Irreversible electroporation: a novel image-guided cancer therapy

Magnetic Resonance Imaging Findings After Percutaneous Irreversible Electroporation of Liver Metastases: A Systematic Longitudinal Study

Objective

The aim of this study was to systematically investigate the course of magnetic resonance (MR) signal intensity (SI) changes that occur in noncirrhotic livers after irreversible electroporation (IRE) of liver metastases.

Methods

This study is an institutional review board–approved prospective longitudinal follow-up study on 27 patients with 37 liver metastases who underwent computed tomography–guided percutaneous IRE and a standardized follow-up protocol by serial hepatic MR imaging studies that consisted of a gadobutrol-enhanced dynamic series, axial T2-weighted (T2w) turbo spin echo, and diffusion-weighted imaging (b = 0/50/800), acquired before, within 2, and at 24 hours after IRE; at 1, 2, 4, 6, 8, and 12 weeks after IRE; and every 3 months thereafter for a follow-up of at least 12 months.

Results

The ablated target lesion remained visible within the ablation zone in 23 (62%) of 37 of cases for a mean time of 21 ± 20 weeks (median, 12 weeks). The ablation zone appeared homogeneously hyperintense on T2w turbo spin echo images on the day of IRE in 37 of 37 cases. By 24 hours after IRE, the ablation zone inverted its SI in 35 of 37 cases to intermediately hypointense, with a rim of T2w bright SI that exhibited arterial phase enhancement; this persisted for 7 ± 5 weeks (median, 4 weeks). The rim resolved in 35 (95%) of 37 cases within 3 months. The ablation zone increased slightly over the first 48 hours, then shrank progressively. Complete healing of the ablation zone was observed in 57% (21/37) after an average of 14 ± 15 (median, 8 weeks).

Average apparent diffusion coefficient values of the ablation zone decreased from 0.74 ± 0.36 × 10⁻³ mm²/s pre-IRE to 0.63 ± 0.27 × 10⁻³ mm²/s within the first 24 hours (P < 0.05), followed by a progressive normalization to 0.91 ± 0.30 × 10⁻³ mm²/s at 2 months.

Conclusions

Knowledge of the broad spectrum of MR imaging findings after IRE is important to avoid diagnostic errors in the follow-up of patients after IRE.

Pain Analysis in Patients with Pancreatic Carcinoma: Irreversible Electroporation versus Cryoablation

The aim of this article is to evaluate and compare the postprocedure pain in patients with pancreatic carcinoma treated with irreversible electroporation (IRE) and cryoablation (CRYO). We compared 22 patients with 22 lesions in pancreas treated with IRE and 26 patients with 27 lesions treated with cryosurgery. All the patients in the two groups were under celiac plexus block (CPB) treatment to alleviate the postprocedure pain. A numerical rating scale (VAS) consisting of 11-point scales and the 24 h total hydromorphone use were recorded for the analysis of the pain level in the patients who underwent these two technologies separately. Other parameters, such as the complications and the ECOG performance status, were also noted. Statistical analysis was performed by Fisher's exact test, the Chi-square test, and Student's t-test. All the pancreatic carcinoma patients in our study were reported to have postprocedure pain in the two groups. But there was no significant difference in the mean pain score (4.95 (IRE) versus 4.85 (CRYO); P = 0.52) and 24 h total hydromorphone use (3.89 mg (IRE) versus 3.97 mg (CRYO); P = 0.30). IRE is comparable to cryotherapy in the amount of pain that patients with pancreatic carcinoma experience.

The Effects of Irreversible Electroporation on the Colon in a Porcine Model

Background and Aim

Irreversible electroporation (IRE) is a method of targeted cell ablation which has been suggested as a potential cancer therapy as it leaves structures such as blood vessels and the extracellular matrix intact, thereby allowing the rapid recovery of healthy tissue. Here, we investigated the effects of IRE on the colon in vivo in a porcine model.

Methods

IRE ablation was performed on the colon walls of 12 female Tibet mini-pigs, creating a total of 24 lesions. Lesions were monitored periodically by endoscopy. The pigs were euthanized 7, 14, 21 or 28 days after IRE ablation and the colons harvested for gross and histological analysis. Sections were stained with hematoxylin and eosin (H&E), Masson’s trichrome (MT) stain and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.

Results

All pigs tolerated the ablation procedure without serious clinical symptoms or complications. There was no evidence of perforation by endoscopy or gross postmortem examination. All lesions were characterized by necrotic cell death with mild inflammation and hyperemia, with a sharp demarcation between ablated and adjacent normal tissue. A fibrous scar was observed in the ablated colon tissue. Histological analysis revealed damage to each layer of the colon. Histopathology findings also showed the preservation of extracellular structures and the recovery of the ablated colon.

Conclusions

The complete ablation of the target area, its rapid recovery and the lack of posttreatment symptoms suggest that IRE ablation may be a promising therapy for tumors located adjacent to or violating the colon wall.

