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

Importance of the enhanced cooling system for more spherical ablation zones: Numerical simulation, ex vivo and in vivo validation

INTRODUCTION

This study aimed to investigate the efficacy of a small-gauge microwave ablation antenna (MWA) with an enhanced cooling system (ECS) for generating more spherical ablation zones.

METHODS

A comparison was made between two types of microwave ablation antennas, one with ECS and the other with a conventional cooling system (CCS). The finite element method was used to simulate in vivo ablation. Two types of antennas were used to create MWA zones for 5, 8, 10 min at 50, 60, and 80 W in ex vivo bovine livers (n = 6) and 5 min at 60 W in vivo porcine livers (n = 16). The overtreatment ratio, ablation aspect ratio, carbonization area, and other characteristcs of antennas were measured and compared using numerical simulation and gross pathologic examination.

RESULTS

In numerical simulation, the ECS antenna demonstrated a lower overtreatment ratio than the CCS antenna (1.38 vs 1.43 at 50 W 5 min, 1.19 vs 1.35 at 50 W 8 min, 1.13 vs 1.32 at 50 W 10 min, 1.28 vs 1.38 at 60 W 5 min, 1.14 vs 1.32 at 60 W 8 min, 1.10 vs 1.30 at 60 W 10 min). The experiments revealed that the ECS antenna generated ablation zones with a more significant aspect ratio (0.92 ± 0.03 vs 0.72 ± 0.01 at 50 W 5 min, 0.95 ± 0.02 vs 0.70 ± 0.01 at 50 W 8 min, 0.96 ± 0.01 vs 0.71 ± 0.04 at 50 W 10 min, 0.96 ± 0.01 vs 0.73 ± 0.02 at 60 W 5 min, 0.94 ± 0.03 vs 0.71 ± 0.03 at 60 W 8 min, 0.96 ± 0.02 vs 0.69 ± 0.04 at 60 W 10 min) and a smaller carbonization area (0.00 ± 0.00 cm2 vs 0.54 ± 0.06 cm2 at 50 W 5 min, 0.13 ± 0.03 cm2 vs 0.61 ± 0.09 cm2 at 50 W 8 min, 0.23 ± 0.05 cm2 vs 0.73 ± 0.05 m2 at 50 W 10 min, 0.00 ± 0.00 cm2 vs 1.59 ± 0.41 cm2 at 60 W 5 min, 0.23 ± 0.22 cm2 vs 2.11 ± 0.63 cm2 at 60 W 8 min, 0.57 ± 0.09 cm2 vs 2.55 ± 0.51 cm2 at 60 W 10 min). Intraoperative ultrasound images revealed a hypoechoic area instead of a hyperechoic area near the antenna. Hematoxylin-eosin staining of the dissected tissue revealed a correlation between the edge of the ablation zone and that of the hypoechoic area.

CONCLUSIONS

The ECS antenna can produce more spherical ablation zones with less charring and a clearer intraoperative ultrasound image of the ablation area than the CCS antenna.

Multimodality quantitative ultrasound envelope statistics imaging based support vector machines for characterizing tissue scatterer distribution patterns: Methods and application in detecting microwave-induced thermal lesions

