The efficacy and safety of percutaneous microwave coagulation by a new microwave delivery system in large hepatocellular carcinomas: four case studies

Percutaneous ultrasound-guided microwave ablation for treatment of hepatocellular carcinomas in dogs: four cases (2019-2020)

OBJECTIVES

To describe ultrasound-guided microwave ablation as a minimally invasive treatment option for primary or metastatic hepatocellular carcinomas.

METHODS

Four client-owned dogs underwent percutaneous ultrasound-guided microwave ablation of three primary and one metastatic hepatocellular carcinoma, diagnosed on cytology/histopathology. In each case, multiple ultrasound-guided thermal lesions were created in a 10 to 40 minutes ablation at 30 to 35 W. Real-time monitoring was performed using 10 MHz diagnostic ultrasound transducers. The procedures were performed without complication and CT scans or abdominal ultrasounds were repeated immediately after. Patients were discharged on oral analgesia on the same day or 24 hours later.

RESULTS

Hepatocellular carcinomas were successfully ablated, which in some cases resulted in an improvement in clinical signs and laboratory values. The patients were followed up for a time ranging between 39 and 649 days and no evidence of disease progression was found. Three out of four patients are still alive at the time of writing.

CLINICAL SIGNIFICANCE

In these four patients, minimally invasive ultrasound-guided microwave ablation was feasible and resulted in no immediate complications. Regular imaging follow-up is recommended after the procedure and further studies on microwave ablation are warranted to establish its effectiveness in dogs with hepatocellular carcinomas.

Perivascular extension of microwave ablation zone: demonstrated using an ex vivo porcine perfusion liver model<sup/>

Microwave ablation (MWA) has been proposed to suffer less from the heat sink effect compared to radiofrequency ablation but has been reported to cause extension of the ablation zone along intrahepatic vessels in clinical practice. To study this effect in detail, eight fresh porcine livers were perfused in an ex vivo organ perfusion system. Livers were perfused with oxygenated, O-positive human blood at 37 °C. Perfusion was discontinued immediately before ablation in the non-perfused group (n = 4) whilst in the perfused group (n = 4) perfusion was maintained during MWA (140 W X 2 min). Large intrahepatic vessels (> 6 mm) were avoided using ultrasound. MWA zones were bisected within 30 min of perfusion termination and sections were fixed in formalin and stained with H&E and NADH to assess cell viability. Magnetic resonance imaging (MRI) was performed on two livers (one perfused, one non-perfused) to provide imaging correlation before sectioning. Twenty-one out of a total of 30 MW ablation zones (70%) showed extension of the ablation zone along a vessel. There was no statistically significant difference (p = 1) in the incidence of ablation zone extension between perfused (9/13, 69%) and non-perfused organs (12/17, 71%). MRI also demonstrated ablation zone extension along blood vessels correlating with macroscopy in two livers. NADH staining also confirmed extension of the ablation zone. Liver MWA appears to be commonly associated with propagated thermal injury along adjacent vessels and occurs independent of active blood flow. In order to avoid possible complications through non-target tissue injury, this effect requires further investigation.

The effect of lipiodol deposition in HCC after TACE on the necrosis range of PMCT

Objective

To study the impact of lipiodol deposition in the lesion of hepatocellular carcinoma (HCC) after transarterial chemoembolization (TACE) on the necrosis area of percutaneous microwave coagulation therapy (PMCT).

Materials and methods

A total of 44 patients with HCC with 56 nodules, with a size ranging from 1.5 to 3.5 cm, was selected in our study. About 23 patients (26 nodules) underwent PMCT treatment only as Group A and 21 patients (30 nodules) were treated by PMCT-combined TACE as Group B. All patients underwent PMCT with single-electrode and one-point ablation. Paired t-test was used to analyze pre- and postoperatively the volume of tumor and the necrosis volume after PMCT. Independent t-test was used to compare the difference in the necrosis area between two groups (α=0.05).