Interventional oncology for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and is increasing in incidence. The overall prognosis of patients with liver cancer is poor. The Barcelona Clinic Liver Cancer (BCLC) classification in 5 stages is endorsed by European Association for the Study of the Liver (EASL) and American Association for the Study of Liver Disease (AASLD). This classification is recommended for treatment allocation. Because a small proportion of patients are suitable for curative surgical treatment, various locoregional therapies are widely used to manage patients with HCC. The image-guided therapies, also called interventional radiology or interventional oncology (IO) techniques consisted in percutaneous or endovascular approach. This article reviews the different IO treatments available in HCC patients and the strength of the data.

Arterial complication of irreversible electroporation procedure for locally advanced pancreatic cancer

Irreversible electroporation (IRE) is a non-thermal ablation technique used especially in locally advanced pancreatic carcinomas that are considered surgically unresectable. We present the first case of acute superior mesenteric artery (SMA) occlusion secondary to pancreatic IRE procedure that has not been reported before in the literature. A 66-year-old man underwent neoadjuvant chemoradiotherapy for locally advanced pancreatic ductal adenocarcinoma. IRE procedure was applied to the patient during laparotomy under general anesthesia. After finishing the procedure, an acute intestinal ischemia was detected. A conventional vascular angiography was performed and a metallic stent was successfully placed to the SMA and blood flow was maintained. It is important to be careful in such cases of tumor involvement of SMA when evaluating for IRE procedure of pancreatic tumor.

Intraoperative adverse events during irreversible electroporation-a call for caution

BACKGROUND

Irreversible electroporation is increasingly used for treatment of solid tumors, but safety data remain scarce. This study aimed to describe intraoperative adverse events associated with irreversible electroporation in patients undergoing solid tumor ablation.

METHODS

We analyzed demographic and intraoperative data for patients (n = 43) undergoing irreversible electroporation for hepato-pancreato-biliary and retroperitoneal malignancies (2012 to 2015). Adverse events were defined as cardiac, surgical, or equipment-related.

RESULTS

Adverse events (n = 20, 47%) were primarily cardiac (90%, n = 18), including blood pressure elevation (77%, n = 14/18) and arrhythmia (16%, n = 7/43). All but one was managed medically, 1 patient with arrhythmia required termination of ablation. Bleeding and technical problems with the equipment occurred in 1 patient each. Multivariable analysis revealed previous cardiovascular disease and needle placement close to the celiac trunk associated with increased likelihood for cardiac events.

CONCLUSIONS

Intraoperative cardiac adverse events are common during irreversible electroporation but rarely impair completion of the procedure.

Ablation Strategies for Locally Advanced Pancreatic Cancer

With the advent of novel and somewhat effective chemotherapy against pancreas cancer, several groups developed a new interest on locally advanced pancreatic cancer (LAPC). Unresectable tumors constitute up to 80% of pancreatic cancer (PC) at the time of diagnosis and are associated with a 5-year overall survival of less than 5%. To control those tumors locally, with perhaps improved patients survival, significant advances were made over the last 2 decades in the development of ablation methods including cryoablation, radiofrequency ablation, microwave ablation, high intensity focused ultrasound and irreversible electroporation (IRE). Many suggested a call for caution for possible severe or lethal complications in using such techniques on the pancreas. Most fears were on the heating or freezing of the pancreas, while non-thermal ablation (IRE) could offer safer approaches. The multimodal therapies along with high-resolution imaging guidance have created some enthusiasm toward ablation for LAPC. The impact of ablation techniques on primarily non-resectable PC remains, however, unclear.

The correlation between the electrode configuration and histopathology of irreversible electroporation ablations in prostate cancer patients

PURPOSE

Irreversible electroporation (IRE) is a novel minimally invasive therapy for prostate cancer using short electric pulses to ablate prostate tissue. The purpose of this study is to determine the IRE effects in prostate tissue and correlate electrode configuration with the histology of radical prostatectomy (RP) specimens. We hypothesize that the area within the electrode configuration is completely ablated and that the area within the electrode configuration is predictive for the ablated area after treatment.

METHODS

A prospective phase I/II study was conducted in 16 consecutive patients with histopathologically confirmed prostate cancer scheduled for RP. Focal or extended IRE treatment of the prostate was performed 4 weeks prior to RP. The locations of the electrodes were used to calculate the planned ablation zone. Following RP, the specimens were processed into whole-mount sections, histopathology (PA) was assessed and ablation zones were delineated. The area of the tissue alteration was determined by measuring the surface. The planned and the histological ablation zones were compared, analysed per individual patient and per protocol (focal vs. extended).

RESULTS

All cells within the electrode configuration were completely ablated and consisted only of necrotic and fibrotic tissue without leaving any viable cells. The histological ablation zone was always larger than the electrodes configuration (2.9 times larger for the 3 electrodes configuration and 2.5 times larger for the ≥4 electrode configuration). These ablation effects extended beyond the prostatic capsule in the neurovascular bundle in 13 out of 15 cases.

CONCLUSIONS

IRE in prostate cancer results in completely ablated, sharply demarcated lesions with a histological ablation zone beyond the electrode configuration. No skip lesions were observed within the electrode configuration.

CLINICAL TRIALS

ClinicalTrials.gov Identifier: NCT01790451 https://clinicaltrials.gov/ct2/show/NCT01790451.