Ultrasound envelope statistics imaging, including ultrasound Nakagami imaging, homodyned-K imaging, and information entropy imaging, is an important group of quantitative ultrasound techniques for characterizing tissue scatterer distribution patterns, such as scatterer concentrations and arrangements. In this study, we proposed a machine learning approach to integrate the strength of multimodality quantitative ultrasound envelope statistics imaging techniques and applied it to detecting microwave ablation induced thermal lesions in porcine liver ex vivo. The quantitative ultrasound parameters included were homodyned-K α which is a scatterer clustering parameter related to the effective scatterer number per resolution cell, Nakagami m which is a shape parameter of the envelope probability density function, and Shannon entropy which is a measure of signal uncertainty or complexity. Specifically, the homodyned-K log10(α), Nakagami-m, and horizontally normalized Shannon entropy parameters were combined as input features to train a support vector machine (SVM) model to classify thermal lesions with higher scatterer concentrations from normal tissues with lower scatterer concentrations. Through heterogeneous phantom simulations based on Field II, the proposed SVM model showed a classification accuracy above 0.90; the area accuracy and Dice score of higher-scatterer-concentration zone identification exceeded 83% and 0.86, respectively, with the Hausdorff distance <26. Microwave ablation experiments of porcine liver ex vivo at 60-80 W, 1-3 min showed that the SVM model achieved a classification accuracy of 0.85; compared with single log10(α),m, or hNSE parametric imaging, the SVM model achieved the highest area accuracy (89.1%) and Dice score (0.77) as well as the smallest Hausdorff distance (46.38) of coagulation zone identification. We concluded that the proposed multimodality quantitative ultrasound envelope statistics imaging based SVM approach can enhance the capability to characterize tissue scatterer distribution patterns and has the potential to detect the thermal lesions induced by microwave ablation.

Ultrasound Homodyned-K Contrast-Weighted Summation Parametric Imaging Based on H-scan for Detecting Microwave Ablation Zones

The homodyned-K (HK) distribution is a generalized model of envelope statistics whose parameters α (the clustering parameter) and k (the coherent-to-diffuse signal ratio) can be used to monitor the thermal lesions. In this study, we proposed an ultrasound HK contrast-weighted summation (CWS) parametric imaging algorithm based on the H-scan technique and investigated the optimal window side length (WSL) of the HK parameters estimated by the XU estimator (an estimation method based on the first moment of the intensity and two log-moments, which was used in the proposed algorithm) through phantom simulations. H-scan diversified ultrasonic backscattered signals into low- and high-frequency passbands. After envelope detection and HK parameter estimation for each frequency band, the α and k parametric maps were obtained, respectively. According to the contrast between the target region and background, the (α or k) parametric maps of the dual-frequency band were weighted and summed, and then the CWS images were yielded by pseudo-color imaging. The proposed HK CWS parametric imaging algorithm was used to detect the microwave ablation coagulation zones of porcine liver ex vivo under different powers and treatment durations. The performance of the proposed algorithm was compared with that of the conventional HK parametric imaging and frequency diversity and compounding Nakagami imaging algorithms. For two-dimensional HK parametric imaging, it was found that a WSL equal to 4 pulse lengths of the transducer was sufficient for estimating the α and k parameters in terms of both parameter estimation stability and parametric imaging resolution. The HK CWS parametric imaging provided an improved contrast-to-noise ratio over conventional HK parametric imaging, and the HK α_cws parametric imaging achieved the best accuracy and Dice score of coagulation zone detection.

A review of antenna designs for percutaneous microwave ablation

Microwave (MW) antenna is a key element in microwave ablation (MWA) treatments as the means that energy is delivered in a focused manner to the tumor and its surrounding area. The energy delivered results in a rise in temperature to a lethal level, resulting in cell death in the ablation zone. The delivery of energy and hence the success of MWA is closely dependent on the structure of the antennas. Therefore, three design criteria, such as expected ablation zone pattern, efficiency of energy delivery, and minimization of the diameter of the antennas have been the focus along the evolution of the MW antenna. To further improve the performance of MWA in the treatment of various tumors through inventing novel antennas, this article reviews the state-of-the-art and summarizes the development of MW antenna designs regarding the three design criteria.

How large is the periablational zone after radiofrequency and microwave ablation? Computer-based comparative study of two currently used clinical devices

Purpose:

To compare the size of the coagulation (CZ) and periablational (PZ) zones created with two commercially available devices in clinical use for radiofrequency (RFA) and microwave ablation (MWA), respectively.

