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

Numerical modeling and validation of combination embolization-ablation therapy in the liver using dynamic contrast-enhanced (DCE)-MRI

Combination transarterial embolization and ablation is an increasingly common strategy for treating solitary, non-resectable hepatocellular carcinomas (HCCs) greater than 3 cm in size. However, manufacturer guidelines do not provide information as to the size of the ablation zone after embolization. This can put the patient at risk for inadvertent thermal damage to nearby anatomy such as the liver capsule, biliary ducts, diaphragm, and body wall. Thus, while combination therapy is associated with improved clinical outcomes, it is also associated with a higher complication rate. The goal of this study was to create a numerical model to evaluate the change in perfusion in embolization and correlate the perfusional change with final microwave ablation volume. This relationship was then validated in combination embolization ablation therapy in an in-vivo porcine liver model, using a novel MR perfusion sequence.

Intratumoral perfusion may affect microwave ablation area of hepatocellular carcinoma

OBJECTIVES

We aimed to evaluate the effect of intratumoral perfusion on microwave ablation (MWA) area in hepatocellular carcinoma (HCC).

METHODS

Patients who underwent curative MWA for HCC between October 2013 and May 2015 were enrolled. Three days before MWA, contrast-enhanced ultrasound (CEUS) was performed to illustrate the perfusion characteristics of the target lesion. Using the Sonoliver quantification software, time-intensity curves of dynamic CEUS were obtained, and quantitative parameters were extracted. Two microwave antennae were inserted into the center of the tumor and MWA was performed with a continuous power output of 50 W for 5 min. A second CEUS was performed to measure the size of the ablated region. Thereafter, an additional MWA procedure was performed until complete ablation with a 5-10-mm safety margin was achieved.

RESULTS

A total of 38 patients who underwent curative MWA for 39 HCC nodules were enrolled. The mean age was 57 years (34-80 years), and the median maximum diameter of the HCC was 3.4 cm (interquartile range, 2-6.8 cm). Time-intensity curves were obtained and the area under the curve (AUC) was selected as a parameter for intratumoral perfusion. The AUC was inversely and linearly correlated with the size of the MWA area, including long- and short-axis diameters and ablation volume. A 1,000-dB·s change in the AUC produced an average change of 1.17 ± 0.44 mm, 0.725 ± 0.355 mm, and 2.4995 ± 0.6575 cm³ in the long- and short-axis diameters and ablation volume, respectively.

CONCLUSIONS

The intratumoral perfusion of HCC was inversely correlated with MWA area size.

Morphometric characterization and temporal temperature measurements during hepatic microwave ablation in swine

PURPOSE

Heat-induced destruction of cancer cells via microwave ablation (MWA) is emerging as a viable treatment of primary and metastatic liver cancer. Prediction of the impacted zone where cell death occurs, especially in the presence of vasculature, is challenging but may be achieved via biophysical modeling. To advance and characterize thermal MWA for focal cancer treatment, an in vivo method and experimental dataset were created for assessment of biophysical models designed to dynamically predict ablation zone parameters, given the delivery device, power, location, and proximity to vessels.

MATERIALS AND METHODS

MWA zone size, shape, and temperature were characterized and monitored in the absence of perfusion in ex vivo liver and a tissue-mimicking thermochromic phantom (TMTCP) at two power settings. Temperature was monitored over time using implanted thermocouples with their locations defined by CT. TMTCPs were used to identify the location of the ablation zone relative to the probe. In 6 swine, contrast-enhanced CTs were additionally acquired to visualize vasculature and absence of perfusion along with corresponding post-mortem gross pathology.

