Effect of vessel size on creation of hepatic radiofrequency lesions in pigs: assessment of the "heat sink" effect

Radiofrequency ablation for colorectal liver metastases

The management of hepatic metastases from colorectal cancer (HMCRC) is multimodal including chemotherapy, surgical resection, radiation therapy, and focused destruction technologies. Radiofrequency ablation (RFA) is the most commonly used focused destruction technology. It represents a therapeutic option that may be potentially curative in cases where surgical excision is contra-indicated. It also increases the number of candidates for surgical resection among patients whose liver metastases were initially deemed unresectable. This article explains the techniques, indications, and results of radiofrequency ablation in the treatment of hepatic colorectal metastases.

Percutaneous microwave ablation for hepatocellular carcinoma adjacent to large vessels: a long-term follow-up

PURPOSE

To retrospectively evaluate the effectiveness and safety of ultrasound (US)-guided percutaneous microwave ablation (MWA) in the treatment of hepatocellular carcinoma (HCC) adjacent to large vessels.

MATERIALS AND METHODS

From February 2006 to February 2013, 452 patients with 605 HCC nodules were treated with US-guided percutaneous MWA. Into large vessels group (Group L), 139 patients with 163 lesions (diameter, 1.0-7.0 cm; mean, 2.5±1.1 cm) located less than 5mm away from large vessels were enrolled. And 313 patients with 442 lesions (diameter, 1.0-8.0 cm; mean, 2.5±1.2 cm) located more than 5mm away from hepatic surface, large vessels, gallbladder and gastrointestinal tract were included in control group (Group C). During the ablation, the temperature of marginal ablation tissues was monitored and controlled.

RESULTS

The median follow-up time was 24.5 months (range 2.1-87.7 months) in Group L, and 25.7 months (range 1.6-93.9 months) in Group C. Technical effectiveness was achieved in 157 of 163 (96.3%) tumors in Group L and 429 of 442 (97.1%) tumors in Group C, respectively (p>0.05). The 1-, 3- and 5-year local tumor progression rates and the 1-, 3- and 5-year accumulative survival rates in the two groups have no significantly statistical differences. In addition, no immediate or periprocedural major complications, no delayed complication of vessels or bile ducts injury were found in both of the two groups.

CONCLUSIONS

With strict temperature monitoring, US-guided percutaneous MWA is an efficient and safe technology in treating hepatocellular carcinoma adjacent to large vessels.

Colorectal cancer metastasis: the DNA repair inhibitor Dbait increases sensitivity to hyperthermia and improves efficacy of radiofrequency ablation

PURPOSE

To assess the usefulness of combining hyperthermia with a DNA repair inhibitor (double-strand break bait [Dbait]) and its potential application to radiofrequency ablation (RFA) in a preclinical model of human colorectal cancer.

MATERIALS AND METHODS

The local ethics committee of animal experimentation approved all investigations. First, the relevance was assessed by studying the survival of four human colorectal adenocarcinoma cell cultures after 1 hour of hyperthermia at 41°C or 43°C with or without Dbait. Human colon adenocarcinoma cells (HT-29) were grafted subcutaneously into nude mice (n = 111). When tumors reached approximately 500 mm(3), mice were treated with Dbait alone (n = 20), sublethal RFA (n = 21), three different Dbait schemes and sublethal RFA (n = 52), or a sham treatment (n = 18). RFA was performed to ablate the tumor center alone. To elucidate antitumor mechanisms, 39 mice were sacrificed for blinded pathologic analysis, including assessment of DNA damage, cell proliferation, and tumor necrosis. Others were monitored for tumor growth and survival. Analyses of variance and log-rank tests were used to evaluate differences.

RESULTS

When associated with mild hyperthermia, Dbait induced cytotoxicity in all tested colon cancer cell lines. Sublethal RFA or Dbait treatment alone moderately improved survival (median, 40 days vs 28 days for control; P = .0005) but combination treatment significantly improved survival (median, 84 days vs 40 days for RFA alone, P = .0004), with approximately half of the animals showing complete tumor responses. Pathologic studies showed that the Dbait and RFA combination strongly enhances DNA damage and coagulation areas in tumors.

CONCLUSION

Combining Dbait with RFA sensitizes the tumor periphery to mild hyperthermia and increases RFA antitumor efficacy.

Microwave ablation of osteoid osteomas using dynamic MR imaging for early treatment assessment: preliminary experience

PURPOSE

To evaluate the efficacy of microwave ablation for osteoid osteomas by using dynamic contrast-enhanced magnetic resonance (MR) imaging in early treatment assessment.

MATERIALS AND METHODS

Ten patients (two female, eight male; mean age, 28 y; range, 16-47 y) presenting with osteoid osteomas were treated between June 2010 and December 2012 with the use of computed tomography (CT)-guided microwave ablation. Osteoid osteomas were found at the femoral neck (n = 4), tibia (n = 3), calcaneus (n = 1), navicular bone (n = 1), and dorsal rib (n = 1). Dynamic contrast-enhanced MR imaging at 3.0 T was performed 1 day before microwave ablation and again after ablation. The procedure was considered successful if the signal intensity (SI) of the lesion on MR imaging decreased by at least 50% and the patient was pain-free within 1 week of intervention.

RESULTS

All patients were pain-free within 1 week after microwave ablation and remained so during the 6 months of follow-up. No major or minor complications developed. On average, SI of the lesions decreased by 75% (range, 55.5%-89.1%) after treatment. The difference in lesion SI before versus after ablation was significant by t test (P < .0001; confidence interval, 120.26-174.96) and Wilcoxon test (P = .0020).

CONCLUSIONS

Microwave ablation treatment of osteoid osteoma was highly successful, without any complications observed. Dynamic contrast-enhanced MR imaging is a useful tool for diagnosing osteoid osteoma and evaluating treatment.

Perivascular versus nonperivascular small HCC treated with percutaneous RF ablation: retrospective comparison of long-term therapeutic outcomes

PURPOSE

To compare the long-term therapeutic outcomes of radiofrequency (RF) ablation for small perivascular hepatocellular carcinoma (HCC) and nonperivascular HCC.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board. Between December 2004 and April 2008, 241 patients (175 men and 66 women; age range, 32-82 years) with a single early-stage HCC that was 3 cm or smaller in the greatest dimension underwent ultrasonography-guided percutaneous RF ablation as a first-line treatment. The patients were divided into two groups according to the presence or absence of contacting hepatic vessels that were 3 mm or larger in axial diameter: a group with perivascular HCC (n = 58) and a group with nonperivascular HCC (n = 183). Cumulative local tumor progression, disease-free and long-term survival rates, and prognostic factors were assessed by using Cox proportional hazard models with Bonferroni correction.