Irreversible electroporation in the treatment of locally advanced pancreas and liver metastases of colorectal carcinoma

AIM OF THE STUDY

Irreversible electroporation is a new, non-thermal ablation technique in the treatment of parenchymal organ tumors which uses short high voltage pulses of electricity in order to induce apoptosis of targeted cells. In this paper the application of this method of treatment in locally advanced pancreatic cancer (LAPC) and liver cancer is analyzed.

MATERIAL AND METHODS

Between 04.2014 and 09.2014 two patients with LAPC and one with colorectal liver metastasis (CRLM) were qualified for treatment with irreversible electroporation. Both patients remained under constant observation and control. PubMed/Medline, Embase and Google Scholar databases were searched and eight original reports on irreversible electroporation of pancreatic and liver tumors based on the biggest groups of patients were found.

RESULTS

Two patients with LAPC and one with CRLM were qualified for ablation with irreversible electroporation. In all three patients a successful irreversible electroporation (IRE) procedure of the whole tumor was conducted. In the minimum seven-month follow-up 100% local control was achieved - without progression. In the literature review the local response to treatment ranged from 41% to 100%. The event-free survival rate in six-month observation was 94%.

CONCLUSIONS

Ablation with irreversible electroporation is a new non-thermal ablation technique which has been demonstrated, both in the previously published studies and in the cases described in this paper, as a safe and efficient therapeutic method for patients with LAPC and CRLM.

The Influence of a Metal Stent on the Distribution of Thermal Energy during Irreversible Electroporation

PURPOSE

Irreversible electroporation (IRE) uses short duration, high-voltage electrical pulses to induce cell death via nanoscale defects resulting from altered transmembrane potential. The technique is gaining interest for ablations in unresectable pancreatic and hepatobiliary cancer. Metal stents are often used for palliative biliary drainage in these patients, but are currently seen as an absolute contraindication for IRE due to the perceived risk of direct heating of the metal and its surroundings. This study investigates the thermal and tissue viability changes due to a metal stent during IRE.

METHODS

IRE was performed in a homogeneous tissue model (polyacrylamide gel), without and with a metal stent placed perpendicular and parallel to the electrodes, delivering 90 and 270 pulses (15-35 A, 90 μsec, 1.5 cm active tip exposure, 1.5 cm interelectrode distance, 1000-1500 V/cm, 90 pulses/min), and in-vivo in a porcine liver (4 ablations). Temperature changes were measured with an infrared thermal camera and with fiber-optic probes. Tissue viability after in-vivo IRE was investigated macroscopically using 5-triphenyltetrazolium chloride (TTC) vitality staining.

RESULTS

In the gel, direct stent-heating was not observed. Contrarily, the presence of a stent between the electrodes caused a higher increase in median temperature near the electrodes (23.2 vs 13.3°C [90 pulses]; p = 0.021, and 33.1 vs 24.8°C [270 pulses]; p = 0.242). In-vivo, no temperature difference was observed for ablations with and without a stent. Tissue examination showed white coagulation 1mm around the electrodes only. A rim of vital tissue remained around the stent, whereas ablation without stent resulted in complete tissue avitality.

CONCLUSION

IRE in the vicinity of a metal stent does not cause notable direct heating of the metal, but results in higher temperatures around the electrodes and remnant viable tissue. Future studies should determine for which clinical indications IRE in the presence of metal stents is safe and effective.

Ablation techniques for primary and metastatic liver tumors

Ablative treatment methods have emerged as safe and effective therapies for patients with primary and secondary liver tumors who are not surgical candidates at the time of diagnosis. This article reviews the current literature and describes the techniques, complications and results for radiofrequency ablation, microwave ablation, cryoablation, and irreversible electroporation.

Towards electroporation based treatment planning considering electric field induced muscle contractions

The electric field threshold for muscle contraction is two orders of magnitudes lower than that for electroporation. Current electroporation treatment planning and electrode design studies focus on optimizing the delivery of electroporation electric fields to the targeted tissue. The goal of one part of this study was to investigate the relation between the volumes of tissue that experience electroporation electric fields in a targeted tissue volume and the volumes of tissue that experience muscle contraction inducing electric fields around the electroporated tissue volume, (V(MC)), during standard electroporation procedures and for various electroporation electrodes designs. The numerical analysis shows that conventional electroporation protocols and electrode design can generate muscle contraction inducing electric fields in surprisingly large volumes of non-target tissue, around the electroporation treated tissue. In studying various electrode configurations, we found that electrode placement in a structure we refer to as a "Current Cage" can substantially reduce the volume of non-target tissue exposed to electric fields above the muscle contraction threshold. In an experimental study on a tissue phantom we compare a commercial two parallel needle electroporation system with the Current Cage design. While tissue electroporated volumes were similar, V(MC) of tissue treated using the Current Cage design electrodes was an order of magnitude smaller than that using a commercially available system. An important aspect of the entire study is that it suggests the benefit of including the calculations of V(MC) for planning of electroporation based treatments such as DNA vaccination, electrochemotherapy and irreversible electroporation.

