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

Current role of microwave ablation in the treatment of small hepatocellular carcinomas

Percutaneous radiofrequency ablation (RFA) can be as effective as surgical resection in terms of overall survival and recurrence-free survival rates in patients with small hepatocellular carcinoma (HCC). Effectiveness of RFA is adversely influenced by heat-sink effect. Other ablative therapies could be considered for larger tumors or for tumors located near the vessels. In this regard, recent improvements in microwave energy delivery systems seem to open interesting perspectives to percutaneous ablation, which could become the ablation technique of choice in the near future. Microwave ablation (MWA) has the advantages of possessing a higher thermal efficiency. It has high efficacy in coagulating blood vessels and is a relatively fast procedure. The time required for ablation is short and the shape of necrosis is elliptical with the older systems and spherical with the new one. There is no heat-sink effect and it can be used to ablate tumors adjacent to major vessels. These factors yield a large ablation volume, and result in good local control and fewer complications. This review highlights the most relevant updates on MWA in the treatment of small (<3 cm) HCC. Furthermore, we discuss the possibility of MWA as the first ablative choice, at least in selected cases.

Evaluation of a robotic system for irreversible electroporation (IRE) of malignant liver tumors: initial results

OBJECTIVE

Comparison of conventional CT-guided manual irreversible electroporation (IRE) of malignant liver tumors and a robot-assisted approach regarding procedural accuracy, intervention time, dose, complications, and treatment success.

METHODS

A retrospective single-center analysis of 40 cases of irreversible electroporation of malignant liver tumors in 35 patients (6 females, 29 males, average age 60.3 years). Nineteen of these ablation procedures were performed manually and 21 with robotic assistance. A follow-up (ultrasound, CT, and MRI) was performed after 6 weeks in all patients.

RESULTS

The time from the planning CT scan to the start of the ablation as well as the dose-length product were significantly lower under robotic assistance (63.5 vs. 87.4 min, [Formula: see text]; 2132 vs. 4714 mGy cm, [Formula: see text]). The procedural accuracy, measured as the deviation of the IRE probes with respect to a defined reference probe, was significantly higher using robotic guidance (2.2 vs. 3.1 mm, [Formula: see text]). There were no complications. There was one incomplete ablation in the manual group.

CONCLUSION

Robotic assistance for IRE of liver tumors allows for faster procedure times with higher accuracy while reducing radiation dose as compared to the manual placement of IRE probes.

Thermal Injury-induced Hepatic Parenchymal Hypoperfusion: Risk of Hepatocellular Carcinoma Recurrence after Radiofrequency Ablation

Purpose To retrospectively evaluate whether thermal injury-induced hepatic parenchymal hypoperfusion can be a significant risk factor for tumor recurrence after radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC). Materials and Methods The institutional review board approved this retrospective study, and the requirement to obtain informed consent was waived. The study population comprised 130 patients (87 men, 43 women; mean age, 61.4 years ± 8.95; age range, 39-84 years) with single nodular HCCs smaller than 5 cm who underwent RFA between January 2011 and December 2012. The development of RFA-induced hepatic parenchymal hypoperfusion was assessed with follow-up computed tomography (CT). After a mean follow-up of 36.7 months ± 10.8, the authors analyzed the overall and recurrence-free survival and the cumulative incidence of each type of recurrence (ie, local tumor progression [LTP], intrahepatic distant recurrence [IDR], and extrahepatic metastasis) by evaluating prognostic factors with use of the Kaplan-Meier method and Cox proportional hazard regression model. Results RFA-induced hepatic parenchymal hypoperfusion developed in 41 of the 130 patients (31.5%) but did not have a significant effect on overall survival (P = .634). However, the estimated 3-year recurrence-free survival rate was 43.3% in the 41 patients with RFA-induced hepatic parenchymal hypoxia and 61.9% in the 89 patients without hypoxia, a statistically significant difference (P = .019). The 3-year cumulative incidence of IDR was significantly higher in patients with RFA-induced hepatic parenchymal hypoperfusion than in those without hypoxia (33.3% vs 54.1%, P = .006). Conversely, the 3-year cumulative incidence of LTP and extrahepatic metastases showed no significant differences (P > .05 for both). Conclusion The development of RFA-induced hepatic parenchymal hypoperfusion is a significant predictive factor of recurrence (of IDR in particular) after RFA of a single nodular HCC. ^© RSNA, 2016 Online supplemental material is available for this article.

An Integrated Nanotechnology-Enabled Transbronchial Image-Guided Intervention Strategy for Peripheral Lung Cancer

Early detection and efficient treatment modality of early-stage peripheral lung cancer is essential. Current nonsurgical treatments for peripheral lung cancer show critical limitations associated with various complications, requiring alternative minimally invasive therapeutics. Porphysome nanoparticle-enabled fluorescence-guided transbronchial photothermal therapy (PTT) of peripheral lung cancer was developed and demonstrated in preclinical animal models. Systemically administered porphysomes accumulated in lung tumors with significantly enhanced disease-to-normal tissue contrast, as confirmed in three subtypes of orthotopic human lung cancer xenografts (A549, H460, and H520) in mice and in an orthotopic VX2 tumor in rabbits. An in-house prototype fluorescence bronchoscope demonstrated the capability of porphysomes for in vivo imaging of lung tumors in the mucosal/submucosal layers, providing real-time fluorescence guidance for transbronchial PTT. Porphysomes also enhanced the efficacy of transbronchial PTT significantly and resulted in selective and efficient tumor tissue ablation in the rabbit model. A clinically used cylindrical diffuser fiber successfully achieved tumor-specific thermal ablation, showing promising evidence for the clinical translation of this novel platform to impact upon nonsurgical treatment of early-stage peripheral lung cancer. Cancer Res; 76(19); 5870-80. ©2016 AACR.