RESULTS

The overall median follow-up period was 58 months (range, 13-92 months). The cumulative local tumor progression rates were 10%, 16%, and 26% at 1, 3, and 5 years, respectively, in the perivascular group, and 6.7%, 15.5%, and 20.5% in the nonperivascular group; the differences were not significant (P = .323). The corresponding disease-free survival rates were 79%, 41%, and 29% in the perivascular group and 71.3%, 38.7%, and 26.0% in the nonperivascular group, with no significant difference (P = .689). The corresponding overall survival rates were 100%, 94%, and 82% in the perivascular group and 100%, 88.4%, and 73.9% in the nonperivascular group, also without significant difference (P = .267). There was no significant prognostic factor for local tumor progression, whereas extrahepatic and intrahepatic distant recurrences were significant prognostic factors for overall survival in multivariable analysis.

CONCLUSION

The long-term therapeutic outcomes of RF ablation as first-line treatment for small perivascular HCC were similar to those for nonperivascular HCC.

Heat shock protein 70 expression and effect of combined transcatheter arterial embolization and radiofrequency ablation in the rabbit VX2 liver tumour model

AIM

To evaluate the effects of a combined therapy using transcatheter arterial embolization (TAE) and radiofrequency ablation (RFA) on heat shock protein 70 (HSP70) expression and treatment effects in a rabbit model of VX2 liver tumours.

MATERIALS AND METHODS

Tumour growth and necrosis rates were evaluated on day 7. Five rabbits were assigned to each group and were killed on days 1, 3, and 7 after treatment. HSP70 expression was detected and quantified by immunohistochemistry, Western blot, and reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Tumour growth rate was significantly decreased and the necrosis rate increased in the TAE + RFA group on day 7 compared with the other groups. HSP70 expression in the TAE group peaked on day 1 and bottomed on days 3 and 7. HSP70 expression in the TAE group was significantly greater than in the control group on days 1, 3, and 7. HSP70 expression was increased on day 1, peaked on day 3, and dropped on day 7 in the RFA and TAE + RFA groups. In the TAE + RFA group, HSP70 expression was significantly greater than in the other groups on days 1, 3, and 7. HSP70 expression in Western blot analysis and HSP70 mRNA peaked on day 3 and dropped on day 7 in the TAE, RFA, and TAE + RFA groups.

CONCLUSIONS

HSP70 over-expression in residual tumours after TAE + RFA could be attributed to the additive effects of hypoxia and hyperpyrexia generated by TAE combined with RFA.

Irreversible electroporation: treatment effect is susceptible to local environment and tissue properties

PURPOSE

To study the effects of the surrounding electrical microenvironment and local tissue parameters on the electrical parameters and outcome of irreversible electroporation (IRE) ablation in porcine muscle, kidney, and liver tissue.

MATERIALS AND METHODS

Animal Care and Use Committee approval was obtained, and National Institutes of Health guidelines were followed. IRE ablation (n = 90) was applied in muscle (n = 44), kidney (n = 28), and liver (n = 18) tissue in 18 pigs. Two electrodes with tip exposure of 1.5-2 cm were used at varying voltages (1500-3000 V), pulse repetitions (n = 70-100), pulse length (70-100 µsec), and electrode spacing (1.5-2 cm). In muscle tissue, electrodes were placed exactly parallel, in plane, or perpendicular to paraspinal muscle fibers; in kidney tissue, in the cortex or adjacent to the renal medulla; and in liver tissue, with and without metallic or plastic plates placed 1-2 cm from electrodes. Ablation zones were determined at gross pathologic (90-120 minutes after IRE) and immunohistopathologic examination (6 hours after) for apoptosis and heat-shock protein markers. Multivariate analysis of variance with multiple comparisons and/or paired t tests and regression analysis were used for analysis.

RESULTS

Mean (± standard deviation) ablation zones in muscle were 6.2 cm ± 0.3 × 4.2 cm ± 0.3 for parallel electrodes and 4.2 cm ± 0.8 × 3.0 cm ± 0.5 for in-plane application. Perpendicular orientation resulted in a cross-shaped zone. Orientation significantly affected IRE current applied (28.5-31.7A for parallel, 29.5-39.7A for perpendicular; P = .003). For kidney cortex, ovoid zones of 1.5 cm ± 0.1 × 0.5 cm ± 0.0 to 2.5 cm ± 0.1 × 1.3 cm ± 0.1 were seen. Placement of electrodes less than 5 mm from the medullary pyramids resulted in treatment effect arcing into the collecting system. For liver tissue, symmetric 2.7 cm ± 0.2 × 1.4 cm ± 0.3 coagulation areas were seen without the metallic plate but asymmetric coagulation was seen with the metallic plate.

CONCLUSION

IRE treatment zones are sensitive to varying electrical conductivity in tissues. Electrode location, orientation, and heterogeneities in local environment must be considered in planning ablation treatment. Online supplemental material is available for this article.

Histological and finite element analysis of cell death due to irreversible electroporation

Irreversible electroporation (IRE) has been shown to be an effective method of killing cells locally. In contrast to radiofrequency ablation, the mechanism by which cells are thought to die via IRE is the creation of pores in cell membranes, without substantial increase in tissue temperature. To determine the degree to which cell death is non-thermal, we evaluated IRE in porcine hepatocytes in vivo. Using pulse widths of 10μs, bursts of 3 kV square-wave pulses were applied through a custom probe to the liver of an anesthetized pig. Affected tissue was evaluated histologically via stainings of hematoxylin & eosin (H&E), nitroblue tetrazolium (NBT) to monitor cell respiration and TUNEL to gauge apoptosis. Temperature was measured during the application of electroporation, and heat transfer was modeled via finite element analysis. Cell death was calculated via Arrhenius kinetics. Four distinct zones were observed within the ring return electrode; heat-fixed tissue, coagulation, necrotic, and viable. The Arrhenius damage integral estimated complete cell death only in the first zone, where the temperature exceeded 70°C, and partial or no cell death in the other zones, where maximum temperature was approximately 45°C. Except for a limited area near the electrode tip, cell death in IRE is predominantly due to a non-thermal mechanism.

