A review of the general aspects of radiofrequency ablation

What is the purpose of launching the World Journal of Methodology?

Congratulations to the publisher, members of the editorial board of the journal, all the authors and readers for launching the World Journal of Methodology (WJM) as a new member of the World series journal family! Scientific advances and important breakthroughs have been facilitated by well developed methodologies or techniques and any misleading findings and theories are exclusively attributable to certain methodological defects. Thus, the role of appropriate methodologies in the development of science and technology cannot be overemphasized and the need for inaugurating this new journal is self-evident. The WJM is a peer-reviewed open-access periodical centered in biomedical sciences but with multidisciplinary coverage. If you want to share any new methodologies, any experiences of the application or improvement of such methodologies and any methodology-related academic issues with your peers, you will find the WJM a good media to publish your papers!

Radiofrequency ablation of hepatocellular carcinoma: Current status

Ablation therapy is one of the best curative treatment options for malignant liver tumors, and can be an alternative to resection. Radiofrequency ablation (RFA) of primary and secondary liver cancers can be performed safely using percutaneous, laparoscopic, or open surgical techniques, and RFA has markedly changed the treatment strategy for small hepatocellular carcinoma (HCC). Percutaneous RFA can achieve the same overall and disease-free survival as surgical resection for patients with small HCC. The use of a laparoscopic or open approach allows repeated placements of RFA electrodes at multiple sites to ablate larger tumors. RFA combined with transcatheter arterial chemoembolization will make the treatment of larger tumors a clinically viable treatment alternative. However, an accurate evaluation of treatment response is very important to secure successful RFA therapy. Since a sufficient safety margin (at least 0.5 cm) can prevent local tumor recurrences, an accurate evaluation of treatment response is very important to secure successful RFA therapy. To minimize complications of RFA, clinicians should be familiar with the imaging features of each type of complication. Appropriate management of complications is essential for successful RFA treatment.

A dual-targeting anticancer approach: soil and seed principle

PURPOSE

To test the hypothesis that targeting the microenvironment (soil) may effectively kill cancer cells (seeds) through a small-molecular weight sequential dual-targeting theragnostic strategy, or dual-targeting approach.

MATERIALS AND METHODS

With approval from the institutional animal care and use committee, 24 rats were implanted with 48 liver rhabdomyosarcomas (R1). First, the vascular-disrupting agent combretastatin A4 phosphate (CA4P) was injected at a dose of 10 mg/kg to cause tumor necrosis, which became a secondary target. Then, the necrosis-avid agent hypericin was radiolabeled with iodine 131 to form (131)I-hypericin, which was injected at 300 MBq/kg 24 hours after injection of CA4P. Both molecules have small molecular weight, are naturally or synthetically derivable, are intravenously injectable, and are of unique targetablities. The tumor response in the dual-targeting group was compared with that in vehicle-control and single-targeting (CA4P or (131)I-hypericin) groups with in vivo magnetic resonance imaging and scintigrams and ex vivo gamma counting, autoradiography, and histologic analysis. Tumor volumes, tumor doubling time (TDT), and radiobiodistribution were analyzed with statistical software. P values below .05 were considered to indicate a significant difference.

RESULTS

Eight days after treatment, the tumor volume of rhabdomyosarcoma in the vehicle-control group was double that in both single-targeting groups (P < .001) and was five times that in the dual-targeting group (P < .0001), without treatment-related animal death. The TDT was significantly longer in the dual-targeting group (P < .0001). Necrosis appeared as hot spots on scintigrams, corresponding to 3.13% of the injected dose of (131)I-hypericin per gram of tissue (interquartile range, 2.92%-3.97%) and a target-to-liver ratio of 20. The dose was estimated to be 100 times the cumulative dose of 50 Gy needed for radiotherapeutic response. Thus, accumulated (131)I-hypericin from CA4P-induced necrosis killed residual cancer cells with ionizing radiation and inhibited tumor regrowth.

CONCLUSION

This dual-targeting approach may be a simple and workable solution for cancer treatment and deserves further exploitation.

Current Technology in Navigation and Robotics for Liver Tumours Ablation

Radiofrequecy ablation is the most widely used local ablative therapy for both primary and metastatic liver tumours. However, it has limited application in the treatment of large tumours (tumours >3cm) and multicentric tumours. In recent years, many strategies have been developed to extend the application of radiofrequency ablation to large tumours. A promising approach is to take advantage of the rapid advancement in imaging and robotic technologies to construct an integrated surgical navigation and medical robotic system. This paper presents a review of existing surgical navigation methods and medical robots. We also introduce our current developed model — Transcutaneous Robot-assisted Ablation-device Insertion Navigation System (TRAINS). The clinical viability of this prototyped integrated navigation and robotic system for large and multicentric umors is demonstrated using animal experiments. Keywords: Computer aided surgery, Liver, Radiofrequency ablation

