An RF treatment system includes first and second catheters with first and second needle electrodes positioned at least partially in lumens of the first and second catheters. Each electrode is surround by a insulator sleeve which is slideable along the electrode and defines an ablation surface. An RF power source is coupled to the first and second needle electrodes. The electrodes provide bipolar RF ablation between the two, defining an ablation volume. A deflectable introducer has a laterally deflectable distal end and an ablation volume temperature sensor positioned at the distal end. The deflectable introducer is advanced in and out of the electrodes distal ends to measure a temperature of tissue in the ablation volume. The treatment system can include more than two electrodes, such as two pairs of electrodes. Further, the system can include a needle electrode extension with a laterally deflectable distal end. The needle electrode extension is positioned in at least one of the distal ends of one of the needle electrodes. It is advanced in and out of the needle electrode distal end to provide monopolar ablation. Additionally, the RF treatment system provides for the introduction of an infusion media, including but not limited to a chemotherapeutic agent, through distribution ports in the needle electrodes, or through one or more infusion devices that can house the needle electrodes and their respective catheters.