An invasive medical device for delivery radio frequency energy to a target tissue region includes an elongate delivery cannula having a lumen in communication with a distal opening. A deployment member is positioned and longitudinally movable in the lumen. An array of electrode elements are secured to a distal end of the deployment member, the deployment member being movable from a delivery position, in which the electrode elements are positioned within the lumen, to a deployed position, in which the electrode elements extend distally out of the cannula distal opening. A sealing member formed from a biocompatible material sufficiently rigid to penetrate solid body tissue partially extends from, and substantially seals, the distal cannula opening when the deployment member is in the delivery position. By way of examples, the sealing member may be carried on a distal end of the deployment member, or on a separately movable deployment member, or frictionally fit in the cannula distal opening.