Methods:

Computer models were used to simulate RFA with a 3-cm Cool-tip applicator and MWA with an Amica-Gen applicator. The Arrhenius model was used to compute the damage index (Ω). CZ was considered when Ω> 4.6 (>99% of damaged cells). Regions with 0.6<Ω< 2.1 were considered as the PZ (tissue that has undergone moderate sub-ablative hyperthermia). The ratio of PZ volume to CZ volume (PZ/CZ) was regarded as a measure of performance, since a low value implies achieving a large CZ while keeping the PZ small.

Results:

Ten-min RFA (51 W) created smaller periablational zones than 10-min MWA (11.3 cm³ vs. 17.2 22.9 cm³, for 60 100 W MWA, respectively). Prolonging duration from 5 to 10 min increased the PZ in MWA more than in RFA (2.7 cm³ for RFA vs. 8.3–11.9 cm³ for 60–100 W MWA, respectively). PZ/CZ for RFA were relatively high (65–69%), regardless of ablation time, while those for MWA were highly dependent on the duration (increase of up to 25% between 5 and 10 min) and on the applied power (smaller values as power was raised, 102% for 60 W vs. 81% for 100 W, both for 10 min). The lowest PZ/CZ across all settings was 56%, obtained with 100 W-5 min MWA.

Conclusions:

Although RFA creates smaller periablational zones than MWA, 100 W-5 min MWA provides the lowest PZ/CZ.

Locoregional Therapy, Immunotherapy and the Combination in Hepatocellular Carcinoma: Future Directions

Image-guided locoregional therapies (LRTs) have long been a vital part of treatment regimens for hepatocellular carcinoma (HCC). Ablation, chemoembolization, and radioembolization are examples of commonly used treatment techniques for HCC. This review describes the various methods utilized to treat HCC in the field of interventional oncology and also focuses on new and novel treatment concepts being developed in the field including the use of novel immunotherapy agents and combination therapy of LRTs with immunotherapy.

Efficacy and safety of cooled and uncooled microwave ablation for the treatment of benign thyroid nodules: a systematic review and meta-analysis

PURPOSE

To evaluate the effectiveness and safety of microwave ablation (MWA), including cooled MWA (cMWA) and uncooled MWA (uMWA), for the treatment of benign thyroid nodules (BTNs).

METHODS

The databases of MEDLINE, EMBASE and Cochrane library were searched up to 3 Jun, 2018. In this meta-analysis, data of volume reduction rates (VRRs) at the 3-, 6- and 12-month follow-up, and complications are obtained to evaluate the effectiveness and safety of cMWA and uMWA for the treatment of BTNs.

RESULTS

Nine studies involving 1461 patients with 1845 BTNs were included. The pooled VRR at the 3-month follow-up after MWA therapy reached 54.3% (95% CI: 45.3-63.3%, I2 = 97.6%), 73.5% (95% CI: 66.7-80.3%, I2 = 94.9%) at the 6-month follow-up, and 88.6% (95% CI: 84.9-92.4%, I2 = 92.7%) at the 12-month follow-up. The pooled proportions of overall, major and minor complications were 52.4% (95% CI: 29.8-74.9%; I2 = 99.5%), 4.8% (95% CI: 2.7-7.0%; I2 = 55.9%) and 48.3% (95% CI: 31.2-65.4%; I2 = 99.7%). Both cMWA and uMWA achieved similar pooled VRR at the 3-month follow-up (58.4 vs 45.3%, P = 0.07) and pooled proportion of major complications (4.9 vs 5.0%, P = 0.49), while uMWA had higher pooled proportions of overall and minor complications than cMWA (97.8 vs 29.7%, P < 0.01; 97.8 vs 21.0%, P < 0.01), with more patients suffering pain and skin burn after uMWA (100 vs 5.5%, P < 0.01; 47.2 vs 0.2%, P < 0.01).

CONCLUSION

MWA is an effective treatment modality for BTNs. When considering the patient's comfort, cMWA would be a more preferable procedure with less complications.

