Stereotactic radiosurgery and radiotherapy: new developments and new directions.

Stereotactic irradiation is a precise method for the delivery of focused radiation beams to small intracranial targets. Treatment can be administered in single or multiple fractions (radiosurgery or stereotactic radiotherapy, respectively). The technology has evolved rapidly because of advances in both hardware and software design. Clinical indications are unfolding through the prospective trial mechanism.