Minimal vascular flows cause strong heat sink effects in hepatic radiofrequency ablation ex vivo

BACKGROUND

The present paper aims to assess the lower threshold of vascular flow rate on the heat sink effect in bipolar radiofrequency ablation (RFA) ex vivo.

METHODS

Glass tubes (vessels) of 3.4 mm inner diameter were introduced in parallel to bipolar RFA applicators into porcine liver ex vivo. Vessels were perfused with flow rates of 0 to 1,500 ml/min. RFA (30 W power, 15 kJ energy input) was carried out at room temperature and 37°C. Heat sink effects were assessed in RFA cross sections by the decrease in ablation radius, area and by a high-resolution sector planimetry.

RESULTS

Flow rates of 1 ml/min already caused a significant cooling effect (P ≤ 0.001). The heat sink effect reached a maximum at 10 ml/min (18.4 mm/s) and remained stable for flow rates up to 1,500 ml/min.

CONCLUSIONS

Minimal vascular flows of ≥1 ml/min cause a significant heat sink effect in hepatic RFA ex vivo. A lower limit for volumetric flow rate was not found. The maximum of the heat sink effect was reached at a flow rate of 10 ml/min and remained stable for flow rates up to 1,500 ml/min. Hepatic inflow occlusion should be considered in RFA close to hepatic vessels.

Imaging Intratumoral Nanoparticle Uptake After Combining Nanoembolization with Various Ablative Therapies in Hepatic VX2 Rabbit Tumors

Combining image-guided therapy techniques for the treatment of liver cancers is a strategy that is being used to improve local tumor control rates. Here, we evaluate the intratumoral uptake of nanoparticles used in combination with radiofrequency ablation (RFA), irreversible electroporation (IRE), or laser induced thermal therapy (LITT). Eight rabbits with VX2 tumor in the liver underwent one of four treatments: (i) nanoembolization (NE) with radiolabeled, hollow gold nanoparticles loaded with doxorubicin (⁶⁴Cu-PEG-HAuNS-DOX); (ii) NE + RFA; (iii) NE + IRE; (iv) NE +LITT. Positron emission tomography/computed tomography (PET/CT) imaging was obtained 1-hr or 18-hrs after intervention. Tissue samples were collected for autoradiography and transmission electron microscopy (TEM) analysis. PET/CT imaging at 1-hr showed focal deposition of oil and nanoparticles in the tumor only after NE+ RFA but at 18-hrs, all animals had focal accumulation of oil and nanoparticles in the tumor region. Autoradiograph analysis demonstrated nanoparticle deposition in the tumor and in the ablated tissues adjacent to the tumor when NE was combined with ablation. TEM results showed the intracellular uptake of nanoparticles in tumor only after NE + IRE. Nanoparticles demonstrated a structural change, suggesting direct interaction, potentially leading to drug release, only after NE + LITT. The findings demonstrate that a combined NE and ablation treatment technique for liver tumors is feasible, resulting in deposition of nanoparticles in and around the tumor. Depending on the ablative energy applied, different effects are seen on nanoparticle localization and structure. These effects should be considered when designing nanoparticles for use in combination with ablation technologies.

Effects of Microwave Ablation on Arterial and Venous Vasculature after Treatment of Hepatocellular Carcinoma

Purpose To characterize vessel occlusion rates and their role in local tumor progression in patients with hepatocellular carcinoma (HCC) who underwent microwave tumor ablation. Materials and Methods This institutional review board approved, HIPAA-compliant retrospective review included 95 patients (75 men and 20 women) with 124 primary HCCs who were treated at a single center between January 2011 and March 2014. Complete occlusion of the portal veins, hepatic veins, and hepatic arteries within and directly abutting the ablation zone was identified with postprocedure contrast material-enhanced computed tomography. For each vessel identified in the ablation zone, its size and antenna spacing were recorded and correlated with vascular occlusion with logistic regression analysis. Local tumor progression rates were then compared between patent and occluded vessels for each vessel type with Fisher exact test. Results Occlusion was identified in 39.7% of portal veins (29 of 73), 15.0% of hepatic veins (six of 40), and 14.2% of hepatic arteries (10 of 70) encompassed within the ablation zone. Hepatic vein occlusion was significantly correlated with a smaller vessel size (P = .036) and vessel-antenna spacing (P = .006). Portal vein occlusion was only significantly correlated with a smaller vessel size (P = .001), particularly in vessels that were less than 3 mm in diameter. Local tumor progression rates were significantly correlated with patent hepatic arteries within the ablation zone (P = .02) but not with patent hepatic (P = .57) or portal (P = .14) veins. Conclusion During microwave ablation of HCC, hepatic veins and arteries were resistant to vessel occlusion compared with portal veins, and only arterial patency within an ablation zone was related to local tumor progression. ^© RSNA, 2016.

