A method for performing intraocular brachytherapy and an apparatus for performing the same is disclosed. The apparatus preferably comprises a hand-held delivery device that advances a radiation source into an associated cannula or probe that is positioned adjacent the target tissue. The handpiece provides for shielded storage of the radiation source when retracted from the cannula and includes a slider mechanism for advancing and retracting the radiation source. The radiation source is mounted to a wire that has a flexible distal end and a relatively stiffer proximal end. A positioning system for the cannula is also disclosed.