Hepatic ablation using bipolar radiofrequency electrocautery

Percutaneous radio-frequency ablation of hepatic metastases from colorectal cancer: long-term results in 117 patients

PURPOSE

To describe the results of an ongoing radio-frequency (RF) ablation study in patients with hepatic metastases from colorectal carcinoma.

MATERIALS AND METHODS

In 117 patients, 179 metachronous colorectal carcinoma hepatic metastases (0.9-9.6 cm in diameter) were treated with RF ablation by using 17-gauge internally cooled electrodes. Computed tomographic follow-up was performed every 4-6 months. Recurrent tumors were retreated when feasible. Time to new metastases and death for each patient and time to local recurrence for individual lesions were modeled with Kaplan-Meier analysis. Modeling determined the effect of number of metastases on the time to new metastases and death and effect of tumor size on local recurrence.

RESULTS

Estimated median survival was 36 months (95% CI; 28, 52 months). Estimated 1, 2, and 3-year survival rates were 93%, 69%, and 46%, respectively. Survival was not significantly related to number of metastases treated. In 77 (66%) of 117 patients, new metastases were observed at follow-up. Estimated median time until new metastases was 12 months (95% CI; 10, 18 months). Percentages of patients with no new metastases after initial treatment at 1 and 2 years were 49% and 35%, respectively. Time to new metastases was not significantly related to number of metastases. Seventy (39%) of 179 lesions developed local recurrence after treatment. Of these, 54 were observed by 6 months and 67 by 1 year. No local recurrence was observed after 18 months. Frequency and time to local recurrence were related to lesion size (P < or =.001).

CONCLUSION

RF ablation is an effective method to treat hepatic metastases from colorectal carcinoma.

Hepatic bipolar radio-frequency ablation between separated multiprong electrodes

Radio-frequency (RF) ablation has become an important means of treatment of nonresectable primary and metastatic liver tumors. Major limitations are small lesion size, which make multiple applications necessary, and incomplete killing of tumor cells, resulting in high recurrence rates. We examined a new bipolar RF ablation method incorporating two probes with hooked electrodes (RITA model 30). We performed monopolar and bipolar in vivo experiments on three pigs. The electrodes were 2.5 cm apart and rotated 45 degrees relative to each other. We used temperature-controlled mode at 95 degrees C. Lesion volumes were 3.9+/-1.8 cm3 (n=7) for the monopolar case and 12.2 +/- 3 cm3 (n=10) for the bipolar case. We generated finite-element models (FEMs) of monopolar and bipolar configurations. We analyzed the distribution of temperature and electric field of the finite element model. The lesion volumes for the FEM are 7.95 cm3 for the monopolar and 18.79 cm3 for the bipolar case. The new bipolar method creates larger lesions and is less dependent on local inhomogenities in liver tissue-such as blood perfusion-compared with monopolar RF ablation. A limitation of the new method is that the power dissipation of the two probes cannot be controlled independently in response to different conditions in the vicinity of each probe. This may result in nonuniform lesions and decreased lesion size.

Radiofrequency thermal ablation of hepatocellular carcinoma: using contrast-enhanced harmonic power doppler sonography to assess treatment outcome

OBJECTIVE

We evaluated the accuracy of contrast-enhanced harmonic power Doppler sonography in assessing the outcome of radiofrequency thermal ablation of hepatocellular carcinoma.

SUBJECTS AND METHODS

Fifty patients with 65 hepatocellular carcinoma nodules (1-5 cm in diameter; mean diameter, 2.5 cm) were studied using unenhanced and contrast-enhanced harmonic power Doppler sonography before and after IV administration of a microbubble contrast agent. The examinations were repeated after treatment of the tumors with radiofrequency ablation. Findings of the Doppler studies were compared with those of dual-phase helical CT, which were used as points of reference for assessing treatment outcome.