Prussian blue nanoparticles: Synthesis, surface modification, and application in cancer treatment

This review outlines recently developed Prussian blue nanoparticle (PB NPs)-based multimodal imaging-guided chemo-photothermal strategies for cancer diagnosis and treatment in order to provide insight into the future of the field. The primary limitation of existing therapeutics is the lack of selectivity in drug delivery: they target healthy and cancerous cells alike. In this paper, we provide a thorough review of diverse synthetic and surface engineering techniques for PB NP fabrication. We have elucidated the various targeting approaches employed to deliver the therapeutic and imaging ligands into the tumor area, and outlined methods for enhancement of the tumor ablative ability of the NPS, including several important combinatorial approaches. In addition, we have summarized different in vitro and in vivo effects of PB NP-based therapies used to overcome both systemic and tumor-associated local barriers. An important new approach - PB NP-based immune drug delivery, which is an exciting and promising strategy to overcome cancer resistance and tumor recurrence - has been discussed. Finally, we have discussed the current understanding of the toxicological effects of PB NPs and PB NP-based therapeutics. We conclude that PB NP-based multimodal imaging-guided chemo-photothermal therapy offers new treatment strategies to overcome current hurdles in cancer diagnosis and treatment.

Experimental Comparison of Photothermal Conversion Efficiency of Gold Nanotriangle and Nanorod in Laser Induced Thermal Therapy

An experimental comparison of the photothermal conversion efficiency (PCE) for gold nanotriangles (GNTs) and nanorods (GNRs) was carried out in the present work. The discrete dipole approximation method was applied to identify the spectral characteristic of GNTs and GNRs with different aspect ratios. On this basis, the PCE of GNTs and GNRs in photothermal therapy were compared theoretically. Afterwards, an in vitro experiment was adopted to investigate the thermal effect of porcine muscle induced by laser irradiation, with and without injected GNTs and GNRs. The influences of laser total power, nanoparticle concentration, and nanoparticle type were investigated. It was found that for the commonly-used wavelengths for photothermal therapy, the PCE of GNTs is higher than that of the GNRs. Furthermore, for GNRs loaded in tissue in vitro, high laser power and high concentration of nanoparticles leads to the degeneration and even carbonization of tissue. However, for the GNTs with the same situation (laser power, nanoparticle volume concentration, and heating time), it could lead to the tissue's evaporation instead of carbonization.

Microwave ablation for treatment of hepatic neoplasia in five dogs

CASE DESCRIPTION 5 dogs between 9 and 11 years of age were evaluated for treatment of primary (n = 2) or metastatic (3) hepatic neoplasia. CLINICAL FINDINGS Patients were evaluated on an elective (n = 3) or emergency (2) basis. Two dogs with primary hepatic neoplasia were evaluated because of lethargy and inappetence. One dog was referred after an enlarged anal sac was detected via palpation per rectum during a routine physical examination. Two dogs were evaluated on an emergency basis because of lethargy and weakness, and hemoabdomen in the absence of a history of trauma was detected. All 5 dogs underwent thoracic radiography and abdominal ultrasonography, with CT performed in both dogs with primary hepatic neoplasia. All dogs had preoperative evidence of abdominal neoplasia, and none had evidence of thoracic metastasis. TREATMENT AND OUTCOME All dogs underwent ventral midline laparotomy and had diffuse hepatic neoplasia that precluded complete resection. Locoregional treatment with MWA was applied to hepatic lesions (0.5 to 2.5 cm diameter) without procedural complications. Histopathologic diagnoses were biliary adenocarcinoma (n = 1), hemangiosarcoma (2), hepatocellular carcinoma (1), and apocrine gland adenocarcinoma (1). CLINICAL RELEVANCE MWA is being increasingly used as an adjunct in the surgical treatment of human patients with primary and metastatic liver disease. Results of the present small case series suggested that MWA is feasible and potentially effective as an adjunctive treatment for appropriately selected dogs with nonresectable hepatic tumors. Further investigation is indicated.