Design of a new probe for tumor treatment in the alternate thermal system based on numerical simulation

A new probe for tumor treatment is designed and simulated in this study. This probe combines the cryosurgery and hyperthermia which is suitable for the treatment of subcutaneous tumors. Simulations of the cooling and heating processes demonstrate that the probes are capable of treating the tumor effectively. And the numerical results indicate that the lengths of the probe, the diameters of the inner tube and the pressures of liquid nitrogen influence the probes' cooling ability. The temperature responses at the tumor base induced by different probes are similar, though the great differences appear on the treatment interface of the probes, thus the temperature gradient within the tumor. Based on the simulation results, the heating effect of the probe is shown to be effective in damaging the tumor while protecting normal tissue in the surrounding. Animal experiments will be carried out using this type of probe to treat tumor in the near future.

Radiofrequency ablation of hepatocellular carcinoma: a literature review

Radiofrequency ablation (RFA) of liver cancers can be performed safely using percutaneous, laparoscopic, or open surgical techniques, and much of the impetus for the use of RFA has come from cohort series that have provided an evidence base for this technique. Here, we give an overview of the current status of radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC), including its physical properties, to assess the characteristics that make this technique applicable in clinical practice. We review the technical development of probe design and summarize current indications and outcomes of reported clinical use. An accurate evaluation of treatment response is very important to secure successful RFA therapy since a sufficient safety margin (at least 0.5 cm) can prevent local tumor recurrences. We also provide a profile of side effects and information on the integration of this technique into the general management of patients with HCC. To minimize complications of RFA, physicians should be familiar with each feature of complication. Appropriate management of complications is essential for successful RFA treatment. Moreover, adjuvant therapy, such as molecular targeted therapies following curative therapy, is expected to further improve survival after RFA.

Radiofrequency ablation of hepatocellular carcinoma: Current status

Ablation therapy is one of the best curative treatment options for malignant liver tumors, and can be an alternative to resection. Radiofrequency ablation (RFA) of primary and secondary liver cancers can be performed safely using percutaneous, laparoscopic, or open surgical techniques, and RFA has markedly changed the treatment strategy for small hepatocellular carcinoma (HCC). Percutaneous RFA can achieve the same overall and disease-free survival as surgical resection for patients with small HCC. The use of a laparoscopic or open approach allows repeated placements of RFA electrodes at multiple sites to ablate larger tumors. RFA combined with transcatheter arterial chemoembolization will make the treatment of larger tumors a clinically viable treatment alternative. However, an accurate evaluation of treatment response is very important to secure successful RFA therapy. Since a sufficient safety margin (at least 0.5 cm) can prevent local tumor recurrences, an accurate evaluation of treatment response is very important to secure successful RFA therapy. To minimize complications of RFA, clinicians should be familiar with the imaging features of each type of complication. Appropriate management of complications is essential for successful RFA treatment.

Radioablation settings affecting the size of lesions created ex vivo in porcine livers with monopolar perfusion electrodes

RATIONALE AND OBJECTIVES

To explore the morphological characteristics of ablated lesions and find which combination of duration, temperature, and power was preferable to create largest lesion size with monopolar perfusion electrodes.

MATERIALS AND METHODS

Using monopolar perfusion electrodes to create 72 lesions in 30 excised porcine livers with radiofrequency radiation at different durations (5, 10, 15, and 20 minutes), temperatures (83 degrees C, 93 degrees C, 103 degrees C, and 113 degrees C), and powers (20, 30, and 40 W). Lesion volumes were calculated from longitudinal diameters and transverse diameters. Morphological characteristics were assessed microscopically from slides stained with hematoxylin and eosin.

RESULTS

Positive correlations were found between duration and longitudinal diameter (r = 0.66; P < .001), transverse diameter (r = 0.66; P < .001), distance of ablation beyond the electrode tip (r = 0.56; P < .001), and volume of lesions (r = 0.66; P < .001). Temperature was also positively correlated with longitudinal diameter (r = 0.70; P < .001), transverse diameter (r = 0.72; P < .001), distance of ablation beyond the electrode tip (r = 0.61; P < .001), and lesion volume (r = 0.711; P < .001). Lesion size did not increase when duration was longer than 15 minutes and temperature was higher than 103 degrees C. Power was not correlated with lesion size. Lesion size did not increase with increasing power. Macroscopically, all lesions were elliptical in cross section and appeared three zones: a central zone (I), a coagulated necrotic zone (II), and a hemorrhagic and edematous zone (III) from inside to outside. Microscopically, cells morphology and the nucleus were irregular or even disappeared in zone I. In zone II and III, cells did not appear deformation.

CONCLUSION

Duration and temperature, not power, affected lesion size. The largest lesion size was about 3.5 cm x 2.5 cm x 2.5 cm as temperature and duration was 15 minutes/103 degrees C.

