Ultrasound monitoring of a novel microwave ablation (MWA) device in porcine liver: lessons learned and phenomena observed on ablative effects near major intrahepatic vessels

Rational Design of Biomaterials to Potentiate Cancer Thermal Therapy

Cancer thermal therapy, also known as hyperthermia therapy, has long been exploited to eradicate mass lesions that are now defined as cancer. With the development of corresponding technologies and equipment, local hyperthermia therapies such as radiofrequency ablation, microwave ablation, and high-intensity focused ultrasound, have has been validated to effectively ablate tumors in modern clinical practice. However, they still face many shortcomings, including nonspecific damages to adjacent normal tissues and incomplete ablation particularly for large tumors, restricting their wide clinical usage. Attributed to their versatile physiochemical properties, biomaterials have been specially designed to potentiate local hyperthermia treatments according to their unique working principles. Meanwhile, biomaterial-based delivery systems are able to bridge hyperthermia therapies with other types of treatment strategies such as chemotherapy, radiotherapy and immunotherapy. Therefore, in this review, we discuss recent progress in the development of functional biomaterials to reinforce local hyperthermia by functioning as thermal sensitizers to endow more efficient tumor-localized thermal ablation and/or as delivery vehicles to synergize with other therapeutic modalities for combined cancer treatments. Thereafter, we provide a critical perspective on the further development of biomaterial-assisted local hyperthermia toward clinical applications.

Cooling Effects Occur in Hepatic Microwave Ablation At Low Vascular Flow Rates and in Close Proximity to Liver Vessels - Ex Vivo

Background. The impact of vascular cooling effects in hepatic microwave ablation (MWA) is controversially discussed. The objective of this study was a systematic assessment of vascular cooling effects in hepatic MWA ex vivo. Methods. Microwave ablations were performed in fresh porcine liver ex vivo with a temperature-controlled MWA generator (902-928 MHz) and a non-cooled 14-G-antenna. Energy input was set to 9.0 kJ. Hepatic vessels were simulated by glass tubes. Three different vessel diameters (3.0, 5.0, 8.0 mm) and vessel to antenna distances (5, 10, 20 mm) were examined. Vessels were perfused with saline solution at nine different flow rates (0-500 mL/min). Vascular cooling effects were assessed at the largest cross-sectional ablation area. A quantitative and semi-quantitative/morphologic analysis was carried out. Results. 228 ablations were performed. Vascular cooling effects were observed at close (5 mm) and medium (10 mm) antenna to vessel distances (P < .05). Vascular cooling effects occurred around vessels with flow rates ≥1.0 mL/min (P < .05) and a vessel diameter ≥3 mm (P < .05). Higher flow rates did not result in more distinct cooling effects (P > .05). No cooling effects were measured at large (20 mm) antenna to vessel distances (P > .05). Conclusion. Vascular cooling effects occur in hepatic MWA and should be considered in treatment planning. The vascular cooling effect was mainly affected by antenna to vessel distance. Vessel diameter and vascular flow rate played a minor role in vascular cooling effects.

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.

Heat Transfer Study in Breast Tumor Phantom during Microwave Ablation: Modeling and Experimental Results for Three Different Antennas

It is worldwide known that the most common type of cancer among women is breast cancer. Traditional procedures involve surgery, chemotherapy and radiation therapy; however, these treatments are invasive and have serious side effects. For this reason, minimally invasive thermal treatments like microwave ablation are being considered. In this study, thermal behavior of three types of slot-coaxial antennas for breast cancer microwave ablation is presented. By using finite element method (FEM), all antennas were modeled to estimate the heat transfer in breast tumor tissue surrounded by healthy breast tissue. Experimentation was carried out by using the antennas inserted inside sphere-shaped-tumor phantoms with two different diameters, 1.0 and 1.5 cm. A microwave radiation system was used to apply microwave energy to each designed antenna, which were located into the phantom. A non-interfering thermometry system was used to measure the temperature increase during the experimentation. Temperature increases, recorded by the thermal sensors placed inside the tumor phantom surrounded by healthy breast phantom, were used to validate the FEM models. The results conclude that, in all the cases, after 240 s, the three types of coaxial slot antenna reached the temperature needed produce hyperthermia of the tumor volume considered in this paper.

Liver microwave ablation: a systematic review of various FDA-approved systems

OBJECTIVES

The aim of the present study is to analyze preclinical and clinical data on the performance of the currently US Food and Drug Administration (FDA)-approved microwave ablation (MWA) systems.

