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

Radiofrequency treatment

This article discusses radiofrequency energy as a treatment of musculoskeletal tumors,focusing on osteoid osteomas. The technique has also been applied to a number of different primary musculoskeletal tumors and is increasingly being used as a palliative method in the management of painful skeletal metastases. Radiofrequency treatment of musculoskeletal tumors can be of great clinical value. When the low-power, highly limited methods are applied to small tumors such as osteoid osteomas, the technique is effective and exceptionally safe. Creation of larger thermal lesions, however, can be accompanied by significant risks, and the risk-to-benefit ratio should be carefully considered before undertaking such a treatment.

Use of an Arterial Tourniquet to Achieve Complete Radiofrequency Ablation of a Renal Metastasis

Radiofrequency (RF) coagulation of skeletal metastases is usually performed for pain relief. However, patients with solitary skeletal metastasis may benefit from more aggressive attempts to achieve local control. The authors report a case in which an arterial tourniquet was used to enhance the effectiveness of RF treatment of a calcaneal renal cell metastasis, leading to long-lasting local control with preservation of ambulation.

Instrument to measure the heat convection coefficient on the endothelial surface of arteries and veins

The primary objective of the paper was to present the design and analysis of an instrument to measure the heat convection coefficient h on the endothelial surfaces of arteries and veins. An invasive thermistor probe was designed to be inserted through the vessel wall and positioned on the endothelial surface. Electrical power was supplied to the thermistor by a constant temperature anemometry circuit. Empirical calibrations were used to relate electrical measurements in the thermistor to the h at the endothelial surface. As the thermal processes are strongly dependent on baseline blood temperature, the instrument was calibrated at multiple temperatures to minimise this potentially significant source of error. Three different sizes of thermistor were evaluated to optimise accuracy and invasiveness, and the smallest thermistors provided the best results. The sensitivity to thermistor position was evaluated by testing the device at multiple locations, varying both depth of thermistor penetration and position along the vessel. Finally, the measurement accuracy of the instrument was determined for the range of h from 430 to 4200 W m(-2)K, and the average error of the reading was 4.9% for the smallest thermistor. Although the instrument was designed specifically for measurements in the portal vein to obtain useful data for current numerical modelling, the device can be used in any large vessel.

Effects of Vascular Perfusion on Coagulation Size in Radiofrequency Ablation of Ex Vivo Perfused Bovine Livers

OBJECTIVES

A standardized perfused ex vivo bovine liver model was used to evaluate the effect of organ perfusion on coagulation size and energy deposition during radiofrequency ablation (RFA) procedures.

MATERIALS AND METHODS

Bovine livers were perfused in a tank after rinsing the prepared liver vessels with anticoagulants. Tyrode's solution, oxygenated and heated to 36.5 degrees C, was used as perfusion medium. A flow and pressure controlled pump regulated Portal vein circulation; a dialysis machine provided pulsatile arterial circulation. Impedance-guided radiofrequency ablations were performed with 4-cm LeVeen electrodes with and without underlying liver perfusion. Two-dimensional diameters (Dv, Dh) of each ablation area were measured after dissecting the livers.

RESULTS

In 4 bovine livers weighing 8.85 +/- 0.83 kg per organ (min, 7.7 kg; max, 9.7 kg) altogether 40 RF ablations were performed. A total of 20 ablations were generated with underlying liver perfusion (group 1) and 20 ablations with no liver perfusion (group 2). In group 1, Dv was 28.4 +/- 5.3 mm, Dh 38.6 +/- 7.8 mm, and energy deposition 36.9 +/- 18.0 kJ. The 20 ablation areas generated without liver perfusion displayed statistically significant differences, with Dv being 35.7 +/- 6.5 mm (P = 0.001), Dh 49.5 +/- 9.4 mm (P = 0.001), and energy deposition 25.5 +/- 13.0 kJ (P = 0.018).

CONCLUSION

The model reproduced the cooling effect of perfused tissue during RFA. The ablation areas produced under perfusion conditions had smaller diameters despite longer exposure times and higher energy deposition.

Complications of percutaneous radiofrequency ablation for hepato-cellular carcinoma: imaging spectrum and management

Percutaneous radiofrequency (RF) ablation is feasible for the treatment of unresectable hepatocellular carcinoma, and experience at the authors' institution during 5 years indicates that percutaneous RF ablation can be performed safely in most cases. However, early or late complications related to mechanical or thermal damage may be observed at follow-up examination. Complications may be classified in three groups: vascular (eg, portal vein thrombosis, hepatic vein thrombosis with partial hepatic congestion, hepatic infarction, and subcapsular hematoma), biliary (eg, bile duct stenosis and biloma, abscess, and hemobilia), and extrahepatic (eg, injury to the gastrointestinal tract, injury to the gallbladder, pneumothorax and hemothorax, and tumor seeding). Most complications can be managed with conservative treatment, percutaneous or endoscopic drainage, or surgical repair. Because an early and accurate diagnosis is necessary for proper management, radiologists should be familiar with the imaging features of each type of complication.

Percutaneous laser ablation in the treatment of hepatocellular carcinoma with small tumors: analysis of factors affecting the achievement of tumor necrosis

PURPOSE

To identify the factors that affect the achievement of tumor necrosis with percutaneous laser ablation (PLA) in patients with hepatocellular carcinoma (HCC) and tumor size no larger than 4.0 cm.

MATERIALS AND METHODS

Ultrasound-guided biopsy results were retrospectively studied in 99 lesions (range, 0.5-4.0 cm; mean, 2.7 cm) from 82 patients (44 men, 38 women; age range, 50-80 years; median, 68 y) who had undergone PLA.

RESULTS

Complete tumor ablation was obtained in 90 lesions (90.9%). Of the nine cases in which complete tumor necrosis was not achieved, six had tumors located in sites that did not allow the optimal placement of fibers, and five of these had a tumor diameter greater than 3 cm. Early discontinuation of PLA as a result of decompensation of liver cirrhosis was the reason for not achieving a complete tumor ablation in three other cases. There was a clear relationship between the energy delivered and the volume of necrosis achieved (r = 0.56; P < .001) regardless of the initial size of HCC tumors. The number of illuminations required, and consequently the amount of energy delivered, was also affected by tumor location. In fact, lesions adjacent to large vessels (> or = 3 mm) required a greater number of illuminations than the other lesions to achieve complete ablation (2.9 +/- 1.4 vs 2.3 +/- 0.9; P = .043). The eight cases with undifferentiated histology required more illuminations than the cases with other histologic types (3.4 +/- 0.9 vs 2.2 +/- 0.9; P < .001). However, these cases were located in sites that did not allow the optimal placement of fibers, therefore requiring multiple treatments.

CONCLUSION

PLA is a highly effective treatment in HCC with a tumor size of 4.0 cm or smaller. In this setting, two variables, tumor size and tumor location, affect the achievement of complete tumor ablation and the number of treatments required to obtain tumor necrosis.

Experimental hepatic radiofrequency ablation using wet electrodes: electrode-to-vessel distance is a significant predictor for delayed portal vein thrombosis

The aim of this study was to examine possible explanatory variables associated with acute and delayed portal vein thrombosis after hepatic radiofrequency (RF) ablation using wet electrodes. Coagulations were created within 1.5 cm of the right portal vein (RPV) branch in 12 pigs with (n = 6) or without (n = 6) Pringle manoeuvre. Sham operations with Pringle manoeuvre were performed in four animals. Rotational portal venography was performed prior to ablation, 10 min after ablation and 4 days after ablation. Vessel diameters and vessel patency was determined from the portal venograms. Distance between the ablation electrode and RPV was measured from 3-dimensional reconstructions of the portal venograms. The portal veins were examined by microscopy. Delayed portal vein thrombosis was found in two of six animals in the Pringle group and three of six animals in the control group 4 days after ablation (P = 1.0, Fisher's exact test). All five occurrences of delayed portal vein thrombosis were found in the six animals with a distance between the ablation electrode and RPV of 5 mm or less (P = 0.030), indicating that the electrode-to-vessel distance may be an independent explanatory factor for delayed portal vein thrombosis after RF ablation with wet electrodes.