Prospective pilot study of CT-guided microwave ablation in the treatment of osteoid osteomas

PURPOSE

The aims of this work were to assess the feasibility and efficacy of CT-guided microwave ablation (MWA) in the treatment of osteoid osteomas (OOs).

MATERIALS AND METHODS

Thirteen consecutive patients (range 11-31 years old) presenting with OO were prospectively included and treated by CT-guided MWA. Power and duration of MWA were both recorded. The patient's pain was assessed using a numeric pain rating scale (NRS), and side effects were recorded during procedures, after 1 day, 7 days and 1 month. The nidus vascularization and the volume of necrosis induced by MWA were assessed using contrast-enhanced MRI. Success was defined as the complete relief of the patient's pain 1 month after the first procedure, associated with necrosis of the nidus on follow-up MRI.

RESULTS

The success rate was up to 92.3% (12/13). At 1 day, 7 days and 1 month, the median NRSs were respectively 5 [interquartile range (IQR) 2-5], 0 (IQR 0-1) and 0 (IQR 0-0). Side effects observed were one partial and self-resolving lesion of a sensory branch of the radial nerve and two skin burns. The median power of the MWA used was 60 W (IQR 50-60) with a 1.5-min duration (IQR 1-2), leading to MWA-induced necrosis measuring on average 23 × 15 × 16 mm.

CONCLUSION

CT-guided MWA of OO has a success rate that appears to be almost similar to that of laser or radiofrequency ablation, but care must be taken to prevent nerve or skin lesions.

Radiofrequency vs Microwave Ablation After Neoadjuvant Transarterial Bland and Drug-Eluting Microsphere Chembolization for the Treatment of Hepatocellular Carcinoma

AIM

To retrospectively compare the initial response, local recurrence, and complication rates of radiofrequency ablation (RFA) vs microwave ablation (MWA) when combined with neoadjuvant bland transarterial embolization (TAE) or drug-eluting microsphere chemoembolization (TACE) for the treatment of hepatocellular carcinoma (HCC).

METHODS

A total of 35 subjects with Barcelona Clinic Liver Cancer (BCLC) very early and early-stage HCC (range: 1.2-4.1cm) underwent TAE (23) or TACE (12) with RFA (15) or microwave ablation (MWA) (20) from January 2009 to June 2015 as either definitive therapy or a bridge to transplant. TAE and TACE were performed with 40-400μm particles and 30-100μm plus either doxorubicin- or epirubicin-eluting microspheres, respectively. Initial response and local progression were evaluated using modified response evaluation criteria in solid tumors. Complications were graded using common terminology criteria for adverse events version 5.0.

RESULTS

Complete response rates were 80% (12/15) for RFA + TAE/TACE and 95% (19/20) for MWA + TAE/TACE (P = 0.29). Local recurrence rate was 30% (4/12) for RFA + TAE/TACE and 0% (0/19) for MWA + TAE/TACE. Durability of response, defined as local disease control for duration of the study, demonstrated a significant difference in favor of MWA (P = 0.0091). There was no statistical difference in complication rates (3 vs 2).

CONCLUSIONS

MWA and RFA when combined with neoadjuvant TAE or TACE have similar safety and efficacy in the treatment of early-stage HCC. MWA provided more durable disease control in this study; however, prospective data remain necessary to evaluate superiority of either modality.

Comparative study evaluating the efficiency of cooled and uncooled single-treatment MWA in thyroid nodules after a 3-month follow up

•

cMWA and uMWA both lead to a significant reduction of thyroid nodule volume.

•

Patient pain level during uMWA is significantly higher than during cMWA.

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cMWA reduces the risk of side effects.

•

Single-treatment session shows comparable results to multiple treatment sessions.

Objective

The aim of this study was to evaluate and compare the efficacy of single-treatment cooled and uncooled microwave ablation in thyroid nodules.