RESULTS

Bench studies demonstrated average ablation zone sizes of 4.13±1.56cm2 and 8.51±3.92cm2, solidity of 0.96±0.06 and 0.99±0.01, ablations centered 3.75cm and 3.5cm proximal to the probe tip, and temperatures of 50 ºC at 14.5±13.4s and 2.5±2.1s for 40W and 90W ablations, respectively. In vivo imaging showed average volumes of 9.8±4.8cm3 and 33.2±28.4cm3 and 3D solidity of 0.87±0.02 and 0.75±0.15, and gross pathology showed a hemorrhagic halo area of 3.1±1.2cm2 and 9.1±3.0cm2 for 40W and 90W ablations, respectfully. Temperatures reached 50ºC at 19.5±9.2s and 13.0±8.3s for 40W and 90W ablations, respectively.

CONCLUSION

MWA results are challenging to predict and are more variable than manufacturer-provided and bench predictions due to vascular stasis, heat-induced tissue changes, and probe operating conditions. Accurate prediction of MWA zones and temperature in vivo requires comprehensive thermal validation sets.

Remote control of transgene expression using noninvasive near-infrared irradiation

This study investigated whether noninvasive near-infrared (NIR) energy could be transduced into heat in deep-seated organs in which adenovirus type-5 vectors tend to accumulate, thereby activating heat shock protein (HSP) promoter-mediated transgene expression, without local administration of photothermal agents. NIR irradiation of the subdiaphragmatic and left dorsocranial part of the abdominal cavity of adult immunocompetent C3H/HeNRj mice with an 808-nm laser effectively increased the temperature of the irradiated regions of the liver and spleen, respectively, resulting in the accumulation of the heat-inducible HSP70 protein. Spatial control of transgene expression was achieved in the NIR-irradiated regions of the mice administered an adenoviral vector carrying a firefly luciferase (fLuc) coding sequence controlled by a human HSP70B promoter, as assessed by bioluminescence and immunohistochemistry analyses. Levels of reporter gene expression were modulated by controlling NIR power density. Spatial control of transgene expression through NIR-focused activation of the HSP70B promoter, as well as temporal regulation by administering rapamycin was achieved in the spleens of mice inoculated with an adenoviral vector encoding a rapamycin-dependent transactivator driven by the HSP70B promoter and an adenoviral vector carrying a fLuc coding sequence controlled by the rapamycin-activated transactivator. Mice that were administered rapamycin and exposed to NIR light expressed fLuc activity in the splenic region, whereas no activity was detected in mice that were only administered rapamycin or vehicle or only NIR-irradiated. Thus, in the absence of any exogenously supplied photothermal material, remote control of heat-induced transgene expression can be achieved in the liver and spleen by means of noninvasive NIR irradiation.

Predictive Factors of Local Recurrence after Colorectal Cancer Liver Metastases Thermal Ablation

Background: Identify risk factors for local recurrence (LR) after radiofrequency (RFA) and microwave (MWA) thermoablations (TA) of colorectal cancer liver metastases (CCLM). Methods: Uni- (Pearson’s Chi2 test, Fisher’s exact test, Wilcoxon test) and multivariate analyses (LASSO logistic regressions) of every patient treated with MWA or RFA (percutaneously and surgically) from January 2015 to April 2021 in Centre Georges François Leclerc in Dijon, France. Results: Fifty-four patients were treated with TA for 177 CCLM (159 surgically, 18 percutaneously). LR rate was 17.5% of treated lesions. Univariate analyses by lesion showed factors associated with LR: sizes of the lesion (OR = 1.14), size of nearby vessel (OR = 1.27), treatment of a previous TA site LR (OR = 5.03), and non-ovoid TA site shape (OR = 4.25). Multivariate analyses showed that the size of the nearby vessel (OR = 1.17) and the lesion (OR = 1.09) remained significant risk factors of LR. Conclusions: The size of lesions to treat and vessel proximity are LR risk factors that need to be considered when making the decision of thermoablative treatments. TA of an LR on a previous TA site should be reserved to specific situations, as there is an important risk of another LR. An additional TA procedure can be discussed when TA site shape is non-ovoid on control imaging, given the risk of LR.

