US-Guide Microwave and Radiofrequency Ablation for Liver Tumors

Abstract

Hepatocellular carcinoma and hepatic metastases are the common malignancy in Taiwan. Surgical resection remains the reference standard in the treatment of malignant liver tumors; however, a large number of patients have disease that is not amenable to surgical therapy. Therefore, several ablative treatment modalities have been developed for local control of liver tumors in patients with malignant hepatic tumors. Radiofrequency ablation (RFA) is the most frequently used of these methods because of its effectiveness, safety in both percutaneous and surgical settings, and relative ease of use. However, RFA is fundamentally restricted by the need to conduct electric energy into the body. The majority of tissue heating is thus due to thermal conduction, which decreases exponentially away from the source. RFA is most effective in the treatment of the hepatic tumors smaller than 3cm. Using multi-probes with switch-controller RFA system can create a larger ablated area for the malignant tumor and can enhance the therapeutic effect in the treatment of medium size (3 to 5 cm) malignant hepatic tumors. Microwave (MW) ablation offers many of the advantages of RF ablation while possibly overcoming some of the limitations. Since MW ablation does not rely on conduction of electricity into tissue, it is not limited by charring. Therefore, temperatures greater than 100°C are readily achieved, which potentially results in a larger zone of ablation, faster treatment time, and more complete tumor kill. In addition, MW ablation has a much broader power field than does RF ablation. This may allow for larger zones of thermal ablation and a more uniform tumor kill. Because the cooling effect of blood flow is most pronounced within the zone of conductive rather than active heating, a larger power field may also enhance treatment of perivascular tumors. MW ablation and multiple-probes RFA with switch controller are both promising new options in the treatment of malignant hepatic neoplasms.