Tissue ablation probes, systems, and methods are provided for treating tissue (e.g., a tumor). The probe comprises an inner probe shaft, and an outer probe shaft disposed around the inner probe shaft. The outer probe shaft has a distal portion fixably mounted to the inner probe shaft, and a proximal portion rotatably mounted to the inner probe shaft. The probe further comprises a coiled ablation electrode disposed between the proximal portion and the distal portion. The electrode is configured for unwinding when the proximal portion rotates about the inner probe shaft in one direction, thereby placing the electrode in a radially expanded geometry, and configured for winding when the proximal portion rotates about the inner probe shaft in another opposite direction, thereby placing the electrode in a radially collapsed geometry.
