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 ϭ 9) and a 17-gauge cooled radiofrequency (RF) electrode (n ϭ 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 Ͻ .05 was considered to indicate a significant difference. Results:Mean diameter (3.32 cm Ϯ 0.19 [standard deviation] vs 2.70 cm Ϯ 0.23, P Ͻ .001) was 25% larger with microwave ablation and mean cross-sectional area (8.25 cm 2 Ϯ 0.92 vs 5.45 cm 2 Ϯ 1.14, P Ͻ .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 Ϯ 0.06 vs 0.82 Ϯ 0.09; P Ͻ .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.

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.

A single generator may effectively deliver microwave power to multiple antennas. Large volumes of tissue may be ablated and large vessels coagulated with multiple-antenna ablation in the same time as single-antenna ablation.

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.

Thermal ablation is increasingly utilized in the treatment of primary and metastatic liver tumors, both as curative therapy and as a bridge to transplantation. Recent advances in high-powered microwave ablation systems have allowed physicians to realize the theoretical heating advantages of microwave energy compared to other ablation modalities. As a result, there is a growing body of literature detailing the effects of microwave energy on tissue heating, as well as its effect on clinical outcomes. This article will discuss the relevant physics, review current clinical outcomes and then describe the current techniques used to optimize patient care when using microwave ablation systems.