Multipolar Radiofrequency Ablation with Internally Cooled Electrodes: Experimental Study in ex Vivo Bovine Liver with Mathematic Modeling

PURPOSE

To evaluate the size and geometry of thermally induced coagulation by using multipolar radiofrequency (RF) ablation and to determine a mathematic model to predict coagulation volume.

MATERIALS AND METHODS

Multipolar RF ablations (n = 80) were performed in ex vivo bovine livers by using three internally cooled bipolar applicators with two electrodes on the same shaft. Applicators were placed in a triangular array (spacing, 2-5 cm) and were activated in multipolar mode (power output, 75-225 W). The size and geometry of the coagulation zone, together with ablation time, were assessed. Mathematic functions were fitted, and the goodness of fit was assessed by using r(2).

RESULTS

Coagulation volume, short-axis diameter, and ablation time were dependent on power output and applicator distance. The maximum zone of coagulation (volume, 324 cm(3); short-axis diameter, 8.4 cm; ablation time, 193 min) was induced with a power output of 75 W at an applicator distance of 5 cm. Coagulation volume and ablation time decreased as power output increased. Power outputs of 100-125 W at applicator distances of 2-4 cm led to a reasonable compromise between coagulation volume and ablation time. At 2 cm (100 W), coagulation volume, short-axis diameter, and ablation time were 66 cm(3), 4.5 cm, and 19 min, respectively; at 3 cm (100 W), 90 cm(3), 5.2 cm, and 22 min, respectively; at 4 cm (100 W), 132 cm(3), 6.1 cm, and 27 min, respectively; at 2 cm (125 W), 56 cm(3), 4.2 cm, and 9 min, respectively; at 3 cm (125 W), 73 cm(3), 4.9 cm, and 12 min, respectively; and at 4 cm (125 W), 103 cm(3), 5.5 cm, and 16 min, respectively. At applicator distances of 4 cm (>125 W) and 5 cm (>100 W), the zones of coagulation were not confluent. Coagulation volume (r(2) = 0.80) and RF ablation time (r(2) = 0.93) were determined by using the mathematic model.

CONCLUSION

Multipolar RF ablation with three bipolar applicators may produce large volumes of confluent coagulation ex vivo. A compromise is necessary between prolonged RF ablations at lower power outputs, which produce larger volumes of coagulation, and faster RF ablations at higher power outputs, which produce smaller volumes of coagulation.

Thermal tumour ablation: devices, clinical applications and future directions

Tumour ablation is clinically applied mainly for non-operable liver tumours, with increasing application to other organ sites like kidney, lung, adrenal gland and bone. Most current devices use radiofrequency (RF) current to heat tumour tissue surrounding the applicator, which is introduced into the tumour under imaging guidance. Tissue temperatures in excess of 100 degrees C are achieved, with cell death due to coagulative necrosis occurring above 50 degrees C. Limitations of current ablation devices include inadequate imaging, limited size of coagulation zone and reduced performance next to large vessels. This paper reviews current interstitial RF and microwave devices, clinical applications and future research directions in the field of high-temperature tumour ablation.

High operative risk of cool-tip radiofrequency ablation for unresectable pancreatic head cancer

BACKGROUND AND OBJECTIVES

To report and discuss the effect, complications and mortality of cool-tip radiofrequency ablation (RFA) for unresectable pancreatic cancer.

METHODS

During October 2003 to July 2004, sixteen patients with unresectable pancreatic cancer were treated by open cool-tip RFA. One-half of the 16 patients had tumors located in the pancreatic head. A 5-mm minimum safe distance between RFA site and major peripancreatic vessels was kept to avoid injury to the vessels.

RESULTS

Six of twelve patients with back pain got pain relief postoperatively. Pancreatic fistula occurred in three patients (18.8%) and healed smoothly in 7-10 days with routine abdominal drainage. The mortality was 25% (4/16). In the four death cases, tumors were all located in the pancreatic head; three patients with tumor close to portal vein died suddenly of massive gastrointestinal hemorrhage on the 4th, 30th, 40th postoperative day respectively and a 79-year-old patient died of acute renal failure on the 2nd postoperative day.

CONCLUSIONS

Standard use of cool-tip RFA was dangerous for pancreatic head cancer close to portal vein, in which a 5-mm minimum safe distance between RFA site and major peripancreatic vessels might not be enough to avoid injury to the vessels.

Osteoid Osteoma in an ex Vivo Animal Model: Temperature Changes in Surrounding Soft Tissue during CT-guided Radiofrequency Ablation

PURPOSE

To assess temperature changes in the soft tissue surrounding bone during radiofrequency (RF) ablation of osteoid osteoma in an ex vivo animal model.

MATERIALS AND METHODS

Intracortical cavities were created in fresh bovine long bone specimens obtained from a slaughterhouse as models for osteoid osteoma. Three groups of three specimens each were defined according to the thickness (1, 3, and 5 mm) of the cortical bone lamella separating the nidus from the periosteum. Three thermocouples were applied to the soft tissue surrounding the bone in defined distances (0, 5, and 10 mm) from the periosteum. Before RF ablation, the thickness of the cortical bone lamella was documented at computed tomography. Specimens were heated in a 37 degrees C basin. As soon as the measured temperature in the cavity of the specimen reached 35 degrees C, RF ablation was performed for 400 seconds, with a target temperature of 95 degrees C. During RF ablation, continuous measurements were performed simultaneously with digital thermometers. No simulation of vessel perfusion was used. The effect of the thickness of residual osseous lamella and the effect of the distance between the thermocouple and the periosteum were tested with an analysis of variance. Post hoc Bonferroni tests were performed.

RESULTS

Mean maximum temperatures of 69.1 degrees, 51.3 degrees, and 42.5 degrees C for 1-mm lamella; 59.2 degrees, 46.5 degrees, and 41.1 degrees C for 3-mm lamella; and 50.6 degrees, 44.8 degrees, and 40.0 degrees C for 5-mm lamella were measured 0, 5, and 10 mm, respectively, from the periosteum. Significant temperature differences were shown with analysis of variance and post hoc tests for the three groups of bone lamella thickness and distance (P < .001).

CONCLUSION

In the model of osteoid osteoma, the surrounding temperature (soft tissue) during RF ablation was shown to depend on the thickness of the cortical bone lamella and the distance from the periosteum.

Bipolar radiofrequency ablation of liver metastases during laparotomy. First clinical experiences with a new multipolar ablation concept

BACKGROUND AND OBJECTIVE

Radiofrequency ablation (RFA) is a promising method for local treatment of liver malignancies. Currently available systems for radiofrequency ablation use monopolar current, which carries the risk of uncontrolled electrical current paths, collateral damages and limited effectiveness. To overcome this problem, we used a newly developed internally cooled bipolar application system in patients with irresectable liver metastases undergoing laparotomy. The aim of this study was to clinically evaluate the safety, feasibility and effectiveness of this new system with a novel multipolar application concept.

PATIENTS AND METHODS

Patients with a maximum of five liver metastases having a maximum diameter of 5 cm underwent laparotomy and abdominal exploration to control resectability. In cases of irresectability, RFA with the newly developed bipolar application system was performed. Treatment was carried out under ultrasound guidance. Depending on tumour size, shape and location, up to three applicators were simultaneously inserted in or closely around the tumour, never exceeding a maximum probe distance of 3 cm. In the multipolar ablation concept, the current runs alternating between all possible pairs of consecutively activated electrodes with up to 15 possible electrode combinations. Post-operative follow-up was evaluated by CT or MRI controls 24-48 h after RFA and every 3 months.