Results

All patients underwent PMCT or PMCT combined with TACE successfully. The tumor and necrosis size of Group A was 16.29±19.23 cm³ and 17.98±18.49 cm³ (P=0.650), and 11.95±12.78 cm³ and 16.60±11.70 cm³ of Group B (P=0.017). There was no significant difference on necrosis volume between the two groups (P=0.581). The necrosis area of Group B was larger than the size of the tumor (P=0.017), but the ablation area of the two groups was smaller than the theoretic area (P=0.001). (The theoretic area means that the necrosis area of ablation should be 1.0 cm larger than the tumor in diameter.)

Conclusion

PMCT combined with TACE could enlarge the ablation area, but will not lead to an ideal necrosis area than the PMCT alone. The lipiodol deposition in the tumor lesion may hinder the expansion of the heating field. Therefore, further research was needed.

Effect of Hepatic Perfusion on Microwave Ablation Zones in an Ex Vivo Porcine Liver Model

PURPOSE

To compare the size of ablation zones derived from nonperfused ex vivo livers with ablation zones created using an ex vivo perfused porcine liver model.

MATERIALS AND METHODS

Six fresh porcine livers were used to evaluate microwave ablation (MWA). Perfused (n = 3) and nonperfused (n = 3) livers were warmed to 37°C by oxygenated, O-positive human blood reconstituted with Ringer solution, using an organ perfusion circuit. During MWA, perfusion was discontinued in the nonperfused group and maintained in the perfused group. After MWA (140 watts × 2 min at 2.45 GHz) with the Acculis MTA System (AngioDynamics, Latham, New York), ablation zones were bisected sagittally. Sections were stained with nicotinamide adenine dinucleotide (NADH) and hematoxylin-eosin to assess viability of cells in ablation and marginal zones.

RESULTS

Comparison of 22 MWA zones (9 in perfused group, 13 in nonperfused group) was performed. Ablation zones demonstrated a central "white" and peripheral "red" zone. Cells in the white zone were nonviable with no NADH staining. The red zone showed progressive NADH staining toward the periphery, suggesting incomplete cell death. White and red zones of the perfused group were significantly smaller compared with the nonperfused group (short axis, 17.8 mm ± 2.7 vs 21.1 mm ± 3.2, P = .003; long axis, 40.69 mm ± 3.9 vs 39.63 mm ± 5.2, P = .44; intermediate zone,1.33 mm ± 0.04 vs 2.7 mm ± 0.14, P < .0001; mean ± SD).

CONCLUSIONS

MWA algorithms provided by this manufacturer are based on nonperfused organ data, which overestimate ablation zone size. Data from perfused liver models may be required for more accurate dosimetry guidelines.

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.

Microwave ablation of hepatic malignancy

Microwave ablation is an extremely promising heat-based thermal ablation modality that has particular applicability in treating hepatic malignancies. Microwaves can generate very high temperatures in very short time periods, potentially leading to improved treatment efficiency and larger ablation zones. As the available technology continues to improve, microwave ablation is emerging as a valuable alternative to radiofrequency ablation in the treatment of hepatic malignancies. This article reviews the current state of microwave ablation including technical and clinical considerations.

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.

Percutaneous microwave ablation of larger hepatocellular carcinoma

AIM

To evaluate the efficacy and safety of percutaneous microwave ablation (MWA) in patients with larger hepatocellular carcinoma (HCC) tumours.

MATERIALS AND METHODS

Eighty HCC patients with the maximum tumour measuring between 3 and 8 cm were treated using MWA. Of these patients, 57 had initial HCC, while 23 had recurrent HCC. Fifty-two patients had a main tumour measuring 3-5 cm, and 28 had a main tumour measuring 5-8 cm. Local tumour control, complications, long-term survival, and prognostic factors were analysed.

RESULTS

Complete ablation after the initial treatment was achieved in 70 of 80 (87.5%) patients. Sixteen of the 72 (22.2%) successfully treated patients developed local recurrence. Major complications occurred in 7.5% patients. No procedure-related mortality was observed. The 1, 2, 3, and 5 year overall survival rates after the initial ablation were 81.1, 68.2, 56.5, and 34.6%, with a median survival of 56 months. Univariate analysis revealed that small tumour size (p = 0.003) and pre-ablation α-foetoprotein (AFP) level ≤400 ng/ml (p = 0.042) were favourable prognostic factors of overall survival. Multivariate analysis identified only tumour size as the independent prognosis factor (p = 0.008).