Percutaneous Image-Guided Musculoskeletal Tumor Treatments

OBJECTIVE

The purpose of this article is to review the current guidelines and recommendations for percutaneous image-guided treatment of musculoskeletal tumors.

CONCLUSION

With the ongoing technologic advances, it is essential that the musculoskeletal interventionalist is familiar with the current tools and techniques available for the treatment of soft-tissue and bone tumors. Fortunately, many of these tools are readily available in a standard interventional radiology department and can be easily applied to the musculoskeletal system.

Management of portal hypertension derived from uncommon causes

Portal hypertension can arise from any condition interfering with normal blood flow at any level within the portal system. Herein, we presented two uncommon cases of the portal hypertension and its treatment with brief literature review. A 71-year-old man who underwent right hemihepatectomy revealed a tumor recurrence adjacent to the inferior vena cava (IVC). After radiofrequency ablation (RFA) with lymph node dissection, he was referred for abdominal distension. The abdomen computed tomography scan showed severe ascites with a narrowing middle hepatic vein (MHV) and IVC around the RFA site. After insertion of two stents at the IVC and MHV, the ascites disappeared. Another 73-year-old man underwent right trisectionectomy of liver and segmental resection of the portal vein (PV). After operation, he underwent conservative management due to continuous abdominal ascites. The abdomen computed tomography scan showed severe ascites with obliteration of the left PV. After insertion of stent, the ascites disappeared. A decrease of the pressure gradient between the PV and IVC is one of the important treatment strategies for portal hypertension. Vascular stent is useful in the reduction of pressure gradient and thus, can be a treatment option for portal hypertension.

Incidence and clinical sequelae of portal and hepatic venous thrombosis following percutaneous cryoablation of liver tumors

PURPOSE

To assess the incidence and sequelae of portal and hepatic venous thrombosis after percutaneous cryoablation of hepatic tumors.

METHODS

From November 1998 through December 2010, 223 hepatic tumors were cryoablated during 170 ablation procedures in 135 patients. 24-h post-procedure MR images were reviewed retrospectively by two abdominal radiologists in consensus to identify tumor ablations that developed one or more new portal or hepatic venous thromboses in or outside the ablation zone. On follow-up MRI and CT examinations the outcomes of thromboses were classified as resolved, partially recanalized, persistent, or propagated.

RESULTS

Venous thrombosis developed in association with 54 (24%) of 223 tumor ablations treated during 53 (31%) ablation procedures in 39 (28.8%) patients (15 women, 24 men; age range 40-82 years, mean 59 years). Of these 54 thromboses, 49 (91%) were located in portal vein branches, four (7%) in both portal and hepatic vein branches, and one (2%) in a hepatic vein branch. Thrombosed veins were outside but abutted the ablation zone in 36 (66.7%), and within it in 18 (33.3%). On follow-up imaging (n = 49), thrombi resolved in 29 (59%), partially recanalized in two (4%), persisted in 18 (37%) and propagated from sub-segmental or segmental branches to the left or right portal branches in five (10%). No thrombus propagated to the main portal vein or inferior vena cava.

CONCLUSION

Portal and hepatic vein branch thromboses are common in small branches following percutaneous cryoablation of hepatic tumors and most resolve spontaneously without sequelae.

A Recent Advance in Image-Guided Locoregional Therapy for Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third most common cause of cancer-related deaths. Hepatic resection and liver transplantation are considered to be the preferred treatment for HCC. However, as novel therapeutic options such as image-guided locoregional therapies have emerged and been refined, the manner in which HCC is treated has changed dramatically compared with what it was considered just 2 decades earlier.

SUMMARY

This study reviews the current results of various image-guided locoregional therapies for treating HCC, especially focusing on thermal ablative and transarterial techniques.

KEY MESSAGE

Advances in image-guided locoregional therapies, including local ablative therapy and transarterial therapy, have led to a major breakthrough in the management of HCC. Both survival rates and cure rates of patients with HCC have improved markedly since the introduction of these techniques.

PRACTICAL IMPLICATIONS

Radiofrequency ablation is currently considered as an alternative to surgical resection for patients with early-stage HCC. A newer technique of ablation such as microwave ablation is increasingly being used, especially for large HCC. Transarterial chemoembolization has become a standard care for asymptomatic patients with multinodular tumors in intermediate-stage disease, and transarterial radioembolization has become the method of choice in HCC cases with portal vein thrombosis. Moreover, combination treatment modalities, such as thermal-based ablation combined with transarterial chemoembolization or ¹²⁵I seed implant brachytherapy, may further broaden their clinical indications for HCC. Moreover, use of localized radiation in combination with thermal ablation has been reported to improve tumor control and long-term survival.

Thermal Ablative Therapies and Immune Checkpoint Modulation: Can Locoregional Approaches Effect a Systemic Response?

Percutaneous image-guided ablation is an increasingly common treatment for a multitude of solid organ malignancies. While historically these techniques have been restricted to the management of small, unresectable tumors, there is an expanding appreciation for the systemic effects these locoregional interventions can cause. In this review, we summarize the mechanisms of action for the most common thermal ablation modalities and highlight the key advances in knowledge regarding the interactions between thermal ablation and the immune system.