Membrane-targeting approaches for enhanced cancer cell destruction with irreversible electroporation

Irreversible electroporation (IRE) is a promising technology to treat local malignant cancer using short, high-voltage electric pulses. Unfortunately, in vivo studies show that IRE suffers from an inability to destroy large volumes of cancer tissue without introduction of cytotoxic agents and/or increasing the applied electrical dose to dangerous levels. This research will address this limitation by leveraging membrane-targeting mechanisms that increase lethal membrane permeabilization. Methods that directly modify membrane properties or change the pulse delivery timing are proposed that do not rely on cytotoxic agents. This work shows that significant enhancement (67-75% more cell destruction in vitro and >100% treatment volume increase in vivo) can be achieved using membrane-targeting approaches for IRE cancer destruction. The methods introduced are surfactants (i.e., DMSO) and pulse timing which are low cost, non-toxic, and easy to be incorporated into existing clinical use. Moreover, when needed, these methods can also be combined with electrochemotherapy to further enhance IRE treatment efficacy.

Flow-dependent vascular heat transfer during microwave thermal ablation

Microwave tumor ablation is an attractive option for thermal ablation because of its inherent benefits over radiofrequency ablation (RFA) in the treatment of solid tumors such as hepatocellular carcinoma (HCC). Microwave energy heats tissue to higher temperatures and at a faster rate than RFA, creating larger, more homogenous ablation zones. In this study, we investigate microwave heating near large vasculature using coupled fluid-flow and thermal analysis. Low-flow conditions are predicted to be more likely to cause cytotoxic heating and, therefore, vessel thrombosis and endothelial damage of downstream tissues. Such conditions may be more prevalent in patient with severe cirrhosis or compromised blood flow. High-flow conditions create the more familiar heat-sink effect that can protect perivascular tissues from the intended thermal damage. These results may help guide placement and use of microwave ablation technologies in future studies.

Computed-tomography-guided high-dose-rate brachytherapy (CT-HDRBT) ablation of metastases adjacent to the liver hilum

PURPOSE

To evaluate technical feasibility and clinical outcome of computed tomography-guided high-dose-rate-brachytherapy (CT-HDRBT) ablation of metastases adjacent to the liver hilum.

MATERIALS AND METHODS

Between November 2007 and May 2012, 32 consecutive patients with 34 metastases adjacent to the liver hilum (common bile duct or hepatic bifurcation ≤5 mm distance) were treated with CT-HDRBT. Treatment was performed by CT-guided applicator placement and high-dose-rate brachytherapy with an iridium-192 source. MRI follow-up was performed 6 weeks and every 3 months post intervention. The primary endpoint was local tumor control (LTC); secondary endpoints included time to progression (TTP) and overall survival (OS).

RESULTS

Patients were available for MRI evaluation for a mean follow-up time of 18.75 months (range: 3-56 months). Mean tumor diameter was 4.3 cm (range: 1.3-10.7 cm). One major complication was observed. Four (11.8%) local recurrences were observed after a local tumor control of 5, 8, 9 and 10 months, respectively. Twenty-two patients (68.75%) experienced a systemic tumor progression during the follow up period. Mean TTP was 12.9 months (range: 2-56 months). Nine patients died during the follow-up period. Median OS was 20.24 months.

CONCLUSION

Minimally invasive CT-HDRBT is a safe and effective option also for unresectable liver metastases adjacent to the liver hilum that would have been untreatable by thermal ablation.

[Irreversible electroporation: the new generation of local ablation techniques for renal cell carcinoma]

BACKGROUND

Local ablation techniques are a major focus of current developments in oncology. The primary aim is to retain organs and preserve organ functions without compromising the oncological outcome.

METHOD

Irreversible electroporation (IRE) is a novel ablation technique that involves the application of high-voltage pulses to induce cell apoptosis without causing thermal damage to the target tissue or adjacent structures.

AIM

First published in 2005 IRE is currently undergoing preclinical and clinical trials in several areas of oncology and the initial results have been promising. The IRE technique could be a significant development in ablation treatment for renal cell carcinoma (RCC) but decisive proof of its effectiveness for local RCC has not yet been provided. This study presents the results of preclinical and initial clinical trials which are discussed and compared with those of other ablation techniques in order to demonstrate the current value of IRE.

Thermal ablation of malignant lung tumors

BACKGROUND

About 50 000 new cases of non-small-cell carcinoma of the lung are diagnosed in Germany each year. More than 20% of the affected patients cannot be offered radical resection because of comorbidity alone. The lung is also the second most common site of distant metastases of extrathoracic tumors; it is the only site of such metastases in 20% of cases. In recent years, image-guided thermoablation has been used with increasing frequency in patients who are unable to undergo surgery for medical reasons.

METHODS

The PubMed database was selectively searched for publications on the indications, complications, and results of the thermoablative techniques currently in clinical use, with special attention to radiofrequency ablation (RFA).

RESULTS

There is only a small evidence base to date concerning the treatment of malignant lung tumors with thermoablation. Retrospective and prospective case series have been published, but no randomized controlled trials have yet been conducted. RFA, the most common technique, involves the image-guided percutaneous placement of one or more probes in the tumor, to which thermal energy is then applied. For peripherally located tumors that measure less than 3 cm in diameter, local control of tumor growth can be achieved in about 90% of cases. The long-term results that are now available from smaller series provisionally indicate 5-year survival rates of 20% to 61%. The most common complication is pneumothorax requiring drainage, which occurs in about 10% of cases. In the intermediate term, thermoablation does not cause any clinically relevant loss of pulmonary function.

CONCLUSION

Image-guided thermoablation cannot now be considered an alternative to surgery for the treatment of malignant lung tumors with curative intent. It does, however, widen the spectrum of therapeutic options for patients who are medically unable to undergo a surgical procedure.

Radiofrequency ablation of the pancreas with and without intraluminal duodenal cooling in a porcine model

OBJECTIVE

To determine the short-term outcome of radiofrequency ablation (RFA) of pancreatic tissue near the duodenum and portomesenteric vessels (PMV) in a porcine model with and without intraluminal duodenal cooling.

BACKGROUND

RFA has been proposed as a new treatment strategy in patients with unresectable locally advanced pancreatic cancer. RFA may cause thermal damage to the duodenum and vascular structures, but these risks and potential protective measures have never been systematically addressed. Intraluminal duodenal cooling during RFA could prevent thermal damage to the duodenum.

METHODS

RFA was performed in 11 pigs during laparotomy with a bipolar probe of 30 mm active length at a power of 30 W until a total energy of 15 kJ was administered. The RFA probe was inserted in the pancreas at 5 or 15 mm from the duodenum, PMV, and in the pancreatic tail. RFA near the duodenum was performed with and without intraluminal duodenal cooling using 100 mL/min saline of 5°C. Histopathologic assessment was performed.