Methods

Eighteen patients (11 women) with an average age of 62 years (range: 41–80) with 18 cold, mainly solid or solid thyroid nodules were treated with cooled or uncooled microwave ablation. Pain during the treatment was measured on a 10-point score. Side effects revealed by ultrasound or patients’ complaints were documented. Laboratory data was evaluated before, 24 h and three months after MWA. Nodule volumes were measured before and three months after MWA.

Results

Cooled MWA was better tolerated than uncooled MWA. A significant reduction of thyroid nodule volume was observed in all cases. The reduction after cMWA was higher (40%) than after uMWA (29%). Pain intensity during cMWA was significantly lower than after uMWA. CMWA and uMWA led to a significant decrease of nodule blood circulation and echogenicity and to a significant increase of nodule elasticity. Thyroid function remained intact in all cases. The energy (kJ/s) administered into the nodules in relation to the ablation time during cMWA was higher than during uMWA.

Conclusions

CMWA leads to a slightly higher but statistically not significant nodule volume reduction than uMWA. Patient comfort during cMWA is higher than during uMWA. The risk of unintended side effects is less in cMWA. A Single-treatment provides sufficient results.

Cooled microwave ablation of thyroid nodules: Initial experience

OBJECTIVE

To evaluate if internally cooled microwave ablation (cMWA) is a safe and effective method for treatment of benign and malign thyroid nodules.

METHODS

9 patients with 11 symptomatic cold benign thyroid nodules and 1 recurrent thyroid carcinoma ranging in volume from 9.1 to 197ml (mean size 52± 57ml) were treated with cMWA. The mean age of the patients was 59 years. Pain during the treatment was measured on a 10-point scale. Side effects revealed by ultrasound or patients' complaints were documented. Periablative efficacy was measured 24h after cMWA as change (Δ) in serum thyreoglobulin (Tg). Nodule elasticity was measured on a 4-point scale, blood circulation and echogenicity on a 3-point scale.

RESULTS

All patients tolerated cMWA well. Median pain intensity averaged 2.1±0.8 (range: 1-3). Postablative hematoma was observed in all cases. In no cases ablation led to hoarseness, superficial burns, nodule ruptures, vagal reactions or dysphagia. cMWA lead to a significant decrease of blood circulation, nodule echogenicity and a significant increase of elasticity (Δ = 1.1 ± 0.33; 0.8 ± 0.4 and 1.1 ± 0.6 points)(p<0.05). An average increase of 4495ng/ml Tg was measured (p<0.05).

CONCLUSIONS

cMWA is an effective and secure method for treatment of thyroid nodules.

Treatment planning in microwave thermal ablation: clinical gaps and recent research advances

Microwave thermal ablation (MTA) is a minimally invasive therapeutic technique aimed at destroying pathologic tissues through a very high temperature increase induced by the absorption of an electromagnetic field at microwave (MW) frequencies. Open problems, which are delaying MTA applications in clinical practice, are mainly linked to the extremely high temperatures, up to 120 °C, reached by the tissue close to the antenna applicator, as well as to the ability of foreseeing and controlling the shape and dimension of the thermally ablated area. Recent research was devoted to the characterisation of dielectric, thermal and physical properties of tissue looking at their changes with the increasing temperature, looking for possible developments of reliable, automatic and personalised treatment planning. In this paper, a review of the recently obtained results as well as new unpublished data will be presented and discussed.