METHODS

A review of the literature, published between January 1, 2005, and December 31, 2016, on seven FDA-approved MWA systems, was conducted. Ratio of ablation zone volume to applied energy R(AZ:E) and sphericity indices were calculated for ex vivo and in vivo experiments.

RESULTS

Thirty-four studies with ex vivo, in vivo, and clinical data were summarized. In total, 14 studies reporting data on ablation zone volume and applied energy were included for comparison R(AZ:E). A significant correlation between volume and energy was found for the ex vivo experiments (r = 0.85, p < 0.001) in contrast to the in vivo experiments (r = 0.54, p = 0.27).

CONCLUSION

Manufacturers' algorithms on microwave ablation zone sizes are based on preclinical animal experiments with normal liver parenchyma. Clinical data reporting on ablation zone volume in relation to applied energy and sphericity index during MWA are scarce and require more adequate reporting of MWA data.

KEY POINTS

• Clinical data reporting on the ablation zone volume in relation to applied energy during microwave ablation are scarce. • Manufacturers' algorithms on microwave ablation zone sizes are based on preclinical animal experiments with normal liver parenchyma. • Preclinical data do not predict actual clinical ablation zone volumes in patients with liver tumors.

Monitoring Thermal Ablation via Microwave Tomography: An Ex Vivo Experimental Assessment

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances.

Feasibility of Using a Novel 2.45 GHz Double Short Distance Slot Coaxial Antenna for Minimally Invasive Cancer Breast Microwave Ablation Therapy: Computational Model, Phantom, and In Vivo Swine Experimentation

Microwave ablation (MWA) by using coaxial antennas is a promising alternative for breast cancer treatment. A double short distance slot coaxial antenna as a newly optimized applicator for minimally invasive treatment of breast cancer is proposed. To validate and to analyze the feasibility of using this method in clinical treatment, a computational model, phantom, and breast swine in vivo experimentation were carried out, by using four microwave powers (50 W, 30 W, 20 W, and 10 W). The finite element method (FEM) was used to develop the computational model. Phantom experimentation was carried out in breast phantom. The in vivo experimentation was carried out in a 90 kg swine sow. Tissue damage was estimated by comparing control and treated micrographs of the porcine mammary gland samples. The coaxial slot antenna was inserted in swine breast glands by using image-guided ultrasound. In all cases, modeling, in vivo and phantom experimentation, and ablation temperatures (above 60°C) were reached. The in vivo experiments suggest that this new MWA applicator could be successfully used to eliminate precise and small areas of tissue (around 20–30 mm²). By modulating the power and time applied, it may be possible to increase/decrease the ablation area.

The Performance of Higher Frequency Microwave Ablation in the Presence of Perfusion

OBJECTIVE

In this paper, we investigate the impact of perfusion on the performance of microwave ablation across a large frequency range.

METHODS

We designed multiple microwave ablation antennas to operate in liver tissue at discrete frequencies in the range 1.9-18 GHz. We performed electromagnetic simulations to calculate microwave power absorption patterns. Five-minute, 25 W ablation experiments were performed at each frequency in perfused and nonperfused ex vivo porcine livers, and thermal lesion dimensions were measured.

RESULTS

The volume of greatest microwave power absorption shrinks by two orders of magnitude as the frequency is increased from 1.9 to 18 GHz. Mean thermal lesion volumes are consistent across the frequency range for a given perfusion state and are about three times smaller under active perfusion. Typical thermal lesion diameters (perpendicular to the antenna axis) were 24 mm and 16 mm for nonperfused and perfused ablations, respectively. No significant differences in axial ratio were observed among different frequency groups in active-perfusion experiments.

CONCLUSION

Higher-frequency microwave ablation produces thermal lesions with volumes comparable to those achieved at lower frequencies, even in strongly perfused environments.

SIGNIFICANCE

Higher-frequency microwave ablation is appealing because it allows for more flexibility in antenna design. A critical issue concerning the feasibility of higher frequency microwave ablation, considering its strong dependence on heat diffusion to grow thermal lesions, is its performance in strongly perfused environments. This paper shows that higher frequency microwave ablation achieves thermal lesions comparable to those from microwave ablation performed at conventional frequencies in both non- and strongly perfused environments.

Radiofrequency ablation vs. microwave ablation for patients with benign thyroid nodules: a propensity score matching study

PURPOSE

To compare the efficacy and the safety of radiofrequency ablation and microwave ablation for treatment of benign thyroid nodules using a propensity score matching study design.

