Paul F. Laeseke

Pulmonary Thermal Ablation: Comparison of Radiofrequency and Microwave Devices by Using Gross Pathologic and CT Findings in a Swine Model

PURPOSE To compare the performance of equivalently sized radiofrequency and microwave ablation applicators in a normal porcine lung model. MATERIALS AND METHODS All experiments were approved by an institutional animal care and use committee. A total of 18 ablations were performed in vivo in normal porcine lungs. By using computed tomographic (CT) fluoroscopic guidance, a 17-gauge cooled triaxial microwave antenna (n = 9) and a 17-gauge cooled radiofrequency (RF) electrode (n = 9) were placed percutaneously. Ablations were performed for 10 minutes by using either 125 W of microwave power or 200 W of RF power delivered with an impedance-based pulsing algorithm. CT images were acquired every minute during ablation to monitor growth. Animals were sacrificed after the procedure. Ablation zones were then excised and sectioned transverse to the applicator in 5-mm increments. Minimum and maximum diameter, cross-sectional area, length, and circularity were measured from gross specimens and CT images. Comparisons of each measurement were performed by using a mixed-effects model; P < .05 was considered to indicate a significant difference. RESULTS Mean diameter (3.32 cm +/- 0.19 [standard deviation] vs 2.70 cm +/- 0.23, P < .001) was 25% larger with microwave ablation and mean cross-sectional area (8.25 cm(2) +/- 0.92 vs 5.45 cm(2) +/- 1.14, P < .001) was 50% larger with microwave ablation, compared with RF ablation. With microwave ablation, the zones of ablation were also significantly more circular in cross section (mean circularity, 0.90 +/- 0.06 vs 0.82 +/- 0.09; P < .05). One small pneumothorax was noted during RF ablation but stabilized without intervention. CONCLUSION Microwave ablation with a 17-gauge high-power triaxial antenna creates larger and more circular zones of ablation than does a similarly sized RF applicator in a preclinical animal model. Microwave ablation may be a more effective treatment of lung tumors.

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°C are achieved, with cell death due to coagulative necrosis occurring above 50°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.

Breast Cancer Liver Metastases: US-guided Percutaneous Radiofrequency Ablation—Intermediate and Long-term Survival Rates

PURPOSE To retrospectively assess the local control and intermediate- and long-term survival of patients with liver metastases from breast cancer who have undergone percutaneous ultrasonography (US)-guided radiofrequency (RF) ablation. MATERIALS AND METHODS This study was approved by the hospital ethics committee, and all patients provided written informed consent. RF ablation was used to treat 87 breast cancer liver metastases (mean diameter, 2.5 cm) in 52 female patients (median age, 55 years). Inclusion criteria were as follows: fewer than five tumors, maximum tumor diameter of 5 cm or smaller, and disease either confined to the liver or stable with medical therapy. Forty-five (90%) of 50 patients had previously undergone chemotherapy, hormonal therapy, or both, and had no response or an incomplete response to the treatment. Contrast material-enhanced computed tomography and US were performed to evaluate complications and technical success and to assess for local tumor progression during follow-up. The Kaplan-Meier method was used to assess survival, and results were compared between groups with a log-rank test. Cox regression analysis was used to assess independent prognostic factors that affected survival. RESULTS Complete tumor necrosis was achieved in 97% of tumors. Two (4%) minor complications occurred. Median time to follow-up from diagnosis of liver metastasis and from RF ablation was 37.2 and 19.1 months, respectively. Local tumor progression occurred in 25% of patients. New intrahepatic metastases developed in 53% of patients. From the time of first RF ablation, overall median survival time and 5-year survival rate were 29.9 months and 27%, respectively. From the time the first liver metastasis was diagnosed, overall median survival time was 42 months, and the 5-year survival rate was 32%. Patients with tumors 2.5 cm in diameter or larger had a worse prognosis (hazard ratio, 2.1) than did patients with tumors smaller than 2.5 cm in diameter. CONCLUSION Survival rates in selected patients with breast cancer liver metastases treated with RF ablation are comparable to those reported in the literature that were achieved with surgery or laser ablation.