Effects of microwave ablation on serum Golgi protein 73 in patients with primary liver cancer

BACKGROUND

Microwave ablation (MWA) is an effective treatment option for patients with primary liver cancer. However, it has been reported that the MWA procedure induces a hepatic inflammatory response and injury, which may negatively affect the efficacy of MWA. As such, the discovery of reliable markers to monitor the patient’s response to MWA is needed. Golgi protein 73 (GP73) has been shown to be associated with chronic liver disease. To date, the potential value of serum GP73 in the dynamic monitoring during MWA of liver cancer remains unclear.

AIM

To examine the effects of MWA on the serum levels of GP73 in patients with primary liver cancer.

METHODS

A total of 150 primary liver cancer patients with a single small lesion (≤ 3 cm in diameter) were retrospectively enrolled spanning the period between January 2016 and October 2018. All of the patients received MWA for the treatment of primary liver cancer. Serum GP73, alpha-fetoprotein (AFP), and widely used liver biochemical indicators [serum albumin, total bilirubin (TBIL), alanine aminotransferase (ALT), and aspartate aminotransferase (AST)] were compared before MWA and at different time points, including 1, 2, and 4 wk following the ablation procedure.

RESULTS

Complete tumor ablation was achieved in 95.33% of the patients at 1 mo after MWA. The 1-, 2-, and 3-year disease-free survival rates were 74.67%, 59.33%, and 54.00%, respectively. The serum AFP levels were significantly decreased at 1, 2, and 4 wk after MWA; they returned to the normal range at 12 wk after MWA; and they remained stable thereafter during follow-up in those cases without recurrence. In contrast, the serum GP73 levels were significantly increased at 1 and 2 wk after MWA. The serum GP73 levels reached the peak at 2 wk after MWA, started to decline after hepatoprotective treatment with glycyrrhizin and reduced glutathione, and returned to the pretreatment levels at 12 and 24 wk after MWA. Notably, the changes of serum GP73 in response to MWA were similar to those of TBIL, ALT, and AST.

CONCLUSION

Serum GP73 is markedly increased in response to MWA of liver cancer. Thus, serum GP73 holds potential as a marker to monitor MWA-induced inflammatory liver injury in need of amelioration.

Contemporary evidence on colorectal liver metastases ablation: toward a paradigm shift in locoregional treatment

Image-guided percutaneous ablation techniques represent an attractive local therapy for the treatment of colorectal liver metastases (CLM) given its low risk of severe complications, which allows for early initiation of adjuvant therapies and spare functional liver parenchyma, allowing repeated treatments at the time of recurrence. However, ablation does not consistently achieve similar oncological outcomes to surgery, with the latter being currently considered the first-line local treatment modality in international guidelines. Recent application of computer-assisted ablation planning, guidance, and intra-procedural response assessment has improved percutaneous ablation outcomes. In addition, the evolving understanding of tumor molecular profiling has brought to light several biological factors associated with oncological outcomes following local therapies. The standardization of ablation procedures, the understanding of previously unknown biological factors affecting ablation outcomes, and the evidence by ongoing prospective clinical trials are poised to change the current perspective and indications on the use of ablation for CLM.

N-acetylcysteine alleviates liver injury by suppressing macrophage-mediated inflammatory response post microwave ablation

OBJECT

To investigate N-acetyl-cysteine (NAC) would able to alleviate liver injury and systemic inflammatory response caused by microwave ablation (MWA) in rats.

MATERIALS AND METHODS

Male Sprague-Dawley rats weighing 150-200 g were randomly divided into sham group (only anesthesia and laparotomy except MWA but with intraperitoneal PBS or NAC solution injection according to different situations), control group (intraperitoneal PBS injection for comparation 2 h prior to MWA), and NAC-treated group (intraperitoneal N-acetyl-cysteine (300 mg/kg) injection 2 h prior to MWA). Experimental rats were sacrificed at 4 h following operation in line with the liver injury severity curve. Liver tissue and serum samples were collected for determination of pathology, apoptosis, macrophages contents and protein expression.