Application of nanoknife ablation in unresectable pancreatic carcinoma: Present situation and prospects

Pancreatic cancer is a common malignant tumor of the digestive system with rapid progression and poor prognosis. The pathogenesis of pancreatic cancer is still unclear. Its incidence of is significantly rising, ranking fourth among all malignant tumors. Up to now, main therapeutic methods for pancreatic cancer contain surgical treatment, local ablation therapy, local radiotherapy, systemic chemotherapy, molecular targeted therapy, biological treatment and so on. Surgical treatment is still the only way to cure pancreatic cancer. However, most cases of pancreatic cancer are diagnosed at advanced stages, and only 20% of patients have a resectable disease. With the development of medical technology, nanoknife ablation, which is based on irreversible electroporation (IRE), has already come into people's vision. Both animal experiments and clinical studies have showed promising results. In this paper, we will discuss the present situation and prospects of application of nanometer knife ablation in the treatment of unresectable pancreatic carcinoma.

Radiofrequency thermo-ablation of PVNS in the knee: initial results

INTRODUCTION

Pigmented villonodular synovitis (PVNS) is normally treated by arthroscopic or open surgical excision. We present our initial experience with radiofrequency thermo-ablation (RF ablation) of PVNS located in an inaccessible location in the knee.

MATERIALS

Review of all patients with histologically proven PVNS treated with RF ablation and with at least 2-year follow-up.

RESULTS

Three patients met inclusion criteria and were treated with RF ablation. Two of the patients were treated successfully by one ablation procedure. One of the three patients had a recurrence which was also treated successfully by repeat RF ablation. There were no complications and all patients returned to their previous occupations following RF ablation.

CONCLUSION

In this study we demonstrated the feasibility of performing RF ablation to treat PVNS in relatively inaccessible locations with curative intent. We have also discussed various post-ablation imaging appearances which can confound the assessment for residual/recurrent disease.

C-arm CT-guided renal arterial embolisation followed by radiofrequency ablation for treatment of patients with unresectable renal cell carcinoma

AIM

To explore the value of using flat detector (FD) equipped angiographic C-arm CT (CACT) systems in treating unresectable renal cell carcinoma (RCC) by selective renal arterial embolisation (RAE) followed by radiofrequency ablation (RFA) (RAE-RFA).

MATERIALS AND METHODS

A total of 28 patients who were not candidates for surgery were enrolled. The average size of tumours was 6.7±2.2 cm (range 4.1-9.6 cm). Twenty-eight tumours were treated with CACT-guided RFA, 5-7 days after CACT-guided RAE.

RESULTS

CACT-guided RAE-RFA was technically successful in all patients. Tumour enhancement disappeared after a single RAE-RFA session in 20 patients, after two RAE-RFA sessions in four patients and after three RAE-RFA sessions in the other four patients. One patient died of lung metastasis and haematuria 13 months after RAE-RFA, and another patient died of pulmonary heart disease 23 months after repeat RAE-RFA. In the 26 living patients, tumours remained controlled during a mean follow-up period of 27 months and showed significant reduction in tumour size (6.7±2.2 cm to 3.9±1.7 cm, p<0.01). There were no significant changes in creatinine levels or urea nitrogen concentrations before and after the last RAE-RFA (p>0.05). There were no serious complications during and after the procedure.

CONCLUSION

CACT-guided RAE followed by RFA appears to be a safe and effective technique for treating patients with inoperable RCC.

Liver Ablation: Best Practice

Tumor ablation in the liver has evolved to become a well-accepted tool in the management of increasing complex oncologic patients. At present, percutaneous ablation is considered first-line therapy for very early and early hepatocellular carcinoma and second-line therapy for colorectal carcinoma liver metastasis. Because thermal ablation is a treatment option for other primary and secondary liver tumors, an understanding of the underlying tumor biology is important when weighing the potential benefits of ablation. This article reviews ablation modalities, indications, patient selection, and imaging surveillance, and emphasizes technique-specific considerations for the performance of percutaneous ablation.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

CT-guided high-dose-rate brachytherapy in the interdisciplinary treatment of patients with liver metastases of pancreatic cancer

BACKGROUND

CT-guided high-dose-rate brachytherapy (CT-HDRBT) is an interventional radiologic technique for local ablation of primary and secondary malignomas applying a radiation source through a brachycatheter percutaneously into the targeted lesion. The aim of this study was to assess local tumor control, safety and efficacy of CT-HDRBT in the treatment of liver metastases of pancreatic cancer.

METHODS

Twenty consecutive patients with 49 unresectable liver metastases of pancreatic cancer were included in this retrospective trial and treated with CT-HDRBT, applied as a single fraction high-dose irradiation (15-20 Gy) using a 192Ir-source. Primary endpoint was local tumor control and secondary endpoints were complications, progression-free survival and overall survival.