RESULTS

Before radiofrequency treatment, intratumoral blood flow was revealed by unenhanced power Doppler sonography in 48 (74%) of 65 hepatocellular carcinoma nodules. After injection of the contrast agent, intratumoral enhancement was observed in 61 (94%) of 65 hepatocellular carcinomas (p < 0.01). After radiofrequency treatment, all 51 (84%) of the 61 hepatocellular carcinomas found to be necrotic on helical CT scans failed to show enhancement on power Doppler sonograms. In nine of the 10 lesions that showed a residual viable tumor on helical CT scans, persistent intratumoral enhancement-matching the enhancing areas on helical CT images-was revealed by power Doppler sonography. These nine hepatocellular carcinomas were subjected to repeated radiofrequency thermal ablation with the guidance of contrast-enhanced power Doppler sonography. Complete necrosis was seen after the second treatment session in six of the nine lesions.

CONCLUSION

Contrast-enhanced harmonic power Doppler sonography is an accurate technique for assessing the outcome of radiofrequency thermal ablation of hepatocellular carcinoma and may be useful in guiding additional treatment in patients with incomplete response to initial efforts.

Essential techniques for successful radio-frequency thermal ablation of malignant hepatic tumors

Radio-frequency thermal ablation is one of the most promising minimally invasive techniques for the treatment of nonresectable hepatic tumors. Essential technical tips to successful radio-frequency ablation therapy were collected from five international experts. They were organized into five categories: understanding the mechanisms and principles of radio-frequency ablation, modulation of tissue physiologic characteristics to increase tumor destruction, strategies of overlapping ablations, strategies to improve ablation according to tumor location, and imaging strategies after ablation to ensure adequate therapy. Established factors for optimal ablation, as well as emerging technical tips, are addressed with illustrations in each section. These essential tips will be very helpful for physicians performing radio-frequency ablation of hepatic tumors.

Percutaneous ablation of liver malignancies: imaging evaluation of treatment response

Interventional procedures for percutaneous tumor ablation have gained an increasingly important role in the treatment of liver malignancies. After interventional therapies, diagnostic imaging has the key role to determine if the treated lesion is completely ablated or contains areas of residual viable neoplastic tissue. This is particularly important since in cases of incomplete necrosis of the lesions, treatment can be repeated, and tumor ablation can be further pursued. The evaluation of the therapeutic effect of the procedure arises different problems according to the histotype of the malignancy. In the case of hepatocellular carcinoma (HCC), detection of residual viable tumor is facilitated by the typical hypervascular pattern of this neoplasm. Contrast-enhanced US can be used to monitor tumor response, and, in cases of partial necrosis, to target the areas of residual viable tumor. With spiral CT or dynamic MR imaging, residual viable HCC is reliably depicted as it stands out in the arterial phase images against the unenhanced areas of coagulation necrosis. In the case of hypovascular metastases, a confident diagnosis of successfull ablation can be made when an area of thermal necrosis exceeding that of the original lesion is depicted. Peripheral inflammatory reaction following ablation procedures, that shows itself as an enhancing halo along the necrotic area boundary on spiral CT or dynamic MR images, should not be misinterpreted as tumor progression.

Radiofrequency tumor ablation: principles and techniques

Radiofrequency (RF) tumor ablation has been demonstrated as a reliable method for creating thermally induced coagulation necrosis using either a percutaneous approach with image-guidance or direct surgical placement of thin electrodes into tissues to be treated. Early clinical trials with this technology have studied the treatment of hepatic, cerebral, and bony malignancies. However, more recently this technology has been used to treat a host of malignant processes throughout the body. This article will discuss the principles and technical considerations of RF ablation with the goal of defining optimal parameters for the therapy of focal lesions. This includes technologic innovations that permit large volume tumor ablation (i.e., hooked and internally cooled electrodes), as well as methods and adjuvant therapies that can modulate tumor biophysiology to permit improved tumor destruction (i.e, altered tissue conductivity and blood flow). Potential biophysical limitations to RF induced coagulation, such as perfusion mediated tissue cooling (vascular flow) will likewise be discussed. Lastly, the principles governing safe usage of the system, such as proper grounding pad placement, will be adressed.