RESULTS

The elevated serum level of liver enzymes, Myeloperoxidase (MPO) and inflammatory factors (TNF-α and CXCL1) in MWA-treated rats revealed injurious and pro- inflammatory effect of MVA. Macrophages aggregation was detected in MWA exposure rats similarly. and NAC pre-conditioning mitigate liver damage and hepatocyte apoptosis, besides macrophages accumulation and following inflammatory response in liver tissue.

CONCLUSION

Our results demonstrated that N-acetyl-cysteine application alleviate macrophages aggregation and inflammatory response in liver suffering microwave ablation, and mitigating liver injury and cell apoptosis.

Percutaneous US-guided MWA of small liver HCC: predictors of outcome and risk factors for complications from a single center experience

The aim of the present study was to identify predictors of outcome and complications in patients with small hepatocellular carcinoma (HCC) treated by percutaneous microwave ablation (MWA). Patients with non-previously treated small (≤ 3 cm) HCCs who underwent ultrasound (US)-guided percutaneous MWA between July 2016 and January 2019 were included. For each patient, the following variables were registered: age, sex, albumin, platelet count, INR/PT, PTT ratio, total bilirubin, liver status, etiology of liver disease, Child-Pugh classification, tumor dimension, margin, and hepatic segment, tumor subcapsular, perihilar or perivascular location, HCC focality, ascites. During follow-up, complications and outcomes were registered. Variables were then analyzed in relation to both outcomes and complications. 74 patients were included. Mean CT follow-up was 6.2 months (range 1-24 months). At least one complication occurred in 48% of patients, the majority being asymptomatic imaging findings not requiring intervention. One major complication was registered (duodenal perforation: 1.3%). The occurrence of complications was associated with HCC multifocality and abnormal INR/PT, duodenal wall edema with tumor dimension, portal vein thrombosis with Child Pugh score, perihepatic free fluid with abnormal platelet count and comorbidities. Incomplete response rate at 1 month was 18.9%. Local tumor progression and new HCC nodules rates were 13.5% and 27%, respectively. Incomplete response at 1 month was associated with both alcoholic etiology of liver disease and II segment tumor location, new HCC nodules with PBC. Despite the small series analyzed, significant factors related with complications and outcomes may be kept in mind when planning the best treatment for each patient.

Microwave Ablation in the Proximity of Surgical Clips: Is there a Safety Issue?

Purpose

The purpose of this study was to evaluate the heat generation of surgical clips within the target area of MWA and the influences on the ablation volume.

Materials and Methods

In bovine liver tissue, 42 ex vivo microwave ablations (60 W; 180 s) were performed. During ablation, the temperature was measured continuously at 4 points of interest (POI), in a distance of 7.5 and 15 mm on each side of the microwave antenna, with a titanium surgical placed at one 7.5-mm POI. Ablation volumes containing large vessels (n = 10) were excluded. For every POI, the mean temperature of 32 ablations was calculated. The mean temperatures were compared between the 4 POI and statistically analyzed using the Student’s t test.

Results

The mean maximum temperatures at the side of the clip were 88.76 °C/ 195 s and 52.97 °C/ 195 s and at the side without clip 78.75 °C/ 195 s and 43.16 °C/ 195 s, respectively, at POI 7.5 mm and POI 15 mm. The maximum difference of mean temperatures for POI 7.5 mm was 12.91 °C at 84 s (p = 0.022) and for POI 15 mm 9.77 °C at 195 s (p = 0.009). No significant changes in size and shape of the ablation zone could be determined.

Conclusions

Our study demonstrated significantly higher temperatures adjacent to surgical clips. Also, the temperatures distal to the titanium clip were higher compared to the control location without clip. These findings suggest an increased risk of thermal damage to surrounding tissues during MWA, especially in case of immediate contact to surgical clips.

4D Flow MR Imaging to Improve Microwave Ablation Prediction Models: A Feasibility Study in an In Vivo Porcine Liver

PURPOSE

To characterize the effect of hepatic vessel flow using 4-dimensional (4D) flow magnetic resonance (MR) imaging and correlate their effect on microwave ablation volumes in an in vivo non-cirrhotic porcine liver model.

