement period (P < 0.001 [n = 13] and P = 0.042 [n = 6]). However, the dimension and dynamics of volume changes were heterogenous both absolutely and relatively.

CONCLUSION

We observed a significant short-term volume reduction of ablated liver tissue in vivo. This volume shrinkage must be considered in clinical practice for technically successful tumor treatment by MWA and therefore it should be further investigated in in vivo studies.

The efficacy of transarterial chemoembolization combined with microwave ablation for unresectable hepatocellular carcinoma: a systematic review and meta-analysis

Purpose: To evaluate the clinical value of transarterial chemoembolization (TACE) combined with microwave ablation (MWA) for unresectable hepatocellular carcinoma (HCC).Patients and methods: Eligible studies were identified using PubMed, MedLine, Embase, the Cochrane Library, and Web of Science, investigating the synergistic effect of TACE + MWA in the treatment of advanced HCC. Endpoints were the 1-, 2- and 3-year survival rates, local control rate (LCR), objective remission rate (ORR), and adverse event (AE). Odds ratio (OR) with 95% confidence interval (CI) was used to determine the effect size.Results: Nine studies including 351 patients in the TACE + MWA group and 653 patients in the TACE group were enrolled in this meta-analysis. The pooled OR for the 1-, 2-, and 3-year survival rates were in favor of TACE + MWA (OR = 3.29, 95% CI 2.26-4.79; OR = 2.82, 95% CI 2.01-3.95; OR = 4.50, 95% CI 2.96-6.86; respectively). The pooled OR for the ORR and LCR were also in favor of TACE + MWA (OR = 4.64, 95%CI 3.11-6.91; OR = 3.93, 95% CI 2.64-5.87; respectively). No significant difference in the incidence of severe AE was observed between TACE + MWA group and TACE group (p > .05). However, subgroup analysis showed that patients with tumor size >5 cm were more likely to be benefited from TACE + MWA, rather than patients with tumor size ≤5 cm.Conclusion: With the current data, we concluded that combination TACE and MWA was safe, and should be strongly recommended to unresectable patients with tumor size >5 cm, but TACE alone was enough for unresectable patients with tumor size ≤5 cm. However, the conclusion needs further validation.

Veterinary Clinics: Tumor Ablation

Over the past decade, interventional oncology techniques have become integrated into the treatment plans of companion animals with cancer on a regular basis. Although procedures such as stenting are performed commonly, other less frequently utilized techniques for locoregional therapy, such as embolization and ablation, are emerging and demonstrating promise. Tumor ablation techniques are categorized into two subgroups: chemical ablation and energy-based ablation. Increased utilization of ablation will allow for the determination of specific indications and evaluation of outcomes for these techniques.

Computed tomography-guided percutaneous microwave ablation of hepatocellular carcinoma in challenging locations: safety and efficacy of high-power microwave platforms

OBJECTIVE

To evaluate the clinical efficacy/safety of CT-guided percutaneous microwave ablation for HCC in challenging locations using high-power microwave platforms.

MATERIALS AND METHODS

A retrospective review was conducted in 26 patients with 36 HCC tumours in challenging locations (hepatic dome, subcapsular, close to the heart/diaphragm/hepatic hilum, exophytic) undergoing CT-guided percutaneous microwave ablation in a single centre since January 2011. Two different microwave platforms were used both operating at 2.45 GHz: AMICA and Acculis MWA System. Patient demographics including age, sex, tumour size and location, as well as technical details were recorded. Technical success, treatment response, patients survival and complication rate were evaluated.

RESULTS

Treated tumours were located in the hepatic dome (n = 14), subcapsularly (n = 16), in proximity to the heart (n = 2) or liver hilum (n = 2), while two were exophytic tumours at segment VI (n = 2). Mean tumour diameter was 3.30 cm (range 1.4-5 cm). In 3/26 patients (diameter >4 cm), an additional session of DEB-TACE was performed due to tumour size. Technical success rate was 100%; complete response rate was recorded in 33/36 tumours (91.6%). According to Kaplan-Meier analysis, survival rate was 92.3% and 72.11% at 24- and 60-month follow-up, respectively. There were no major complications; two cases of minor pneumothorax and two cases of small subcapsular haematoma were resolved only with observation requiring no further treatment.