Image-guided therapy: evolution and breakthrough

Beyond the advances made in computer-assisted interventions and robotic systems, the demand for more efficient and safer therapies remains challenging. Thus, if it is possible to improve the instrument tracking, steering, and target localization, to miniaturize the sensors and actuators, and to conduct preoperatively planned minimally invasive therapies, we still need new resources to achieve permanent destruction of abnormal tissues or suppression of pathological processes. Most of the physics-based (or energy-based) therapeutic principles at our disposal have been established a long time ago, but their actions on basic cellular and molecular mechanisms are not yet fully understood. They all have a wide spectrum of clinical targets in terms of organs and pathologies, modes of application (external, interstitial, intraluminal, etc.) with advantages and side-effect drawbacks, proven indications, and contraindications. Some of them may still face controversies regarding their outcomes. This short article, mainly focused on tumor destruction, briefly reviews in its first part some of these techniques and sketches the next generation under investigation. The former include radio frequency (RF), high-intensity focused ultrasound (HiFU), microwaves, and cryotherapy, of which all are temperature based. Laser-based approaches [e.g., photodynamic therapy (PDT) at large] are also discussed. Radiotherapy and its variants (hadrontherapy, brachytherapy, Gamma Knife, and CyberKnife) remain, of course, as the reference technique in cancer treatment. The next breakthroughs are examined in the second part of the article. They are based on the close association between imaging agents, drugs, and some stimulation techniques. The ongoing research efforts in that direction show that, if they are still far from clinical applications, strong expectations are made. From the point of view of interventional planning and image guidance, all of them share a lot of concerns.

Effect of Input Waveform Pattern and Large Blood Vessel Existence on Destruction of Liver Tumor Using Radiofrequency Ablation: Finite Element Analysis

Much research has been directed at improving the effectiveness of the radiofrequency (RF) ablation of hepatocellular carcinomas. In that point of view, this study was performed to provide comprehensive information of the relation between RF waveforms and thermodynamic response of the tissue with the consideration of four different types of RF waveforms (half-sine, half-square, half-exponential, and damped-sine) to maximize the amount of tumor tissue removed while maintaining the advantages of RF ablation. For the aim of this study, finite element models incorporating results from previous numerical models were used and validated with ex vivo experiments. From analyses of the entire results, we concluded that this study may prove valuable as a first step in providing comprehensive information of the relation between various RF waveforms and thermodynamic responses within the tissue during the RF ablation process. This study may also contribute toward studies to determine an optimum RF waveform capable of maximizing the amount of tumor tissue removed while maintaining the advantages of RF ablation.

Computer-assisted needle positioning for liver tumour radiofrequency ablation (RFA)

BACKGROUND

The RFA procedures rely on a precise positioning of the radiofrequency electrode and the complete destruction of the tumour. This article presents new optimization techniques to improve such surgical procedures.

METHODS

A method to optimize the coverage of the tumour by successive RFA destructions and an in vitro procedure with simulated tumours have been developed.

RESULTS

The guidance system and optimization coverage have been tested on 3D simulation and by the surgeon in vitro on a heifer liver. In this context, the RFA electrode is optically tracked and guided.

CONCLUSIONS

The optimization method provides needle placements that ensure a complete theoretical ablation of the tumour, and the guidance system helps the surgeon to reach each position of destruction.

A systematic review on the clinical benefit and role of radiofrequency ablation as treatment of colorectal liver metastases

AIM

To evaluate the role of radiofrequency ablation (RFA) as treatment of colorectal cancer liver metastases (CLMs).

METHOD

A PubMed literature search for original articles published until August 2008 was performed. Studies with 40 patients, 18 month median follow-up and reported 3 year overall survival (OS) rates after RFA of CLM were selected for analysis.

RESULTS

Thirteen clinical series and 8 non-randomised comparative studies were analysed. Median progression free survival after RFA ranged between 6 and 13 months. Median and 5-year OS after RFA (RFA plus resection) ranged between 24-59 months and 18-40% (36-46 months and 27-30%). Comparative studies indicated significantly improved OS after RFA versus chemotherapy alone, RFA plus chemotherapy versus RFA alone and up-front RFA versus RFA following second-line chemotherapy.

CONCLUSION

Our findings support that RFA prolongs time without toxicity and survival as an adjunct to hepatectomy and/or chemotherapy in well-selected patients, but not as an alternative to resection.

