RFA is executed antiangiogenic with the use of a percutaneously inserted electrode, typically under imaging guidance, which deposits energy in the form of an alternating electrical current to cause focal coagulation necrosis. Heat energy is distributed radially within the target tissue and a margin of normal tissue surrounding the tumor . Yamakado et al. assessed 155 unresectable lung metastases from colorectal cancer in 71 patients treated with RFA. The 3-year overall survival was 46% and intrapulmonary recurrence occurred in 47% of patients in this cohort. Patients who had no extrapulmonary metastases and tumors ��3cm had a 3-year survival of 78%. On multivariate analysis, extrapulmonary metastasis (P < 0.02, CI 1.3�C14.8) and tumor size >3cm (P < 0.001, CI 3.4�C52.6) lead to decreased survival.
Pneumothorax, typically self-limited or requiring short term small bore chest tube, was the most common complication occurring in 37% of patients . Nakamura et al. retrospectively reviewed 20 patients with 89 pulmonary metastases from sarcomas. The median followup was 18 months, in which the median survival was 12.9 months and the 3-year survival rate was 29%. The only prognostic indicator on univariate and multivariate analyses in this study was the ability to ablate all lung tumors. Patients with complete ablation of all tumors had a 1- and 3-year survival rate of 88.9% and 59.2%, respectively. Pneumothorax again was the most common complication, which occurred in 38% of patients. Thus, the authors concluded that RFA for pulmonary metastases was a safe and beneficial therapeutic option for appropriate candidates .
3.2. Cryoablation Whereas RFA applies heat to treat the targeted tissue, cryoablation exposes tumors to freezing temperatures to treat various malignancies. Cryoablation involves the insertion of dual chamber probe(s) into the target tissue. Typically, high pressure argon gas, which is supplied by a large in-room tank, is passed through the probe. Within a few seconds, there is rapid expansion and cooling, which leads to the production of temperatures of approximately ?100��C. This generates a ball of ice up to 3.5cm in size (Figures 3(a)-3(b)). Cell death is known to occur when temperatures are below ?20��C. Multiple probes can be used to allow for the creation of larger balls of ice and, thus, the treatment of larger lesions .
Figure 3 Recurrent hepatocellular carcinoma after right lobe resection (a) and ablation zone (b). Cell death from cryoablation is due to ice formation within the cell through immediate freezing of tissue adjacent to the probe. Gradual cooling away GSK-3 from the probe causes osmotic variation between the cell and membrane, leading to cell dehydration and eventual death . Cryoablation has been utilized in the treatment of liver metastasis, particularly from colorectal primaries. Weaver et al.