RESULTS

In a total of six patients (four male, two female; 61-68 years), ten metastases (1.0-5.5 cm) were treated with a total of 14 RF applications. In four metastases three probes were used, and in another four and two metastases, two and one probes were used, respectively. During a mean ablation time of 18.8 min (10-31), a mean energy of 48.8 kJ (12-116) for each metastases was applied. No procedure-related complications occurred. The patients were released from the hospital between 7 and 12 days post-intervention (median 9 days). The post-interventional control showed complete tumour ablation in all cases.

CONCLUSIONS

Bipolar radiofrequency using the novel multipolar ablation concept permits a safe and effective therapy for the induction of large volumes of coagulation in the local treatment of liver metastases.

In-vivo evaluation of a novel bipolar radiofrequency device for interstitial thermotherapy of liver tumors during normal and interrupted hepatic perfusion

BACKGROUND

Only monopolar systems have thus far been available for radiofrequency ablation of liver tumors, whose application is restricted because of the incalculable energy flow, reduction of electrical tissue conduction, and limited lesion size. The aim of this study was to evaluate a novel internally cooled bipolar radiofrequency application device under in vivo conditions and to compare the effect of this system on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion.

MATERIALS AND METHODS

In a porcine liver model, RFA (60 W, 12 min) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). RFA parameters (impedance, power output, temperature, applied energy) were determined continuously during therapy. RFA lesions were macroscopically assessed after liver dissection.

RESULTS

Bipolar RFA induced clinical relevant ellipsoid thermal lesions without complications. Hepatic inflow occlusion led to a 4.3-fold increase in lesion volume after arterial microembolization and a 5.8-fold increase after complete interruption (7.4 cm(3)versus 31.9 cm(3)versus 42.6 cm(3), P < 0.01).

CONCLUSIONS

The novel bipolar RFA device is a safe and effective alternative to monopolar RFA-systems. Interrupting hepatic perfusion significantly increases lesion volumes in bipolar RFA. This beneficial effect can also be achieved in the percutaneous application mode by RFA combined with arterial microembolization via a hepatic artery catheter.

Transpulmonary CT-guided radiofrequency ablation of liver metastasis

The percutaneous approach for RF ablation of liver lesions high up in the dome is always difficult. The authors describe a transpulmonary approach that may be simpler and safer to use.

Complications of radiofrequency ablation in hepatocellular carcinoma

Radiofrequency thermal ablation has been accepted as a promising technique to treat unresectable liver tumors. However, any interventional procedure should be performed only if the procedure is safe, with minimal morbidity and mortality rates. Recently, three separate multicenter surveys have reported acceptable morbidity and mortality rates for a minimally invasive technique. The mortality rate ranged from 0.1% to 0.5%, the major complication rate ranged from 2.2% to 3.1%, and the minor complication rate ranged from 5% to 8.9%. The most common causes of death were sepsis and hepatic failure, and the most common complications were intraperitoneal bleeding, hepatic abscess, bile duct injury, hepatic decompensation, and grounding pad burns. Minor complications and side effects are more common than major complications, but most of them are transient and self-limiting. Several strategies for avoiding or limiting the impact of complications after radiofrequency ablation are recommended: (a) careful patient selection, (b) combined treatment with other techniques when appropriate, (c) selection of the most appropriate guiding modality and approach, and (d) early detection and appropriate management of any major complications. Knowledge of the broad spectrum of complications and relevant management enables the operator to minimize the incidence and effect of any complications that occur after radiofrequency ablation.

Microwave ablation of hepatic tumors using dual-loop probes: results of a phase I clinical trial

Hepatic tumors are a common cause of death worldwide. However, few patients are candidates for resection at the time of presentation. Microwave ablation is a viable alternative available for these patients. To date, only straight antennas are used for microwave ablation. Recently, a prototype loop-shaped microwave antenna was developed that, in animal studies, more effectively kills tumors. For this study, the dual-probe lesions were created by placing the probes in both tumors and normal livers. Lesions were created with 60 watts applied power for 5-7 minutes. The livers were sectioned and stained for viability. The average ablation volume was 63.9 +/- 8.7 cm(3). Microwave ablation with the loop probes results in complete tumor kill at the ablation/tumor interface, and adjacent to surrounding blood vessels. In addition, vessels within the ablation/tumor interface failed to show viable cells. The shape of the lesions was not distorted by proximity to blood vessels. The advantages of this configuration over conventional straight probes include the ability to encircle a tumor, deliver large amounts of precisely targeted microwave energy to the tumor, and spare normal liver outside the loop.

Image-guided tumor ablation: standardization of terminology and reporting criteria

The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency (RF), laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes. The intent of this standardization of terminology is to provide an appropriate vehicle for reporting the various aspects of image-guided ablation therapy.

Radiofrequency Ablation Combined with CO2Injection for Treatment of Retroperitoneal Tumor: Protecting Surrounding Organs Against Thermal Injury

OBJECTIVE

The objective of this study was to separate target tumors from adjacent structures by injecting carbon dioxide (CO2) around the tumor to avoid thermal injury and the heat-sink effect from the blood vessel during percutaneous radiofrequency ablation.

CONCLUSION

We successfully achieved complete ablation of a retroperitoneal tumor without thermal injury. Imaging-guided percutaneous CO2 injection is useful for preventing thermal injury while achieving complete ablation of the tumor during radiofrequency ablation.

Radiofrequency ablation: importance of background tissue electrical conductivity--an agar phantom and computer modeling study

PURPOSE

To determine whether radiofrequency (RF)-induced heating can be correlated with background electrical conductivity in a controlled experimental phantom environment mimicking different background tissue electrical conductivities and to determine the potential electrical and physical basis for such a correlation by using computer modeling.

MATERIALS AND METHODS

The effect of background tissue electrical conductivity on RF-induced heating was studied in a controlled system of 80 two-compartment agar phantoms (with inner wells of 0.3%, 1.0%, or 36.0% NaCl) with background conductivity that varied from 0.6% to 5.0% NaCl. Mathematical modeling of the relationship between electrical conductivity and temperatures 2 cm from the electrode (T2cm) was performed. Next, computer simulation of RF heating by using two-dimensional finite-element analysis (ETherm) was performed with parameters selected to approximate the agar phantoms. Resultant heating, in terms of both the T2cm and the distance of defined thermal isotherms from the electrode surface, was calculated and compared with the phantom data. Additionally, electrical and thermal profiles were determined by using the computer modeling data and correlated by using linear regression analysis.

RESULTS

For each inner compartment NaCl concentration, a negative exponential relationship was established between increased background NaCl concentration and the T2cm (R2= 0.64-0.78). Similar negative exponential relationships (r2 > 0.97%) were observed for the computer modeling. Correlation values (R2) between the computer and experimental data were 0.9, 0.9, and 0.55 for the 0.3%, 1.0%, and 36.0% inner NaCl concentrations, respectively. Plotting of the electrical field generated around the RF electrode identified the potential for a dramatic local change in electrical field distribution (ie, a second electrical peak ["E-peak"]) occurring at the interface between the two compartments of varied electrical background conductivity. Linear correlations between the E-peak and heating at T2cm (R2= 0.98-1.00) and the 50 degrees C isotherm (R2= 0.99-1.00) were established.

CONCLUSION

These results demonstrate the strong relationship between background tissue conductivity and RF heating and further explain electrical phenomena that occur in a two-compartment system.

Photodynamic therapy with 5,10,15,20-tetrakis(m-hydroxyphenyl) bacteriochlorin for colorectal liver metastases is safe and feasible: results from a phase I study

BACKGROUND

The prognosis for patients with liver metastases from colorectal carcinoma is limited because of the low number of patients who are eligible for curative hepatic resection. In this phase I study, 31 liver metastases in 24 patients with nonresectable metastases from colorectal carcinoma were treated with photodynamic therapy (PDT).