Tumor models and specific contrast agents for small animal imaging in oncology

Despite the widespread use of various imaging modalities in clinical and experimental oncology without or with combined application of commercially available nonspecific contrast agents (CAs), development of tissue- or organ- or disease-specific CAs has been a continuing effort for pursuing ever-improved sensitivity, specificity, and applicability. This is particularly true with magnetic resonance imaging (MRI) due to its intrinsic superb spatial/temporal/contrast resolutions and adequate detectability for tiny amount of substances. In this context, research using small animal tumor models has played an indispensible role in preclinical exploration of tissue specific CAs. Emphasizing more on methodological and practical aspects, this article aims to share our cumulated experiences on how to create tumor models for evaluation and development of new tissue specific MRI CAs and how to apply such models in imaging-based research studies. With the results that are repeatedly confirmed by later clinical applications in cancer patients, some of our early preclinical studies have contributed to the designs of subsequent clinical trials on the new CAs, some studies have predicted new utilities of these CAs; and other studies have led to the discoveries of new tissue- or disease-specific CAs with novel diagnostic or even therapeutic potentials. Among commonly adopted tumor models, the chemically induced and surgically implanted nodules in the liver prove very useful to simulate primary and metastatic intrahepatic tumors, respectively in clinical patients. The methods to create tumor models have eased procedures and yielded high success rates. The specific properties of the new CAs could be outshined by intraindividual comparison to the commercial CAs as nonspecific controls. Meticulous imaging-microangiography-histology matching techniques guaranteed colocalization of the lesion on in vivo MRI and postmortem tissue specimen, hence correct imaging interpretation and longstanding conclusions. As exemplified in the real study cases, the present experimental set-up proves applicable in small animals for imaging-based oncological investigations, and may provide a platform for the currently booming molecular imaging in a multimodality environment.

A surgical device for radiofrequency ablation of large liver tumors

Radiofrequency ablation has become an accepted treatment option of patients with primary and metastatic liver tumors. We propose an ablation electrode array consisting of 4-8 blade shaped electrodes arranged in a circular geometry for the treatment of large liver tumors. We developed a 3D code based on the finite difference method for evaluating the effect of different numbers of electrodes (4, 6 and 8) and electrode distance on lesion size. The configuration with six electrodes can ablate a volume of 70 x 70 x 40 mm(3) in approximately 5 min, with tissue temperature above 50 degrees C throughout the treatment volume. We then performed an experimental study in polyacrylamide gel in order to validate the theoretical results. The average temperature error between the simulation and the experiment was 3.8% at the center of the electrode array. This study shows that the proposed device potentially allows more rapid treatment of large tumors than current radiofrequency ablation devices.

Hepatocellular cancer response to radiofrequency tumor ablation: contrast-enhanced ultrasound

Radiofrequency ablation (RFA) is increasingly being used as percutaneous treatment of choice for patients with early stage hepatocellular carcinoma (HCC). An accurate assessment of the RFA therapeutic response is of crucial importance, considering that a complete tumor ablation significantly increases patient survival, whereas residual unablated tumor calls for additional treatment. Imaging modalities play a pivotal role in accomplishing this task, but ultrasound (US) is not considered a reliable modality for the evaluation of the real extent of necrosis, even when color/power Doppler techniques are used. Recently, newer microbubble-based US contrast agents used in combination with grey-scale US techniques, which are very sensitive to non-linear behavior of microbubbles, have been introduced. These features have opened new prospects in liver ultrasound and may have a great impact on daily practice, including cost-effective assessment of therapeutic response of percutaneous ablative therapies. Technical evolution of CEUS focusing on findings after RFA are illustrated. These latter are detailed, cross-referenced with the literature and discussed on the basis of our personal experience. Timing of CEUS posttreatment assessment among with advantages and limitations of CEUS are also described with a perspective on further technologic refinement.

Toric HIFU transducer for large thermal ablation

A new geometry of High Intensity Focused Ultrasound (HIFU) transducer is described to enlarge the coagulated volume and decrease treatments time. Eight transducer elements and their quarter-wave plate were diced out of a single toric piezocomposite element. Each transducer operates at a frequency of 3 MHz. The focal zone is conic and located at 70 mm from the transducer. A 7.5 MHz ultrasound imaging probe is placed in the centre of the device for guiding the treatment. Optimal exposure parameters were determined from numerical simulations. This new geometry allows achieving a thermal ablation of 7.5 cm3 when each of the eight transducers has performed a 5-s ultrasound exposure alternatively and consecutively. In vivo trials have been performed on five pigs to demonstrate this new principle. 33 elementary lesions have been performed. All lesions were reproducible and homogeneous. The average diameter of an elementary lesion obtained in 40 seconds was 19.5 +/- 3.8 mm (min 10 - max 29 mm). The coagulated volume obtained in 40 seconds was on average 9.1 +/- 4.6 cm3 (min 1.5 - max 17.6 cm3).

Five-year survival following radiofrequency ablation of small, solitary, hepatic colorectal metastases

PURPOSE

Radiofrequency (RF) ablation is an increasingly accepted treatment for nonsurgical candidates with a limited number of colorectal hepatic metastases. RF ablation is most effective in tumors smaller than 4.0 cm. This report describes 5-year survival in patients with single tumors with a maximum diameter of 4 cm.