CONCLUSION

Percutaneous MWA is effective and safe for treating larger HCC tumours. The local tumour control and long-term survival are acceptable.

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

PURPOSE

To compare the effectiveness of microwave ablation (MWA) and multipolar radiofrequency ablation (RFA) in ex vivo porcine livers, in both cases using a pair of internally cooled interstitial applicators.

MATERIALS AND METHODS

MWA was performed on ex vivo porcine livers (n = 60) using a pair of simultaneously powered, internally cooled shaft interstitial antennae. Four power settings were used: 50 W, 60 W, 70 W and 80 W (n = 15 per setting). Multipolar RFA was also performed on ex vivo porcine livers (n = 30), also using a pair of simultaneously powered, internally cooled shaft interstitial bipolar applicators. This was performed for two applicator types T30 (3 cm length) and T40 (4 cm length) at a manufacturer prescribed power of 60 W and 80 W, respectively (n = 15 per applicator). Spacing between the two probes was 2 cm in all cases. Each power setting was applied for 15 ablations for 10 min each. The long-axis diameter (Dl), short-axis diameter (Ds) and the ratio Ds/Dl for each ablation were measured. Temperature data were recorded at 10 positions. Temperature curves were recorded at 3 locations, as well as the time required for the temperature to rise to 50°C.

RESULTS

Dl and Ds for all the power settings of MWA were significantly larger than that of both kinds of multipolar RFA (P < 0.05). The rates of temperature to rise to 50°C in all the MW ablations power settings were significantly faster than those in both multipolar RF ablations.

CONCLUSION

MWA by the simultaneous application of double antennae may be more advantageous for treating larger liver tumour than multipolar RFA.

Partial response of hepatocellular carcinoma to percutaneous microwave ablation: risk factors and preventive measures

AIM: To investigate the risk factors and preventive measures for partial response of hepatocellular carcinoma to percutaneous microwave ablation.

METHODS: The clinical data for 465 patients with hepatocellular carcinoma (796 tumor nodules) who underwent percutaneous microwave ablation from October 2004 to June 2010 were retrospectively analyzed. The risk factors and preventive measures for partial response to percutaneous microwave ablation were summarized.

RESULTS: Partial response occurred in 48 patients (69 tumor nodules), and the overall partial response rate was 9.15% (69/754). Of these 48 patients, 45 (64 tumor nodules) underwent percutaneous microwave ablation again and achieved complete ablation in 93.94% (62/64) of tumor nodules; 1 (2 tumor nodules) received percutaneous ethanol injection and achieved successful ablation; and 2 received palliative surgery. The incidence of partial response was positively correlated with large tumor diameter, tumor location (at the hepatic hilum or near the diaphragm or hepatic capsule), multiple tumors, and ill-defined margins on ultrasound(all P < 0.01), and complete ablation was negatively correlated with previous treatment by TACE (3.60% vs 12.39%, P < 0.01). Multivariate analysis showed that tumor size, number of nodules, tumor location, and previous treatment by TACE were independent risk factors for partial response of hepatocellular carcinoma to percutaneous microwave ablation.

CONCLUSION: Large tumor size, multiple tumors, subcapsular lesion, and previous treatment by TACE are often associated with partial response of hepatocellular carcinoma to percutaneous microwave ablation. Percutaneous microwave ablation is an effective and safe method for treatment of partial response of hepatocellular carcinoma.

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.

Microwave tumor ablation: mechanism of action, clinical results, and devices

Microwave ablation uses dielectric hysteresis to produce direct volume heating of tissue. Microwaves are capable of propagating through many tissue types, even those with high impedance such as lung or bone, with less susceptibility to "heat-sink" effects along vessels. Microwaves are highly conducive to the use of multiple applicators, showing the synergy seen with other energies, but also the potential capability for phasing of the electromagnetic field. As a result, larger, more customizable ablation zones may be created in less time. Although multiple microwave ablation systems are currently available, further study and continued development are needed.

