Figure 4a. Radio-frequency ablation treatment strategies. On the basis of a 3-cm-diameter spherical thermal injury created by a single ablation, the following three ablation strategies can be used to treat most tumors. (a) Schematic illustrates how tumors less than 2 cm can easily be treated with one ablation. The active elements of the ablation needle are centered across the tumor. (b) Schematic shows how tumors 2-3 cm in diameter are treated by six overlapping ablations. Four ablations are performed in the x-y plane, and two are performed along the z axis. All ablations are positioned to touch the center of the tumor. If placed correctly, the ablations create an inner spherical injury that measures 3.7 cm in diameter. (c) Schematic depicts systematically overlapped "thermal cylinders," which are a more effective way to ablate large tumors, rather than creating random overlapping ablations (such as seen in b). Each cylinder is created by overlapping individual ablations along a single needle tract from the deepest to the most superficial portions of a tumor. Each ablation and thermal cylinder is overlapped by 50%.