MATERIALS AND METHODS

Forty of 291 patients (14%; 24 men, 16 women; mean age, 67 years; age range, 34-86 y) with no or treated extrahepatic disease were identified who were not candidates for resection and who had a minimum follow-up of 6 months. Sixteen had undergone hepatic resection and two had undergone lung resection and lung ablation. Thirty-two (80%) received chemotherapy. Thirty-five were treated under general anesthesia and five under conscious sedation. Our standard ablation protocol used internally water-cooled electrodes introduced percutaneously with ultrasonography and computed tomography guidance and monitoring. Follow-up data were obtained from primary care physicians or oncologists.

RESULTS

Mean tumor diameter was 2.3 cm (range, 0.8-4.0 cm). There were two successfully treated systemic complications: a chest infection and an exacerbation of asthma. There were no local complications. Mean follow-up was 38 months (range, 6-132 months). The median survival duration and 1-, 3-, and 5-year survival rates were 59 months and 97%, 84%, 40%, respectively, after ablation; and 63 months, 100%, 88%, and 54%, respectively, from the diagnosis of liver metastases. History of liver resection did not impact survival.

CONCLUSIONS

RF ablation of solitary liver metastases 4 cm or smaller can be performed with minimal morbidity and results in excellent long-term survival, approaching that of surgical resection, even in patients who are not surgical candidates.

Bimodal electric tissue ablation-long term studies of morbidity and pathological change

BACKGROUND

Radiofrequency ablation is a popular method of treating unresectable liver tumors but tumors greater than 3 cm in diameter have a much greater risk of local recurrence after treatment. Bimodal electric tissue ablation is a modified form of radiofrequency ablation that creates significantly larger ablations by the addition of extra direct current circuitry. This may help to reduce the risk of local recurrence in these larger tumors. Prior to use in a clinical setting, a long term study was performed to assess associated morbidity and the pathological changes in the ablations.

METHODS

In eight pigs, six ablations were performed in each liver. Pigs were euthanized at 2 d, 2 wk, 2 mo, and 4 mo, and the ablations were assessed macroscopically and microscopically for pathological change. Regular blood tests were performed to assess changes in liver function. At death, any other abnormalities detected were reported.

RESULTS

Histopathological examination of ablation zones revealed tissue death by coagulative necrosis and healing by fibrotic scarring. Transient rises in serum liver enzymes were seen in the postoperative period. Skin necrosis was noted at the site of the positive electrode of the direct electrical current but no other form of morbidity was seen associated with the procedure.

CONCLUSIONS

Although the positive electrode placement requires further consideration, bimodal electric tissue ablation appears to be safe and behaves in a similar fashion to other thermal therapies such as standard radiofrequency ablation.

Imaging appearances following thermal ablation

Radiofrequency ablation (RFA) has an increasingly important role in the management of a number of solid tumours. Treatments usually take place at specialist centres that draw patients from a wide geographical area, but follow-up imaging is often undertaken at the referring institution. This review aims to describe and illustrate the range of normal and abnormal post-ablative appearances encountered in the most commonly treated organs, i.e. liver, lung, and kidney, to equip radiologists with the necessary knowledge for confident interpretation of post-ablation imaging in this diverse patient group.

Radiofrequency ablation versus resection for resectable colorectal liver metastases: time for a randomized trial?

BACKGROUND

Surgical resection is the gold standard in the treatment of resectable colorectal liver metastases (CRLM). In several centers, resection is being replaced by radiofrequency ablation (RFA), even though there is no evidence yet from randomized trials to support this. The aim of this study was to critically review the oncological evidence for and against the use of RFA for resectable CRLM.

METHODS

An exhaustive review of RFA of colorectal metastases was carried out.

RESULTS

Five-year survival data after RFA for resectable CRLM are not available. Percutaneous RFA is associated with worse local control, worse staging, and a small risk of electrode track seeding when compared with resection (level V evidence). For tumors </=3 cm, local control after surgical RFA is equivalent to resection, especially if applied by experienced physicians to nonperivascular tumors (level V evidence). There is indirect evidence for profoundly different biological effects of RFA and resection.

CONCLUSIONS

A subgroup of patients has been identified for whom local control after RFA might be equivalent to resection. Whether this is true, and whether this translates into equivalent survival, remains to be proven. The time has come for a randomized trial.

Trajectory optimization for the planning of percutaneous radiofrequency ablation of hepatic tumors

Radiofrequency ablation is increasingly used in the treatment of hepatic tumors. Planning the percutaneous intervention is essential and particularly difficult. In this paper, we focus on an automated computation of optimal needle insertion in computer-assisted surgery with 3D visualization. First, we review our method which delineates on the skin of a virtual patient the candidate zones for needle insertion, i.e., those which allow safe access to the tumor. In each case, we look for the trajectory that minimizes the volume of burnt tissue. Secondly, we introduce a quasi-exhaustive method that allies sampling and certified minimization to form a strong argument for the accuracy of our results. We also compare results of applying both methods on 7 representative reconstructed patient cases.