MATERIALS AND METHODS

Microwave ablation antennas were placed under ultrasound guidance in each liver lobe of swine (n = 3 in each animal) for a total of 9 ablations. Pre- and post-ablation 4D flow MR imaging was acquired to quantify flow changes in the hepatic vasculature. Flow measurements, along with encompassed vessel size and vessel-antenna spacing, were then correlated with final ablation volume from segmented MR images.

RESULTS

The linear regression model demonstrated that the preablation measurement of encompassed hepatic vein size (β = -0.80 ± 0.25, 95% confidence interval [CI] -1.15 to -0.22; P = .02) was significantly correlated to final ablation zone volume. The addition of hepatic vein flow rate found via 4D flow MRI (β = -0.83 ± 0.65, 95% CI -2.50 to 0.84; P = .26), and distance from antenna to hepatic vein (β = 0.26 ± 0.26, 95% CI -0.40 to 0.92; P = .36) improved the model accuracy but not significantly so (multivariate adjusted R² = 0.70 vs univariate (vessel size) adjusted R² = 0.63, P = .24).

CONCLUSIONS

Hepatic vein size in an encompassed ablation zone was found to be significantly correlated with final ablation zone volume. Although the univariate 4D flow MR imaging-acquired measurements alone were not found to be statistically significant, its addition to hepatic vein size improved the accuracy of the ablation volume regression model. Pre-ablation 4D flow MR imaging of the liver may assist in prospectively optimizing thermal ablation treatment.

Stereotactic ablative radiotherapy for hepatocellular carcinoma: History, current status, and opportunities

A variety of surgical and other local-regional approaches to the management of hepatocellular carcinoma (HCC) are in clinical use. External beam radiation therapy is a relative newcomer to the portfolio of treatment options. Advances in planning and delivery of radiation therapy, developing in parallel with and inspiring changing paradigms of tumor management in the field of radiation oncology, have led to growing interest in radiation therapy as a viable treatment option for HCC as well as other liver tumors. In this review, we discuss these advances, current trends in liver radiotherapy, as well as avenues of future clinical and basic research. Liver Transplantation 24 420-427 2018 AASLD.

Hong Kong Consensus Statements for the Management of Unresectable Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is highly prevalent in Hong Kong due to the high prevalence of chronic hepatitis B infection. Liver cancer is the fourth most common cancer and the third most common cause of cancer death. Due to the high case load, there is a high level of local expertise in treating HCC, and the full spectrum of treatment modalities is available. This document summarizes how these modalities should be used based on the latest evidence.

SUMMARY

In 2 meetings held in early 2017, a multidisciplinary group of Hong Kong clinicians, including liver surgeons, interventional radiologists, clinical oncologists, and medical oncologists, met to update local consensus statements for management of HCC. These statements are based on the latest evidence and give detailed guidance on how to deploy these modalities, in particular for cases of HCC which are not suited to surgical resection.

KEY MESSAGES

These statements give detailed information on how to decide if a patient is a candidate for resection, methods to improve candidacy for resection, and guidance for use of various nonsurgical interventions to manage patients ineligible for resection.

Effects of silibinin-loaded thermosensitive liposome-microbubble complex on inhibiting rabbit liver VX2 tumors in sub-hyperthermia fields

