Methods, medical probe kits, and systems are provided for treating a tissue region within a patient, e.g., a margin of tissue surrounding an interstitial space created by removing abnormal tissue. A delivery cannula is introduced within the patient. A hydrophilic electrode is advanced through the cannula adjacent the tissue region, e.g., within the interstitial cavity. An ablation probe is advanced though the cannula into contact with the hydrophilic electrode, and ablation energy is conveyed from the ablation probe into the tissue region via the hydrophilic electrode.