Bimodal electric tissue ablation-modified radiofrequency ablation with a le veen electrode in a pig model

Radiofrequency ablation (RFA) is a method of treating non-resectable liver tumors by use of a high-frequency alternating electrical current. Concerns have been raised as the local recurrence rates following treatment have been reported to be as high as 47%. The size of the ablation is limited by charring of adjacent tissues. It is hypothesized that by hydrating the liver, we can reduce charring, thus producing larger ablations, and that this can be achieved by addition of a direct electrical current to the electrical circuit. Using a pig model, standard RFA control ablations were created in the left lobe of the liver. Ablations using the modified circuit were created in the right lobe. At the end of the procedure, the pig was killed by lethal injection and the liver harvested. From the explanted liver, the diameter of each ablation was measured and the modified ablations were compared with controls using restricted maximum likelihood variance analysis. From 4 pigs, 14 controls and 12 modified ablations were produced. The mean diameter of the controls was 27.78 mm (+/- SE 3.37 mm). The mean diameter of the modified ablation was 49.55 mm (+/- SE 3.46 mm), which was significantly larger than the controls (P < 0.001). This study has shown that by modification of the standard RFA circuit with the addition of a direct electrical current, significantly larger ablations can be produced. By using this technique, the number of ablations required to treat one tumor would be less and it is anticipated this could reduce the rate of local recurrence.

Switching Monopolar Radiofrequency Ablation Technique Using Multiple, Internally Cooled Electrodes and a Multichannel Generator

OBJECTIVE

We sought to determine the optimal switching time and interprobe distance for creating a large coagulation zone in the liver by switching monopolar radiofrequency ablation (RFA) technique using a prototype multichannel radiofrequency generator and multiple electrodes.

MATERIALS AND METHODS

Using 3, 17-gauge, internally cooled electrodes and a prototype multichannel radiofrequency (RF) generator to allow automatic switching of RF energy among 3 electrodes according to their impedance changes, RF energy was applied in a switching monopolar mode to explanted bovine livers or to the livers of 7 dogs. In the ex vivo study, we evaluated the effect of the switching time (5, 15, 30, and 60 seconds) and the interprobe distance (3 cm and 4 cm) on the mean volume of the ablation zone using the switching RFA; we then compared the ablation volume of the switching RFA group (12 minutes) with that of the overlapping RFA group (12 minutes x 3 = 36 minutes). In our preliminary in vivo experiments using 2 dogs, the electrodes were placed in a triangular array (spacing 2 cm, 3 cm, 3.5 cm, or 4 cm) and were activated for 12 minutes or 20 minutes in a monopolar mode (power output 200 W). In our primary experiments using 5 dogs, RFA in a switching mode created 10 coagulation zones at a 2- to 3-cm interprobe distance. The duration of the RFA was 12 minutes. The size and geometry of the coagulation zone also were assessed.

RESULTS

In this ex vivo study, switching monopolar RFA at a 3-cm interprobe distance and at a 30-second switching time allowed the creation of a large, confluent ablation zone. There was no significant difference in the mean ablation volume between the overlapping (72.9 +/- 12.6(3) cm) and the switching RFA groups (65.7 +/- 12.6 cm(3); P>0.05). In the preliminary in vivo experiments, RFA created spherical coagulations at interprobe distances of 2 cm and 3 cm but at larger distances than 3 cm, RFA created partially confluent coagulation zones. In our principal experiments, switching RFA created areas of well-defined coagulation, ie, at a 2-cm interprobe distance, the volume and short-axis coagulation diameter were 35.5+/- 5.7(3) cm and 4.6 +/- 0.5 cm, respectively, whereas at 3 cm, they were 40.7 +/- 12.8(3) cm and 4.8 +/- 0.8 cm, respectively. The mean values of the circularity (isometric ratio) of the coagulation at the 2- and 3-cm interprobe distances were 0.95 +/- 0.02, and 0.85+/- 0.06, respectively.

CONCLUSIONS

Our study demonstrated that switching monopolar RFA using the multichannel RF system at a 2- or 3-cm interprobe distance and at a 30-second switching time can create a large, confluent coagulation zone in the liver within a clinically acceptable time frame. We believe that this technology will provide a useful tool for the treatment of large liver tumors.

Intrahepatic tumor recurrence after partial hepatectomy: value of percutaneous radiofrequency ablation

PURPOSE

To determine the risks and benefits of percutaneous radiofrequency (RF) ablation of recurrent hepatic tumors in patients who have undergone hepatic resection.