Microwave ablation with a triaxial antenna: results in ex vivo bovine liver

We apply a new triaxial antenna for microwave ablation procedures to an ex vivo bovine liver. The antenna consists of a coaxial monopole inserted through a biopsy needle positioned one quarter-wavelength from the antenna base. The insertion needle creates a triaxial structure, which enhances return loss more than 10 dB, maximizing energy transfer to the tissue while minimizing feed cable heating and invasiveness. Numerical electromagnetic and thermal simulations are used to optimize the antenna design and predict heating patterns. Numerical and ex vivo experimental results show that the lesion size depends strongly on ablation time and average input power, but not on peak power. Pulsing algorithms are also explored. We were able to measure a 3.8-cm lesion using 50 W for 7 min, which we believe to be the largest lesion reported thus far using a 17-gauge insertion needle.

Microwave Ablation versus Radiofrequency Ablation in the Kidney: High-power Triaxial Antennas Create Larger Ablation Zones than Similarly Sized Internally Cooled Electrodes

PURPOSE To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than radiofrequency (RF) ablation with similarly sized internally cooled electrodes. MATERIALS AND METHODS Twenty-eight 12-minute ablations were performed in an in vivo porcine kidney model. RF ablations were performed with a 200-W pulsed generator and either a single 17-gauge cooled electrode (n = 9) or three switched electrodes spaced 1.5 cm apart (n = 7). Microwave ablations were performed with one (n = 7), two (n = 3), or three (n = 2) 17-gauge triaxial antennas to deliver 90 W continuous power per antenna. Multiple antennas were powered simultaneously. Temperatures 1 cm from the applicator were measured during two RF and microwave ablations each. Animals were euthanized after ablation and ablation zone diameter, cross-sectional area, and circularity were measured. Comparisons between groups were performed with use of a mixed-effects model with P values less than .05 indicating statistical significance. RESULTS No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm(2)) and single-antenna microwave (mean area, 10.9 cm(2)) ablation zones were significantly larger than single-electrode RF zones (mean area, 5.6 cm(2); P = .001 and P = .0355, respectively). No significant differences were detected between single-antenna microwave and multiple-electrode RF. Ablation zone circularity was similar across groups (P > .05). Tissue temperatures were higher during microwave ablation (maximum temperature of 123 degrees C vs 100 degrees C for RF). CONCLUSIONS Microwave ablation with high-power triaxial antennas created larger ablation zones in normal porcine kidneys than RF ablation with similarly sized applicators.

Unintended thermal injuries from radiofrequency ablation: protection with 5% dextrose in water.

OBJECTIVE Radiofrequency ablation of hepatic tumors can lead to thermal injury of surrounding structures. Both saline and 5% dextrose in water (D5) have been used to displace these surrounding structures before radiofrequency ablation. The purpose of this study was to determine the relative effectiveness of these two fluids for protecting the diaphragm and lung during radiofrequency ablation. MATERIALS AND METHODS Ten female domestic swine (mean weight, 45 kg) underwent radiofrequency ablation at open surgery. Group 1 (n = 12 lesions) was pretreated with peritoneal D5 before radiofrequency ablation. Group 2 (n = 11 lesions) was pretreated with peritoneal 0.9% saline. A 2.7-mm spacer was placed between the liver surface and diaphragm in groups 1 and 2. Group 3 (n = seven lesions) served as a control group with no pretreatment regimen. Group 4, an additional control group (n = eight lesions), consisted of animals pretreated with D5 in which a larger spacer was used. After radiofrequency ablation, the animals were sacrificed and the liver, diaphragm, and lung were removed. The extent of thermal injury to the surface of each organ was recorded. RESULTS The animals in the D5 and saline pretreatment groups experienced fewer diaphragm injuries than the control animals (D5, p = 0.02). The smallest lesions in the lung and diaphragm were in the D5 group, followed by the saline and control groups (diaphragm, p = 0.0001; lung, p = 0.13). Diaphragm lesions were significantly smaller in the D5 and saline groups than in the control group (p = 0.0001 and 0.01, respectively). CONCLUSION Instillation of D5 into the peritoneal cavity before hepatic radiofrequency ablation decreases the risk and severity of diaphragm and lung injuries compared with no pretreatment or pretreatment with 0.9% saline in this animal model. Pretreatment with D5 may increase both the safety of and the number of patients eligible for treatment with thermal therapies.