CONCLUSION

CT-guided percutaneous microwave ablation for hepatocellular carcinoma tumours in challenging locations and up to 5 cm in diameter can be performed with high efficacy and safety rates.

Increasing radiofrequency ablation volumes with the use of internally cooled electrodes and injected hydrochloric acid in ex vivo bovine livers

PURPOSE

We used an impedance-controlled generator with an internally cooled electrode to perform radiofrequency ablation (RFA) in ex vivo bovine livers, with a single injection of either 38.5% sodium chloride (NaCl) or 10% hydrochloric acid (HCl), to determine the relative effects of these two solutions on tissue impedance, temperature and ablation volume.

MATERIALS AND METHODS

We performed 10 ablations each with injections of NaCl (NaCl-RFA), HCl (HCl-RFA) or nothing (RFA-alone), with a power setting of 200 W for 15 minutes. We recorded tissue impedance before and after injection. We logged temperatures obtained from thermocouple probes positioned 5, 10, 15 and 20 mm from the internally cooled RF electrode. After ablation, we measured ablation zone longitudinal and transverse diameters, and we calculated a spherical ratio (SR) for each ablation.

RESULTS

Mean post-injection impedance of 30.3 (standard deviation [SD] 2.5) ohms for HCl was significantly lower than that of 55.4 (SD 3.5) ohms for NaCl (p < .001). Mean maximum temperatures recorded at each respective distance from the RFA electrode were all highest for HCl-RFA and lowest for RFA-alone (p < .001). Mean longitudinal and transverse diameters after HCl-RFA (5.50 [SD 0.25] cm and 5.28 [SD 0.22] cm, respectively) were significantly larger than those after NaCl-RFA (4.24 [SD 0.35] cm and 3.55 [SD 0.43] cm, respectively) and after RFA-alone (3.60 [SD 0.10] cm and 2.70 [SD 0.13] cm, respectively) (p < .001). Mean SR after HCl-RFA (0.93, SD 0.02) was significantly higher than mean SR after NaCl-RFA (0.76, SD 0.06) and RFA-alone (0.72, SD 0.04) (p < .001).

CONCLUSION

Monopolar, impedance-controlled RFA, with an internally cooled electrode and a single 10% HCl injection may allow larger tumors to be treated, potentially resulting in improved patient outcomes.

Percutaneous ablation of pancreatic cancer

Pancreatic ductal adenocarcinoma is a highly aggressive tumor with an overall 5-year survival rate of less than 5%. Prognosis and treatment depend on whether the tumor is resectable or not, which mostly depends on how quickly the diagnosis is made. Chemotherapy and radiotherapy can be both used in cases of non-resectable pancreatic cancer. In cases of pancreatic neoplasm that is locally advanced, non-resectable, but non-metastatic, it is possible to apply percutaneous treatments that are able to induce tumor cytoreduction. The aim of this article will be to describe the multiple currently available treatment techniques (radiofrequency ablation, microwave ablation, cryoablation, and irreversible electroporation), their results, and their possible complications, with the aid of a literature review.

Percutaneous microwave ablation of T1a and T1b renal cell carcinoma: short-term efficacy and complications with emphasis on tumor complexity and single session treatment

PURPOSE

To update the oncologic outcomes and safety for microwave (MW) ablation of T1a (≤4.0 cm) and T1b (4.1-7.0 cm) renal cell carcinoma (RCC) with emphasis on tumor complexity and single session treatment.