METHODS

Two hundred and sixty patients with benign thyroid nodules were studied retrospectively, including 102 patients treated with radiofrequency ablation and 158 treated with microwave ablation. To reduce confounding bias due to retrospective assignment, propensity score matching was performed to balance the preablation data of the two groups. After matching, a total of 102 patient pairs (1:1) were created. The volume reduction ratio, therapeutic success rate, symptom and cosmetic score, and major complication were compared between the two groups at 1, 3, 6, and 12 months after treatment.

RESULTS

Between the well-matched groups, no significant differences were found in all nodule volume-related end points at 6 months (volume reduction ratio: 79.4 vs. 77.2 %, P = 0.108; symptom score: 2.1 vs. 1.9, P = 0.456; cosmetic score: 2.1 vs. 2.3, P = 0.119; therapeutic success rate: 99 vs. 97 %, P = 0.621) and 12 months (volume reduction ratio: 83.6 vs. 81.6 %, P = 0.144; symptom score: 1.5 vs. 1.5, P = 0.869; cosmetic score: 1.6 vs. 1.7, P = 0.409; therapeutic success rate: 100 vs. 100 %, P > 0.99) after treatment. No major complications occurred in either group (P > 0.99).

CONCLUSIONS

With well-matched groups and consistent procedure design, our results demonstrated that the volume reduction ratio, therapeutic success rate, symptom and cosmetic score, and complications related to treatment for the two techniques are equivalent. Radiofrequency ablation and microwave ablation are both effective and safe methods in treating benign thyroid nodules.

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.

Effect of Change in Portal Venous Blood Flow Rates on the Performance of a 2.45-GHz Microwave Ablation Device

PURPOSE

To investigate the effect of change in portal venous blood flow rates on the size and shape of ablations created by a 2.45-GHz microwave ablation device.

MATERIALS AND METHODS

This study was exempt from review by the institutional animal care and use committee. An in vitro bovine liver model perfused with autologous blood via the portal vein at five flow rates (60, 70, 80, 90, and 100 mL/min per 100 g of liver) was used to evaluate the effect of change in flow rates on the size and shape of coagulation created by a 2.45-GHz, 140-W microwave ablation device operated for 5 and 10 minutes. Three ablations per ablation time were conducted in each of 10 livers, with two livers perfused at each flow rate. Short- and long-axis diameters were measured from gross specimens, and volume and sphericity index were calculated. General linear mixed models that accounted for correlations within the liver were used to evaluate the effects of lobe, flow, and ablation time on size and sphericity index of ablations.

RESULTS

Flow did not have a significant effect on the size or shape of coagulation created at 5 or 10 minutes (P > .05 for all tests). The mean short- and long-axis diameters and volume were 3.2 cm (95% confidence interval [CI]: 3.1, 3.3), 5.6 cm (95% CI: 5.4, 5.8), and 30.2 cm(3) (95% CI: 28.4, 32.1) for the 5-minute ablations and 3.8 cm (95% CI: 3.7, 3.9), 6.5 cm (95% CI: 6.3, 6.7), and 49.3 cm(3) (95% CI: 47.5, 51.2), for the 10-minute ablations, respectively. The mean sphericity index for both 5- and 10-minute ablations was 34.4% (95% CI: 32%, 36.7%).

CONCLUSION

Change in portal venous blood flow rates did not have an effect on the size and shape of ablations created by a 2.45-GHz microwave ablation device.

Heat sink effect on tumor ablation characteristics as observed in monopolar radiofrequency, bipolar radiofrequency, and microwave, using ex vivo calf liver model

Thermal ablation of liver tumors near large blood vessels is affected by the cooling effect of blood flow, leading to incomplete ablation. Hence, we conducted a comparative investigation of heat sink effect in monopolar (MP) and bipolar (BP) radiofrequency ablation (RFA), and microwave (MW) ablation devices.With a perfused calf liver, the ablative performances (volume, mass, density, dimensions), with and without heat sink, were measured. Heat sink was present when the ablative tip of the probes were 8.0 mm close to a major hepatic vein and absent when >30 mm away. Temperatures (T1 and T2) on either side of the hepatic vein near the tip of the probes, heating probe temperature (T3), outlet perfusate temperature (T4), and ablation time were monitored.With or without heat sink, BP radiofrequency ablated a larger volume and mass, compared with MP RFA or MW ablation, with latter device producing the highest density of tissue ablated. MW ablation produced an ellipsoidal shape while radiofrequency devices produced spheres.Percentage heat sink effect in Bipolar radiofrequency : Mono-polar radiofrequency : Microwave was (Volume) 33:41:22; (mass) 23:56:34; (density) 9.0:26:18; and (relative elipscity) 5.8:12.9:1.3, indicating that BP and MW devices were less affected.Percentage heat sink effect on time (minutes) to reach maximum temperature (W) = 13.28:9.2:29.8; time at maximum temperature (X) is 87:66:16.66; temperature difference (Y) between the thermal probes (T3) and the temperature (T1 + T2)/2 on either side of the hepatic vessel was 100:87:20; and temperature difference between the (T1 + T2)/2 and temperature of outlet circulating solution (T4), Z was 20.33:30.23:37.5.MW and BP radiofrequencies were less affected by heat sink while MP RFA was the most affected. With a single ablation, BP radiofrequency ablated a larger volume and mass regardless of heat sink.