RESULTS

The mean tumor diameter was 29 mm (range 10-73). The mean irradiation time was 20 minutes (range 7-42). The mean coverage of the clinical target volume was 98% (range 88%-100%). The mean D100 was 18.1 Gy and the median D100 was 19.78 Gy. Three major complications occurred with post-interventional abscesses, three of which were seen in 15 patients with biliodigestive anastomosis (20%) and overall 15%. The mean follow-up time was 13.7 months (range 1.4-55.0). The median progression-free survival was 4.9 months (range 1.4-42.9, mean 9.4). Local recurrence occurred in 5 (10%) of 49 metastases treated. The median overall survival after CT-HDRBT was 8.6 months (range 1.5-55.3). Eleven patients received chemotherapy after ablation with a median progression-free survival of 4.9 months (mean 12.9). Nine patients did not receive chemotherapy after intervention with a median progression-free survival of 3.2 months (mean 5.0). The rate of local tumor control was 91% in both groups after 12 months.

CONCLUSION

CT-HDRBT was safe and effective for the treatment of liver metastases of pancreatic cancer.

Irreversible Electroporation of Malignant Hepatic Tumors--Alterations in Venous Structures at Subacute Follow-Up and Evolution at Mid-Term Follow-Up

Purpose

To evaluate risk factors associated with alterations in venous structures adjacent to an ablation zone after percutaneous irreversible electroporation (IRE) of hepatic malignancies at subacute follow-up (1 to 3 days after IRE) and to describe evolution of these alterations at mid-term follow-up.

Materials and Methods

43 patients (men/women, 32/11; mean age, 60.3 years) were identified in whom venous structures were located within a perimeter of 1.0 cm of the ablation zone at subacute follow-up after IRE of 84 hepatic lesions (primary/secondary hepatic tumors, 31/53). These vessels were retrospectively evaluated by means of pre-interventional and post-interventional contrast-enhanced magnetic resonance imaging or computed tomography or both. Any vascular changes in flow, patency, and diameter were documented. Correlations between vascular change (yes/no) and characteristics of patients, lesions, and ablation procedures were assessed by generalized linear models.

Results

191 venous structures were located within a perimeter of 1.0 cm of the ablation zone: 55 (29%) were encased by the ablation zone, 78 (41%) abutted the ablation zone, and 58 (30%) were located between 0.1 and 1.0 cm from the border of the ablation zone. At subacute follow-up, vascular changes were found in 19 of the 191 vessels (9.9%), with partial portal vein thrombosis in 2, complete portal vein thrombosis in 3, and lumen narrowing in 14 of 19. At follow-up of patients with subacute vessel alterations (mean, 5.7 months; range, 0 to 14 months) thrombosis had resolved in 2 of 5 cases; vessel narrowing had completely resolved in 8 of 14 cases, and partly resolved in 1 of 14 cases. The encasement of a vessel by ablation zone (OR = 6.36, p<0.001), ablation zone being adjacent to a portal vein (OR = 8.94, p<0.001), and the usage of more than 3 IRE probes (OR = 3.60, p = 0.035) were independently associated with post-IRE vessel alterations.

Conclusion

Venous structures located in close proximity to an IRE ablation zone remain largely unaffected by this procedure, and thrombosis is rare.

High-powered microwave ablation of larger hepatocellular carcinoma: evaluation of recurrence rate and factors related to recurrence

AIM

To evaluate the safety and efficacy of high-powered (80-100 W) percutaneous microwave ablation (MWA) at a frequency of 2450±10 MHz for treating larger hepatocellular carcinoma (HCC) and to predict the risk factors of local recurrence after high-powered MWA.

MATERIALS AND METHODS

The study was approved by the Institutional Review Board, and informed consent was waived because of the retrospective study design. Forty-five patients with a total of 60 lesions received high-power (80-100 W) MWA at a frequency of 2450±10 MHz through a percutaneous approach that was guided by ultrasound. Of the 60 lesions with a maximum tumour measuring 3-8 cm, 46 lesions were 3-5 cm and 14 were 5-8 cm. The complete ablation rates, local recurrence rates, complications, and short-term survival were analysed. Ten possible risk factors for local recurrence were analysed.

RESULTS

The complete ablation rates were 82.61% for the first ablation and 100% for the second ablation for 3-5 cm lesions. The complete ablation rates were 64.29% (82.61% versus 64.29%, p=0.037) for the first ablation and 85.71% (100% versus 85.71%, p=0.055) for the second ablation for 5-8 cm lesions. Local recurrence was observed in 11 out of the 45 (24.44%) successfully treated patients. The 1-year and 2-year survival rates were 95.56% (43/45) and 86.67% (39/45), respectively. No procedure-related mortality was observed and no major bleeding, liver rupture, or liver abscesses occurred. Univariate analysis showed that a positive correlation existed between the number of lesions (p=0.022), proximity to the risk area (p=0.001), pre-ablation alpha-fetoprotein (AFP) levels (p=0.025), hepatitis B virus (HBV)-DNA replication (p=0.027) and local recurrence. Multivariate analysis identified HBV-DNA (p=0.031) and proximity to the risk area (p=0.039) as the independent prognosis factors causing postoperative HCC local recurrence.

CONCLUSION

High-powered MWA of larger hepatocellular carcinomas appears to be a safe and effective treatment. HBV-DNA and proximity to the risk area appear to be independent predictors of local tumour recurrence.