MATERIALS AND METHODS

Retrospective review of 29 consecutive patients (30 tumors) with localized (NOMO) RCC (23 T1a; 7 T1b) treated with percutaneous MW ablation between 3/2013 and 6/2014. Primary outcomes investigated were technical success, local tumor progression (LTP), and complications. Technical success was assessed with contrast-enhanced computed tomography (CECT) immediately after MW ablation. Presence of LTP was assessed with CECT or contrast-enhanced magnetic resonance at 6-month target intervals for the first two years and annually thereafter. Complications were categorized using the Clavien-Dindo classification system.

RESULTS

Median tumor diameter was 2.8 cm [IQR 2.1-3.3] for T1a and 4.7 cm [IQR 4.1-5.7] for T1b tumors. Median RENAL nephrometry score was 7 [IQR 4-8] for T1a tumors and 9 [IQR 6.25-9.75] for T1b tumors. Technical success was achieved for 22 T1a (96%) and 7 T1b (100%) tumors. There were no LTP during a median imaging follow-up of 12.0 months [IQR 6-18] for the 23 patients (24 tumors) with greater than 6 months of follow-up. There were three Clavien-Dindo grade I-II complication (10%) and no Clavien-Dindo grade III-V complications (0%). All but two patients (93%) are alive without metastatic disease; two patients died after 12-month follow-up of causes unrelated to the MW ablation.

CONCLUSION

Percutaneous MW ablation appears to be a safe and effective treatment option for low, moderate, and highly complex T1a and T1b RCC in early follow-up.

Preliminary Outcome of Microwave Ablation of Hepatocellular Carcinoma: Breaking the 3-cm Barrier?

PURPOSE

To evaluate preliminary outcomes after microwave ablation (MWA) of hepatocellular carcinoma (HCC) up to 5 cm and to determine the influence of tumor size.

MATERIALS AND METHODS

Electronic records were searched for HCC and MWA. Between January 2011 and September 2014, 173 HCCs up to 5 cm were treated by MWA in 129 consecutive patients (89 men, 40 women; mean age, 66.9 y ± 9.5). Tumor characteristics related to local tumor progression and primary and secondary treatment efficacy were evaluated by univariate analysis. Outcomes were compared between tumors ≤ 3 cm and tumors > 3 cm.

RESULTS

Technical success, primary efficacy, and secondary efficacy were 96.5%, 99.4%, and 94.2% at a mean follow-up period of 11.8 months ± 9.8 (range, 0.8-40.6 mo). Analysis of tumor characteristics showed no significant risk factor for local tumor progression, including subcapsular location (P = .176), tumor size (P = .402), and perivascular tumor location (P = .323). The 1-year and 2-year secondary or overall treatment efficacy rates for tumors measuring ≤ 3 cm were 91.2% and 82.1% and for tumors 3.1-5 cm were 92.3% and 83.9% (P = .773). The number of sessions to achieve secondary efficacy was higher in the larger tumor group (1.13 vs 1.06, P = .005). There were three major complications in 134 procedures (2.2%).

CONCLUSIONS

With use of current-generation MWA devices, percutaneous ablation of HCCs up to 5 cm can be achieved with high efficacy.

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.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Ex Vivo Liver Experiment of Hydrochloric Acid-Infused and Saline-Infused Monopolar Radiofrequency Ablation: Better Outcomes in Temperature, Energy, and Coagulation

OBJECTIVE

To compare temperature, energy, and coagulation between hydrochloric acid-infused radiofrequency ablation (HAIRFA) and normal saline-infused radiofrequency ablation (NSIRFA) in ex vivo porcine liver model.

MATERIALS AND METHODS

30 fresh porcine livers were excised in 60 lesions, 30 with HAIRFA and the other 30 with NSIRFA. Both modalities used monopolar perfusion electrode connected to a RF generator set at 103 °C and 30 W. In each group, ablation time was set at 10, 20, or 30 min (10 lesions from each group at each time). We compared tissue temperatures (at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm away from the electrode tip), average power, deposited energy, deposited energy per coagulation volume (DEV), coagulation diameters, coagulative volume, and spherical ratio between the two groups.