RESULTS

The maximum RFA-induced temperature was 92°C. RFA with one single probe induced adequate ablation lesions with a diameter of 20 mm over a length of 30 mm. Without duodenal cooling, RFA induced duodenal thermal damage, whereas with duodenal cooling, no damage was observed. RFA at 15 mm from the PMV resulted in minimal superficial focal vascular damage, without thrombosis or hemorrhage.

CONCLUSIONS

RFA provides adequate ablation zones in the pancreas of the porcine. Thermal damage to the duodenum can be prevented by intraluminal duodenal cooling without loss of ablation effectivity.

Percutaneous ablation of lymph node metastases using CT-guided high-dose-rate brachytherapy

OBJECTIVE

To assess the technical feasibility, safety and clinical outcome of CT-guided high-dose-rate brachytherapy (CT-HDRBT) for achieving local tumour control (LTC) in isolated lymph node metastases.

METHODS

From January 2008 to December 2011, 10 patients (six males and four females) with isolated nodal metastases were treated with CT-HDRBT. Five lymph node metastases were para-aortic, three were at the liver hilum, one at the coeliac trunk and one was a left iliac nodal metastasis. The mean lesion diameter was 36.5 mm (range 12.0-67.0 mm). Patients were followed up by either contrast-enhanced CT or MRI 6 weeks and then every 3 months after the end of treatment. The primary end point was LTC. Secondary end points included primary technical effectiveness rate, adverse events and progression-free survival.

RESULTS

The first follow-up examination after 6 weeks revealed complete coverage of all nodal metastases treated. There was no peri-interventional mortality or major complications. The mean follow-up period was 13.2 months (range 4-20 months). 2 out of 10 patients (20%) showed local tumour progression 9 and 10 months after ablation. 5 out of 10 patients (50%) showed systemic tumour progression. The mean progression-free interval was 9.2 months (range 2-20 months).

CONCLUSION

CT-HDRBT is a safe and effective technique for minimally invasive ablation of nodal metastases.

ADVANCES IN KNOWLEDGE

CT-HDRBT of lymph node metastases is feasible and safe. CT-HDRBT might be a viable therapeutic alternative to obtain LTC in selected patients with isolated lymph node metastases.

Unresectable lung malignancy: combination therapy with segmental pulmonary arterial chemoembolization with drug-eluting microspheres and radiofrequency ablation in 17 patients

PURPOSE

To evaluate the feasibility, safety, and effectiveness of combining segmental pulmonary arterial chemoembolization (SPACE) and percutaneous radiofrequency (RF) ablation in patients with unresectable lung neoplasms or patients with resectable neoplasms who refused surgery and to compare the local tumor progression (LTP) rate with that in previous studies of RF ablation alone.

MATERIALS AND METHODS

After institutional review board approval and informed consent, 17 patients with primary and metastatic lung cancer were enrolled in this prospective study. Between January 2008 and February 2011, 20 nodules (median diameter, 3.0 cm; range, 2.0-5.0 cm) were treated during 19 sessions. Antineoplastic agents loaded on 50-100-µm microspheres were selectively infused into specific pulmonary arteries. Percutaneous computed tomography (CT)-guided RF ablation of lung nodules was performed 48 hours after SPACE. Follow-up consisted of enhanced CT 48 hours after combination treatment was completed, after 30 days, and every 3 months thereafter. Fluorine 18 fluorodeoxyglucose positron emission tomography was performed 3 months after combination therapy and then every 6 months. The t test was used to compare groups.

RESULTS

Technical success was achieved in 100% of cases. Ventilation-lung single photon emission computed tomography showed a wide area without ventilation in the lung parenchyma treated with SPACE. The LTP rate was 21% (three of 14 nodules) in 3-5-cm-diameter tumors and 0% (zero of six nodules) in tumors of 3 cm or smaller in diameter. Complete response was achieved in 65% (11 of 17) of patients at minimum follow-up of 6 months. Overall, treatment was well tolerated. Major complications were pneumothorax in five of 19 sessions (26%) and one bronchopleural fistula (one of 19, 5%). No treatment-related changes in general lung function were noted.

CONCLUSION

Combination therapy with RF ablation after SPACE to treat unresectable lung tumors is technically feasible, safe, and effective and may represent an advantage over RF ablation alone.

Controlled swine bile duct ablation with a bipolar radiofrequency catheter

BACKGROUND

Radiofrequency (RF) power is capable of ablation of neoplastic tissue arising from Barrett's esophagus. Endoscopic catheter bipolar RF ablation is a new technique for ablation of neoplastic tissue in the bile duct.

OBJECTIVE

To determine the effect of RF power on bile duct and solid organ histology.

DESIGN

Nonsurvival animal study.

SETTING

Academic center.

PATIENTS

This study involved 4 Yorkshire farm swine.

INTERVENTION

After we made a midline laparotomy incision, a bipolar RF catheter was placed with 3 power (5, 7, 10 W) and voltage settings (66, 132, 190 V) in the bile duct and solid organs (liver, spleen, kidney, and pancreas). Gross and histologic examinations were performed.

MAIN OUTCOME MEASUREMENTS

Depth of ablation in the bile duct wall, characteristics of the ablation in the solid organs.

RESULTS

An endoscopic bipolar RF catheter produced incomplete (bile duct), patchy ablation (pancreas) with 5 watts, intramural (bile duct) or confluent ablation with 7 watts, and transmural (bile duct) ablation at 10 W. The depth of ablation in the bile duct was 0.9 ± 0.3, 1.5 ± 0.2, 2.3 ± 0.6 mm at 5, 7, and 10 W, respectively (analysis of variance; P = .02). Histologic ablation was not achieved in the liver, although gross changes were seen.

LIMITATIONS

Animal study, normal bile duct.

CONCLUSION

RF energy applied to the bile duct or solid organs resulted in controlled ablation with a linear relationship between the depth of ablation in the bile duct and RF power.

Irreversible electroporation in porcine liver: short- and long-term effect on the hepatic veins and adjacent tissue by CT with pathological correlation

OBJECTIVE

The objective of the study was to determine the short- and long-term effects of irreversible electroporation (IRE) on the hepatic veins and the perivascular tissue through serial computed tomography (CT) with pathological correlation.

MATERIALS AND METHODS

Multiple IRE lesions were created percutaneously by ultrasound guidance in livers of 11 Yorkshire pigs using a prototype IRE generator. Paired electrodes were used. Three pigs were killed at the same day; 2 pigs, at 2 days; 2 pigs, at 2 weeks; 2 pigs, at 4 weeks; and 2 pigs, at 8 weeks. Contrast-enhanced CT was performed in all pigs initially and thereafter at selected intervals. Pathological sections were performed for correlation. Initial CT scans were analyzed for lesions for degree of circumferential contact (< 25%, 26%-50%, 51%-75%, and 76%-100%) to the hepatic veins for analysis of any contour deformity. The hepatic veins were also analyzed for any thrombus and for any narrowing. Those lesions with follow-up scans were also analyzed for changes over time.