Radiofrequency Ablation of Peripheral Liver Tumors: Intraperitoneal 5% Dextrose in Water Decreases Postprocedural Pain

OBJECTIVE Our objective was to evaluate the clinical efficacy of the intraperitoneal instillation of 5% dextrose in water (D5W) during radiofrequency ablation of peripheral liver tumors for decreasing postradiofrequency pain and narcotic use. MATERIALS AND METHODS This case-control study compared the hospital course of the last 20 patients to undergo radiofrequency ablation of peripheral liver tumors at our institution. Ten consecutive subjects in the D5W group (seven women and three men; age range, 37-78 years; mean, 58 years) were pretreated with intraperitoneal D5W (average, 963 +/- 436 [SD] mL) before the ablation. This group was compared with a control group of 10 patients (five men and five women; age range, 36-73 years; mean, 54 years) who did not receive intraperitoneal D5W. The size of the ablation zone, degree of liver capsule involvement, number of burns, patient-reported pain, patient-controlled analgesia use, and length of hospital stay were recorded and compared between the groups. RESULTS The patients in the D5W group reported significantly less pain in the first 24 hr after the procedure than did the controls (2.3 vs 6.3, p = 0.003) despite a significant decrease in patient-controlled analgesia use (17.3 vs 125.1 mg of morphine, p = 0.003). The differences in pain and patient-controlled analgesia use were greatest in the first 16 hr and decreased over time in both groups. The total volume of ablation (61.9 vs 45.2 cm(3), p = 0.44), liver surface involvement (6.2 vs 6.0 cm, p = 0.73), and number of burns (1.8 vs 1.1, p = 0.14) were slightly higher in the D5W group than in the control group, but this difference was not statistically significant. CONCLUSION Pretreatment with intraperitoneal D5W before radiofrequency ablation of peripheral liver tumors decreased pain, narcotic use, and length of hospital stay. The effect of pretreatment with D5W is greatest in the first 16 hr after the procedure.

Microwave Ablation with Triaxial Antennas Tuned for Lung: Results in an in Vivo Porcine Model

PURPOSE To prospectively determine in swine the size and shape of coagulation zones created in normal lung tissue by using small-diameter triaxial microwave antennas and to prospectively quantify the effects of bronchial occlusion and multiple antennas on the coagulation zone. MATERIALS AND METHODS The study was approved by the research animal care and use committee, and all husbandry and experimental studies were compliant with the National Research Councils Guide for the Care and Use of Laboratory Animals. Twenty-four coagulation zones (three per animal) were created at thoracotomy in eight female domestic swine (mean weight, 55 kg) by using a microwave ablation system with 17-gauge lung-tuned triaxial antennas. Ablations were performed for 10 minutes each by using (a) a single antenna, (b) a single antenna with bronchial occlusion, and (c) an array of three antennas powered simultaneously. The animals were sacrificed immediately after ablation. The coagulation zones were excised en bloc and sectioned into approximately 4-mm slices for measurement of size, shape, and circularity. Analysis of variance and two-sample t tests were used to identify differences between the three ablation groups. RESULTS The overall mean diameters of coagulation achieved with a single antenna and bronchial occlusion (4.11 cm +/- 1.09 [standard deviation]) and with multiple-antenna arrays (4.05 cm +/- 0.69) were significantly greater than the overall mean diameter achieved with a single antenna alone (3.09 cm +/- 0.83) (P = .016 for comparison with multiple antennas, P = .032 for comparison with bronchial occlusion). No significant differences in size were seen between the coagulation zones created with bronchial occlusion and those created with multiple antennas (P = .68). The coagulation zones in all groups were very circular (isoperimetric ratio > 0.80) at cross-sectional analysis. CONCLUSION A 17-gauge triaxial microwave ablation system tuned for lung tissue yielded large circular zones of coagulation in vivo in porcine lungs. The coagulation zones created with bronchial occlusion and multiple antennas were significantly larger than those created with one antenna.