In the present study, the effects of silibinin-loaded thermosensitive liposome-microbubble complex (STLMC) on rabbit liver VX2 tumors in sub-hyperthermia fields were investigated using two-dimensional ultrasonography (2D US), contrast-enhanced US (CEUS), hematoxylin and eosin (H&E) staining, immunohistochemistry and ultrastructure observation. 50 rabbits with VX2 liver tumors were divided into five groups: Sub-hyperthermia microwave ablation group (SHM), STLMC injection group (STLMC), SHM ablation plus STLMC injection group (SHM + STLMC), microbubble injection group and blank control group without any treatment. Rabbits in each group were examined using 2D US and CEUS in order to evaluate the tumor volume and diameter before treatment and at day 7 and 21 after treatment. Morphology, expression of CD163 and CD206, and ultrastructure of the tumors were assessed. The average post-treatment volume of tumors in group SHM + STLMC was 1.17±0.88 cm³ at day 7 and 2.15±0.96 cm³ at day 21, which was significantly decreased compared with all other groups (P<0.05). H&E staining indicated that the number of disordered macrophages in the SHM + STLMC group significantly increased compared with the other groups (P<0.05). Immunohistochemical results demonstrated that in the SHM + STLMC, the expression of CD163 and CD206 significantly decreased compared with all other groups (P<0.05). These results suggested that STLMC has a potential function in preventing tumor growth, which may be due to its inhibitory effect on tumor-associated macrophages in the tumor microenvironment.

Hong Kong consensus recommendations on the management of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is particularly prevalent in Hong Kong because of the high prevalence of chronic hepatitis B (CHB) infection; HCC is the fourth commonest cancer in men and the seventh commonest in women, and it is the third leading cause of cancer death in Hong Kong. The full spectrum of treatment modalities for HCC is available locally; however, there is currently no local consensus document detailing how these modalities should be used.

SUMMARY

In a series of meetings held between May and October 2013, a multidisciplinary group of Hong Kong clinicians - liver surgeons, medical oncologists, clinical oncologists, hepatologists, and interventional radiologists - convened to formulate local recommendations on HCC management. These recommendations consolidate the most current evidence pertaining to HCC treatment modalities, together with the latest thinking of practicing clinicians engaged in HCC management, and give detailed guidance on how to deploy these modalities effectively for patients in various disease stages.

KEY MESSAGES

Distinct from other regional guidelines, these recommendations provide guidance on the use of antiviral therapy to reduce the incidence of HCC in CHB patients with cirrhosis and to reduce recurrence of CHB-related HCC.

Optimal Ablation Volumes Are Achieved at Submaximal Power Settings in a 2.45-GHz Microwave Ablation System

Introduction. Local ablative therapies, including microwave ablation (MWA), are common treatment modalities for in situ tumor destruction. Currently, 2.45-GHz ablation systems are gaining prominence because of the shorter application times required. The aims of this study were to determine optimal power and time to ablation volume (AbV) ratios for a new 1.8-mm–2.45-GHz antenna using ex vivo tissue models. Methods. The 1.8-mm–2.45-GHz Accu2i MWA system was employed to perform ablations in bovine liver, porcine muscle, and porcine kidney ex vivo. Whole tissues were prewarmed (35°C) and multiple ablations performed at power settings of 60 to 180 W for 2- to 6-minute time intervals. Postablation, tissues were dissected, AbVs calculated, and correlations to power and time settings made. Results. Significant increases in AbV were measured between each of the time points for a constant power setting in all 3 tissues. Increasing power settings led to significant increases in AbV at power settings ≤140 W. However, no significant increase in AbV was obtained at power settings >140 W. Conclusions. Optimal efficiency for MWA using a new 1.8-mm–2.45-GHz system is achieved at settings of ≤140 W for 6 minutes in a range of ex vivo tissue and no additional benefit occurs by increasing the power setting to 180 W in these tissues.

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.

Creation of short microwave ablation zones: in vivo characterization of single and paired modified triaxial antennas

PURPOSE

To characterize modified triaxial microwave antennas configured to produce short ablation zones.

MATERIALS AND METHODS

Fifty single-antenna and 27 paired-antenna hepatic ablations were performed in domestic swine (N = 11) with 17-gauge gas-cooled modified triaxial antennas powered at 65 W from a 2.45-GHz generator. Single-antenna ablations were performed at 2 (n = 16), 5 (n = 21), and 10 (n = 13) minutes. Paired-antenna ablations were performed at 1-cm and 2-cm spacing for 5 (n = 7 and n = 8, respectively) and 10 minutes (n = 7 and n = 5, respectively). Mean transverse width, length, and aspect ratio of sectioned ablation zones were measured and compared.