RESULTS

Twenty-three lesions showed contiguity to the hepatic veins between 3 to 9 mm in size at the initial CT. No contour deformity due to perivascular tissue sparing is detected for any lesion. There was no thrombus detected in any vessel at any time point. Vessel narrowing was seen in 9 of 23 veins on the initial CT, all less than 50% in diameter and all with lesion contact of greater than 25% in circumference, but 2 of 3 veins with follow-up scans showed return-to-normal caliber. No late narrowing of any hepatic vein was seen on the long-term follow-up.

CONCLUSION

Irreversible electroporation creates uniform tissue ablation around the hepatic veins without perivascular tissue sparing. Vessel narrowing may occur acutely but without long-term sequela.

Local ablation for hepatocellular carcinoma in taiwan

Hepatocellular carcinoma (HCC) is the second commonest cancer in Taiwan. The national surveillance program can detect HCC in its early stages, and various curative modalities (including surgical resection, orthotopic liver transplantation, and local ablation) are employed for the treatment of small HCC. Local ablation therapies are currently advocated for early-stage HCC that is unresectable because of co-morbidities, the need to preserve liver function, or refusal of resection. Among the various local ablation therapies, the most commonly used modalities include percutaneous ethanol injection and radiofrequency ablation (RFA); percutaneous acetic acid injection and microwave ablation are used less often. RFA is more commonly employed than other local ablative modalities in Taiwan because the technique is highly effective, minimally invasive, and requires fewer sessions. RFA is therefore advocated in Taiwan as the first-line curative therapy for unresectable HCC or even for resectable HCC. However, current RFA procedures are less effective against tumors that are in high-risk or difficult-to-ablate locations, are poorly visualized on ultrasonography (US), or are large. Recent advancements in RFA in Taiwan can resolve these issues by the creation of artificial ascites or pleural effusion, application of real-time virtual US assistance, use of combination therapy before RFA, or use of switching RF controllers with multiple electrodes. This review article provides updates on the clinical outcomes and advances in local ablative modalities (mostly RFA) for HCC in Taiwan.

Imaging after percutaneous radiofrequency ablation of hepatic tumors: Part 2, Abnormal findings

OBJECTIVE

The purpose of this article is to review the spectrum of early and delayed abnormal cross-sectional imaging findings after radiofrequency ablation (RFA) of hepatic tumors.

CONCLUSION

Recognition of abnormal post-RFA imaging findings and differentiation of abnormal findings from normal postprocedural changes are important for diagnostic and interventional radiologists. Early identification of residual or recurrent disease and complications can facilitate timely retreatment, management, and follow-up care.

Irreversible electroporation ablation: is all the damage nonthermal?

PURPOSE

To determine whether high-dose irreversible electroporation (IRE) ablation induces thermal effects in normal liver tissue.

MATERIALS AND METHODS

Animal care and use committee approval was obtained prior to the experiments. IRE ablation (n = 78) was performed by a single four-person team in vivo in 22 porcine livers by applying electric current to two 1.3-cm-diameter circular flat-plate electrodes spaced 1 cm apart. Cardiac-gated IRE pulses (n = 40-360) were systematically applied at varying voltages (1500-2900 V). End temperatures at the ablation zone center were measured and were correlated with ablation time, energy parameters, and resultant treatment effect as determined at gross pathologic and histopathologic examination. Temperatures were then monitored at the center and periphery of four ablations created by using a four-electrode IRE array (3000 V, 90 pulses per electrode pair). Data were analyzed by using multivariate analysis of variance with multiple comparisons and/or paired t tests and regression analysis, as appropriate.

RESULTS

Temperature rose above the 34°C baseline after IRE in all flat-plate experiments and correlated linearly (R(2) = 0.39) with IRE "energy dose" (product of voltage and number of pulses) and more tightly in univariate analysis with both voltage and number of pulses. Thus, mean temperatures as high as 86°C ± 3 (standard deviation) were seen for 2500 V and 270 pulses. Ablations of 90 pulses or more at 2500 V produced temperatures of 50°C or greater and classic gross and histopathologic findings of thermal coagulation (pyknotic nuclei and streaming cytoplasm). For lower IRE doses (ie, 2100 V, 90 pulses), temperatures remained below 45°C, and only IRE-associated pathologic findings (ie, swollen sinusoids, dehydrated cells, and hemorrhagic infiltrate) were seen. For the four-electrode arrays, temperatures measured 54.2°C ± 6.1 at the electrode surfaces and 38.6°C ± 3.2 at the ablation zone margin.

CONCLUSION

In some conditions of high intensity, IRE can produce sufficient heating to induce "white zone" thermal coagulation. While this can be useful in some settings to increase tumor destruction, further characterization of the thermal profile created with clinical electrodes and energy parameters is therefore needed to better understand the best ways to avoid unintended damage when ablating near thermally sensitive critical structures.

Intraoperative hyperthermic chemotherapy perfusion for malignant pleural mesothelioma: an in vitro evaluation

OBJECTIVES

Hyperthermic chemotherapy perfusion has been used in the treatment of both pleural and peritoneal mesothelioma without an extensive basic science foundation. Clinical data are limited with no prospective randomized trials to support the use of this potentially toxic therapy. We sought to generate basic scientific support for this clinical practice and to define the optimal conditions for use in future clinical trials.

METHODS

Growth of a variety of in vitro established cell lines, including a hyperthermia-sensitive Chinese hamster ovary (CHO)-K1 cell line, a normal lung fibroblast line (MRC-5), a lung cancer line (A549), and 3 human mesothelioma cell lines (NCI-H28, NCI-H2052, and MSTO-211H), was assessed using a novel tetrazolium compound (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt [MTS]) and an electron coupling reagent (phenazine methosulfate), which measures the absorbance at 490 nm of a formazan product reduced from MTS by living cells (MTS metabolic assay), or a standard dilution clonogenic assay, which enumerates colony-forming units of more than 50 cells. Each cell line was plated into flasks and then exposed to varying combinations of chemotherapy agents and hyperthermia (37°C-45°C). The cells then were harvested and assessed in either assay. The role of chemotherapeutic agents currently most commonly used in clinical practice, including cisplatin, gemcitabine, and pemetrexed, was assessed with and without simultaneous heat exposure.