Liver-directed therapies in metastatic colorectal cancer

Colorectal cancer (CRC) is a major health concern in the United States (US) with over 140,000 new cases diagnosed in 2012. The most common site for CRC metastases is the liver. Hepatic resection is the treatment of choice for colorectal liver metastases (CLM), with a 5-year survival rate ranging from 35% to 58%. Unfortunately, only about 20% of patients are eligible for resection. There are a number of options for extending resection to more advanced patients including systemic chemotherapy, portal vein embolization (PVE), two stage hepatectomy, ablation and hepatic artery infusion (HAI). There are few phase III trials comparing these treatment modalities, and choosing the right treatment is patient dependent. Treating hepatic metastases requires a multidisciplinary approach and knowledge of all treatment options as there continues to be advances in management of CLM. If a patient can undergo a treatment modality in order to increase their potential for future resection this should be the primary goal. If the patient is still deemed unresectable then treatments that lengthen disease-free and overall-survival should be pursued. These include chemotherapy, ablation, HAI, chemoembolization, radioembolization (RE) and stereotactic radiotherapy.

Liver metastases in close contact to hepatic veins ablated under vascular exclusion

BACKGROUND

Liver metastases (LM) in close contact to hepatic veins (HV) are a frequent cause of unresectability. Reconstruction of hepatic veins is technically difficult and outcomes are poor. Intra-operative radiofrequency ablation (IRFA) with vascular exclusion (VE) may be a useful approach.

METHODS

Out of 358 patients operated for LM, 22 with LM close to a HV treated by IRFA under VE with at least one year of follow-up were included in this retrospective study. Technical success was evaluated at four months by CT scan of the ablated lesion. Complications; local, hepatic and extra-hepatic recurrence rates, and overall survival are reported.

RESULTS

The median number of metastases was 4.5 [range: 1-12]. Seventeen patients had bilateral metastases. The median size of ablated lesions was 2 cm [range: 1-5.5]. Seven complications occurred (1 Grade 1, 2 Grade 3b and 4 Grade IVa), with no mortality. No recurrence of ablated lesions was detected at four months or during follow-up. Seventeen patients had new or extra-hepatic lesions. Median overall survival for colorectal patients was 40 months 95%CI[17.5-not reached].

CONCLUSIONS

IRFA plus VE for LM in close contact to a HV is a novel approach, appearing to be a safe and effective technique which can extend the applications of liver metastases surgery.

Image-guided tumor ablation: emerging technologies and future directions

As the trend continues toward the decreased invasiveness of medical procedures, image-guided percutaneous ablation has begun to supplant surgery for the local control of small tumors in the liver, kidney, and lung. New ablation technologies, and refinements of existing technologies, will enable treatment of larger and more complex tumors in these and other organs. At the same time, improvements in intraprocedural imaging promise to improve treatment accuracy and reduce complications. In this review, the latest advancements in clinical and experimental ablation technologies will be summarized, and new applications of image-guided tumor ablation will be discussed.

Thermal tumor ablation therapy for colorectal cancer hepatic metastasis

Surgical resection for colorectal hepatic metastases (CRHM) is the preferred treatment for suitable candidates, and the only potentially curative modality. However, due to various limitations, the majority of patients with CRHM are not candidates for liver resection. In recent years, there has been an increasing interest in the role of thermal tumor ablation (TTA) as a component of combined resection-ablation strategies, staged hepatic resections, or as standalone adjunct treatment for patients with CRHM. Thus, ablative approaches have expanded the group of patients with CRHM that may benefit from liver-directed treatment strategies.

