Microwave liver ablation: influence of hepatic vein size on heat-sink effect in a porcine model

International multicentre prospective study on microwave ablation of liver tumours: preliminary results

BACKGROUND

Microwave ablation (MWA) is increasingly utilized in the treatment of hepatic tumours. Promising single-centre reports have demonstrated its safety and efficacy, but this modality has not been studied in a prospective, multicentre study.

METHODS

Eighteen international centres recorded operative and perioperative data for patients undergoing MWA for tumours of any origin in a voluntary Internet-based database. All patients underwent operative MWA using a 2.45-GHz generator with a 5-mm antenna.

RESULTS

Of the 140 patients, 114 (81.4%) were treated with MWA alone and 26 (18.6%) were treated with MWA combined with resection. Multiple tumours were treated with MWA in 40.0% of patients. A total of 299 tumours were treated in these 140 patients. The median size of ablated lesions was 2.5 cm (range: 0.5-9.5 cm). Tumours were treated with a median of one application (range: 1-6 applications) for a median of 4 min (range: 0.5-30.0 min). A power setting of 100 W was used in 78.9% of cases. Major morbidity was 8.3% and in-hospital mortality was 1.9%.

CONCLUSIONS

These multi-institution data demonstrate rapid ablation time and low morbidity and mortality rates in patients undergoing operative MWA with a high rate of multiple ablations and concomitant hepatic resection. Longterm follow-up will be required to determine the efficacy of MWA relative to other forms of ablative therapy.

Thermal ablation of lung tumors

The 5-year survival for all stages of nonsmall cell lung cancer (NSCLC) remains bleak, having increased from 13% to just 16% over the past 30 years. Despite promising results in nonoperative patients with NSCLC and pulmonary metastatic disease, thermal ablation appears to be limited by large tumor size and proximity to large vessels. This article discusses the particular challenges of performing thermal ablation in aerated lung tissue and reviews important considerations in performing ablation including treatment complications and imaging follow-up. The article compares and contrasts the three major thermal ablation modalities: radiofrequency ablation, microwave ablation, and cryoablation.

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.

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.

Microwaves create larger ablations than radiofrequency when controlled for power in ex vivo tissue

PURPOSE

To compare ablation zones created with equal amounts of 2.45 GHz microwave and 480 kHz radiofrequency (RF) energy in ex vivo liver and lung.

METHODS

A total of 38 ablations were performed in ex vivo liver and lung for 10 min each. Nineteen RF ablations (nine liver, ten lung) were performed with a 480 kHz system (200 W max, impedance-based pulsing) and cooled electrode while measuring the average RF power applied. Nineteen microwave ablations (nine liver, ten lung) were then created using a cooled triaxial antenna to deliver 2.45 GHz at the same power level as in RF experiments. Ablation zones were then sectioned and measured for minimum, maximum and mean diameters, and circularity. Measurements were compared using t-tests, with P < 0.05 indicating statistical significance.

RESULTS

Mean diameters of microwave ablations were greater than RF ablations in both liver and lung (4.4 +/- 0.3 vs 3.3 +/- 0.2 cm in liver; 2.45 +/- 0.3 vs 1.6 +/- 0.5 cm in lungs; P < 0.0005 all comparisons). There was no significant difference in the mean power applied during microwave or RF ablations in either organ (54.44 +/- 1.71 W vs 56.4 +/- 6.7 W in liver, P > 0.05; 40 +/- 0.95 W vs 44.9 +/- 7.1 W in lung, P > 0.05).

CONCLUSIONS

Using a single cooled applicator, microwave energy at 2.45 GHz produces larger ablations than an equivalent amount of 480 kHz RF energy in normal liver and lung. This was more apparent in lung, likely due to the high baseline impedance which limits RF, but not microwave power delivery.

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.

Hepatic tumor ablation

Ablation of liver tumors is part of a multimodality liver-directed strategy in the treatment of various tumors. The goal of ablation is complete tumor destruction, and ultimately improvement of quality and quantity of life for the patient. Technology is evolving rapidly, with important improvements in efficacy. The current state of ablation technology and indications for ablation are described in this review.

Microwave tissue ablation: biophysics, technology, and applications

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

Microwave ablation versus radiofrequency ablation in the kidney: high-power triaxial antennas create larger ablation zones than similarly sized internally cooled electrodes

PURPOSE

To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than radiofrequency (RF) ablation with similarly sized internally cooled electrodes.

MATERIALS AND METHODS

Twenty-eight 12-minute ablations were performed in an in vivo porcine kidney model. RF ablations were performed with a 200-W pulsed generator and either a single 17-gauge cooled electrode (n = 9) or three switched electrodes spaced 1.5 cm apart (n = 7). Microwave ablations were performed with one (n = 7), two (n = 3), or three (n = 2) 17-gauge triaxial antennas to deliver 90 W continuous power per antenna. Multiple antennas were powered simultaneously. Temperatures 1 cm from the applicator were measured during two RF and microwave ablations each. Animals were euthanized after ablation and ablation zone diameter, cross-sectional area, and circularity were measured. Comparisons between groups were performed with use of a mixed-effects model with P values less than .05 indicating statistical significance.

RESULTS

No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm(2)) and single-antenna microwave (mean area, 10.9 cm(2)) ablation zones were significantly larger than single-electrode RF zones (mean area, 5.6 cm(2); P = .001 and P = .0355, respectively). No significant differences were detected between single-antenna microwave and multiple-electrode RF. Ablation zone circularity was similar across groups (P > .05). Tissue temperatures were higher during microwave ablation (maximum temperature of 123 degrees C vs 100 degrees C for RF).

CONCLUSIONS

Microwave ablation with high-power triaxial antennas created larger ablation zones in normal porcine kidneys than RF ablation with similarly sized applicators.

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.