METHODS

The photosensitizer 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (mTHPBC) was intravenously administered in a dose of .6 mg/kg (n = 12) or .3 mg/kg (n = 12). After 120 hours (n = 18) or 48 hours (n = 6), tumors were illuminated for 300 to 600 seconds through percutaneously inserted optical fibers with a light dose of 60 J/cm of diffuser (740 nm).

RESULTS

Tumor necrosis at 1 month after PDT was achieved in all treated lesions. Laser treatment was associated with mild pain (n = 8) and transient subclinical hepatotoxicity (n = 21). In one patient, PDT damage to the pancreas was inflicted, and in another patient, PDT damage of the skin occurred, but no serious clinical complications from PDT were reported. Administration of .6 mg/kg of mTHPBC led to transient phlebitis in 10 patients, and 3 patients experienced mild skin phototoxicity after excess light exposure.

CONCLUSIONS

Colorectal liver metastases that are ineligible for resection can be safely and effectively treated with interstitial mTHPBC-based PDT.

Local recurrence after hepatic radiofrequency coagulation: multivariate meta-analysis and review of contributing factors

OBJECTIVE

The purpose of this study was to analyze the factors that influence local recurrence after radiofrequency coagulation of liver tumors.

SUMMARY BACKGROUND DATA

Local recurrence rate varies widely between 2% and 60%. Apart from tumor size as an important risk factor for local recurrence, little is known about the impact of other factors.

METHODS

An exhaustive literature search was carried out for the period from January 1, 1990 to January 1, 2004. Only series with a minimal follow-up of 6 months and/or mean follow-up of 12 months were included. Univariate and multivariate meta-analyses were carried out.

RESULTS

Ninety-five independent series were included, allowing the analysis of the local recurrence rate of 5224 treated liver tumors. In a univariate analysis, tumor-dependent factors with significantly less local recurrences were: smaller size, neuroendocrine metastases, nonsubcapsular location, and location away from large vessels. Physician-dependent favorable factors were: surgical (open or laparoscopic) approach, vascular occlusion, general anesthesia, a 1-cm intentional margin, and a greater physician experience. In a multivariate analysis, significantly less local recurrences were observed for small size (P < 0.001) and a surgical (versus percutaneous) approach (P < 0.001).

CONCLUSIONS

Radiofrequency coagulation by laparoscopy or laparotomy results in superior local control, independent of tumor size. The percutaneous route should mainly be reserved for patients who cannot tolerate a laparoscopy or laparotomy. The short-term benefits of less invasiveness for the percutaneous route do not outweigh the longer-term higher risk of local recurrence.

Local therapeutic treatments for focal liver disease

Patients diagnosed with primary hepatic malignancies or metastases to the liver remain a difficult population to treat. A small percentage of these people can undergo surgical resection or transplantation. The remaining nonsurgical aggregate does not often benefit from conventional radiation and chemotherapy; minimally invasive means either to cure or palliate these patients are a requirement for complete cancer care. This article discusses image-guided local therapies used to treat this difficult patient population, focusing predominantly on radiofrequency ablation.

Radiofrequency versus microwave ablation in a hepatic porcine model

PURPOSE

To compare microwave (MW) and radiofrequency (RF) ablation in a hepatic porcine model.

MATERIALS AND METHODS

Institutional animal research committee approval was obtained. Nineteen pigs were divided into groups based on time of sacrifice (group A, immediate; group B, 2 days; group C, 28 days; group D, 28 days). Groups A, B, and C each underwent a combination of RF and MW ablation. Group D underwent either four MW or four RF ablations. Ablation was performed with a prototype MW device (915 Mhz, 40 W, 10 minutes) and a commercial RF system (150 W, 10 minutes, 3-cm deployment). Computed tomography (CT) was performed in groups B and C at 2 days and in group C at 28 days. Group D underwent serial laboratory testing. Specimens were serially sectioned, and short-axis diameter and length of each were measured. The percentage deflection caused by local blood vessels (heat-sink effect) was also measured in group A. Likelihood ratio tests and unpaired t tests were used for statistical analyses as appropriate.

RESULTS

MW ablation zones were longer at days 0, 2, and 28 (P < .05), but short-axis diameter was not different from that with RF ablation at any time point (P > .05). Local blood vessels caused 3.5% +/- 5.3 (standard deviation) deflection at MW ablation compared with 26.2% +/- 27.9 at RF ablation (P < .05). MW and RF ablation zones were indistinguishable at CT or pathologic evaluation. Laboratory test results were similar between RF ablation-only animals and MW ablation-only animals, with the exception of a slightly higher alkaline phosphatase levels at day 2 in RF ablation-only animals (P < .02).

CONCLUSION

MW and RF ablation zones are similar in pathologic appearance and imaging characteristics. Increased length with MW ablation is likely caused by the length of the radiating segment of the antenna. MW ablation may be less affected by the heat-sink effect that is thought to contribute to local recurrence after RF ablation.

Multiple applicator approaches for radiofrequency and microwave ablation

Treatment of tumours greater than 2 cm by radiofrequency (RF) or microwave ablation typically use multiple sequential applications, since most currently available ablation devices are limited to use of a single applicator at a time. A major focus of current ablation research is on methodologies that allow increasing the coagulation zone to more rapidly treat large tumours. The ability to use multiple applicators simultaneously would satisfy this need. It would significantly reduce treatment time and may lead to a reduction in local tumour progression, especially in perivascular locations. Several methods have been suggested that potentially allow simultaneous use of multiple applicators, both with radiofrequency (RF) and microwave (MW) ablation. This review compares the different methods of multiple applicator use, investigating advantages and disadvantages of each modality.

Combination radiofrequency ablation with intratumoral liposomal doxorubicin: effect on drug accumulation and coagulation in multiple tissues and tumor types in animals

PURPOSE

To determine whether use of radiofrequency (RF) ablation combined with intravenously (IV) administered liposomal doxorubicin, as compared with use of RF ablation or doxorubicin alone, facilitates increased tissue coagulation and interstitial drug accumulation in animal models.

MATERIALS AND METHODS

The institutional animal care and use committee approved this study. In experiment 1, multiple canine sarcomas were implanted in seven mildly immunosuppressed dogs and grown to a mean diameter of 4.8 cm. Tumors were assigned to three treatment groups: internally cooled RF ablation (12 minutes, 2000-mA pulsed technique) followed by IV liposomal doxorubicin (10 mg per animal) (n = 6), RF ablation alone (n = 6), and liposomal doxorubicin alone (n = 4). In experiment 2, the livers and kidneys of 10 rabbits and the thigh muscles of 10 rats were randomly assigned to one of two treatment groups: conventional RF ablation (90 degrees C +/- 2, 5 minutes) followed by IV liposomal doxorubicin (5 mg per rabbit, 1 mg per rat) or RF ablation alone (n = 5, each). Coagulation diameter and interstitial doxorubicin concentration (tissues were homogenized in acid alcohol, with doxorubicin extracted for 24 hours at 5 degrees C and quantified with fluorimetry) were measured 48 hours after treatment and compared. Multivariate analysis of variance and subsequent pairwise t tests (alpha = .05, two-tailed test) were performed.