Microwave ablation of hepatocellular carcinoma

Although surgical resection is still the optimal treatment option for early-stage hepatocellular carcinoma (HCC) in patients with well compensated cirrhosis, thermal ablation techniques provide a valid non-surgical treatment alternative, thanks to their minimal invasiveness, excellent tolerability and safety profile, proven efficacy in local disease control, virtually unlimited repeatability and cost-effectiveness. Different energy sources are currently employed in clinics as physical agents for percutaneous or intra-surgical thermal ablation of HCC nodules. Among them, radiofrequency (RF) currents are the most used, while microwave ablations (MWA) are becoming increasingly popular. Starting from the 90s’, RF ablation (RFA) rapidly became the standard of care in ablation, especially in the treatment of small HCC nodules; however, RFA exhibits substantial performance limitations in the treatment of large lesions and/or tumors located near major heat sinks. MWA, first introduced in the Far Eastern clinical practice in the 80s’, showing promising results but also severe limitations in the controllability of the emitted field and in the high amount of power employed for the ablation of large tumors, resulting in a poor coagulative performance and a relatively high complication rate, nowadays shows better results both in terms of treatment controllability and of overall coagulative performance, thanks to the improvement of technology. In this review we provide an extensive and detailed overview of the key physical and technical aspects of MWA and of the currently available systems, and we want to discuss the most relevant published data on MWA treatments of HCC nodules in regard to clinical results and to the type and rate of complications, both in absolute terms and in comparison with RFA.

Microwave ablation: state-of-the-art review

This paper reviews state-of-the-art microwave ablation (MWA) of tumors. MWA is a novel method for treating inoperable tumors, ie, tumors that cannot be treated surgically. However, patients generally choose removal of the tumor by conventional techniques. A literature review of MWA for breast, liver, lung, and kidney tumors is reported here, with tabulation of our findings according to the type of technique used, with a detailed description of the time, type of microwave generator used, and number of patients treated with MWA. In some cases, the subjects were not human patients, but pig or bovine liver specimens. MWA is a technique that has proved to be promising and likely to be used increasingly in the ablation of cancerous tumors. However, MWA needs to be used more widely to establish itself as a common tool in the treatment of inoperable tumors.

Percutaneous microwave ablation of renal tumors using a gas-cooled 2.4-GHz probe: technique and initial results

The feasibility, safety, and preliminary effectiveness of microwave ablation (MWA) in the treatment of renal tumors using a high-powered, carbon dioxide-cooled probe were evaluated. There were 15 tumors treated in 14 patients. Computed tomography was performed immediately after MWA, and follow-up imaging was performed to evaluate for recurrence. Immediate technical effectiveness was 100%. One complication involved the formation of a renal artery pseudoaneurysm. At follow-up (mean interval, 12.5 wk) evaluation, 14 of 15 (93.3%) tumors demonstrated complete necrosis. MWA is a safe, effective treatment modality; larger studies are warranted to demonstrate long-term oncologic outcomes.

New tumor ablation techniques for cancer treatment (microwave, electroporation)

Since the introduction of radiofrequency ablation (RFA) for the treatment of liver tumors at the end of the 1990s, indications for local ablation techniques have been extended to other organs, in particular, the lungs, kidneys and bones. These techniques have also been improved, in particular to try and overcome the limitations of radiofrequency techniques, especially the significant decrease in complete ablation rates for tumors larger than 3cm and tumors that are contiguous to vessels larger than 3mm. Microwave ablation is a rapidly developing thermal ablation technique similar to RFA but with numerous differences. Electroporation, a non-thermal ablation technique with other possibilities, is in earlier stages of clinical development.

High-powered gas-cooled microwave ablation: shaft cooling creates an effective stick function without altering the ablation zone

OBJECTIVE

The purpose of our study was to validate the ability of a new gas-cooled microwave device to secure antennas into tissue before ablation via shaft cooling and to verify that such cooling does not compromise the intended ablation.

MATERIALS AND METHODS

The force required to extract several types of applicators from ex vivo bovine liver before and after ablation was measured. Six groups were compared: cooled needle and multitined radiofrequency electrodes, secured and unsecured cryoprobes, and gas-cooled microwave antennas (n = 6 each). Ablations were next created in in vivo porcine livers for 2 and 10 minutes (n = 6 each) using the gas-cooled microwave system at 140 W. Extraction force was again measured before and after ablation and compared between groups using analysis of variance with post hoc Student t tests. Histologic analysis of the ablation zone was performed to evaluate cellular necrosis along the antenna shaft.