Percutaneous irreversible electroporation of locally advanced pancreatic carcinoma using the dorsal approach: a case report

Irreversible electroporation (IRE) is a novel image-guided ablation technique that is increasingly used to treat locally advanced pancreatic carcinoma (LAPC). We describe a 67-year-old male patient with a 5 cm stage III pancreatic tumor who was referred for IRE. Because the ventral approach for electrode placement was considered dangerous due to vicinity of the tumor to collateral vessels and duodenum, the dorsal approach was chosen. Under CT-guidance, six electrodes were advanced in the tumor, approaching paravertebrally alongside the aorta and inferior vena cava. Ablation was performed without complications. This case describes that when ventral electrode placement for pancreatic IRE is impaired, the dorsal approach could be considered alternatively.

Percutaneous Irreversible Electroporation of Unresectable Hilar Cholangiocarcinoma (Klatskin Tumor): A Case Report

Irreversible electroporation (IRE) is a novel image-guided ablation technique that is rapidly gaining popularity in the treatment of malignant tumors located near large vessels or bile ducts. The presence of metal objects in the ablation zone, such as Wallstents, is generally considered a contraindication for IRE, because tissue heating due to power conduction may lead to thermal complications. This report describes a 66-year-old female with a Bismuth-Corlette stage IV unresectable cholangiocarcinoma with a metallic Wallstent in the common bile duct, who was safely treated with percutaneous IRE with no signs for relapse 1 year after the procedure.

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.

Factors associated with short-term local recurrence of liver cancer after percutaneous ablation using irreversible electroporation: a prospective single-center study

PURPOSE

To evaluate the risk factors associated with short-term local recurrence of malignant liver lesions after irreversible electroporation (IRE).

MATERIALS AND METHODS

Thirty-nine consecutive patients (79 malignant liver lesions) were treated with IRE, of whom 14 were excluded from the analysis (including 12 without 6 mo of follow-up and two with incomplete ablation). The remaining 25 patients (aged 59.4 y ± 11.2) had 48 malignant liver lesions, including 22 hepatocellular carcinomas (HCCs), six cholangiocellular carcinomas, and 20 metastatic liver cancers. Multivariate analyses were used to evaluate the associations of risk factors with early recurrence. The characteristics of patients, lesions, and IRE procedures were assessed by logistic regression.

RESULTS

Fourteen of the 48 treated lesions (29.2%) showed early local recurrence after 6 months. Tumor volume (< 5 cm(3) vs ≥ 5 cm(3); P = .022) and underlying disease type (HCC, cholangiocellular carcinoma, or metastatic disease; P = .023) were independently associated with early local recurrence. However, distances to the surrounding portal veins (< 0.5 cm vs ≥ 0.5 cm; P = .810), hepatic veins (P = .170), hepatic arteries (P = .761), and bile ducts (P = .226) were not significantly associated with local recurrence.

CONCLUSIONS

Because short distances to the surrounding vessels were not associated with early local recurrence, percutaneous IRE might provide an alternative treatment option for perivascular tumors. However, patients with larger tumor volumes appeared to be poor candidates for percutaneous IRE. Regarding the different types of treated lesions, patients with HCC had significantly better outcomes.

Risk of local failure after ultrasound guided irreversible electroporation of malignant liver tumors

INTRODUCTION

Irreversible electroporation (IRE) is considered superior to thermoablations for tumors in the vicinity of larger vessels and the liver hilum. We report on an initial clinical experience of IRE.

MATERIALS AND METHODS

Indications included focal liver lesions <3 cm, irresectability due to contraindications and expected complications and/or irradicality following radiofrequency ablation (RFA). Ultrasound was chosen for guidance and needle placement.

RESULTS

IRE was intended to perform in 14 patients with 1 procedure aborted due to technical failure. Among the 13 successfully treated were 7 percutaneous, 4 laparoscopic, and 2 open surgical procedures. The average age was 63 ± 10 years. Twelve solitary nodules and one bifocal disease were treated with an average size of 1.5 cm ± 0.5 cm. Median follow-up was 6 months. Three incomplete ablations account for 21% (3/14), 2 of them occurring in 2 metastases larger than 2 cm percutaneously treated with 5 needles instead of 4 used for smaller tumor sizes.

CONCLUSION

IRE was introduced without difficulties into clinical practice. As a main obstacle emerged in visualization of the needles, computed tomography may offer advantages in the guidance of percutaneous IRE of liver metastases larger than 2 cm. Local failure occurred in 21%.

Anaesthetic management during open and percutaneous irreversible electroporation

BACKGROUND

Irreversible electroporation (IRE) is a novel tumour ablation technique involving repetitive application of electrical energy around a tumour. The use of pulsed electrical gradients carries a risk of cardiac arrhythmias, severe muscle contractions, and seizures. We aimed to identify IRE-related risks and the appropriate precautions for anaesthetic management.

METHODS

All patients who were treated with IRE were prospectively included. Exclusion criteria were arrhythmias, congestive heart failure, active coronary artery disease, and epilepsy. All procedures were performed under general anaesthesia with complete muscle relaxation during ECG-synchronized pulsing. Adverse events, cardiovascular effects, blood samples, cerebral activity, and post-procedural pain were analysed.

RESULTS

Twenty-eight patients underwent 30 IRE sessions for tumours in the liver, pancreas, kidney, and lesser pelvis. No major adverse events occurred during IRE. Median systolic and diastolic blood pressure increased by 44 mm Hg (range -7 to 108 mm Hg) and 19 mm Hg (range 1-50 mm Hg), respectively. Two transient minor cardiac arrhythmias without haemodynamic consequences were observed. Muscle contractions were mild and IRE caused no reactive brain activity on a simplified EEG. Pain in the first 24 h after percutaneous IRE was generally mild, but higher pain scores were reported after pancreatic treatment (mean VAS score 3; range 0-9).