RESULTS

Data are means +/- standard errors of the mean. A larger diameter of tumor destruction was observed in canine sarcomas treated with RF ablation-liposomal doxorubicin (3.7 cm +/- 0.6) compared with that in tumors treated with RF ablation (2.3 cm +/- 0.1) or liposomal doxorubicin (0.0 cm +/- 0.0) alone (P < .01). A new finding was a completely necrotic red zone (1.6 cm +/- 0.7) surrounding the central RF ablation-induced white coagulation zone. Greater but nonuniform drug uptake was observed particularly in this red zone (77.0 ng/g +/- 18.2) compared with uptake in the central zone (15.1 ng/g +/- 3.2), peripheral area of untreated tumor (38.9 ng/g +/- 8.0), and tumors treated with liposomal doxorubicin alone (43.9 ng/g +/- 6.7 for all regions) (P < .01 for all individual comparisons). In experiment 2, use of combined therapy led to increased coagulation in all tissues (liver: 17.6 mm +/- 3.1, P = .03; kidney: 11.0 mm +/- 3.1, P = .03; muscle: 13.1 mm +/- 1.3, P < .01) compared with use of RF ablation alone (liver, 13.4 mm +/- 1.5; kidney, 7.9 mm +/- 0.7; muscle, 8.6 mm +/- 0.5). Combined therapy, as compared with liposomal doxorubicin therapy alone, was also associated with increased doxorubicin accumulation in liver, kidney, and muscle (1.56 microg/g +/- 0.34, 4.36 microg/g +/- 1.78, and 3.63 microg/g +/- 1.43, respectively, vs 1.00 microg/g +/- 0.18, 1.23 microg/g +/- 0.32, and 0.87 microg/g +/- 0.53, respectively) (P < or = .01 for all individual comparisons).

CONCLUSION

Use of RF ablation combined with liposomal doxorubicin facilitates increased tissue coagulation and interstitial doxorubicin accumulation in multiple tissues and tumor types and may be useful for treatment of large tumors and achieving an ablative margin within the untreated tissue surrounding RF ablation-treated tumors.

Image-guided tumor ablation: standardization of terminology and reporting criteria

The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency, laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes.

Radiofrequency ablation in the liver close to the bile ducts: can intraductal cooling offer protection?

BACKGROUND

One complication of radiofrequency ablation (RFA) of the liver is biliary duct damage. Intraductal cooling (IDC) has been proposed as a means of protection.

METHODS

In the first experiment, designed to evaluate the influence of IDC on the RFA procedure per se and on lesion formation, lesions were created in vivo in pig liver with and without IDC. The RFA needle was placed with a 1.5-cm safety margin from the bile ducts. In the second experiment, designed to evaluate the potential protective effects of IDC, lesions were created close to a bile duct with and without IDC.

RESULTS

With the safety margin, the RFA parameters and lesion size were not negatively affected by IDC. Microscopic examination revealed that IDC had a protective effect in most of the lesions created close to a bile duct.

CONCLUSIONS

The IDC procedure was feasible and had no negative effect on the RFA procedure or the lesions. However, the protective effect of IDC was not statistically significant (p = 0.12).

Effect of vessel diameter on the creation of ovine lung radiofrequency lesions in vivo: Preliminary results

OBJECTIVE

We sought to evaluate the effect of radiofrequency ablation (RFA) on pulmonary vessels with respect to potential of injury of these structures, to assess perfusion-mediated "heat sink" effect, and to consider acute and chronic complications.

MATERIAL AND METHODS

RFAs targeted to perihilar, middle third, and peripheral lung regions were created in vivo in the lung of 10 crossbred sheep. The RITA generator and the Starburst XLi electrode with deployable hooks were used. The approach was open, performed under general anesthesia. Lesions 4 cm in diameter at a target temperature of 80 degrees C were created. Acute (immediate postinterventional euthanasia), subacute (96 h), and chronic (28 days) lesions were evaluated macroscopically, and histologic analysis of the vessels was performed. Patency of the vessels, both arteries and veins, was macroscopically assessed by presence or absence of thrombus and the degree of vascular injury and the viability of perivascular pneumocytes as well as endobronchial injury were histologically assessed.

RESULTS

In the acute, subacute, and chronic setting, heat sink effect, indicated by invagination of the tissue between vessel and ablated region, was only observed in vessels greater than 3 mm in diameter. Thrombus was seen in 20% of the vessels smaller than 3 mm. On histopathology, vessels smaller than 3 mm showed at least partial vessel wall injury, characterized by endothelial cell necrosis and luminal thrombus. In the vessels greater than 3 mm the extent of vessel wall injury decreased with increasing vessel diameter. No acute complications were noted. For the chronic complications a bronchopleural fistula and a lung abscess were found.

CONCLUSION

There seems to be a narrow transition zone for pulmonary vessels around 3 mm, beyond which the heat sink effect was seen consistently and substantial vascular injury was rare.

Radiofrequency ablation of hepatocellular carcinoma: treatment success as defined by histologic examination of the explanted liver

PURPOSE

To retrospectively evaluate the effectiveness of radiofrequency (RF) ablation of hepatocellular carcinoma (HCC) by using histologic examination of the explanted liver.

MATERIALS AND METHODS

The study was approved by the medical center Institutional Review Board, with waiver of informed consent. Forty-seven HCC nodules in 24 patients (18 men, six women; age range, 33-71 years; mean age, 56 years) were treated with single or double RF ablation sessions prior to liver transplantation. Histologic data from hematoxylin-eosin staining of explanted liver specimens were retrospectively reviewed to determine treatment success, which was defined as the absence of residual or recurrent viable carcinoma cells at treatment site. Tumor size and the presence of large (> or =3 mm) abutting vessels that were observed during imaging were tested as potential predictors of treatment success or failure (Fisher exact test). In patients who underwent postablation computed tomographic (CT) or magnetic resonance (MR) imaging within 3 months prior to transplantation (21 patients with 44 tumors), imaging results were analyzed for sensitivity and specificity of residual or recurrent tumor by using histologic data as the reference standard.

RESULTS

Thirty-five (74%) of 47 ablated tumors, including 29 (83%) of 35 tumors less than 3 cm, were found to be successfully treated on the basis of histologic findings after a mean interval of 7.5 months between RF ablation and transplantation. Nodules that were successfully treated had mean maximal diameter of 2.0 cm, and nodules that were unsuccessfully treated had mean maximal diameter of 3.1 cm (P=.014). Seven (47%) of 15 perivascular lesions were successfully treated whereas 28 (88%) of 32 nonperivascular lesions were successfully treated (P <.01). Imaging correlation showed 100% (33 of 33) specificity and 36% (four of 11) sensitivity of postablation CT and MR imaging for the depiction of residual or recurrent tumor.

CONCLUSION

Histologic evidence directly validates RF ablation as an effective treatment of small (<3 cm) HCC.

Large-volume radiofrequency ablation of ex vivo bovine liver with multiple cooled cluster electrodes

Three methods of creating large thermal lesions with cool-tip cluster electrodes were compared. Three cluster electrodes were arranged 4 cm apart in a triangular array. Eight lesions were created ex vivo in fresh bovine liver (from a butcher) with each method: sequential ablation (three electrodes, 12 minutes each); simultaneous activation of electrodes (12 minutes); and rapid switching of power between electrodes (12 minutes), for which an electronic computer-controlled switch was developed. For sequential, rapid switching, and simultaneous methods, lesion volumes were 137.5 cm(3)+/- 22.2, 116.4 cm(3)+/- 15.2, and 22.3 cm(3)+/- 6.4 (P < .05), respectively, and final temperatures at lesion center were 80 degrees C +/- 5, 97 degrees C +/- 8, and 41 degrees C +/- 3 (P < .001), respectively. Because of electrical interference between electrodes, simultaneous method led to little heating at the center between the electrodes and created small discontinuous lesions. Rapid switching created large round lesions by employing multiple electrodes concurrently, which substantially reduced treatment time and resulted in more effective heating between electrodes.

Combined radiofrequency and alcohol injection for percutaneous hepatic tumor ablation

OBJECTIVE

We sought to determine if alcohol potentiates radiofrequency energy by obtaining larger ablative volumes in 30 liver tumors in human patients.