RESULTS

Temperature-time curves showed that HAIRFA provided progressively greater heating than that of NSIRFA. At 30 min, mean average power, deposited energy, coagulation volumes (113.67 vs. 12.28 cm(3)) and diameters, and increasing in tissue temperature were much greater with HAIRFA (P < 0.001 for all), except DEV was lower (456 vs. 1396 J/cm(3), P < 0.001). The spherical ratio was closer to 1 with HAIRFA (1.23 vs. 1.46). Coagulation diameters, volume, and average power of HAIRFA increased significantly with longer ablation times. While with NSIRFA, these characteristics were stable till later 20 min, except the power decreased with longer ablation times.

CONCLUSIONS

HAIRFA creates much larger and more spherical lesions by increasing overall energy deposition, modulating thermal conductivity, and transferring heat during ablation.

The effects of fat layer on temperature distribution during microwave atrial fibrillation catheter ablation

To investigate the effects of fat layer on the temperature distribution during microwave atrial fibrillation catheter ablation in the conditions of different ablation time; 3D finite element models (fat layer and no fat layer) were built, and temperature distribution was obtained based on coupled electromagnetic-thermal analysis at 2.45 GHz and 30 W of microwave power. Results shown: in the endocardial ablation, the existence of the fat layer did not affect the shape of the 50 °C contour before 30 s. The increase speed of depth became quite slowly in the model with fat layer after 30 s. When ablation depth needed fixed, there are no significant effect on effectively ablation depth whether fat layer over or not. However, the existence of fat layer makes the temperature lower in the myocardium, and maximum temperature point closer to the myocardium surface. What is more, in the model with fat layer, effective ablation reach lower maximum temperature and the shallower depth of 50 °C contour. But there are larger ablation axial length and transverse width. In this case, doctor should ensure safety of normal cardiac tissue around the target tissue. In the epicardial ablation, the existence of fat layer seriously affects result of the microwave ablation. The epicardial ablation needs more heating time to create lesion. But epicardial ablation can be better controlled in the shape of effective ablation area because of the slowly increase of target variables after the appearing of 50 °C contour. Doctor can choose endocardial or epicardial ablation in different case of clinic requirement.

Update in management of hepatocellular carcinoma in Eastern population

Hepatocellular carcinoma (HCC) is one of the commonest malignant tumours in the East. Although the management of HCC in the West is mainly based on the Barcelona Clinic for Liver Cancer staging, it is considered too conservative by Asian countries where the number of HCC patients is huge. Scientific and clinical advances were made in aspects of diagnosis, staging, and treatment of HCC. HCC is well known to be associated with cirrhosis and the treatment of HCC must take into account the presence and stage of chronic liver disease. The major treatment modalities of HCC include: (1) surgical resection; (2) liver transplantation; (3) local ablation therapy; (4) transarterial locoregional treatment; and (5) systemic treatment. Among these, resection, liver transplantation and ablation therapy for small HCC are considered as curative treatment. Portal vein embolisation and the associating liver partition with portal vein ligation for staged hepatectomy may reduce dropout in patients with marginally resectable disease but the midterm and long-term results are still to be confirmed. Patient selection for the best treatment modality is the key to success of treatment of HCC. The purpose of current review is to provide a description of the current advances in diagnosis, staging, pre-operative liver function assessment and treatment options for patients with HCC in the east.

Characterisation of tissue shrinkage during microwave thermal ablation

PURPOSE

The aim of this study was to characterise changes in tissue volume during image-guided microwave ablation in order to arrive at a more precise determination of the true ablation zone.

MATERIALS AND METHODS

The effect of power (20-80 W) and time (1-10 min) on microwave-induced tissue contraction was experimentally evaluated in various-sized cubes of ex vivo liver (10-40 mm ± 2 mm) and muscle (20 and 40 mm ± 2 mm) embedded in agar phantoms (N = 119). Post-ablation linear and volumetric dimensions of the tissue cubes were measured and compared with pre-ablation dimensions. Subsequently, the process of tissue contraction was investigated dynamically during the ablation procedure through real-time X-ray CT scanning.