CONCLUSIONS

Side-effects during IRE on tumours in the liver, pancreas, kidney, and lesser pelvis seem mild and manageable when current recommendations for anaesthesia management, including deep muscle relaxation and ECG synchronized pulsing, are followed. Electrical pulses do not seem to cause reactive cerebral activity and evidence for pre-existing atrial fibrillation as an absolute contra-indication for IRE is questionable.

Tumor ablation: common modalities and general practices

Tumor ablation is a minimally invasive technique that is commonly used in the treatment of tumors of the liver, kidney, bone, and lung. During tumor ablation, thermal energy is used to heat or cool tissue to cytotoxic levels (less than -40°C or more than 60°C). An additional technique is being developed that targets the permeability of the cell membrane and is ostensibly nonthermal. Within the classification of tumor ablation, there are several modalities used worldwide: radiofrequency, microwave, laser, high-intensity focused ultrasound, cryoablation, and irreversible electroporation. Each technique, although similar in purpose, has specific and optimal indications. This review serves to discuss general principles and technique, reviews each modality, and discusses modality selection.

Regional hepatic therapies: an important component in the management of colorectal cancer liver metastases

The treatment of colorectal cancer liver metastases (CRLM) has evolved significantly in the last 15 years. Currently, complete surgical resection remains the only potentially curative option; unfortunately, approximately 80% of patients with CRLM are not candidates for complete tumor resection. For patients with unresectable CRLM the available treatment options were historically limited; however, the development of regional hepatic therapies (RHT) and improvement of systemic chemotherapeutic regimens have emerged as viable options to improve overall survival and quality of life for this group of patients. The selection, sequence and integration of interventions into a multi-modal approach is a complex and evolving discipline. In this article, the currently available RHT modalities for CRLM are presented as a guide to the options for clinical treatment decisions.

Irreversible electroporation for nonthermal tumor ablation in the clinical setting: a systematic review of safety and efficacy

PURPOSE

To provide an overview of current clinical results of irreversible electroporation (IRE), a novel, nonthermal tumor ablation technique that uses electric pulses to induce cell death, while preserving structural integrity of bile ducts and vessels.

METHODS

All in-human literature on IRE reporting safety or efficacy or both was included. All adverse events were recorded. Tumor response on follow-up imaging from 3 months onward was evaluated.

RESULTS

In 16 studies, 221 patients had 325 tumors treated in liver (n = 129), pancreas (n = 69), kidney (n = 14), lung (n = 6), lesser pelvis (n = 1), and lymph node (n = 2). No major adverse events during IRE were reported. IRE caused only minor complications in the liver; however, three major complications were reported in the pancreas (bile leak [n = 2], portal vein thrombosis [n = 1]). Complete response at 3 months was 67%-100% for hepatic tumors (93%-100% for tumors o 3 cm). Pancreatic IRE combined with surgery led to prolonged survival compared with control patients (20 mo vs 13 mo) and significant pain reduction.

CONCLUSIONS

In cases where other techniques are unsuitable, IRE is a promising modality for the ablation of tumors near bile ducts and blood vessels. This articles gives an extensive overview of the available evidence, which is limited in terms of quality and quantity. With the limitations of the evidence in mind, IRE of central liver tumors seems relatively safe without major complications, whereas complications after pancreatic IRE appear more severe. The available limited results for tumor control are generally good. Overall, the future of IRE for difficult-to-reach tumors appears promising.

Rapid dramatic alterations to the tumor microstructure in pancreatic cancer following irreversible electroporation ablation

AIM

NanoKnife(®) (Angiodynamics, Inc., NY, USA) or irreversible electroporation (IRE) is a newly available ablation technique to induce the formation of nanoscale pores within the cell membrane in targeted tissues. The purpose of this study was to elucidate morphological alterations following 30 min of IRE ablation in a mouse model of pancreatic cancer.

MATERIALS & METHODS

Immunohistochemistry markers were compared with diffusion-weighted MRI apparent diffusion coefficient measurements before and after IRE ablation.

RESULTS

Immunohistochemistry apoptosis index measurements were significantly higher in IRE-treated tumors than in controls. Rapid tissue alterations after 30 min of IRE ablation procedures (structural and morphological alterations along with significantly elevated apoptosis markers) were consistently observed and well correlated to apparent diffusion coefficient measurements.

DISCUSSION

This imaging assay offers the potential to serve as an in vivo biomarker for noninvasive detection of tumor response following IRE ablation.

The electromagnetic spectrum: current and future applications in oncology

The electromagnetic spectrum is composed of waves of various energies that interact with matter. When focused upon and directed at tumors, these energy sources can be employed as a means of lesion ablation. While the use of x-rays is widely known in this regard, a growing body of evidence shows that other members of this family can also achieve oncologic success. This article will review therapeutic application of the electromagnetic spectrum in current interventions and potential future applications.