Interstitial microwave transition from hyperthermia to ablation: historical perspectives and current trends in thermal therapy

This work reviews the transition from hyperthermia to ablation for cancer treatment with interstitial microwave (MW) antennas. Early work utilising MW energy for thermal treatment of cancer tissue began in the late 1970s using single antennas applied interstitially or the use of multiple interstitial antennas driven with the same phase and equal power at 915 or 2450 MHz. The original antenna designs utilised monopole or dipole configurations. Early work in thermal therapy in the hyperthermia field eventually led to utilisation of these antennas and methods for MW ablation of tumours. Efforts to boost the radiated MW power levels while decreasing antenna shaft temperatures led to incorporation of internally cooled antennas for ablation. To address larger tumours, MW treatment utilised arrays that were simultaneously activated by either non-synchronous or synchronous phase operation, benefiting both hyperthermia and ablation strategies. Numerical modelling was used to provide treatment planning guidance for hyperthermia treatments and is expected to provide a similar benefit for ablation therapy. Although this is primarily a review paper, some new data are included. These new data show that three antennas with 2.5 cm spacing at 45 W/channel and 10 min resulted in a volume of 89.8 cm(3) when operated synchronously, but only 53.4 cm(3) non-synchronously. Efficiency was 1.1 (synchronous) versus 0.7 (non-synchronous). MW systems, treatment planning, and image guidance continue to evolve to provide better tools and options for clinicians and patients in order to provide better approach and targeting optimisation with the goal of improved treatment for the patient.

Comparison of percutaneous 915 MHz microwave ablation and 2450 MHz microwave ablation in large hepatocellular carcinoma

PURPOSE

To compare the effectiveness of ultrasound (US)-guided percutaneous 915 MHz microwave (MW) ablation with the 2450 MHz MW ablation for large hepatocellular carcinoma (HCC) (>4 cm in diameter).

MATERIALS AND METHODS

Patients with HCC >4 cm in diameter who underwent US-guided percutaneous MW ablation with curative intention between March 2007 and December 2008 (39) were randomly divided into two groups, 915 MHz MW group and 2450 MHz MW group. We compared the results of ablation between the two groups.

RESULTS

Fewer antenna insertions for each tumour were required in the 915 MHz MW group (3.69 +/- 0.6) than in the 2450 MHz MW group (4.71 +/- 1.61) (p = 0.01). According to the follow-up contrast-enhanced imagings, technique effectiveness rate was 85.7% (18/21) and 73.7% (14/19) in the 915 MHz MW group and 2450 MHz MW group, respectively (p = 0.44). The rate of local tumour progression (LTP) was 14.3% (3/21) and 26.3% (5/19) in the 915 MHz MW group and 2450 MHz MW group, respectively (p = 0.44). There were no deaths and no thrombosis of major vessels in any patient.

CONCLUSIONS

Compared with 2450 MHz MW ablation, our initial experience showed that percutaneous 915 MHz MW ablation with cooled-shaft antennae was safe and could achieve a high technique effectiveness rate with fewer insertion numbers in the treatment of large HCC. Therefore, percutaneous 915 MHz MW ablation may provide a new method for the treatment of large HCC.

[Interventional radiological treatment of hepatocellular carcinoma]

During the last years, interventional radiological treatment of hepatocellular cancer has changed dramatically. The percutaneous ethanol infiltration is partly replaced by thermoablative methods, mainly by radiofrequency ablation. Cooled-tip electrodes and volumetric therapy planning increased the treatment success. Embolisation beads made vessel occlusion more precise and predictable, while the development of the drug eluting beads led to the most effective way of chemoembolisation. The so called radioembolisation with Yttrium 90 isotopes filled into glass microbeads is slowly gaining acceptance worldwide. Thermoablation and embolisation or chemoembolisation are the main tools for downstaging tumors, or avoiding disease progression in liver transplant recipients on the waiting list. All of these therapeutic options have their well established places in well known and worldwide accepted protocols, such as the algorithm of the Barcelona group (BCLC). In the near future, further results can be expected from the combination of available treatments, including sorafenib medication.