RESULTS

For single antennas, mean ablation zone lengths were 2.9 cm ± 0.45, 3.5 cm ± 0.55, and 4.2 cm ± 0.40 at 2, 5, and 10 minutes, respectively. Mean widths were 1.8 cm ± 0.3, 2.0 cm ± 0.32, and 2.5 cm ± 0.25 at 2, 5, and 10 minutes, respectively. For paired antennas, mean length at 5 minutes with 1-cm and 2-cm spacing and 10 minutes with 1-cm and 2-cm spacing was 4.2 cm ± 0.9, 4.9 cm ± 1.0, 4.8 cm ± 0.5, and 4.8 cm ± 1.3, respectively. Mean width was 3.1 cm ± 1.0, 4.4 cm ± 0.7, 3.8 cm ± 0.4, and 4.5 cm ± 0.7, respectively. Paired-antenna ablations were more spherical (aspect ratios, 0.72-0.79 for 5-10 min) than single-antenna ablations (aspect ratios, 0.57-0.59). For paired-antenna ablations, 1-cm spacing appeared optimal, with improved circularity and decreased clefting compared with 2-cm spacing (circularity, 0.85 at 1 cm, 0.78 at 2 cm).

CONCLUSIONS

Modified triaxial antennas can generate relatively short, spherical ablation zones. Paired-antenna ablations were rounder and larger in transverse dimension than single antenna ablations, with 1-cm spacing optimal for confluence of the ablation zone.

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.

Microwave ablation of pancreatic head cancer: safety and efficacy

PURPOSE

To evaluate the safety and efficacy of percutaneous microwave (MW) ablation treatment in locally advanced, nonresectable, nonmetastatic pancreatic head cancer.

MATERIALS AND METHODS

Ten patients with pancreatic head cancer treated with percutaneous (n = 5) or laparotomic (n = 5) MW ablation were retrospectively reviewed. The MW generator used (45 W at 915 MHz) was connected by coaxial cable to 14-gauge straight MW antennas with a 3.7- or 2-cm radiating section. One or two antennae were used, with an ablation time of 10 minutes. Ultrasonographic (US) and combined US/cone-beam computed tomographic (CT) guidance were used in five patients each. Follow-up was performed by CT after 1, 3, 6, and, when possible, 12 months. Tumor response was assessed per Response Evaluation Criteria In Solid Tumors (version 1.1) and Choi criteria. The feasibility, safety, and major and minor complications associated with quality of life (QOL) were recorded prospectively.

RESULTS

The procedure was feasible in all patients (100%). One late major complication was observed in one patient, and no visceral injury was detected. No patient had further surgery, and all minor complications resolved during the hospital stay. An improvement in QOL was observed in all patients despite a tendency to return to preoperative levels in the months following the procedure, without the influence of minor complications. No repeat treatment was performed.

CONCLUSIONS

Despite the small number of patients, the present results can be considered encouraging, showing that MW ablation is a feasible approach in the palliative treatment of pancreatic tumors.

Percutaneous microwave ablation of hepatic tumors: prospective evaluation of postablation syndrome and postprocedural pain

PURPOSE

To prospectively investigate the frequency and severity of postablation syndrome (PAS) and postprocedural pain in a cohort of patients undergoing hepatic microwave ablation.

MATERIALS AND METHODS

From March 2009 to November 2011, 54 consecutive patients undergoing microwave ablation for liver tumors were enrolled. A questionnaire was administered to investigate PAS and pain at 1, 7, and 40 days after ablation. Four patients did not complete all three questionnaires and were excluded from the analysis. Additionally, laboratory tests with results known to significantly increase or decrease after ablation were performed, and ablation parameters were recorded. Potential predictors of PAS and pain at 1 and 7 days were evaluated by a logistic regression model.