SUBJECTS AND METHODS

We compared two groups of patients: one group treated with radiofrequency ablation alone (radiofrequency-alone group), and a second group treated with radiofrequency ablation and immediate prior injection of alcohol (combined group). The radiofrequency-alone group comprised 20 ablations (mean diameter, 8.4 cm; colorectal cancer metastases [n = 15]; other metastases [n = 5]). The combined group consisted of 30 radiofrequency ablations (mean diameter, 8.8 cm; metastatic colorectal cancer [n = 17]; other metastases [n = 8]; and hepatocellular carcinoma [n = 5]) treated with alcohol injection immediately before radiofrequency ablation. The amount of alcohol injected was determined by the size and location of tumors. Preprocedural laboratory tests (complete blood cell count with differential, liver function tests, and coagulation parameters) were performed in all patients, along with pre- and postprocedural CT, MRI, and PET. Measurements of tissue necrosis were obtained on the postprocedural CT scans and MR images. Volumes of necrosis calculated in each group were corrected for the number of radiofrequency applications and were statistically compared using the Student's t test. In addition, tissue impedances obtained during the radiofrequency ablation procedure were compared between the two groups.

RESULTS

The mean ablation volumes for the radiofrequency-alone group were 32.3 cm(2) (median, 28.6 cm(2); range, 14.4-61.8 cm(2)) and for the combined group, 84.6 cm(2) (median, 78.3 cm(2); range, 34.6-149 cm(2)). The difference in the necrosis volumes was significantly larger (p < 0.0001) in the combined group. Overall, the combined treatment group underwent fewer radiofrequency applications per session. Tissue impedance during radiofrequency ablation was higher in the combined group (mean, 62.7 vs 57.3 Omega in the radiofrequency alone group; p = 0.0005) at comparable times during the ablations. No major complications were seen in either group.

CONCLUSION

Percutaneous radiofrequency ablation appears to be potentiated by immediate prior alcohol injection into the tumor. Consistently larger lesions are obtainable in fewer sessions, without any increase of complications, using the combined method.

Radiofrequency ablation of primary and metastatic hepatic malignancies

Radiofrequency interstitial tissue ablation is a local ablative therapy in which tumors are destroyed in situ by thermal coagulation and protein denaturation through frictional heating produced by tissue ionic agitation from high-frequency alternating current. This technology can be used to destroy primary and metastatic hepatic lesions generally considered nonresectable or nonoperable, thus providing patients with these tumors, who have few treatment options, a relatively safe and effective alternative with the potential for improved chance of survival. Knowledge of the broad spectrum of potential complications associated with radiofrequency ablation (RFA) is essential for prevention, early detection, and proper management. Combining RFA with other modalities such as surgical resection or hepatic artery infusional chemotherapy is feasible, has increased the pool of operable patients, and may improve treatment efficacy and clinical outcome in properly selected patients. The approach to perform RFA percutaneously, laparoscopically, or during laparatomy should take into consideration tumor characteristics, imaging and technical limitations, and the role of other treatment modalities. Therefore, patients considered for RFA should be evaluated within the context of a multidisciplinary approach to insure proper patient selection and coordination of adjunct therapy.

Review of radiofrequency ablation for renal cell carcinoma

This review will discuss how minimally invasive, image-guided radiofrequency (RF) tumor ablation [i.e., coagulating tumor using short-duration heating (<15 minutes) by directly applying temperatures >50 degrees C via needle electrodes] is being incorporated as a clinical tool for the treatment of renal cell carcinoma. RF ablation has been used to treat focal liver tumors. Potential benefits of this thermal therapy include reduced morbidity and mortality compared with standard surgical resection and the ability to treat nonsurgical patients. More recently, this technique has been introduced to treat focal renal tumors, particularly incidental lesions smaller than 3 cm in elderly patients and those with comorbid conditions. Other uses have included treatment in patients with von Hippel-Lindau syndrome and other diseases that predispose patients to multiple renal carcinomas, where renal parenchymal preservation is desired. Techniques, complications, and results will be discussed. Additionally, strategies that we are currently studying to improve RF outcomes and enable the potential treatment of larger tumors will be addressed. Most notably, recent data on increased coagulation achieved by combining RF ablation with antivascular/antiangiogenic therapies, such as arsenic trioxide, that reduce blood flow and promote heat retention are provided.

Image-guided ablation of renal cell carcinoma

An increasing number of small asymptomatic renal cell carcinomas (RCCs) are being detected by cross-sectional imaging. Because of the nonaggressive biologic behavior of many of these tumors, there is increasing interest in minimally invasive treatment modalities,particularly for the elderly, infirm, and patients with comorbid conditions. Radiofrequency(RF) ablation, cryoablation, microwave ablation, and laser ablation have all shown promise for the treatment of RCC, with high local control and low complication rates for RF ablation and cryoablation. However, the clinical trial data remain early, and survival data are not yet available for a definitive comparison with conventional surgical techniques for removal of RCC.

Minimizing central bile duct injury during radiofrequency ablation: use of intraductal chilled saline perfusion--initial observations from a study in pigs

PURPOSE

To determine whether intraductal perfusion with chilled saline reduces thermal injury to bile ducts during radiofrequency (RF) ablation.

MATERIALS AND METHODS

In swine, anesthesia was induced and the common bile duct was surgically cannulated with a pediatric feeding tube. RF thermal lesions were created adjacent to bile ducts by using an expandable-hook 2-cm RF electrode and 90-W generator. In three pigs, chilled saline was perfused through the ducts at 1.5 L/h (26 mL/min), and in another pig, room-temperature saline was perfused at the same rate. In three pigs (control group), RF lesions were created without perfusion. After 48 hours, animals were sacrificed. Periductal sections from all animals were reviewed by a liver pathologist. The degree of injury to biliary epithelium and subepithelial glands was assessed on a scale of 0%-100%. Significance of differences between degrees of injury was assessed with the Mann-Whitney test.

RESULTS

In the control group, there was a mean of 100% injury to biliary ductal epithelium and 99.3% to subepithelial ductal glands. In the room-temperature saline group, there was a mean of 100% biliary epithelial injury and 84.4% glandular injury. In the chilled saline group, there was a mean of 52.9% ductal epithelial injury and 12.1% subepithelial glandular injury. In comparison with the control group, there was significantly less (P <.05) thermal injury to biliary epithelium in the chilled saline group and to subepithelial glands in both the room-temperature and chilled saline perfusion groups.

CONCLUSION

RF-induced bile duct injury may be decreased significantly with an intraductal infusion of chilled saline.

Radiofrequency thermal ablation of abdominal tumors: lessons learned from complications

Radiofrequency (RF) thermal ablation has shown promise as a technique for treating inoperable solid tumors involving the liver, kidney, adrenal gland, and lung. However, like all other imaging-guided interventional procedures, RF ablation involves some element of risk. Varying degrees of complications can be expected, depending on factors such as the organ site and the aggressiveness of the procedure. General complications of RF ablation may be related to either imaging-guided electrode placement (eg, bleeding, infection, tumor seeding, pneumothorax) or thermal therapy (eg, nontarget thermal damage, grounding pad burns). Liver and renal-adrenal ablation may be associated with organ-specific complications. A fundamental understanding of RF ablation principles, along with adequate operator training and experience and familiarity with both thermal ablation and the broad spectrum of postablation complications, are necessary to maximize the safety and efficacy of this procedure. The standard of care for decreasing the morbidity of complications consists of prevention (including careful patient selection), early detection, and prompt, appropriate treatment.

Effects of perfusion on radiofrequency ablation in swine kidneys

PURPOSE

To evaluate the effect of vascular occlusion on the size of radiofrequency (RF) ablation lesions and to evaluate embolization as an occlusion method.

MATERIALS AND METHODS

The kidneys of six swine were surgically exposed. Fifteen RF ablation lesions were created in nine kidneys by using a 2-cm-tip single-needle ablation probe in varying conditions: Seven lesions were created with normal blood flow and eight were created with blood flow obstructed by means of vascular clamping (n = 5) or renal artery embolization (n = 3). The temperature, applied voltage, current, and impedance were recorded during RF ablation. Tissue-cooling curves acquired for 2 minutes immediately after the ablation were compared by using regression analysis. Lesions were bisected, and their maximum diameters were measured and compared by using analysis of variance.