Niche Applications of Irreversible Electroporation

Irreversible electroporation (IRE) induces cell death by exposing it to high-voltage, low-energy DC current pulses. The mechanism of cell death and healing is a departure from the other existing technologies such as radiofrequency ablation, microwave ablation, and cryoablation. These thermal ablative technologies have several applications in oncology but have limitations that have also been established. IRE has shown promise to overcome some of these limitations and has enabled the use of an ablative technology in treating lesions close to the bile ducts and vasculature and in organs such as the pancreas. This review highlights some of the niche applications of IRE and the data so far.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Irreversible electroporation: evolution of a laboratory technique in interventional oncology

Electroporation involves applying electric field pulses to cells, leading to the alteration or destruction of cell membranes. Irreversible electroporation (IRE) creates permanent defects in cell membranes and induces cell death. By directly targeting IRE to tumors, percutaneous nonthermal ablation is possible. The history of IRE, evolution of concepts, theory, biological applications, and clinical data regarding its safety and efficacy are discussed.

Image-guided therapies in the treatment of hepatocellular carcinoma: A multidisciplinary perspective

A multidisciplinary approach to the treatment of patients with unresectable hepatocellular carcinoma (HCC) has led to improvements in screening, detection, and treatments. Interventional techniques include thermal ablation, transarterial chemoembolization, and radioembolization whilst stereotactic body radiation therapy also uses imaging to target the radiation. Both survival rates and cure rates have improved markedly since the introduction of these techniques. This review article describes the image guided techniques used for the treatment of HCC.

Radiofrequency ablation combined with transcatheter therapy in rabbit VX2 liver tumors: effects and histopathological characteristics

BACKGROUND

Transarterial chemoembolization (TACE) combined with radiofrequency ablation (RFA) treatment (TACE-RFA) has been confirmed superior to TACE or RFA alone in animal liver tumors. TACE before RFA was shown to increase hepatocellular damage. Further optimization of the combination strategy for transcatheter arterial embolization (TAE) or TACE combined with RFA is warranted.

PURPOSE

To determine the optimal strategy for radiofrequency ablation combined with transcatheter therapies in VX2 liver tumors in a rabbit model.

MATERIAL AND METHODS

Twenty-four Japanese White rabbits with VX2 liver tumors were randomly divided into four groups: TACE-RFA (TACE-RFA group), transcatheter arterial embolization (TAE) combined with RFA treatment (TAE-RFA group), RFA only group, and TACE only group. Blood samples were collected 1 day before the operation and at 3 and 7 days postoperatively. Seven days after the operation, maximal diameters of coagulation or infarcted zones in the gross specimens, CT images, histopathological characteristics, tumor necrotic rate, and growth rate were compared.

RESULTS

Significantly larger mean long-axis (P < 0.05) and short-axis (P < 0.05) diameters of coagulation and infarction were observed in the TACE-RFA group compared with the TAE-RFA, RFA, and TACE groups on day 7; and the TAE-RFA group showed a significant (P < 0.05) increase versus the RFA and TACE groups on day 7. There were no significant differences in tumor growth rate (109.3 ± 37.5 vs. 119.0 ± 43.1%, P = 0.45) and necrotic rate (89.5 ± 12.0 vs. 83.5 ± 9.3%, P = 0.73) between the TACE-RFA and TAE-RFA groups. TACE-RFA was more effective for achieving tumor destruction than the other treatment strategies, but led to increased rabbits discomfort and more severe liver dysfunction compared with TAE-RFA.

CONCLUSION

TAE-RFA appears to be a beneficial therapeutic modality for treating VX2 liver tumors in a rabbit model.

Predictors of thrombosis in hepatic vasculature during microwave tumor ablation of an in vivo porcine model

PURPOSE

To evaluate and model the risk of in vivo thrombosis in each hepatic vessel type during hepatic microwave ablation as a function of vessel diameter, velocity, and vessel-antenna spacing.

MATERIALS AND METHODS

A single microwave ablation antenna was inserted into a single porcine lobe (n = 15 total) adjacent to a hepatic artery, hepatic vein, or portal vein branch. Conventional ultrasound and Doppler ultrasound were used to measure the vessel diameter, blood flow velocity, and vessel-antenna spacing. A microwave ablation zone was created at 100 W for 5 minutes. Thrombus formation was evaluated on ultrasound performed immediately after the procedure. Logistic regression was used to evaluate the predictive value of vessel diameter, blood flow velocity, and vessel-antenna spacing on vascular thrombosis.

RESULTS

Thrombosis was identified in 53% of portal veins, 13% of hepatic veins, and 0% of hepatic arteries. The average peak blood flow rate of the hepatic artery was significantly greater than the average peak blood flow rate of the hepatic vein and portal vein. Peak blood flow velocity < 12.45 cm/s, vessel diameter < 5.10 mm, and vessel-antenna spacing < 3.75 mm were strong predictors of hepatic vein thrombosis. However, these individual factors were not predictive of the more common portal vein thrombosis.

CONCLUSIONS

Hepatic arteries do not appear to be at risk for thrombosis during microwave ablation procedures. Portal vein thrombosis was more common than hepatic vein thrombosis during microwave ablation treatments but was not as predictable based on vessel diameter, flow velocity, or vessel-antenna spacing alone.