Computer-aided dynamic simulation of microwave-induced thermal distribution in coagulation of liver cancer

To develop a method of dynamic three-dimensional (3-D) simulation of thermal distribution in ultrasound-guided microwave coagulation therapy of liver cancer and to verify its accuracy. The specific absorption rate (SAR) values were established by measuring the temperature in equivalent phantom tests. Those values were different under different power output condition. Dynamic 3-D temperature distributions were reconstructed with a finite-element model. Testing and rectification were performed through animal experiments and clinical trials, respectively. The temperature curves in the experiments corresponded well with simulated ones in vitro--91.4% and 88.9% using single and double electrodes, respectively. The measured coagulated boundary and simulated temperature boundary had a good correspondence in 85.7% of the specimens. In both in vivo experiments and clinical trials, blood perfusion influenced the rise in temperature significantly. Temperature curves between the simulations and actual measured results showed good correspondence--67.8% (19/28) in the patients with hepatocellular carcinoma. Distance between electrodes and combined thermal distributions were both optimized with computer-aided simulation during simultaneous two-electrode coagulation. The results demonstrated that computer-aided simulation of microwave thermal distribution is an accurate and reliable method which provides a theoretical and technical basis for controlling coagulated tissue volume and placement of the electrodes during microwave coagulation therapy of liver cancer.

Radiofrequency liver ablation: experimental comparative study of water-cooled versus expandable systems

OBJECTIVE

We evaluate the uniformity and reproducibility of thermal lesion ablation and quantify the volume of tissue destruction and hemorrhage induced with two different commercially available radiofrequency ablation devices.

MATERIALS AND METHODS

A four-array anchor expandable needle electrode and a triple-cluster cooled-tip needle electrode were used to induce lesions in three explanted calf livers and in vivo in eight swine livers. The sizes of the radiofrequency-induced lesions were macroscopically evaluated by measuring two perpendicular dimensions immediately after the experiment. Bleeding was evaluated by weighing gauze swabs used to dry the hemorrhage caused by electrode insertions.

RESULTS

In explanted liver, the mean diameter of the radiofrequency-induced lesion was 5.3 +/- 0.7 cm for the cooled-tip needle and 3.7 +/- 0.4 cm for the expandable needle (p = 0.042), which correspond to approximate volumes of 65.35 +/- 26.22 cm(3) and 26.67 +/- 9.59 cm(3), respectively (p < 0.002). In vivo, the mean diameter was 3.7 +/- 0.4 cm for the cooled-tip needle and 3 +/- 0.4 cm for the expandable needle (p < 0.0001), which correspond to approximate volumes of 24.18 +/- 7.56 cm(3) and 11.16 +/- 3.65 cm(3), respectively (p < 0.0001). Blood loss attained a median value of 3.5 g for the cooled-tip needle and 2.6 g for the expandable needle; this difference was not statistically significant (p = 0.06).

CONCLUSION

The cooled-tip needle induced significantly larger lesions than the expandable needle, but the lesions produced by the expandable needle are more reproducible, uniform, and spheric. The larger size of the lesions produced by the cooled-tip needle may be attributed to the higher maximum power used by the generator and the higher energy deposition, which is due to the cooling of the needle electrode.

Tumor ablation with radio-frequency energy

Tumor ablation by using radio-frequency energy has begun to receive increased attention as an effective minimally invasive approach for the treatment of patients with a variety of primary and secondary malignant neoplasms. To date, these techniques have been used to treat tumors located in the brain, musculoskeletal system, thyroid and parathyroid glands, pancreas, kidney, lung, and breast; however, liver tumor ablation has received the greatest attention and has been the subject of a large number of published reports. In this article, the authors review the technical developments and early laboratory results obtained with radio-frequency ablation techniques, describe some of the early clinical applications of these techniques, and conclude with a discussion of challenges and opportunities for the future.

Hepatocellular carcinoma treated with percutaneous radio-frequency ablation: usefulness of power Doppler US with a microbubble contrast agent in evaluating therapeutic response-preliminary results

PURPOSE

To evaluate the usefulness of power Doppler ultrasonography (US) with a microbubble contrast agent in assessing the therapeutic response of hepatocellular carcinomas (HCCs) treated with percutaneous radio-frequency (RF) ablation.