Percutaneous microwave ablation for liver cancer adjacent to the diaphragm

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Multifunctional microbubbles and nanobubbles for photoacoustic imaging

Photoacoustic imaging is an emerging imaging modality for noninvasive detection of tissue structural and functional anomalies. Multifunctional microbubbles (MBs) and nanobubbles (NBs) are contrast agents integrating multiple disease-targeting, imaging and therapeutic functions. Multifunctional MBs and NBs represent an enabling technology for many potential applications in the field of photoacoustic imaging. Highly absorbing optical contrast agents, such as gold nanoparticles, India ink and Indocyanine Green, can be encapsulated in MBs and NBs for stable absorption properties and multimodal imaging contrasts. The surface of MBs and NBs can be modified for high disease-targeting affinity, reduced immunogenicity and prolonged circulation lifetime. Low boiling point perfluorocarbon compounds can be encapsulated in MBs and NBs for selective activation by external energy sources. The activation of these MBs and NBs may introduce significant contrast enhancement and facilitate a variety of potential clinical applications, such as image-guided drug delivery and therapeutic margin assessment. MB and NB enhanced photoacoustic imaging is still in its infancy. Further development and validation works are necessary for successful translation of the technology from the benchtop to the bedside.

Microwave ablation of the liver: a description of lesion evolution over time and an investigation of the heat sink effect

AIM

Microwave ablation has been successfully used to treat unresectable liver tumours for many years. However, despite its widespread use, there seems to be a relative paucity of experimental data regarding lesion evolution and the effects of any surrounding vasculature on ablation morphology. The aim of this study was to investigate the principal pathological changes in the liver following microwave ablation, in particular the heat sink effect. In addition we carefully reviewed the available literature to provide an overview of all relevant pathological studies.

METHODS

Microwave ablation was carried out on male rats at various distances from the hilum. Histological (H&E) and immunocytochemical (caspase 3) analyses of the lesion were performed at various time points; 0, 4, 24, 48  hours, 2 weeks and 1 month. A literature review was carried out using Medline, Embase and the Cochrane database to identify all relevant histological studies.

RESULTS

The lesion underwent complete coagulative necrosis and was extremely regular at the ablation edge with no evidence of any influence from surrounding blood vessels at all time points. H&E and caspase 3 results were consistent and microwave caused little collateral damage outside the intended ablation zone.

CONCLUSION

This study suggests that microwave ablation is extremely concise and is minimally affected by the heat sink effect. Comparative investigations with other treatment modalities are required.

Characterization of irreversible electroporation ablation in in vivo porcine liver

OBJECTIVE

The purpose of this study was to prospectively characterize and optimize irreversible electroporation ablation to determine the best parameters to achieve the largest target zones of coagulation for two electrodes.

MATERIALS AND METHODS

Ultrasound-guided irreversible electroporation ablation (n=110) was performed in vivo in 25 pig livers using two 18-gauge electroporation electrodes and an irreversible electroporation generator. Five variables for energy deposition and electrode configuration were sequentially studied: number of electrical pulses (n=20-90), length of pulses (20-100 microseconds), generator voltage (2250-3000 V), interelectrode spacing (1.5-2.5 cm), and length of active electrode exposure (1.0-3.0 cm). Zones of ablation were determined at gross pathology and histopathology 2-3 hours after irreversible electroporation. Dimensions were compared and subjected to statistical analysis.

RESULTS

For 1.5-cm spacing and 2-cm electrode exposure at 2250 V, there was no statistical difference in the size of coagulation when varying the number or length of pulses from 50 to 90 repetitions or 50-100 microseconds, respectively, with each parameter combination yielding 3.0±0.4×1.7±0.4×3.0±0.6 cm (width, depth, and height, respectively). Yet, increasing the pulse width or number over 70 caused increased hyperechogenic or gas and coagulation around the electrode. Increasing the voltage from 2250-3000 V for 70 pulses of 70 microseconds increased coagulation to 3.1±0.4×2.0±0.2 cm (p<0.01 for depth). Greater coagulation width of 3.9±0.5 cm (p<0.01) was achieved at 2-cm interelectrode spacing (with similar depth of 1.9±0.4 cm). However, consistent results required 90 repetitions and a 100-microsecond pulse width; 2.5-cm spacing resulted in two separate zones of ablation. Although electrode exposure did not influence width or depth, a linear correlation (r2=0.77) was noted for height, which ranged from 2.0±0.2-5.0±0.8 cm (for 1- and 3-cm exposures, respectively).

CONCLUSION

Predictable zones of tissue destruction can be achieved for irreversible electroporation. Ablation dimensions are sensitive to multiple parameters, suggesting that precise technique and attention to detail will be particularly important when using this modality.