RESULTS

The mean diameter of ablation lesions created when blood flow was obstructed was 60% greater than that of lesions created when blood flow was normal (1.38 cm +/- 0.05 [standard error of mean] vs 0.86 cm +/- 0.07, P <.001). The two methods of flow obstruction yielded lesions of similar mean sizes: 1.40 cm +/- 0.06 with vascular clamping and 1.33 cm +/- 0.07 with embolization. The temperature at the probe tip when lesions were ablated with normal blood flow decreased more rapidly than did the temperature when lesions were ablated after flow obstruction (P <.001), but no significant differences in tissue-cooling curves between the two flow obstruction methods were observed.

CONCLUSION

Obstruction of renal blood flow before and during RF ablation resulted in larger thermal lesions with potentially less variation in size compared with the lesions created with normal nonobstructed blood flow. Selective arterial embolization of the kidney vessels may be a useful adjunct to RF ablation of kidney tumors.

Radiofrequency ablation: Effect of pharmacologic modulation of hepatic and renal blood flow on coagulation diameter in a VX2 tumor model

PURPOSE

To determine whether pharmacologic agents can be used to modulate blood flow in hepatic and renal tumors sufficiently to alter the extent of radiofrequency (RF)-induced coagulation.

MATERIALS AND METHODS

VX2 tumors (8-15 mm) were implanted in the liver (n = 25) or kidney (n = 8) of 33 New Zealand White rabbits. RF was applied to tumors for 6 minutes with use of conventional electrodes (125 mA +/- 35; 90 degrees C +/- 2 degrees C tip temperature). In the hepatic model, blood flow was modulated with use of halothane, epinephrine, or arsenic trioxide (2-6 mg/kg). Laser Doppler flowmetry was used to quantify changes in hepatic blood flow. Correlation of blood flow with induced coagulation diameter was performed. RF ablation was then performed in a renal model with and without arsenic trioxide.

RESULTS

For liver tumors, halothane and arsenic trioxide reduced blood flow to 40.3% +/- 17.8% and 29% +/- 15% of normal, respectively, whereas epinephrine increased blood flow to 207.8% +/- 97.9%. Correlation of blood flow to coagulation diameter was demonstrated (R(2) = 0.40). Coagulation measured 7 mm +/- 1 with epinephrine, 10 mm +/- 1 with normal blood flow, 12 mm +/- 3 with halothane, and 13 mm +/- 3 with arsenic trioxide (P <.04 compared with controls). In the renal model, arsenic trioxide decreased blood flow (44% +/- 16%) and increased coagulation diameter (10.9 mm +/- 1) compared with controls (84% +/- 11% and 7.6 mm +/- 1; P <.01, both comparisons).

CONCLUSIONS

RF-induced coagulation necrosis in rabbit hepatic and renal tumors is affected by tumor blood flow. Pharmacologic modulation of tumor blood flow may provide a noninvasive way to decrease blood flow during thermally mediated ablation therapy, potentially enabling the creation of larger zones of coagulation necrosis.

Radiofrequency ablation of cancer

Radiofrequency ablation (RFA) has been used for over 18 years for treatment of nerve-related chronic pain and cardiac arrhythmias. In the last 10 years, technical developments have increased ablation volumes in a controllable, versatile, and relatively inexpensive manner. The host of clinical applications for RFA have similarly expanded. Current RFA equipment, techniques, applications, results, complications, and research avenues for local tumor ablation are summarized.

Microwave Ablation with Loop Antenna: In Vivo Porcine Liver Model

PURPOSE

To determine the effectiveness of tissue ablation with a loop microwave antenna in various configurations in porcine liver tissue.

MATERIALS AND METHODS

Microwave energy was applied for 7 minutes at 60 W in six porcine livers (mean weight, 68.2 kg) by using single (n = 7) or dual 2.7-cm loop microwave probes in parallel (n = 9) or orthogonal (n = 9) configurations. Volume, diameter, shape, and temperature of the zone of necrosis and the presence of viable tissue inside the loop were determined and compared by means of factorial analysis of variance.

RESULTS

Mean lesion volume and maximum diameter, respectively, were 32.2 cm(3) +/- 14.4 (SD) and 4.6 cm +/- 1.4 for lesions ablated with parallel probes (parallel lesions), 29.5 cm(3) +/- 8.1 and 4.3 cm +/- 0.6 for lesions ablated with orthogonal probes (orthogonal lesions), and 6.4 cm(3) +/- 1.9 and 3.4 cm +/- 0.62 for lesions ablated with single probes (single lesions) (P <.05, single vs parallel and orthogonal lesions). Mean minimum diameter was greatest for orthogonal lesions (3.5 cm +/- 0.53; P =.017, parallel vs orthogonal lesions). Orthogonal lesions had the highest mean internal temperature (97.2 degrees C) versus parallel (91.9 degrees C) and single (60.0 degrees C) lesions. All orthogonal lesions heated to 60 degrees C in comparison to eight of nine parallel and four of seven single lesions. The mean time to reach 60 degrees C was shortest for orthogonal lesions (93.3 seconds) versus parallel (123.8 seconds) and single (263.0 seconds) lesions. Orthogonal lesions were the most spherical. Viable tissue was present in the center of five of seven single, six of nine parallel, and zero of nine orthogonal lesions.

CONCLUSION

Loop microwave antennas allow precise control and effective ablation of targeted tissue, particularly in the orthogonal configuration.

Radiofrequency ablation: effect of surrounding tissue composition on coagulation necrosis in a canine tumor model

PURPOSE

To determine the effect of surrounding tissue type on coagulation necrosis from radiofrequency (RF) ablation in a homogeneous animal tumor model.

MATERIALS AND METHODS

Thirty canine venereal sarcomas were implanted in three tissue sites (subcutaneous, kidney, and lung) in 13 mildly immunosuppressed dogs. Five of 25 tumors, which were 19 mm +/- 3 (mean +/- SD) in diameter, were allocated to each of five groups: (a) subcutaneous tumors, (b) kidney tumors, (c) lung tumors with blood flow, and (d) subcutaneous and (e) renal tumors without blood flow, which was achieved by sacrificing the animal to eliminate tumor perfusion. A sixth group comprised larger subcutaneous tumors (mean diameter, 46 mm +/- 4) that were also treated. RF ablation was performed with a 1-cm tip and 5 minutes of ablation at 90 degrees C +/- 1. Impedance, temperature, and resultant coagulation diameter were recorded and compared. Data were analyzed statistically, including one-way analysis of variance to determine the effect of tissue conductivity (ie, systemic impedance) on necrosis size and tissue temperatures. Linear regression analysis was used to compare changes in impedance between the control and experimental groups.

RESULTS

Increasing linear correlation was observed between tumor coagulation diameter and overall baseline system impedance (R(2) = 0.65). RF ablation of lung tumors resulted in the greatest coagulation diameter (13.0 mm +/- 3.5) compared with that in the other groups (P <.01). The smallest coagulation diameter was observed in kidney tumors in the presence of blood flow (7.3 mm +/- 0.6) compared with that in the other groups (P <.01). Elimination of blood flow in kidney tumors increased coagulation diameter to 10.3 mm +/- 0.6 (P <.01). After RF ablation, coagulation diameter in the subcutaneous tumor groups was the same (mean, 9.8 mm +/- 1.0) (difference not significant), regardless of tumor size or presence of blood flow.

CONCLUSION

The characteristics of tissue that surrounds tumor, including vascularity and electric conductivity, affect ablation outcome. Predominance of tissue-specific characteristics will likely result in site-specific differences in RF-induced coagulation necrosis.

