[Radiofrequency ablation of liver and lung tumors]

Radiofrequency ablation is an image-guided technique of percutaneous tumor destruction using high frequency alternating current. Accuracy in needle placement and the selection of the imaging modality are key elements of the success of the procedure. The volume of ablation with a single needle insertion is limited to about 40 mm and the technique is most successful for tumors less than 3 cm in diameter with rapid decrease in efficacy for larger tumors. Tumors further away from large vessels are also more efficiently treated with this technique since heat loss from flowing blood in nearby vessels larger than 3mm causes a four-fold increase in treatment failure. Under the best of circumstances (tumor less than 25 mm, away from vessels), RF ablation and surgical tumorectomy have respective failure rates of 6% and 7,3%. RF ablation of an isolated liver metastasis less than 4 cm in diameter results in survival rates at 1, 3 and 5 years of 97%, 84% and 40% respectively. In the liver, follow-up imaging is performed to detect residual tumor characterized by early enhancement. Thin peripheral enhancement (less than 1mm) of the necrotic area and well-defined triangular shaped regions of enhancement are not signs of tumor recurrence but indicate the presence of inflammation or arterial to portal venous fistula. In the lung, an area of ground glass attenuation four times larger than the initial tumor is a predictive factor of success. PET-CT is the best imaging modality for follow-up of lung lesions following RF ablation.