Image-guided tumor ablation: standardization of terminology and reporting criteria--a 10-year update

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes.

Various complications of percutaneous radiofrequency ablation for hepatic tumors: radiologic findings and technical tips

Radiofrequency ablation is a safe and effective treatment for primary and secondary liver malignancies and has a low complication rate; however, there are various radiofrequency ablation-related complications which can occur from the thorax to the pelvis. Although most of these complications are usually minor and self-limited, they may become fatal if diagnosis and treatment are delayed. It is important for radiologists performing radiofrequency ablation to have a perspective regarding the possible radiofrequency ablation-related complications and their risk factors as well as the radiologic findings for their timely detection and increase of the treatment efficacy, and thereby encouraging the use of the radiofrequency ablation technique. This article illustrates the various imaging features of common and rare radiofrequency ablation-related complications as well as offers technical tips in order to avoid these complications.

Vessel patency post irreversible electroporation

PURPOSE

The purpose of the study was to evaluate the effect of Irreversible Electroporation (IRE) on vessel patency in close proximity to the ablation zone.

MATERIALS AND METHODS

Between January 2010 and November 2013, 101 patients underwent percutaneous IRE procedures using the NanoKnife for primary and metastatic tumors in different organs. Age ranged from 24 to 83 years. A total of 129 lesions were treated. [liver (100), pancreas (18), kidney (3), pelvis (1), aorto-caval lymph nodes (2), adrenal (2), lung (1), retroperitoneal (1), surgical bed of a prior Whipple procedure (1)]. Post treatment contrast-enhanced CT and MRI scans were reviewed to evaluate caliber, patency, and flow defects of vessels in close proximity to the ablation zone (defined as vessels within 0-1 cm from the treatment zone).

RESULTS

A total of 158 vessels were examined for patency on follow-up. The mean distance of the vessel from the treatment zone was 2.3 ± 2.5 mm. Ten vessels within the treatment zone were encased by tumor. Mean tumor size was 2.7 + 1.5 cm. Overall mean follow-up was 10.3 months. Abnormal vascular changes were noted in 7 of 158 (4.4%) vessels. No significant association was found between distances from the treatment zone and presence of narrowing/thrombosis at the follow-up imaging. (Mann-Whitney U, p = 0.772; logistic regression: p = 0.593; odds ratio: 0.908; CI 0.637-1.294).

CONCLUSION

This study demonstrates safety of IRE for the treatment of tumors near the large blood vessels and tumors already encasing the vessels. Further studies to substantiate these findings are essential to validate this crucial advantage of IRE.

Thermal ablation of stage I non-small cell lung carcinoma

Ablation options for the treatment of localized non-small cell lung carcinoma (NSCLC) include radiofrequency ablation, microwave ablation, and cryotherapy. Irreversible electroporation is a novel ablation method with the potential of application to lung tumors in risky locations. This review article describes the established and novel ablation techniques used in the treatment of localized NSCLC, including mechanism of action, indications, potential complications, clinical outcomes, postablation surveillance, and use in combination with other therapies.

Thermal fixation of swine liver tissue after magnetic resonance-guided high-intensity focused ultrasound ablation

The aim of this study was to investigate experimental conditions for efficient and controlled in vivo liver tissue ablation by magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) in a swine model, with the ultimate goal of improving clinical treatment outcome. Histological changes were examined both acutely (four animals) and 1 wk after treatment (five animals). Effects of acoustic power and multiple sonication cycles were investigated. There was good correlation between target size and observed ablation size by thermal dose calculation, post-procedural MR imaging and histopathology, when temperature at the focal point was kept below 90°C. Structural histopathology investigations revealed tissue thermal fixation in ablated regions. In the presence of cavitation, mechanical tissue destruction occurred, resulting in an ablation larger than the target. Complete extra-corporeal MR-guided HIFU ablation in the liver is feasible using high acoustic power. Nearby large vessels were preserved, which makes MR-guided HIFU promising for the ablation of liver tumors adjacent to large veins.

Combining locoregional therapies in the treatment of hepatocellular carcinoma

In an effort to promote more durable local control of larger lesions, thermal ablation has been combined with chemical ablative techniques and with vaso-occlusive procedures such as chemoembolization and bland embolization in an effort to mitigate the limitations inherent in the use of any single treatment for hepatocellular carcinoma (HCC) >3 cm. The heat-sink effect is the underlying principle for combining vaso-occlusive therapies with ablative techniques. Combination therapies do present viable options for abrogating tumor progression and potentially downsizing tumors to facilitate transplant. We discuss the two most commonly used combination locoregional therapies by the interventionalist and the evidence defining the best techniques in practice.

Image-guided tumor ablation: standardization of terminology and reporting criteria--a 10-year update

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes. Online supplemental material is available for this article .