RESULTS

Overall, substantial shrinkage of 52-74% of initial tissue volume was noted. The shrinkage was non-uniform over time and space, with observed asymmetry favouring the radial (23-43 % range) over the longitudinal (21-29%) direction. Algorithmic relationships for the shrinkage as a function of time were demonstrated. Furthermore, the smallest cubes showed more substantial and faster contraction (28-40% after 1 min), with more considerable volumetric shrinkage (>10%) in muscle than in liver tissue. Additionally, CT imaging demonstrated initial expansion of the tissue volume, lasting in some cases up to 3 min during the microwave ablation procedure, prior to the contraction phenomenon.

CONCLUSIONS

In addition to an asymmetric substantial shrinkage of the ablated tissue volume, an initial expansion phenomenon occurs during MW ablation. Thus, complex modifications of the tissue close to a radiating antenna will likely need to be taken into account for future methods of real-time ablation monitoring.

Comparative experiments on phantom and ex vivo liver tissue in microwave ablation

PURPOSE

The aim of this study is to investigate the thermal field distribution of phantom and ex vivo liver tissue in microwave ablation. We intent to verify if the phantom can be used in future studies in lieu of actual tissue.

METHODS

This experiment was divided into two groups of phantom and ex vivo porcine liver tissue. 2450 MHz is set. The tests last up to 240 s in 60 W. The velocity of the circulating water pumps were adjusted to 40 rounds/min. Twenty-five copper-constantan thermocouples (TCs) were inserted at the specified position to record temperature data.

RESULT

For the cooling water, the temperature field was non-symmetric distribution at the gap before (z > z < 0 mm) of two groups of experiments. At the part without cooling water (z > 0 mm), effective ablation areas were larger; near the microwave antenna, the temperature curves showed good consistency for both materials. Far away from the microwave antenna, the value difference increased between phantom and liver tissue. Moreover, the effect of cooling water in phantom is more obvious than it in liver tissue. The shapes of ablation areas from two groups are not same.

CONCLUSION

The result of the present work implied that heating patterns of liver tissue and phantom are comparable. But the difference of temperature field between two kinds of materials cannot be ignored. In cases of using phantom to verify temperature field in lieu of actual tissue, the researchers should pay full attention to these difference points.

Practice guidelines for ultrasound-guided percutaneous microwave ablation for hepatic malignancy

Primary liver cancer and liver metastases are among the most frequent malignancies worldwide, with an increasing number of new cases and deaths every year. Traditional surgery is only suitable for a limited proportion of patients and imaging-guided percutaneous thermal ablation has achieved optimistic results for management of hepatic malignancy. This synopsis outlines the first clinical practice guidelines for ultrasound-guided percutaneous microwave ablation therapy for hepatic malignancy, which was created by a joint task force of the Society of Chinese Interventional Ultrasound. The guidelines aim at standardizing the microwave ablation procedure and therapeutic efficacy assessment, as well as proposing the criteria for the treatment candidates.

Quantification of tissue shrinkage and dehydration caused by microwave ablation: experimental study in kidneys for the estimation of effective coagulation volume

PURPOSE

To quantify the extent of tissue shrinkage and dehydration caused by microwave (MW) ablation in kidneys for estimation of effective coagulation volume.

MATERIALS AND METHODS

MW ablations were carried out in ex vivo porcine kidneys. Six study groups were defined: groups 1A, 2A, and 3A for MW ablation (90 W for 5 min, 7.5 min, or 10 min), and groups 1B, 2B, and 3B for control (without MW ablation). Pre- and postinterventional volume analyses were performed. Effective coagulation volumes (original tissue included in coagulation) were determined. Postinterventional dehydration analyses were performed with calculation of mean mass fractions of water.