RESULTS

Conditions initially were explored using hyperthermia alone in CHO-K1, A549, and NCI-H28 cell lines using temperatures of 37°C, 42°C, and 45°C for 20, 40, and 60 minutes, respectively. This showed a reproducible dose-response curve in CHO-K1 cells with increasing temperature producing lower survival to only 1.5% of the control at 45°C for 60 minutes (P < .01). The A549 cells also showed a response but only at the highest temperature, and the NCI-H28 cells showed a more modest reduction to 65% at 45°C for 60 minutes (P < .01). When the 2 assays were directly compared, the MTS assay failed to detect differences between groups and therefore was discontinued from the remainder of these experiments. Next, hyperthermia was limited to the physiologic limit of 42°C, and the addition of chemotherapy was assessed. Doses were chosen on the basis of prior pharmacokinetic data from studies showing a maximum tissue/blood level of 200 ng/mL for cisplatin pleural instillation and were thought to more accurately reflect actual tumor levels. Cisplatin alone modestly reduced the clonogenic potential to 26%, 16.4%, and 13.6% at 42°C, respectively, for 60 minutes (P < .01); however, this was only a further reduction of 29.6%, 33.8%, and 34.2%, respectively, from the cisplatin alone control. Therefore, most of the reduction was attributable to chemotherapy and not hyperthermia. With combinations of cisplatin/gemcitabine and cisplatin/pemetrexed, the effect was larger, with reduction to 9.6%, 0%, and 0%, respectively (P < .01) (incremental reduction of 16.5%, 0%, and 0%, respectively, due to hyperthermia). Cisplatin/pemetrexed produced essentially identical results.

CONCLUSIONS

Intrapleural chemotherapy seems to be most effective when using 2 drug combinations. All mesothelioma cell lines showed no particular sensitivity to heat. The use of hyperthermia alone or with chemotherapy produces at best only a modest effect and does not necessarily support its current clinical use.

Linear enhancement after radio-frequency ablation for hepatocellular carcinoma: is it a sign of recurrence?

This prospective study was performed in 179 hepatocellular carcinoma (HCC) lesions treated by radio-frequency ablation (RFA) to explore the clinical outcome of "linear enhancement" on contrast-enhanced sonogram. Thirty-three lesions (18.4%) showed linear enhancement, a linear-shaped positive enhancement in the RFA-treated area. Seventeen of them were followed up with no treatment (remaining 16; dropout in eight, additional RFA in six and ineffective treatment in two) and three lesions (3/17, 17.6%) showed local tumor progression corresponding to linear enhancement at 7, 14, 19 months after RFA. Although there was no significant difference in local recurrence rate between the lesions with (3/17) and without linear enhancement (10/35), local tumor progression inside the ablation zone occurred only in the lesions with linear enhancement. In conclusion, linear enhancement inside the RFA-treated area should be followed up within 7 months because it has a risk of local tumor progression. Histology of linear enhancement and its influence on distant recurrence remain to be solved.

Combined Hepatic Arterial Embolization and Hepatic Ablation for Unresectable Colorectal Metastases to the Liver

Liver-directed therapy for hepatic metastases includes: intra-arterial techniques such as trans-arterial chemoembolization (TACE) and yttrium-90 resin (90Y) microsphere radioembolization and ablative technologies: cryoablation, radiofrequency ablation, and microwave ablation. Combining embolization techniques with liver ablation may enhance the therapeutic benefit of each and result in improved patient survival. We retrospectively reviewed our experience with combined intra-arterial therapies and ablation for unresectable hepatic colorectal metastases from 1996 to 2011. Patient demographics, tumor characteristics, specific liver-directed treatments, procedure-related morbidity and mortality, and overall survival were recorded. There were 17 (53%) males and 15 (47%) females. Average age for the group was 74.1 years (median, 75.5 years). Fifteen patients (46.9%) had a single hepatic metastasis. Eleven (34%) patients had bilobar tumor distribution and seven (22%) patients had vascular invasion of the portal vein or hepatic/caval venous structures. Seven (21%) tumors were greater than 5 cm in diameter. Twenty-seven (84.4%) patients received TACE and five (15.6%) received 90Y. Fourteen (43%) were embolized before any ablation. Fifty-three per cent of patients required multiple hepatic ablation sessions. Median length of hospital stay was 1 day. There were no procedure-related mortalities and complications occurred in six (18.8%) patients. Mean follow-up for the group was 33 months. Kaplan-Meier 1-, 3-, and 5-year estimated survival was 93.8, 50.0, and 10.1 per cent, respectively. Median survival for the group was 46 months. Hepatic ablation and embolization techniques can be combined safely with minimal morbidity. In our series, we observed 5-year survival in 10 per cent of patients.

Combination therapy of radiofrequency ablation and bevacizumab monitored with power Doppler ultrasound in a murine model of hepatocellular carcinoma

PURPOSE

The purpose of this study was to monitor tumour blood flow with power Doppler ultrasound following antiangiogenic therapy with bevacizumab in order to optimally time the application of radiofrequency (RF) ablation to increase ablation diameter.

MATERIALS AND METHODS

Athymic nude mice bearing human hepatocellular carcinoma xenografts were treated with bevacizumab and imaged daily with power Doppler ultrasound to quantify tumour blood flow. Mice were treated with RF ablation alone or in combination with bevacizumab at the optimal time, as determined by ultrasound. Ablation diameter was measured with histology and tumour microvascular density was calculated with immunohistochemistry. A computational thermal model of RF ablation was used to estimate ablation volume.

RESULTS

A maximum reduction of 27.8 ± 8.6% in tumour blood flow occurred on day 2 following antiangiogenic therapy, while control tumours increased 29.3 ± 17.1% (p < 0.05). Tumour microvascular density was similarly reduced by 45.1 ± 5.9% on day 2 following antiangiogenic therapy. Histology demonstrated a 13.6 ± 5.6% increase in ablation diameter (40 ± 21% increase in volume) consistent with a computational model.

CONCLUSION

Quantitative power Doppler ultrasound is a useful biomarker to monitor tumour blood flow following antiangiogenic treatment and to guide the application of RF ablation as a drug plus device combination therapy.

Radiofrequency ablation of the liver: effect of variation of portal venous blood flow on lesion size in an in-vitro perfused bovine liver

RATIONALE AND OBJECTIVES

An in vitro perfused bovine liver model was used to evaluate the relationship between the sizes of radiofrequency ablation lesions and variation in portal venous blood flow.