MATERIALS AND METHODS

Forty patients with 45 nodular HCC lesions 1.0-3.8 cm in diameter underwent power Doppler US before and after intravenous injection of a microbubble contrast agent. The same procedures were repeated after US-guided percutaneous RF ablation. The results of these studies were compared with those of three-phase helical computed tomography (CT) performed immediately after RF ablation.

RESULTS

Before RF ablation, nonenhanced power Doppler US demonstrated flow signals within tumor in 33 of 45 HCCs. After contrast agent administration, flow signals increased or newly appeared in all cases. After RF ablation, none of the ablated tumors showed intratumoral flow signals at nonenhanced power Doppler US, whereas six showed marginal intratumoral flow signals at contrast agent-enhanced power Doppler US. These six tumors were found to have small enhancing foci, suggestive of viable tumor, in corresponding areas at immediate follow-up CT. Additional RF ablation or transcatheter arterial chemoembolization was performed in these tumors.

CONCLUSION

The results of power Doppler US with a microbubble contrast agent in HCCs treated with RF ablation correlated well with those of contrast-enhanced CT. Preliminary data suggest that contrast-enhanced power Doppler US can be a promising noninvasive technique for assessing therapeutic response.

A comparative study on validation of a novel cooled-wet electrode for radiofrequency liver ablation

RATIONALE AND OBJECTIVES

A cooled-wet electrode has been developed for radiofrequency ablation (RFA) that allows simultaneous internal-cooling perfusion ("cooled") and interstitial hypertonic saline infusion ("wet"). The present comparative study was conducted to validate this new device for the increased coagulation volume in RFA.

METHODS

Under low-power (50 W, groups A through F) and high-power (90 W, groups A' through F') control modes, 240 RFA lesions were created on excised beef liver to compare the cooled-wet electrode with other monopolar electrodes. The experimental regimens were as follows: groups A and A', conventional RF electrode; groups B and B', cooled electrode; groups C and C', wet electrode; groups D and D', cooled-wet electrode; groups E and E', cooled-wet electrode but suspended wet function; and groups F and F', cooled-wet electrode but suspended cooled function. The ablation efficacy was evaluated by comparing the lesion sizes as well as parameters of impedance, power output, current, and tip temperature.

RESULTS

With lower impedance and tip temperature but higher power output, the lesion size in groups D (4.90 +/- 0.60 cm) and D' (6.6 +./- 0.99 cm) was significantly larger than that in other groups.

CONCLUSIONS

The use of the cooled-wet electrode could efficiently increase the lesion size for liver ablation.

Pulse sequences for interventional magnetic resonance imaging

Interventional magnetic resonance imaging (iMRI) is different from diagnostic magnetic resonance imaging (MRI) in its spatial, temporal, and contrast resolution requirements due to its specific clinical applications. As a result, the pulse sequences used in iMRI often are significantly different than those used in the more conventional diagnostic arena. The focus of this article is to summarize how iMRI is different from diagnostic MRI, to describe a variety of MRI pulse sequences and sequence strategies that have evolved because of these differences, and to describe some MRI sequence strategies that are in development and may be seen in future iMRI applications.

Hepatic lesion ablation with bipolar saline-enhanced radiofrequency in the audible spectrum

RATIONALE AND OBJECTIVES

The authors' purpose was to create larger and more regular liver lesions in vitro by testing a new hyperthermia approach that uses a bipolar saline-enhanced electrode for radiofrequency (RF) in the audible spectrum and a greater power supply.

MATERIALS AND METHODS

The authors' hyperthermia approach (group A, n = 23) was used in excised porcine livers, and the results were compared with those of a previously described monopolar saline-enhanced electrode procedure (group B, n = 23). In each set of experiments, RF in the audible spectrum current (50 Hz) was provided for 15 minutes with a similar ablation protocol. Electrical variables (impedance, current, voltage, power, and energy), temperatures in the lesions, volume size, regularity ratio of the lesion, and microscopic findings were measured.

RESULTS

In group A, the mean volume size and the mean regularity ratio values were 144.8 cm3 +/- 59.8 and 0.78 +/- 0.1, respectively. In group B, the mean volume size and regularity ratio values were 62.1 cm3 +/- 36.4 and 0.62 +/- 0.1, respectively. The values in group B were thus significantly lower than those in group A (P < .01). The lesions in group A were also more homogeneous. No significant differences were found in electrical variables.

