RESEARCH COMMUNICATION Microwave Ablation Treatment of Liver Cancer with a 2,450- MHz Cooled-shaft Antenna: Pilot Study on Safety and Efficacy

Imaging-guided thermal ablation using different energy sources (such as RF, microwave, or laser) continues to gain favor as a minimally invasive technique for the treatment of primary and metastatic hepatic malignant tumors (Ng et al., 2005; Pacella et al., 2005; Cabassa et al., 2006; Clasen et al., 2006; Shibata et al., 2006). Regardless of the primary energy source, all of these modalities induce cellular destruction by means of the direct effects of heat, with irreversible cellular damage occurring at temperatures above 50°C when applied for 4~6 minutes and almost instantaneously at temperatures above 60°C (Goldberg et al., 2006). Thus, the main difference between modalities lies in the ability to translate energy efficiently into heat throughout the entire tumor ablation target volume. During the past decades, most studies have focused on the potential of radiofrequency (RF) ablation, fueled in part by the substantial morbidity and mortality associated with hepatic resection (Lencioni et al., 2005; Tateishi et al., 2005). Results of studies on RF ablation suggest that characteristics of the tissue, such as electrical conductivity, can substantially affect and occasionally retard energy deposition and heating throughout a tumor (Goldberg et al., 2001). Additionally, exponential rises in electrical impedances of tumor tissue may result from the application of high RF current, thus limiting the total amount of energy that can be delivered into tissue (Goldberg et al., 2000).This limits the amount of coagulation that can be