MATERIALS AND METHODS

Fourteen bovine livers were perfused with autologous heparinized blood at 37°C and 40% to 50% oxygenation via the portal vein. Flow rates were adjusted from 10 to 50 mL/min/100 g tissue. A 480-kHz generator and a 3.0-cm monopolar internally cooled electrode were used to create 57 ablations. The long-axis diameter, short-axis diameter (SAD), and volume of each ablation zone were measured and calculated from the dissected livers. Correlations between SAD, long-axis diameter, and volume versus blood flow were assessed using linear regression analysis.

RESULTS

SAD and lesion volume demonstrated inverse linear correlations with blood flow (for SAD, y = -0.044x + 3.925, r = 0.836, P < .001; for volume, y = -0.556x + 31.574, r = 0.842, P < .001). A 10 mL/min/100 g change in flow rate produced an average 4.4 ± 0.4 mm change in SAD and an average 5.6 ± 0.5 cm(3) change in volume. Long-axis diameter was not correlated with blood flow (y = -0.7694x + 4.1899, r = 0.2173, P = .111).

CONCLUSIONS

The SAD and volume of radiofrequency ablation lesions have statistically significant inverse linear correlations with portal venous blood flow, with an average 4.4-mm change in SAD and an average 5.6-cm(3) change in volume for each 10 mL/min/100 g change in flow rate.

Locoregional drug delivery using image-guided intra-arterial drug eluting bead therapy

Lipiodol-based transarterial chemoembolization (TACE) has been performed for over 3 decades for the treatment of solid tumors and describes the infusion of chemotherapeutic agents followed by embolization with particles. TACE is an effective treatment for inoperable hepatic tumors, especially hypervascular tumors such as hepatocellular carcinoma. Recently, drug eluting beads (DEBs), in which a uniform embolic material is loaded with a drug and delivered in a single image-guided step, have been developed to reduce the variability in a TACE procedure. DEB-TACE results in localization of drug to targeted tumors while minimizing systemic exposure to chemotherapeutics. Once localized in the tissue, drug is eluted from the DEB in a controlled manner and penetrates hundreds of microns of tissue from the DEB surface. Necrosis is evident surrounding a DEB in tissue days to months after therapy; however, the contribution of drug and ischemia is currently unknown. Future advances in DEB technology may include image-ability, DEB size tailored to tumor anatomy and drug combinations.

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.

Intrahepatic radiofrequency ablation versus electrochemical treatment ex vivo

BACKGROUND

Radiofrequency ablation (RFA) and electrochemical treatment (ECT) are two methods of local liver tumor ablation. A reproducible perfusion model allowed us to compare these methods when applied in proximity to vascular structures.

MATERIAL AND METHODS

In a porcine liver perfusion model, we used RFA (group A) and ECT (group B) to perform ablations under ultrasound guidance within 10 mm of a vessel and examined the induced necrosis macroscopically and histologically.

RESULTS

We created 83 lesions (RFA: 59, ECT: 24) in 27 livers. In group A (mean liver weight: 2046 g), perfusion was macroscopically found to limit necrosis in 52.5% of the procedures. Histology demonstrated the destruction of only 30.4% of the vessel walls within the ablation areas. In group B (mean liver weight: 1885 g), we detected reproducible and sharply demarcated ablation areas both macroscopically and histologically. Necrosis was unaffected by nearby vessels. No viable cells were found perivascularly. Histology showed destruction of the vascular endothelium without any discontinuities. We measured pH values of 0.9 (range: 0.6-1.8) at the anode and 12.2 (range: 11.4-12.6) at the cathode. Treatment time was 100 min when a charge of 300 coulombs was delivered.

CONCLUSIONS

Electrochemical treatment is a method of ablation that creates reproducible and predictable volumes of necrosis. It produces sharply demarcated areas of complete necrosis also in perivascular sites. ECT, however, requires much longer treatment times than RFA. In our model, the effects of RFA were considerably limited by perfusion, which caused incomplete areas of necrosis in proximity to vessels.

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.

Venous thrombosis after radiofrequency ablation for hepatocellular carcinoma

OBJECTIVE

This study was designed to evaluate the frequency, morphological patterns, sequential changes, and clinical significance of venous thrombosis after radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

A total of 1379 RFAs performed in 1046 patients with HCC (mean tumor size, 1.93 cm) were surveyed. We retrospectively reviewed all radiologic reports before and after RFA and selected 15 patients with newly developed procedure-related venous thrombosis. Procedure-related thrombosis was defined as being adjacent to the ablation zone and developing within 4 months after the procedure. We evaluated the frequency, morphological patterns, sequential changes, and clinical course of venous thrombosis (mean follow-up, 662.9 days). Four cases with local tumor progression were identified among the 15 patients, and their clinical implications were evaluated.

RESULTS

A total of 15 venous thromboses (1.08%; 12 portal and three hepatic veins) developed after RFA (range, 0-128 days; mean, 37 days). The thromboses were found in central (n = 10), peripheral (n = 4), and both central and peripheral (n = 1) locations in the ablation zones. Thrombosis was decreased in nine (69.2%), persisted in one (7.6%), and increased in three (23.0%) of 13 patients who underwent follow-up CT for more than 12 months. Local tumor progression was noted in four patients (26.6%); it abutted to venous thrombosis in two patients, separated from the venous thrombosis in one patient, and exhibited malignant thrombosis in one patient.

CONCLUSION

The development of portal or hepatic venous thromboses after RFA in patients with HCC is rare and usually is associated with favorable prognoses. Further investigation is warranted to elucidate whether venous thrombosis after RFA is related to local tumor progression around ablation zones.

The healing process of intracorporeally and in situ devitalized distal femur by microwave in a dog model and its mechanical properties in vitro

Background

Limb-salvage surgery has been well recognized as a standard treatment and alternative to amputation for patients with malignant bone tumors. Various limb-sparing techniques have been developed including tumor prosthesis, allograft, autograft and graft-prosthesis composite. However, each of these methods has short- and long-term disadvantages such as nonunion, mechanical failures and poor limb function. The technique of intracorporeal devitalization of tumor-bearing bone segment in situ by microwave-induced hyperthermia after separating it from surrounding normal tissues with a safe margin is a promising limb-salvage method, which may avoid some shortcomings encountered by the above-mentioned conventional techniques. The purpose of this study is to assess the healing process and revitalization potential of the devitalized bone segment by this method in a dog model. In addition, the immediate effect of microwave on the biomechanical properties of bone tissue was also explored in an in vitro experiment.