CONCLUSION

The new bipolar saline-enhanced electrode produced larger, more regular, and more homogeneous lesions ex vivo than the previously used monopolar saline-enhanced electrode method. Using a greater power supply increased the amount of coagulative necrosis.

Radiofrequency Ablation: A Novel Primary and Adjunctive Ablative Technique for Hepatic Malignancies

The majority of primary and metastatic tumors of the liver are not amenable to surgical resection at presentation. Radiofrequency ablation (RFA) is a new modality for local tumor destruction with minimal local and systemic complications. We prospectively reviewed the experience with RFA at a single institute as a primary or adjunctive ablative technique in the treatment of hepatic malignancies. Between November 1997 and December 1998, 30 patients with primary or metastatic hepatic lesions were treated with RFA at the John Wayne Cancer Institute and the Cancer Center at Century City Hospital. Pathology of the treated lesions included colorectal metastases (29 in 14 patients), neuroendocrine metastases (29 in 4 patients), noncolorectal metastases (29 in 9 patients), and hepatocellular carcinoma (6 in 3 patients). Twelve patients underwent RFA laparoscopically, 12 at celiotomy, and the remaining 6 patients had percutaneous ablation. RFA was the only procedure in 17 patients, whereas the remainder underwent a combination of RFA and other procedures including resection, cryosurgical ablation, and hepatic artery infusion pump placement. Median length of stay for all patients was 6 days (2 days for laparoscopic patients). A single complication of a delayed intrahepatic abscess was noted in this series (3%). There have been no deaths associated with RFA. At a median follow-up of 5 months, 16 patients remain disease free, and 10 are alive with disease. RFA is a safe and effective method of tumor ablation for hepatic malignancies. This technique can be performed laparoscopically, at celiotomy, or percutaneously and can be used as a primary technique or in conjunction with other interventional procedures.

EUS-guided radiofrequency ablation in the pancreas: results in a porcine model

BACKGROUND

Our aim in this study was to investigate the feasibility and safety of performing radiofrequency (RF) ablation in the pancreas with endoscopic ultrasound (EUS).

METHODS

RF was applied to normal pancreatic tissue in 13 anesthetized Yorkshire pigs with specially modified 19-gauge needle electrodes (1.0 to 1.5 cm tip). The pancreas was localized with EUS and punctured through a transgastric approach. RF current (285 +/- 120 mA) was delivered for 6 minutes. Diagnostic imaging (EUS and CT) and serum amylase and lipase levels were obtained at baseline, immediately after ablation, and 1 to 14 days after the procedure. Pigs were killed immediately (n = 5), 1 to 2 days after ablation (n = 2), and 2 weeks after the procedure (n = 6). Pathologic examination was performed.

RESULTS

Sixteen ablations were performed. During ablation, round hyperechoic foci (diameter to 1.0 cm) gradually surrounded the tip of the electrode. Immediately after the procedure CT demonstrated 1 cm hypodense foci that did not enhance with iodinated contrast. In pigs killed immediately and 1 to 2 days after ablation, pathologic examination showed discrete, well-demarcated spherical foci of coagulation necrosis measuring 8 to 12 mm in diameter surrounded by a 1 to 2 mm rim of hemorrhage. Radiologic-pathologic correlation was within 2 mm. In 4 of 6 (67%) pigs killed on day 14, retraction of the coagulated focus was observed. A 1 to 3 mm fibrotic capsule surrounded the coagulated tissue in the remaining 2 pigs. One pig had mild hyperlipasemia, a focal zone of pancreatitis (<1 cm), and later a pancreatic fluid collection. Biochemical parameters were normal in the remaining pigs. Other complications included three gastric and one intestinal burn caused by improper electrode placement.

CONCLUSIONS

EUS-guided RF ablation can be used safely to produce discrete zones of coagulation necrosis in the porcine pancreas. Potential clinical uses of this technology include management of small neuroendocrine tumors and possibly palliation of unresectable pancreatic adenocarcinoma.