RESULTS

Ex vivo, the secured cryoprobe and microwave antenna required significantly more force to remove than unsecured radiofrequency, cryoprobe, and microwave applicators (p < 0.05, all comparisons). The multitined radiofrequency electrode and cooled radiofrequency electrode required significantly more force to remove after ablation than before ablation (p = 0.006 and 0.02, respectively). In vivo, the secured antenna required significantly more force to remove before ablation than after ablation at both 2 (p < 0.0001) and 10 minutes (p < 0.0001). There was no histologic evidence of cell preservation along the antenna shaft.

CONCLUSION

The gas cooling used in this microwave device can effectively secure antennas into tissue without altering ablation shape or reducing the intended thermal damage.

Experimental study of destruction to porcine spleen in vivo by microwave ablation

AIM: To discuss the safety, feasibility and regularity of destruction to porcine spleen in vivo with congestion and tumescence by microwave ablation (MWA).

METHODS: Ligation of the splenic vein was used to induce congestion and tumescence in vivo in five porcine spleens, and microwave ablation was performed 2-4 h later. A total of 56 ablation points were ablated and the ablation powers were 30-100 W. The ablation time (1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 min) was performed at a power of 60 W. After ablation, the ablation size was measured in pigs A, C, D and E and spleen resection. In pig B, the ablation size was measured and 2 ablation points were sent for pathology analysis and all tissues were sutured following ablation. Pig B was killed 1 wk later and the ablation points were sent for pathology analysis. Bleeding, tissue carbonization surrounding electrodes, and pathological changes were observed, and the effect on destruction volume relative to different ablation powers, times and positions was analyzed.

RESULTS: The incidence of bleeding (only small am-ounts, < 20 mL) in the course of ablation was 5.4% (3/56) and was attributed to tissue carbonization surrounding electrodes, which also exhibited an incidence of 5.4% (3/56). The destruction volume was influenced by different ablation powers, times and points. It showed that the ablation lesion size increased with increased ablation time, from 1 to 10 min, when the ablation power was 60 W. Also, the ablation lesion size increased with the increase of ablation power, ranging from 30 to 100 W when the ablation time was set to 3 min. A direct correlation was seen between the destruction volume and ablation time by the power of 60 W (r = 0.97542, P < 0.0001, and also between the destruction volume and ablation powers at an ablation time of 3 min (r = 0.98258, P < 0.0001). The destruction volume of zone II (the extra-2/3 part of the spleen, relative to the first or second class vascular branches), which was near the hilum of the spleen, was noteably larger than the destruction volume of zoneI(the intra-1/3 part of the spleen) which was distal from the hilum of the spleen (P = 0.0015). Pathological changes of ablation occurring immediately and 1 wk after MWA showed large areas of coagulation. Immediately following ablation, intact spleen tissues were observed in the areas of coagulation necrosis, mainly around arterioles, and there were no obvious signs of hydropsia and inflammation, while 1 wk following the ablation, the coagulation necrosis was well distributed and complete, as many nuclear fragmentations were detected, and there were obvious signs of hydropsia and inflammation.

CONCLUSION: In vivo treatment of congestion and tumescence in the spleen using microwave ablation of water-cooled antenna is a safe and feasible method that is minimally invasive.

[New techniques of tumor ablation (microwaves, electroporation)]

Since the introduction of radiofrequency tumor ablation of liver tumors in the late 1990s, local destructive therapies have been applied to lung, renal and bone lesions. In addition, new techniques have been introduced to compensate for the limitations of radiofrequency ablation, namely the reduced rate of complete ablation for tumors larger than 3 cm and tumors near vessels larger than 3 mm. Microwave ablation is currently evolving rapidly. While it is a technique based on thermal ablation similar to radiofrequency ablation, there are significant differences between both techniques. Electroporation, of interest because of the non-thermal nature of the ablation process, also is under evaluation.