Efficient electroporation of liposomes doped with pore stabilizing nisin

CONTEXT

Liposomes have a long history as passive and active drug carriers. Recently, a few methods have been realized to control the release from liposomes, including heating, ultrasound and laser.

OBJECTIVE

We report on a new approach to drive release from liposomes using electric fields.

MATERIALS AND METHODS

Liposomes were manufactured containing a high concentration of (quenched) 5-6 carboxyfluorescein dye. Nisin, a well-known amphiphilic peptide lantibiotic that works by stabilizing pores formed in cell membranes, was mixed in solution inside or outside the liposomes. The liposomes were then electroporated using a range of voltages, and assayed for increases in fluorescence due to release of dye. Release was measured against positive and negative controls, with positive control release driven by a strong detergent.

RESULTS

Our results demonstrate that the addition of nisin significantly reduces the electric field required to release the contents of liposomes, from 2000 V/m to approximately 200 V/m. This result proves that, in principle, electroporation (EP) of liposomes doped with small amounts of amphiphilic pore stabilizing peptides may be a practical means to drive release of liposomal contents in vivo.

CONCLUSION

Drug delivery from liposomes doped with amphiphilic peptides using EP is feasible. This technique could be developed into a potent adjuvant to tumor ablation using irreversible EP.

Immunologic response to tumor ablation with irreversible electroporation

Background

Irreversible electroporation (IRE) is a promising technique for the focal treatment of pathologic tissues, which involves placing minimally invasive electrodes within the targeted region. However, the knowledge about the therapeutic efficacy and immune reactions in response to IRE remains in its infancy.

Methods

In this work, to detect whether tumor ablation with IRE could trigger the immunologic response, we developed an osteosarcoma rat model and applied IRE directly to ablate the tumor. In the experiment, 118 SD rats were randomized into 4 groups: the control, sham operation, surgical resection, and IRE groups. Another 28 rats without tumor cell implantation served as the normal non-tumor-bearing group. We analyzed the changes in T lymphocyte subsets, sIL-2R and IL-10 levels in the peripheral blood one day before operation, as well as at 1, 3, 7,14 and 21 days after the operation. Moreover, splenocytes were assayed for IFN-γ and IL-4 production using intracellular cytokine staining one day before the operation, as well as at 7 and 21 days after operation.

Results

We found that direct IRE completely ablated the tumor cells. A significant increase in peripheral lymphocytes, especially CD3⁺ and CD4⁺ cells, as well as an increased ratio of CD4⁺/CD8⁺ were detectable 7 days after operation in both the IRE and surgical resection groups. Compared with the surgical resection group, the IRE group exhibited a stronger cellular immune response. The sIL-2R level of the peripheral blood in the IRE group decreased with time and was significantly different from that in the surgical resection group. Moreover, ablation with IRE significantly increased the percentage of IFN-γ-positive splenocytes.

Conclusion

These findings indicated that IRE could not only locally destroy the tumor but also change the status of cellular immunity in osteosarcoma-bearing rats. This provides experimental evidence for the clinical application of IRE in osteosarcoma treatment.

Therapeutic potential of irreversible electroporation in sarcoma

Irreversible electroporation is a newly developed nonthermal tissue ablation technique in which certain short-duration electrical fields are used to permanently permeabilize the cell membrane to disrupt cellular homeostasis. This disruption of cellular homeostasis initiates apoptosis, which leads to permanent cell death. Sarcomas are generally divided into soft-tissue and bone sarcomas based on their different mesenchymal origins and anatomical locations. Each of these sarcomas present in different ways, exhibit different behaviors and prognoses, and present unique therapeutic challenges. In this article, a series of recently conducted irreversible electroporation treatment for sarcomas based on local nonthermal ablation are summarized, and the therapeutic potential of this newly developed technique is assessed.

Diagnostic imaging and image-guided therapy of skeletal metastases

BACKGROUND

The high incidence of skeletal metastases in cancer patients warrants careful detection with imaging and follow-up. Efforts are needed to manage pain associated with skeletal metastases as part of overall patient management.

METHODS

This article reviews the current methods of diagnostic imaging in the evaluation of skeletal metastases and image-guided treatment of bone metastases for the palliation of pain based primarily on the assessment of imaging and interventional radiologic literature.

RESULTS

Approaches to diagnostic imaging of skeletal metastases are summarized. Skeletal scintigraphy provides high sensitivity for detecting skeletal metastases, but targeted computed tomography (CT) or magnetic resonance imaging (MRI) may be needed to increase specificity. Newer imaging modalities, such as positron emission tomography (PET)/CT, improve detection of both lytic and blastic metastases. Minimally invasive percutaneous ablative treatment techniques, including radiofrequency ablation, microwave ablation, and cryoablation, are examined. They provide alternative approaches to radiation therapy to effectively palliate pain of bone metastases. Preliminary results of MR-guided focused ultrasound surgery (MRgFUS) demonstrate its effectiveness in palliating pain from skeletal metastases.

CONCLUSIONS

Skeletal scintigraphy is the most common imaging modality for detecting skeletal metastases. Additional imaging may be required based on the type of tumor, the disease state, or treatment options. External-beam radiation therapy remains the mainstay for palliation of pain from bone metastases. Alternative minimally invasive and noninvasive image-guided treatment options can provide effective pain palliation.