Real-time ultrasound imaging of irreversible electroporation in a porcine liver model adequately characterizes the zone of cellular necrosis

BACKGROUND

  Irreversible electroporation (IRE) is a largely non-thermal method for the ablation of solid tumours. The ability of ultrasound (US) to measure the size of the IRE ablation zone was studied in a porcine liver model.

METHODS

  Three normal pig livers were treated in vivo with a total of 22 ablations using IRE. Ultrasound was used within minutes after ablation and just prior to liver harvest at either 6 h or 24 h after the procedure. The area of cellular necrosis was measured after staining with nitroblue tetrazolium and the percentage of cell death determined by histomorphometry.

RESULTS

  Visible changes in the hepatic parenchyma were apparent by US after all 22 ablations using IRE. The mean maximum diameter of the ablation zone measured by US during the procedure was 20.1 ± 2.7 mm. This compared with a mean cellular necrosis zone maximum diameter of 20.3 ± 2.9 mm as measured histologically. The mean percentage of dead cells within the ablation zone was 77% at 6 h and 98% at 24 h after ablation.

CONCLUSIONS

  Ultrasound is a useful modality for measuring the ablation zone within minutes of applying IRE to normal liver tissue. The area of parenchymal change measured by US correlates with the area of cellular necrosis.

Colorectal liver metastases

BACKGROUND

Despite major advances in therapies for liver metastases, colorectal cancer remains one of the commonest causes of cancer-related deaths in the UK.

SOURCES OF DATA

The international literature on the management of colorectal liver metastases (CLM) was reviewed.

AREAS OF AGREEMENT

Due to a combination of highly active systemic agents and low perioperative mortality achieved by high-volume centres, a growing number of patients are being offered liver resection with curative intent. Patients with bilobar and/or extrahepatic disease who would previously have received palliative treatment only, are undergoing major surgery with good results. This review focuses on preoperative evaluation, surgical planning and the role of adjuvant therapies in the management of patients with CLM.

AREAS OF CONTROVERSY

Can ablative therapies match the outcomes of surgical resection? How can even more patients be rendered resectable?

GROWING POINTS

The use of other therapies, such as radiofrequency ablation and selective internal radiation therapy.

AREAS TIMELY FOR DEVELOPING RESEARCH

New chemotherapy regimens for neo-adjuvant therapy and the development of new modalities of liver tumour ablation.

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.

Novel laparoscopic bipolar radiofrequency energy technology for expedited hepatic tumour ablation

BACKGROUND

Monopolar radiofrequency ablation (RFA) is a well accepted modality for local control of hepatic tumours, but its effectiveness is challenged by prolonged ablation time, an inconsistent ablation zone and susceptibility to energy loss from convective heat loss from adjacent high-velocity blood flows ('heat sinks'). Bipolar RFA employs a dual parallel electrode array; the energy wave travels unidirectionally between and not around electrodes. This 'line-of-sight' delivery streams energy between two fixed points and concentrates energy delivery to the area between the probes. Bipolar RFA is postulated to yield reduced ablation time and to reduce or eliminate convective heat loss from adjacent high-velocity blood flows. The current study evaluated the feasibility, time and safety of this novel FDA-approved bipolar RFA technology using a laparoscopic approach in human liver tumours.

METHODS

Using the prospectively maintained surgical oncology hepatic-pancreatic-biliary database, 17 consecutive patients (26 liver tumours) who underwent laparoscopic bipolar ablations were reviewed. Electrodes were placed using guidance by intraoperative ultrasound and trajectory planning needles. Ablation time was recorded and postoperative computed tomography scans were obtained.

RESULTS

A total of 18 lesions (in 12 patients) represented metastatic colorectal cancer. Three lesions (in two patients) were hepatocellular carcinoma. Four lesions (in two patients) represented locally advanced symptomatic gallbladder cancer invading the liver bed or symptomatic intrahepatic liver metastases from gallbladder cancer. One lesion was benign hepatic adenoma. Mean tumour size was 3.07 +/- 1.42 cm. Mean ablation time was 358 +/- 120 sec. No major complications were observed in the < or = 30-day or >30-day periods post-RFA.

CONCLUSIONS

Laparoscopic bipolar RFA is a quick, safe technique which adds a new tool to our armamentarium for treating hepatic tumours. Establishing its longterm oncological outcome will require longer follow-up and the exact role of this technique in the current multimodality management remains to be defined.