MATERIALS AND METHODS

Retrospective review of the institutional RF ablation database yielded 35 patients with recurrent hepatic tumor after hepatectomy. Sixty-one recurrent hepatic tumors (mean diameter +/- SD, 1.7 +/- 1.1 cm; range, 0.5-5.3 cm) were ablated percutaneously under sonographic guidance or combined guidance with sonographic and fluoroscopic computed tomography (CT). Follow-up CT, magnetic resonance imaging, or both were used for assessment of the primary and secondary therapeutic effectiveness rate and failure of RF ablation. Patients' survival status was determined by contacting the primary care physician or searching the Social Security Death Index.

RESULTS

Complete ablation was accomplished in 54 of 61 hepatic tumors (primary therapeutic effectiveness rate, 88.5%). During a mean follow-up time of 18 months (range, 1-65 months), 14.8% of the tumors (n = 9) were incompletely ablated. Three of the nine incompletely ablated tumors were treated with a second RF ablation, all three of which failed (secondary therapeutic effectiveness rate, 0%). Distant intrahepatic tumor progression appeared in 23 of 35 patients (65.7%). One major complication (2.1%, one of 48 sessions) and eight minor complications (16.7%, eight of 48 sessions) were reported. The major complication was hepatic abscess formation. The overall survival rates for all patients at 1, 2, and 3 years were 76%, 68%, and 45%, respectively. For patients with metastases from colorectal cancer (n = 14), the overall survival rates were 72%, 60%, and 60% at 1, 2, and 3 years, respectively; and for patients with hepatocellular carcinoma (n = 8), the overall survival rates were 72%, 58%, and 44% at 1, 2, and 3 years, respectively.

CONCLUSION

Percutaneous RF ablation offers a safe and effective treatment option for recurrent hepatic tumors after previous partial hepatectomy.

Experimental and Clinical Radiofrequency Ablation: Proposal for Standardized Description of Coagulation Size and Geometry

BACKGROUND

Radiofrequency (RF) ablation is used to obtain local control of unresectable tumors in liver, kidney, prostate, and other organs. Accurate data on expected size and geometry of coagulation zones are essential for physicians to prevent collateral damage and local tumor recurrence. The aim of this study was to develop a standardized terminology to describe the size and geometry of these zones for experimental and clinical RF.

METHODS

In a first step, the essential geometric parameters to accurately describe the coagulation zones and the spatial relationship between the coagulation zones and the electrodes were defined. In a second step, standard terms were assigned to each parameter.

RESULTS

The proposed terms for single-electrode RF ablation include axial diameter, front margin, coagulation center, maximal and minimal radius, maximal and minimal transverse diameter, ellipticity index, and regularity index. In addition a subjective description of the general shape and regularity is recommended.

CONCLUSIONS

Adoption of the proposed standardized description method may help to fill in the many gaps in our current knowledge of the size and geometry of RF coagulation zones.

Double radiofrequency ablation is more extensive with a spherical zone shape compared to single ablation in a pig liver model

OBJECTIVE

We compared the duration of ablation and the area of coagulation necrosis between a single ablation method (SAM) and a double ablation method (DAM) with a 'multitined expandable' electrode (LeVeen 2 cm) for radiofrequency ablation (RFA) using pig liver.

METHOD

In the SAM group, ablation was completed after the first roll-off. In the DAM group, an additional ablation was performed to achieve a second roll-off. The comparison was made of the time required for roll-off and the extent of coagulation necrosis between the both groups. The Ellipticity index (EI) quantitatively describes the shape of the general RF ablation zone in the axial plane.

RESULTS

There was no statistically significant difference in the interval until the first roll-off between both groups (SAM group: 100.7+/-24.7 seconds vs DAM group: 103.2+/-37.7 seconds, P=0.43). In the DAM group, the interval from the start of the additional ablation until the second roll-off was 154.0+/-86.9 seconds, longer than the interval for the first roll-off (P=0.023). The extent of coagulation necrosis was significantly more extensive in the DAM group (axial diameter, mean+/-SD, 26.2+/-2.8mm) x (maximal diameter: 29.3+/-1.6mm) x (minimal diameter: 26.5+/-3.6mm) compared to the SAM group with (23.0+/-3.3mm) x (23.7+/-3.1mm) x (20.0+/-2.5mm), respectively. Although there was no statistically significant difference in the EI between both groups, macroscopically, the shape of coagulation necrosis tended to be non-spherical in the SAM group and spherical in the DAM group.

CONCLUSIONS

The DAM with a 'multitined expandable' electrode was more extensive with a spherical zone shape compared to the SAM.

Current role of radiofrequency ablation for the treatment of colorectal liver metastases

BACKGROUND AND METHOD

This paper reviews the current status of radiofrequency ablation in the treatment of colorectal liver metastases. Relevant studies with at least ten patients that reported rates of complete tumour ablation, local recurrence, or survival from 1 to 5 years after treatment were included in the review.