RESULTS

Fifty patients underwent a single microwave ablation session, 33 for hepatocellular carcinoma (HCC) and 17 for liver metastasis. Median ablation volumes on computed tomography were 31 cm(3) for HCC and 42 cm(3) for metastasis. Sixty percent of patients experienced PAS in the first week. Aspartate aminotransferase (AST) levels after ablation were significantly associated with PAS during postprocedure days 1-7. Median visual analog scale scores for pain at the puncture site were 1 and 0.24 at 1 and 7 days, respectively. The risk of having at least moderate pain in the first week was significantly related to ablation volume and time and postablation increase in AST level.

CONCLUSIONS

The incidence and severity of PAS with hepatic microwave ablation is similar to that reported for radiofrequency ablation, with the best predictive factor being postablation AST level elevation. Postablation pain was best predicted by total ablation volume and AST level.

Computational modelling of microwave tumour ablations

Microwave tissue heating is being increasingly utilised in several medical applications, including focal tumour ablation, cardiac ablation, haemostasis and resection assistance. Computational modelling of microwave ablations is a precise and repeatable technique that can assist with microwave system design, treatment planning and procedural analysis. Advances in coupling temperature and water content to electrical and thermal properties, along with tissue contraction, have led to increasingly accurate computational models. Developments in experimental validation have led to broader acceptability and applicability of these newer models. This review will discuss the basic theory, current trends and future direction of computational modelling of microwave ablations.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Patterns of histological changes following hepatic electrolytic ablation in an ex-vivo perfused model

Electrolytic ablation (EA) destroys the liver by releasing toxic radicles and producing modifications in the local pH without increasing the tissue temperature. We assessed the histological changes produced by EA using an ex-vivo perfused model. Five porcine livers were harvested, preserved in ice and reperfused for six hours in an extracorporeal circuit using autologous normothermic blood. One hour after reperfusion EA was performed and liver biopsies collected at the end of the experiments. The main necrotic zone consisted of coagulative necrosis, sinusoidal dilatation and haemorrhage with an unusual morphological pattern. The coagulative necrosis and haemorrhage affected mainly the peripheral area of the lobule with relative sparing of the area surrounding the centrilobular vein. Contrasting with this sinusoidal dilatation appeared to be more prominent in the centrilobular area. EA produces patterns of tissue destruction that have not been observed with the more commonly used thermal techniques. Further studies should obtain more information about the influence of adjacent biliary and vascular structures so that appropriate clinical trials can be designed.

A comparison of direct heating during radiofrequency and microwave ablation in ex vivo liver

PURPOSE

This study was designed to determine the magnitude and spatial distribution of temperature elevations when using 480 kHz RF and 2.45 GHz microwave energy in ex vivo liver models.

METHODS

A total of 60 heating cycles (20 s at 90 W) were performed in normal, RF-ablated, and microwave-ablated liver tissues (n = 10 RF and n = 10 microwave in each tissue type). Heating cycles were performed using a 480-kHz generator and 3-cm cooled-tip electrode (RF) or a 2.45-GHz generator and 14-gauge monopole (microwave) and were designed to isolate direct heating from each energy type. Tissue temperatures were measured by using fiberoptic thermosensors 5, 10, and 15 mm radially from the ablation applicator at the depth of maximal heating. Power delivered, sensor location, heating rates, and maximal temperatures were compared using mixed effects regression models.

RESULTS

No significant differences were noted in mean power delivered or thermosensor locations between RF and microwave heating groups (P > 0.05). Microwaves produced significantly more rapid heating than RF at 5, 10, and 15 mm in normal tissue (3.0 vs. 0.73, 0.85 vs. 0.21, and 0.17 vs. 0.09 °C/s; P < 0.05); and at 5 and 10 mm in ablated tissues (2.3 ± 1.4 vs. 0.7 ± 0.3, 0.5 ± 0.3 vs. 0.2 ± 0 °C/s, P < 0.05). The radial depth of heating was ~5 mm greater for microwaves than RF.

CONCLUSIONS

Direct heating obtained with 2.45-GHz microwave energy using a single needle-like applicator is faster and covers a larger volume of tissue than 480-kHz RF energy.