Heat Sink Phenomenon of Bipolar and Monopolar Radiofrequency Ablation Observed Using Polypropylene Tubes for Vessel Simulation

Background. Radiofrequency ablation (RFA) is widely used for treating liver tumors; recurrence is common owing to proximity to blood vessels possibly due to the heat sink effect. We seek to investigate this phenomenon using unipolar and bipolar RFA on an egg white tumor tissue model and an animal liver model. Materials and methods. Temperature profiles during ablation (with and without vessel simulation) were studied, using both bipolar and unipolar RFA probes by 4 strategically placed temperature leads to monitor temperature profile during ablation. The volume of ablated tissue was also measured. Results. The volume ablated during vessel simulation confirmed the impact of the heat sink phenomenon. The heat sink effect of unipolar RFA was greater compared with bipolar RFA (ratio of volume affected 2:1) in both tissue and liver models. The volume ablated using unipolar RFA was less than the bipolar RFA (ratio of volume ablated = 1:4). Unipolar RFA achieved higher ablation temperatures (122°C vs 98°C). Unipolar RFA resulted in tissue damage beyond the vessel, which was not observed using bipolar RFA. Conclusion. Bipolar RFA ablates a larger tumor volume compared with unipolar RFA, with a single ablation. The impact of heat sink phenomenon in tumor ablation is less so with bipolar than unipolar RFA with sparing of adjacent vessel damage.

CT-guided irreversible electroporation in an acute porcine liver model: effect of previous transarterial iodized oil tissue marking on technical parameters, 3D computed tomographic rendering of the electroporation zone, and histopathology

PURPOSE

To evaluate the effect of previous transarterial iodized oil tissue marking (ITM) on technical parameters, three-dimensional (3D) computed tomographic (CT) rendering of the electroporation zone, and histopathology after CT-guided irreversible electroporation (IRE) in an acute porcine liver model as a potential strategy to improve IRE performance.

METHODS

After Ethics Committee approval was obtained, in five landrace pigs, two IREs of the right and left liver (RL and LL) were performed under CT guidance with identical electroporation parameters. Before IRE, transarterial marking of the LL was performed with iodized oil. Nonenhanced and contrast-enhanced CT examinations followed. One hour after IRE, animals were killed and livers collected. Mean resulting voltage and amperage during IRE were assessed. For 3D CT rendering of the electroporation zone, parameters for size and shape were analyzed. Quantitative data were compared by the Mann-Whitney test. Histopathological differences were assessed.

RESULTS

Mean resulting voltage and amperage were 2,545.3 ± 66.0 V and 26.1 ± 1.8 A for RL, and 2,537.3 ± 69.0 V and 27.7 ± 1.8 A for LL without significant differences. Short axis, volume, and sphericity index were 16.5 ± 4.4 mm, 8.6 ± 3.2 cm(3), and 1.7 ± 0.3 for RL, and 18.2 ± 3.4 mm, 9.8 ± 3.8 cm(3), and 1.7 ± 0.3 for LL without significant differences. For RL and LL, the electroporation zone consisted of severely widened hepatic sinusoids containing erythrocytes and showed homogeneous apoptosis. For LL, iodized oil could be detected in the center and at the rim of the electroporation zone.

CONCLUSION

There is no adverse effect of previous ITM on technical parameters, 3D CT rendering of the electroporation zone, and histopathology after CT-guided IRE of the liver.

Local control of perivascular malignant liver lesions using percutaneous irreversible electroporation: initial experiences

PURPOSE

This study was designed to assess efficacy and safety in the treatment of perivascular malignant liver lesions using percutaneous, computed tomography (CT)-guided irreversible electroporation (IRE).

METHODS

Fourteen patients (mean age 58 ± 11 years) with 18 malignant liver lesions were consecutively enrolled in this study. IRE was performed in patients not eligible for surgery and lesions abutting large vessels or bile ducts. Follow-up exams were performed using multislice-CT (MS-CT) or MRI.

RESULTS

Medium lesion diameter was 20 ± 5 mm. Ten of 14 (71 %) were successfully treated with no local recurrence to date (mean follow-up 388 ± 160 days). One case left initial tumor control unclear and additional RFA was performed 4 weeks after IRE. Complications occurred in 4 of 14 (29 %) cases. In one case, intervention was terminated and abdominal bleeding required laparotomy. In two cases, a postinterventional hematothorax required intervention. In another case, abdominal bleeding could be managed conservatively. No complications related to the bile ducts occurred.

CONCLUSIONS

Percutaneous IRE seems to be effective in perivascular lesions but is associated with a higher complication rate compared with thermoablative techniques.

MAFR. Complications of radiofrequency ablation of hepatic tumors: Frequency and risk factors

Radiofrequency ablation (RFA) has become an important option in the therapy of primary and secondary hepatic tumors. Surgical resection is still the best treatment option, but only a few of these patients are candidates for surgery: multilobar disease, insufficient liver reserve that will lead to liver failure after resection, extra-hepatic disease, proximity to major bile ducts and vessels, and co-morbidities. RFA has a low mortality and morbidity rate and is considered to be safe. Thus, complications occur and vary widely in the literature. Complications are caused by thermal damage, direct needle injury, infection and the patient’s co-morbidities. Tumor type, type of approach, number of lesions, tumor localization, underlying hepatic disease, the physician’s experience, associated hepatic resection and lesion size have been described as factors significantly associated with complications. The physician in charge should promptly recognize high-risk patients more susceptible to complications, perform a close post procedure follow-up and manage them early and adequately if they occur. We aim to describe complications from RFA of hepatic tumors and their risk factors, as well as a few techniques to avoid them. This way, others can decrease their morbidity rates with better outcomes.