RESULTS AND CONCLUSION

Only six studies that reported at least 3-year survival were identified, with results ranging from 37 to 58 per cent. Some of these figures are promising, given that the patients were considered to have unresectable disease. However, available evidence is limited and hepatic resection remains the standard of care when feasible; radiofrequency ablation cannot be considered an equivalent. Radiofrequency ablation does, however, appear to have a role in treating unresectable disease, and may also be used in conjunction with resection to extend its limits.

Hepatic radiofrequency ablation using perfusion electrodes in a pig model: Effect of the Pringle manoeuvre

AIM

To assess the influence of the Pringle manoeuvre on volume and geometry of coagulations close to the portal vein using an impedance-controlled radiofrequency ablation system with perfusion electrodes.

METHODS

Twelve pigs were randomly assigned to a control group (n = 6) and a group where the Pringle manoeuvre was applied during ablation (n = 6). One coagulation was made in each animal close to the portal vein. All animals were sacrificed 4 days after ablation, and the livers were removed for gross and histopathologic analysis.

RESULTS

Effective coagulation volume in the Pringle group (10.8 +/- 5.0 cm(3)) was significantly increased (p = 0.03) compared to the control group (4.1 +/- 4.1 cm(3)). The efficacy ratio, defined as the effective coagulation volume divided by the coagulation volume, was not significantly different in the Pringle group (0.47 +/- 0.27) compared to the control group (0.33 +/- 0.22). The geometrical centre of the effective coagulation volume did not correspond to the position of the ablation electrode. Thermal damage of the gallbladder was found in three animals, all belonging to the Pringle group.

CONCLUSIONS

The Pringle manoeuvre was associated with increased effective coagulation volume, but did not significantly influence the predictability of coagulation volume or geometry.

Magnetic resonance imaging after radiofrequency ablation in a rodent model of liver tumor: tissue characterization using a novel necrosis-avid contrast agent

We exploited a necrosis-avid contrast agent ECIV-7 for magnetic resonance imaging (MRI) in rodent liver tumors after radiofrequency ablation (RFA). Rats bearing liver rhabdomyosarcoma (R1) were randomly allocated to three groups: group I, complete RFA, group II, incomplete RFA, and group III, sham ablation. Within 24 h after RFA, T1-weighted (T1-w) MRI was performed before and after injection of ECIV-7 at 0.05 mmol/kg and followed up from 6-24 h. Signal intensities (SIs) were measured with relative enhancement (RE) and contrast ratio (CR) calculated. The MRI findings were verified histomorphologically. On plain T1-w MRI the contrasts between normal liver, RFA lesion, residual and/or intact tumor were vague. Early after administration of ECIV-7, the liver SI was strongly enhanced (RE=40-50%), leaving the RFA lesion as a hypointense region in groups I and II. At delayed phase, two striking peri-ablational enhancement patterns appeared (RE=90% and CR=1.89%), i.e., "O" type of hyperintense rim in group I and "C" type of incomplete rim in group II. These MRI manifestations could be proven histologically. In this study, tissue components after RFA could be characterized with discernable contrasts by necrosis-avid contrast agent (NACA)-enhanced MRI, especially at delayed phase. This approach may prove useful for defining the ablated area and identifying residual tumor after RFA.

The use of radiofrequency in cancer

Radiofrequency ablation (RFA) provides an effective technique for minimally invasive tissue destruction. An alternating current delivered via a needle electrode causes localised ionic agitation and frictional heating of the tissue around the needle. Image-guided, percutaneous ablation techniques have been developed in most parts of the body, but the most widely accepted applications are for the treatment of hepatocellular carcinoma (HCC) in early cirrhosis, limited but inoperable colorectal liver metastases, inoperable renal cell carcinoma and inoperable primary or secondary lung tumours. The procedures are well tolerated and the complication rates low. Patients with coexistent morbidity who are not suitable for surgery are often able to undergo RFA. Most treatments in the lung, kidney and for HCC are performed under conscious sedation with an overnight hospital stay or as a day-case. Larger more complicated ablations, for example, in hepatic metastases may require general anaesthesia. Limitations of RFA include the volume of tissue that can be ablated in a timely fashion, that is, most centres will treat 3-5 tumours up to 4-5 cms in diameter. Early series reporting technical success and complications are available for lung and renal ablation. Liver ablation is better established and 5-year survival figures are available from several centres. In patients with limited but inoperable colorectal metastases, the 5-year survival ranges from 26 to 30% and for HCC it is just under 50%. In summary, RFA provides the opportunity for localised tissue destruction of limited volumes of tumour; it can be offered to nonsurgical candidates and used in conjunction with systemic therapy.