RESULTS

Mean deployed energies were 21.6 kJ ± 1.1 for group 1A, 29.9 kJ ± 1.0 for group 2A, and 42.1 kJ ± 0.5 kJ for group 3A, and were significantly different (P < .0001). Differences between pre- and postinterventional volumes were -3.8% ± 0.6 for group 1A, -5.6% ± 0.9 for group 2A, and -7.2% ± 0.4 for group 3A, and -1.1% ± 0.3 for group 1B, -1.8% ± 0.4 for group 2B, and -1.1% ± 0.4 for group 3B. Postinterventional volumes were significantly smaller than preinterventional volumes for all groups (P < .01). Underestimations of effective coagulation volume from visualized coagulation volume were 26.1% ± 3.5 for group 1A, 35.2% ± 11.2 for group 2A, and 42.1% ± 4.9 for group 3A, which were significantly different (P < .01). Mean mass fractions of water were 64.2% ± 1.4 for group 1A, 63.2% ± 1.7 for group 2A, and 62.6% ± 1.8% for group 3A, with significant differences versus corresponding control groups (P < .01).

CONCLUSIONS

For MW ablation in kidneys, underestimation of effective coagulation volume based on visualized coagulation volume is significantly greater with greater deployed energy. Therefore, local dehydration with tissue shrinkage is a potential contributor.

Comparison of four microwave ablation devices: an experimental study in ex vivo bovine liver

PURPOSE

To compare volume, sphericity, and short-axis diameter of the coagulation zone of four commercially available microwave ablation systems with three technical concepts in an ex vivo setting and to formulate mathematical models to predict these quantities.

MATERIALS AND METHODS

Two high-power systems (systems A and B), a system that enables simultaneous use of three antennas (system C), and a non-perfusion-cooled system that automatically adapts power and frequency (system D) were tested in ex vivo bovine livers (108 ablations). Coagulation volume, sphericity, and mean short-axis diameter were assessed, and mathematical functions were fitted for each system and assessed with the coefficient of determination (R(2)). Analysis of variance and Tukey post hoc tests were used for interdevice comparison after 5 and 10 minutes and after maximum recommended ablation time.

RESULTS

Volume and short-axis diameter were determined by using a mathematical model for every system, with coefficients of determination of 0.75-0.98 and 0.70-0.97, respectively. Correlation for determination of sphericity was lower (R(2) = 0.01-0.68). Mean results with ablation performed according to manufacturer recommendations were as follows: Volume, sphericity, and short-axis diameter were 57.5 cm(3), 0.75, and 43.4 mm, respectively, for system A; 72.3 cm(3), 0.68, and 45.5 mm, respectively, for system B; 17.1 cm(3), 0.58, and 26.8 mm, respectively, for system C (one antenna); 76.5 cm(3), 0.89, and 50.6 mm, respectively, for system C (three antennas); and 56.0 cm(3), 0.64, and 40.9 mm, respectively, for system D. Systems A (mean volume, 52.4 cm(3) ± 4.5 [standard deviation]) and B (39.4 cm(3) ± 1.7) reach large ablation zones with 5-minute ablation.

CONCLUSION

The largest ablation zone is obtained with systems B and C (three antennas) under maximum recommended ablation duration and with system A under short ablation time. The most spherical zone is obtained with system C (three antennas).

Determining a minimal safe distance to prevent thermal injury to intrahepatic bile ducts in radiofrequency ablation of the liver: a study in dogs

PURPOSE

To determine a minimal safe distance between the radiofrequency ablation (RFA) electrode tip and major intrahepatic bile ducts to prevent thermal injury during hepatic RFA in a canine model.

MATERIALS AND METHODS

Forty healthy mongrel dogs were randomised equally into four groups based on the distance between the electrode and large intrahepatic bile ducts during RFA of the liver, as follows: 1.0-2.9 mm, 3.0-4.9 mm, 5.0-7.9 mm, or 8.0-10.0 mm. The RFA electrodes were opened uniformly at 2 cm. During RFA, energy was sequentially raised, starting at 5 W and increasing by 5 W increments every minute to a maximum of 95 W. Animals were monitored for a maximum of 14 days post-RFA for complications and by bilirubin testing, after which they were euthanised and their livers were surgically removed for cholangiographic and pathological examination.