Pain analysis in patients with hepatocellular carcinoma: irreversible electroporation versus radiofrequency ablation-initial observations

PURPOSE

To retrospectively compare the postprocedure pain of hepatocellular carcinoma treated with irreversible electroporation (IRE) with radiofrequency ablation (RFA).

METHODS

This Health Insurance Portability and Accountability Act-compliant, institutional review board-approved study compared postprocedure pain in 21 patients (15 men, six women; mean age 61.5 years) who underwent IRE of 29 intrahepatic lesions (mean size 2.20 cm) in 28 IRE sessions with 22 patients (16 men, six women; mean age 60.2 years) who underwent RFA of 27 lesions (mean size 3.38 cm) in 25 RFA sessions. Pain was determined by patient-disclosed scores with an 11-point numerical rating scale and 24 h cumulative hydromorphone use from patient-controlled analgesia pump. Complications were noted. Statistical significance was evaluated by Fisher's exact test, the Chi-square test, and Student's t test.

RESULTS

There was no significant difference in the cumulative hydromorphone dose (1.54 mg (IRE) vs. 1.24 mg (RFA); P = 0.52) and in the mean pain score (1.96 (IRE) vs. 2.25 (RFA); P = 0.70). In nine (32.14 %) of 28 IRE sessions and 11 (44.0 %) of 25 RFA sessions, patients reported no pain. Complications occurred in three (10.7 %) of 28 IRE treatments and included pneumothorax (n = 1), pleural effusion (n = 1), and bleeding in the form of hemothorax (n = 1); one (4 %) of 25 RFA treatments included burn.

CONCLUSION

IRE is comparable to RFA in the amount of pain that patients experience and the amount of pain medication self-administered. Both modalities were well tolerated by patients. Prospective, randomized trials are necessary to further evaluate these findings.

Comprehensive review of the diagnosis and treatment of biliary tract cancer 2012. Part II: multidisciplinary management

Biliary tract cancers (gallbladder cancer, intra- and extra-hepatic cholangiocarcinoma and selected periampullary cancers) accounted for 12,760 new cases of cancer in the USA in 2010. These tumors have a dismal prognosis with most patients presenting with advanced disease. Early, accurate diagnosis is essential, both for potential cure where possible and for optimal palliative therapy in all others. This review examines the currently available and emerging technologies for diagnosis and treatment of this group of diseases.

Irreversible electroporation for focal ablation at the porta hepatis

Patients with chemotherapy-refractory liver metastases who are not candidates for surgery may be treated with focal ablation techniques with established survival benefits. Irreversible electroporation is the newest of these and has the putative advantages of a nonthermal action, preventing damage to adjacent biliary structures and bowel. This report describes the use of irreversible electroporation in a 61-year-old man with a solitary chemoresistant liver metastasis unsuitable for radiofrequency ablation as a result of its proximity to the porta hepatis. At 3 months, tumor size was decreased on computed tomography from 28 × 19 to 20 × 17 mm, representing stable disease according to the response evaluation criteria in solid tumors. This corresponded to a decrease in tumor volume size from 5.25 to 3.16 cm(3). There were no early or late complications. Chemoresistant liver metastases in the proximity of the porta hepatis that are considered to be too high a risk for conventional surgery or thermal ablation may be considered for treatment by the novel ablation technique of irreversible electroporation.

Electrode activation sequencing employing conductivity changes in irreversible electroporation tissue ablation

Irreversible electroporation (IRE) uses high-voltage pulses applied to tissue, which cause dielectric breakdown of cell membranes resulting in cell death. IRE is a promising technique for ablation of nonresectable tumors because it can be configured to spare critical structures such as blood vessels. A consequence of pulse application is an increase in tissue electrical conductivity due to current pathways being opened in cell membranes. We propose a novel IRE method introducing electrode switching and pulse sequencing in which tissue conductivity is first increased using preparatory pulses in order to form high-conductivity zones, which then helps provide higher electric field intensity within the targeted tissue as subsequent pulses are applied, and hence, enhances the efficiency and selectivity of the IRE treatment. We demonstrate the potential of this method using computational models on simple geometries.

US findings after irreversible electroporation ablation: radiologic-pathologic correlation

PURPOSE

To characterize ultrasonographic (US) findings after irreversible electroporation (IRE) to determine the utility of these findings in the accurate assessment of ablation margins.

MATERIALS AND METHODS

The institutional animal care and use committee approved the study. IRE ablation (n = 58) was performed in vivo in 16 pig livers by using two 18-gauge electroporation electrodes with 2-cm tip exposure, 1.5- or 2.0-cm interelectrode spacing, and an electroporation generator. Energy deposition was applied at 2250-3000 V (pulse length, 50-100 μsec; pulse repetition, 50-100). Ablations were performed under US guidance. Images were obtained during ablation and at defined intervals from 1 minute to 2 hours after the procedure. Zones of ablation were determined at gross and histopathologic examination of samples obtained from animals sacrificed 2-3 hours after IRE. Dimensions of the histologic necrosis zone and US findings were compared and subjected to statistical analysis, including a Student t test and multiple linear regression.