Methods

We applied the microwave-induced hyperthermia to devitalize the distal femurs of dogs in situ. Using a monopole microwave antenna, we could produce a necrotic bone of nearly 20 mm in length in distal femur. Radiography, bone scintigraphy, microangiography, histology and functional evaluation were performed at 2 weeks and 1, 2, 3, 6, 9 and 12 months postoperatively to assess the healing process. In a biomechanical study, two kinds of bone specimens, 3 and 6 cm in length, were used for compression and three-point bending test respectively immediately after extracorporeally devitalized by microwave.

Findings

An in vivo study showed that intracorporeally and in situ devitalized bone segment by microwave had great revitalization potential. An in vitro study revealed that the initial mechanical strength of the extracorporeally devitalized bone specimen may not be affected by microwave.

Conclusion

Our results suggest that the intracorporeal microwave devitalization of tumor-bearing bone segment in situ may be a promising limb-salvage method.

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.

Targeted vessel ablation for more efficient magnetic resonance-guided high-intensity focused ultrasound ablation of uterine fibroids

Purpose

To report the first clinical experience with targeted vessel ablation during magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) treatment of symptomatic uterine fibroids.

Methods

Pretreatment T1-weighted contrast-enhanced magnetic resonance angiography was used to create a detailed map of the uterine arteries and feeding branches to the fibroids. A three-dimensional overlay of the magnetic resonance angiography images was registered on 3D T2-weighted pretreatment imaging data. Treatment was focused primarily on locations where supplying vessels entered the fibroid. Patients were followed 6 months after treatment with a questionnaire to assess symptoms and quality of life (Uterine Fibroid Symptom and Quality of Life) and magnetic resonance imaging to quantify shrinkage of fibroid volumes.

Results

In two patients, three fibroids were treated with targeted vessel ablation during MR-HIFU. The treatments resulted in almost total fibroid devascularization with nonperfused volume to total fibroid volume ratios of 84, 68, and 86%, respectively, of treated fibroids. The predicted ablated volumes during MR-HIFU in patients 1 and 2 were 45, 40, and 82 ml, respectively, while the nonperfused volumes determined immediately after treatment were 195, 92, and 190 ml respectively, which is 4.3 (patient 1) and 2.3 (patient 2) times higher than expected based on the thermal dose distribution. Fibroid-related symptoms reduced after treatment, and quality of life improved. Fibroid volume reduction ranged 31–59% at 6 months after treatment.

Conclusion

Targeted vessel ablation during MR-HIFU allowed nearly complete fibroid ablation in both patients. This technique may enhance the use of MR-HIFU for fibroid treatment in clinical practice.

Comparison between different thickness umbrella-shaped expandable radiofrequency electrodes (SuperSlim and CoAccess): Experimental and clinical study

The purpose of the present study was to compare the size and configuration of the ablation zones created by SuperSlim and CoAccess electrodes, using various ablation algorithms in ex vivo bovine liver and in clinical cases. In the experimental study, we ablated explanted bovine liver using 2 types of electrodes and 4 ablation algorithms (combinations of incremental power supply, stepwise expansion and additional low-power ablation) and evaluated the ablation area and time. In the clinical study, we compared the ablation volume and the shape of the ablation zone between both electrodes in 23 hepatocellular carcinoma (HCC) cases with the best algorithm (incremental power supply, stepwise expansion and additional low-power ablation) as derived from the experimental study. In the experimental study, the ablation area and time by the CoAccess electrode were significantly greater compared to those by the SuperSlim electrode for the single-step (algorithm 1, p=0.0209 and 0.0325, respectively) and stepwise expansion algorithms (algorithm 2, p=0.0002 and <0.0001, respectively; algorithm 3, p= 0.006 and 0.0407, respectively). However, differences were not significant for the additional low-power ablation algorithm. In the clinical study, the ablation volume and time in the CoAccess group were significantly larger and longer, respectively, compared to those in the SuperSlim group (p=0.0242 and 0.009, respectively). Round ablation zones were acquired in 91.7% of the CoAccess group, while irregular ablation zones were obtained in 45.5% of the SuperSlim group (p=0.0428). In conclusion, the CoAccess electrode achieves larger and more uniform ablation zones compared with the SuperSlim electrode, though it requires longer ablation times in experimental and clinical studies.

Coagulation necrosis induced by radiofrequency ablation in the liver: histopathologic and radiologic review of usual to extremely rare changes

As the clinical role of radiofrequency ablation (RFA) of the liver grows, the importance of radiologic imaging after liver RFA to depict the diversity of post-RFA manifestations is also increasing. Because RFA induces coagulation necrosis of the hepatic parenchyma, cross-sectional imaging studies, in principle, demonstrate an area with a defect in contrast enhancement. However, for various reasons, such as the occurrence of a complication, the RFA zone may demonstrate different patterns or be accompanied by other abnormalities. In this investigation, a large number of imaging studies performed after more than 4000 procedures of liver RFA during the past 10-year period were reviewed, and various radiologic manifestations of the RFA zone were compiled. Herein, the basic principles of RFA, as well as the histopathologic features of coagulation necrosis of the liver, are catalogued to provide a more complete understanding of such changes. Through this review, the reader will become more familiar with the usual and unusual radiologic findings of coagulation necrosis induced by RFA in the liver. This increased familiarity will not only facilitate the daily practice of radiology but also deepen understanding of the therapeutic modality of RFA.

Thermal ablation

Image-guided tumor ablation refers to a group of treatment modalities that have emerged during the past 2 decades as important tools in the treatment of a wide range of tumors throughout the body. Although most widely recognized in the treatment of hepatic and renal malignancies, the role of thermal ablation has expanded to include lesions of the lung, breast, prostate, bone, as well as other organs and its clinical applications continue to increase. In the following article, we discuss the major thermal ablation modalities, their respective strengths and weaknesses, potential complications and how to avoid them, as well as possible future applications.

Emerging local ablation techniques

Local ablation technologies for hepatic malignancy have developed rapidly in the past decade, with advances in several percutaneous or externally delivered treatment methods including radiofrequency ablation, microwave ablation, laser ablation, and high-intensity focused ultrasound. Research has focused on increasing the size of the ablation zone and minimizing heat-sink effects. More recent developments include improvements in treatment planning and navigation with integration of several imaging modalities, as well as automated delivery of the ablation through robotics. These improvements will allow increased consistency in treatment delivery and will facilitate translation to the community setting. Combination therapies with multimodality guidance are on the cutting edge of image-guided, minimally invasive cancer therapies. Local ablation is being combined with regional therapies, such as arterial chemoembolization and local activation of systemically administered drugs, with promising results. Potential combinations with local ablation also include external radiation therapy and antitumor immune modulation. Image-guided oncology is emerging as an important part of the interventional radiology practice, thanks in part to the innovation and imaging background that lies at the roots of our discipline.