Prevention of chronic allograft nephropathy with vitamin D.

Chronic allograft nephropathy (CAN) is the leading cause of late allograft loss in kidney transplantation. Interstitial fibrosis and glomerulosclerosis are characteristic of CAN. Transforming growth factor beta‐1 (TGFβ‐1) is associated with both of these histologic findings in the transplant setting. Recent studies have suggested that vitamin D signaling pathways may interact with and regulate TGFβ‐1 mediated events. We examined the efficacy of 1,25‐dihydroxyvitamin D3, the active metabolite of vitamin D [1,25‐(OH)2D3], the active metabolite of vitamin D, as monotherapy to prolong allograft survival and preserve renal function in a rat model of CAN, the Fisher 344 to Lewis model. Recipients went without treatment or were treated with cyclosporine A (CSA; 10 days) or 1,25(OH)2D3 (1000, 500 or 250 ng/kg/day). Grafts were harvested at the time of rejection or at 24 weeks post‐transplant. A portion of the graft was processed for histology and immunohistochemistry and a second portion was analyzed for protein expression by western blotting. Not only did 1,25‐(OH)2D3 treatment significantly prolong graft survival, but it also prevented histological changes associated with CAN. 1,25‐(OH)2D3 treatment significantly decreased Smad 2 expression. This TGFβ signaling molecule is likely involved in fibrosis. Moreover, 1,25‐(OH)2D3 treatment increased Smad 7 expression, an important feedback molecule in the TGFβ‐1 signaling pathway. This suggests that 1,25‐(OH)2D3 interacts with TGFβ‐1 in limiting histological injury in this model of CAN. Furthermore, 1,25‐(OH)2D3, treatment increased expression of matrix metalloproteinase 2 (MMP‐2), thus directly affecting levels of another important matrix molecule. Taken together our data suggests that 1,25‐(OH)2D3 mitigates CAN in this model by altering TGFβ‐1 and matrix‐regulating molecules.

Multiple-Electrode Radiofrequency Ablation of Hepatic Malignancies: Initial Clinical Experience

OBJECTIVE The objective of our study was to retrospectively analyze our initial clinical experience with percutaneous multiple-electrode radiofrequency ablation and evaluate its safety and efficacy for treating hepatic malignancies. MATERIALS AND METHODS Thirty-eight malignant hepatic tumors (mean diameter, 2.7 cm; range, 0.7-10.0 cm) in 23 patients (12 men and 11 women; mean age, 65 years; range, 40-84 years) were treated in 26 radiofrequency ablation sessions with an impedance-based multiple-electrode system. One, two, or three (mean, 2.4) 17-gauge electrodes were placed, and tumors were ablated using a combination of CT and sonography for guidance and monitoring. Electrodes were placed in close proximity (mean spacing: two electrodes, 1.0 cm; three electrodes, 1.4 cm) to treat large tumors or were used independently to treat several tumors simultaneously. Contrast-enhanced CT scans were obtained immediately after ablation to determine technical success and evaluate for complications. Follow-up CT scans at 1, 3, 6, 9, and 12 months (mean, 4 months) after ablation were obtained to assess for tumor progression and new metastases. RESULTS Local control was achieved in 37 of 38 tumors, 34 of which were treated in one session. Ablations created with closely spaced electrodes had a mean diameter of 4.9 cm. The total ablation time was reduced by approximately 54% compared with an equivalent number of ablations performed with a single-electrode system (1,014 vs 2,196 minutes). Three complications occurred: one death from a presumed postprocedure pulmonary embolus, one pneumothorax, and one asymptomatic perihepatic hemorrhage. CONCLUSION Multiple-electrode radiofrequency ablation appears to be a safe and effective means of achieving local control in large or multiple hepatic malignancies at short-term follow-up.