Effects of superparamagnetic iron oxide on radio-frequency-induced temperature distribution: in vitro measurements in polyacrylamide phantoms and in vivo results in a rabbit liver model

PURPOSE

To determine whether contrast medium containing superparamagnetic iron oxide (SPIO) alters radio-frequency (RF)-related temperature distribution in acrylamide phantoms and in an in vivo model.

MATERIALS AND METHODS

In nine acrylamide phantoms with increasing SPIO content, RF was applied with simultaneous measurement of temperature profile along the probe track. Additionally, magnetic resonance imaging-guided RF ablation was performed in the liver of six rabbits after the intravenous administration of SPIO (0.05 mL per kilogram of body weight) 40 minutes prior to ablation (SPIO group) and in another six rabbits without prior SPIO administration (control group). Coagulation diameter was evaluated on the basis of postprocedural imaging and subsequent gross pathologic findings. Statistical analysis was performed with the Student t test.

RESULTS

In the phantoms, progressive increases in iron content resulted in higher temperatures along the RF electrode track (P < .05). In the in vivo model, however, SPIO at physiologic concentrations did not significantly increase the diameter of coagulation on the basis of either postprocedural imaging or subsequent gross pathologic findings. Additionally, no significant differences were seen in other RF-related parameters including impedance, voltage, current, and grounding pad temperature.

CONCLUSION

Administration of SPIO in conjunction with RF ablation of focal liver lesions is feasible and safe, but no significant difference in the extent of induced coagulation can be expected.

Percutaneous radiofrequency tissue ablation: optimization of pulsed-radiofrequency technique to increase coagulation necrosis

PURPOSE

To develop a computerized algorithm for pulsed, high-current percutaneous radiofrequency (RF) ablation, which maximally increases the extent of induced coagulation necrosis.

MATERIALS AND METHODS

An automated, programmable algorithm for pulsed-RF deposition was designed to permit high-current deposition by periodically reducing current for 5-30 seconds during RF application. Two strategies for pulsed-RF deposition were evaluated: (i) constant peak current (900-1,800 mA) of variable duration and (ii) variable peak current (1,200-2,000 mA) for a specified minimum duration. The extent of induced coagulation was compared to results obtained with continuous (lower current) RF application. Trials were performed in ex vivo calf liver (n = 115) and in vivo porcine liver (n = 30) and muscle (n = 18) with use of 2-4-cm tip, internally cooled electrodes.

RESULTS

For 3-cm electrodes in ex vivo liver, applying pulsed-RF with constant peak current for 12 minutes produced 3.5 cm +/- 0.2 of necrosis. Greater necrosis was produced with use of the variable current strategy, in which 4.5 cm +/- 0.2 of coagulation was achieved with use of an initial current > or =1,500 mA (minimum peak-RF duration of 10 sec, with 15 sec of reduced current to 100 mA between peaks; P < .01). This variable peak current algorithm also produced 3.7 cm +/- 0.6 of necrosis in in vivo liver, and 6.5 cm +/- 0.9 in in vivo muscle. Without pulsing, a maximum of 750 mA, 1,100 mA, and 1,500 mA could be applied in ex vivo liver, in vivo liver, and in vivo muscle, respectively, which resulted in 2.9 cm +/- 0.2, 2.4 cm +/- 0.2, and 5.1 cm +/- 0.4 of coagulation (P < .05, all comparisons).

CONCLUSIONS

A variable peak current algorithm for pulsed-RF deposition can increase coagulation necrosis diameter over other ablation strategies. This innovation may ultimately enable the percutaneous treatment of larger tumors.

Radiofrequency thermal ablation of liver tumors

Chemotherapy and radiation therapy are ineffective against primary and secondary malignant hepatic tumors. Surgical resection has been considered the only potentially curative option, but few patients with hepatic tumors are candidates for surgery. Recent results suggest that radiofrequency thermal ablation may be an effective, minimally invasive technique for treating malignant hepatic tumors. Sonography is the primary technique for guiding percutaneous ablative procedures. We review the current research and clinical experience with radiofrequency thermal ablation for treating malignant hepatic tumors.