1. A method of percutaneous treatment of a prostate lesion using radio frequency, comprising: with an imaging device, acquiring an image of a patient's prostate; identifying within the patient's prostate at least one location to be treated; selecting a bipolar electrode assembly for radio frequency treatment, the assembly comprising an outer helical electrode and an inner electrode arranged concentric with the outer helical electrode; representing a planned target region on the image of the patient's prostate, comprising a graphical representation of at least an active part of the outer helical electrode superimposed on the image at a target position, wherein the planned target region encloses at least in part the at least one location to be treated; positioning the bipolar electrode assembly in proximity of a patient's perineum, comprising positioning a guiding member in proximity of the patient's perineum, the guiding member comprising an outer member, an inner member, a first through-passage between the outer member and the inner member, and a second through-passage arranged through the inner member; determining an external starting position of the bipolar electrode assembly outside the patient by projecting the graphical representation along a direction of insertion; positioning the guiding member according to the graphical representation projecting along the direction of insertion; disposing the outer helical electrode in the first through-passage and inserting the outer helical electrode percutaneously into the patient's prostate; disposing the inner electrode through the second through-passage, and inserting the inner electrode percutaneously into the patient's prostate; wherein the guiding member maintains a position outside the patient during insertion of the outer helical electrode and the inner electrode; and capturing the outer helical electrode that is inserted into the patient's prostate with the imaging device and then displaying the outer helical electrode with the planned target region on the image of the patient's prostate so as to obtain a direct verification of a degree of match between a position of the outer helical electrode and the planned target region.