Multiple probe radiofrequency ablation: pilot study in an animal model

PURPOSE

Radiofrequency ablation (RFA) is becoming increasingly popular for the minimally invasive treatment of benign and malignant tumors. Currently available systems are limited to the use of a single probe because of electrical interactions between probes. The purpose of this study was to test a new prototype multiple probe generator with a built-in switching mechanism to determine if multiple zones of necrosis could be formed simultaneously without a significant penalty in terms of lesion size and procedure time.

MATERIALS AND METHODS

A dual probe generator was created by modifying a commercially available system into an alternating monopolar system with an external electronic switch controlled by a temperature feedback loop. A total of 20 radiofrequency (RF) lesions (conventional single probe, n = 10; switched dual probe, n = 10) were created in the livers of six adult pigs (temperature, 100 degrees C; 10-minute ablation). Lesions were excised and examined for volume, minimum diameter, and maximum diameter.

RESULTS

The time to target temperature was slightly greater for dual (3.5 minutes) versus single ablations (2.7 minutes). However, this resulted in only a 48 second (6.5%) longer total ablation time. There was no significant difference between conventional single and dual lesions for lesion volume (13.6 +/- 9.3 cm(3) versus 13.7 +/- 7.0 cm(3); P >.05), minimum diameter (1.63 +/- 0.56 cm(3) versus 1.61 +/- 0.53; P >.05) or maximum diameter (3.3 +/- 0.84 versus 3.4 +/- 0.55, P >.05).

CONCLUSION

A multiple probe RFA system that can simultaneously ablate multiple areas in the liver is feasible. If multiple probe units become clinically available, large or irregularly shaped lesions could be treated more effectively than with conventional single probe units, and multiple tumors could be ablated simultaneously, thus potentially decreasing procedure time and anesthetic complications.

Influence of large peritumoral vessels on outcome of radiofrequency ablation of liver tumors

PURPOSE

The effect of large vessels (>/=3 mm) contiguous to hepatic tumors was evaluated with respect to clinical tumor recurrence rates after radiofrequency (RF) ablation.

MATERIALS AND METHODS

The first 105 malignant liver tumors treated by RF ablation therapy at our institution with pathologic analysis or a minimum of 6 months of clinical follow-up were reviewed. The original pretreatment imaging studies were reviewed by a radiologist who was blinded to the cases, and, based on lesion contiguity to vessels of at least 3 mm, the lesions were categorized as perivascular or nonperivascular. Treatment outcomes with respect to local tumor recurrence between these two groups were then compared. Logistic regression analysis was performed to take into account other variables and to determine whether this categorization was an independent predictor of treatment outcome.

RESULTS

There were 74 nonperivascular tumors and 31 perivascular tumors. Mean tumor size was 2.4 cm and mean follow-up was 11.3 months. Residual or locally recurrent tumors were documented in 20 of 105 cases (19%). In the nonperivascular group, five of 74 (7%) had either incompletely treated tumor (manifested within 6 months) or local recurrence beyond 6 months. In the perivascular group, 15 of 31 (48%) had incompletely treated or locally recurrent tumor (P <.001). Subanalysis of lesion size (61 tumors </=2.5 cm, 33 tumors 2.6-4 cm, and 11 tumors >4 cm), tumor type (40 hepatocellular carcinomas, 48 colorectal metastases, and 17 other metastases), access (53 intraoperative, 52 percutaneous), and RF device (45 Radiotherapeutics electrodes, 18 Rita electrodes, and 42 Radionics electrodes) showed similar results. Multivariate logistic regression analysis showed that presence or absence of a large peritumoral vessel is an independent, and the dominant, predictor of treatment outcome.

CONCLUSION

The presence of vessels at least 3 mm in size contiguous to hepatic tumors is a strong independent predictor of incomplete tumor destruction by RF ablation. Modified ablation strategies should be considered to improve destruction of these tumors.

Percutaneous pulmonary radiofrequency ablation: difficulty achieving complete ablations in big lung lesions

The size of both primary and metastatic lung tumours often exceeds 3 cm in diameter at the time of diagnosis. The radiofrequency (RF) electrodes of the three leading companies currently in use are designed for a maximum ablation diameter of 5 cm. Therefore, the tumour to be ablated should not exceed 3 cm in maximum diameter, as a 1 cm safety ablation margin surrounding the tumour should ideally be achieved. A possible solution in treating larger tumours is to create overlapping ablations, a method successfully used in the radiofrequency ablation (RFA) of liver tumours. We report on the percutaneous overlapping ablation of three large lung metastases, 4 cm, 4.5 cm and 5 cm in their longest diameter. The largest of them showed incomplete ablation with residual viable tumour tissue. The overlapping percutaneous RFA of large lung tumours is feasible although the bigger the lesion, the higher the risk of incomplete ablation appears compared with smaller tumours treated by a single ablation.

Radiofrequency Ablation in a Previously Irradiated Liver

A patient with renal cell carcinoma underwent external-beam radiation therapy (XRT) to treat a painful chest-wall metastasis. One month later, she underwent radiofrequency (RF) ablation of two metastatic deposits within the liver; one of the target lesions was in the recent irradiation zone and the other was outside of the radiation field. RF ablation within the irradiated liver produced a slightly larger ablation zone with prominent needle tract scarring, and required less energy input than treatment in the unirradiated liver. RF ablation and XRT may interact, possibly producing a synergistic effect. Further study of the potentially adjunctive relationship between these two modalities is warranted.

Adverse events during radiofrequency treatment of 582 hepatic tumors

OBJECTIVE

We describe the rates and potential risk factors of complications of radiofrequency ablation of hepatic tumors. SUBJECTS AND METHODS. Over a 5-year period, 312 patients underwent 350 sessions of radiofrequency ablation (124 intraoperative and 226 percutaneous) for treatment of 582 liver tumors including 115 hepatocellular carcinomas and 467 metastatic tumors. The chi-square test was used for a group-to-group comparison of the occurrence of adverse events.

RESULTS

Thirty-seven (10.6%) adverse events and five (1.4%) deaths were related to radiofrequency treatment. The deaths were caused by liver insufficiency (n = 1), colon perforation (n = 1), and portal vein thrombosis (n = 3). Portal vein thrombosis was significantly (p < 0.00001) more frequent in cirrhotic livers (2/5) than in noncirrhotic livers (0/54) after intraoperative radiofrequency ablation performed during a Pringle maneuver. Liver abscess (n = 7) was the most common complication. Abscess occurred significantly (p < 0.00001) more frequently in patients bearing a bilioenteric anastomosis (3/3) than in other patients (4/223). We encountered five pleural effusions, five skin burns, four hypoxemias, three pneumothoraces, two small subcapsular hematomas, one acute renal insufficiency, one hemoperitoneum, and one needle-tract seeding. The 6.3% of minor complications did not require specific treatment or a prolonged hospital stay. Among the 5.7% major complications, 3.7% required less than 5 days of hospitalization for treatment or surveillance and 2% required more than 5 days for treatment.

CONCLUSION

Radiofrequency ablation of liver tumors is a well-tolerated technique, but caution should be exercised when treating patients with a bilioenteric anastomosis, and radiofrequency ablation during vascular occlusion in cirrhotic livers should be avoided.

Image-guided tumor ablation: proposal for standardization of terms and reporting criteria

The field of image-guided tumor ablation requires standardization of terms and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments with different technologies, such as chemical ablation (ethanol or acetic acid) and thermal therapies, such as radiofrequency, laser, microwave, ultrasound, and cryoablation. On the basis of this premise, a working committee was established with the goal of producing a proposal on such standardization. The intent of the Working Group is to provide a framework that will facilitate the clearest communication between investigators and will provide the greatest flexibility in comparisons between the many new, exciting, and emerging technologies. The members of the Working Group now propose a vehicle for reporting the various aspects of image-guided ablation therapy, including classifications of therapies and procedures, appropriate descriptors of image guidance, and terms to define imaging and pathologic findings. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's hope and intention that adherence to the recommendations of this proposal will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and ultimately to improved patient outcomes.