RESULTS

Within 20-50 pulse repetitions of IRE energy, the ablation zone appeared as a hypoechoic area with well-demarcated margins. During the next 8-15 minutes, this zone decreased in size from 3.4 cm ± 0.5 to 2.5 cm ± 0.4 and became progressively more isoechoic. Subsequently, a peripheral hyperechoic rim measuring 2-7 mm (mean, 4 mm ± 1) surrounding the isoechoic zone developed 25-90 minutes (mean, 41 minutes ± 19) after IRE. The final length of the treatment zone, including the rim, increased to 3.3 cm ± 0.6. The final dimensions of the outer margin of this rim provided greatest accuracy (1.7 mm ± 0.2) and tightest correlation (r(2) = 0.89) with gross pathologic findings. Histologic examination demonstrated widened sinusoidal spaces that progressively filled with spatially distributed hemorrhagic infiltrate on a bed of hepatocytes with pyknotic nuclei throughout the treatment zone.

CONCLUSION

US findings in the acute period after IRE are dynamic and evolve. The ablation zone can be best predicted by measuring the external hyperechoic rim that forms 90-120 minutes after ablation. This rim is possibly attributable to evolving hemorrhagic infiltration via widened sinusoids.

Cryosurgery with pulsed electric fields

This study explores the hypothesis that combining the minimally invasive surgical techniques of cryosurgery and pulsed electric fields will eliminate some of the major disadvantages of these techniques while retaining their advantages. Cryosurgery, tissue ablation by freezing, is a well-established minimally invasive surgical technique. One disadvantage of cryosurgery concerns the mechanism of cell death; cells at high subzero temperature on the outer rim of the frozen lesion can survive. Pulsed electric fields (PEF) are another minimally invasive surgical technique in which high strength and very rapid electric pulses are delivered across cells to permeabilize the cell membrane for applications such as gene delivery, electrochemotherapy and irreversible electroporation. The very short time scale of the electric pulses is disadvantageous because it does not facilitate real time control over the procedure. We hypothesize that applying the electric pulses during the cryosurgical procedure in such a way that the electric field vector is parallel to the heat flux vector will have the effect of confining the electric fields to the frozen/cold region of tissue, thereby ablating the cells that survive freezing while facilitating controlled use of the PEF in the cold confined region. A finite element analysis of the electric field and heat conduction equations during simultaneous tissue treatment with cryosurgery and PEF (cryosurgery/PEF) was used to study the effect of tissue freezing on electric fields. The study yielded motivating results. Because of decreased electrical conductivity in the frozen/cooled tissue, it experienced temperature induced magnified electric fields in comparison to PEF delivered to the unfrozen tissue control. This suggests that freezing/cooling confines and magnifies the electric fields to those regions; a targeting capability unattainable in traditional PEF. This analysis shows how temperature induced magnified and focused PEFs could be used to ablate cells in the high subzero freezing region of a cryosurgical lesion.

Angiography in the isolated perfused kidney: radiological evaluation of vascular protection in tissue ablation by nonthermal irreversible electroporation

PURPOSE

The nonthermal irreversible electroporation (NTIRE) is a novel nonthermal tissue ablation technique by local application of high-voltage current within microseconds leading to a delayed apoptosis. The purpose of this experimental study was the first angiographic evaluation of the acute damage of renal vascular structure in NTIRE.

METHODS

Results of conventional dynamic digital substraction angiography (DSA) and visualization of the terminal vascular bed of renal parenchyma by high-resolution X-ray in mammography technique were evaluated before, during, and after NTIRE of three isolated perfused porcine ex vivo kidneys.

RESULTS

In the dedicated investigation, no acute vascular destruction of the renal parenchyma and no dysfunction of the kidney perfusion model were observed during or after NTIRE. Conspicuous were concentric wave-like fluctuations of the DSA contrast agent simultaneous to the NTIRE pulses resulting from NTIRE pulse shock wave.

CONCLUSION

The NTIRE offers an ablation method with no acute collateral vascular damage in angiographic evaluation.

A parametric study delineating irreversible electroporation from thermal damage based on a minimally invasive intracranial procedure

BACKGROUND

Irreversible electroporation (IRE) is a new minimally invasive technique to kill undesirable tissue in a non-thermal manner. In order to maximize the benefits from an IRE procedure, the pulse parameters and electrode configuration must be optimized to achieve complete coverage of the targeted tissue while preventing thermal damage due to excessive Joule heating.

METHODS

We developed numerical simulations of typical protocols based on a previously published computed tomographic (CT) guided in vivo procedure. These models were adapted to assess the effects of temperature, electroporation, pulse duration, and repetition rate on the volumes of tissue undergoing IRE alone or in superposition with thermal damage.

RESULTS

Nine different combinations of voltage and pulse frequency were investigated, five of which resulted in IRE alone while four produced IRE in superposition with thermal damage.

CONCLUSIONS

The parametric study evaluated the influence of pulse frequency and applied voltage on treatment volumes, and refined a proposed method to delineate IRE from thermal damage. We confirm that determining an IRE treatment protocol requires incorporating all the physical effects of electroporation, and that these effects may have significant implications in treatment planning and outcome assessment. The goal of the manuscript is to provide the reader with the numerical methods to assess multiple-pulse electroporation treatment protocols in order to isolate IRE from thermal damage and capitalize on the benefits of a non-thermal mode of tissue ablation.