the longitudinal axis of the apparatus shaft this pitched slot translates the radial movement of the push paddle 52 to a longitudinal movement or travel of the central shaft 36 the pitch of the slot is calibrated to provide a predetermined longitudinal movement of the shaft corresponding to specific radial movement of the push paddle for example movement of the push paddle through 180 degrees results in 0 060 inch travel for the central shaft 36 relative to the outer shaft 40 in use once the tip 20 has been located in the tissue to be treated the outer shaft 40 is preferably fixed relative to the patient or relative to the tissue being treated by means of a stereotactic frame 195 fig1 or similar device movement of the central shaft 36 in a proximal direction relative to the outer shaft 40 along the longitudinal axis of the body 10 simultaneously opens the valve means 38 and expands the dam 81 at the distal end of the body 10 this longitudinal movement of the central shaft 36 is controlled by radial movement of the push paddle which can be connected to the central shaft 36 and the terminal fixture 49 in any suitable way such that the necessary movement of the central shaft can be effected embodiments of the apparatus having one two three or more shafts are contemplated by the inventors for example instead of an apparatus having three coaxial shafts with one shaft controlling the dam expansion an apparatus could be constructed having only one or two shafts with.