RESULTS

When the electrodes were less than 5.0 mm from the bile ducts during RFA, either full or partial-thickness bile duct necrosis occurred, leading to a variety of serious complications. In contrast, when the distance was more than 5.0 mm between the RFA electrode and bile ducts, serious complications occurred rarely, with pathological examinations showing either normal bile ducts or vacuolar changes of the biliary ductal epithelium.

CONCLUSION

A minimum safe distance of 5.0 mm between the RFA electrode and intrahepatic bile ducts was effective in preventing serious complications secondary to bile duct injury in a canine model.

[Microwave tumor ablation. New devices, new applications?]

CLINICAL ISSUE

The majority of patients with hepatic malignancies are not amenable to surgical resection. In some of these cases minimally invasive ablative therapies are a treatment option.

STANDARD TREATMENT

Besides radiofrequency ablation, the most common ablative therapies are cryoablation, laser ablation and microwave ablation.

TREATMENT INNOVATIONS

The classic fields of application of microwave ablation are the treatment of malignancies of the liver, kidneys and lungs. Furthermore, cases of treatment of bone tumors and tumors of the adrenal gland have been reported as well as treatment of secondary hypersplenism.

PERFORMANCE

The manufacturers of microwave systems pursue different strategies to reach an optimal ablation zone, such as water or gas cooling of the antenna, the simultaneous use of different antennas or an automatic modulation of the microwave energy and frequency.

ACHIEVEMENTS

In contrast to other tumor ablation methods microwave ablation causes a direct heating of a tissue volume, thus this method is less vulnerable to the cooling effect of vessels in the ablation zone. Moreover the electric conductivity of the treated tissue does not influence microwave radiation so that microwave ablation has advantages for the treatment of high-resistance organs, such as the lungs or bone. Some publications have shown that microwave ablation causes larger ablation zones in less time in comparison to radiofrequency ablation.

PRACTICAL RECOMMENDATIONS

Classic indications for microwave ablation are the treatment of malignancies of the liver, lungs and kidneys. Initial technical problems have been solved, so that an increasing significance of the microwave ablation among the ablative therapies is to be expected.

Microwave ablation of ex vivo human liver and colorectal liver metastases with a novel 14.5 GHz generator

PURPOSE

This study assessed the relationship between time, power and ablation size using a novel high-frequency 14.5 GHz microwave applicator in ex vivo human hepatic parenchyma and colorectal liver metastases. Previous examination has demonstrated structurally normal but non-viable cells within the ablation zone. This study aimed to further investigate how ablation affects these cells, and to confirm non-viability.

MATERIALS AND METHODS

Ablations were performed in ex vivo human hepatic parenchyma and tumour for a variety of time (10-180 s) and power (10-50 W) settings. Histological examination was performed to assess cellular anatomy, whilst enzyme histochemistry was used to confirm cellular non-viability. Transmission electron microscopy was used to investigate the subcellular structural effects of ablation within these fixed cells. Preliminary proteomic analysis was also performed to explore the mechanism of microwave cell death.

RESULTS

Increasing time and power settings led to a predictable and reproducible increase in size of ablation. At 50 W and 180 s application, a maximum ablation diameter of 38.8 mm (±1.3) was produced. Ablations were produced rapidly, and at all time and power settings ablations remained spherical (longest:shortest diameter <1.2). Routine histological analysis using haematoxylin-eosin (H&E) confirmed well preserved cellular anatomy despite ablation. Transmission electron microscopy demonstrated marked subcellular damage. Enzyme histochemistry showed complete absence of viability in ablated tissue.

CONCLUSIONS

Large spherical ablation zones can be rapidly and reproducibly achieved in ex vivo human hepatic parenchyma and colorectal liver metastases using a 14.5 GHz microwave generator. Despite well preserved cellular appearance, ablated tissue is non-viable.