THE GAMMA-KNIFE AND ITS ROLE IN NEUROSURGERY

The gamma knife is a stereotactic radiosurgery device which allows wel l defined, deep seated brain tumors, or arterio venous malformations h aving a diameter of less than 3 cm, to be treated in a single session under local anesthesia. This technique, which was first described over 40 years ago, has undergone major development in recent years and is the most commonly used method for radiosurgery worldwide. The principl e relies on the overlapping of narrow collimated beams from 201 cobalt -60 sources. The technique, which was introduced into Switzerland in S eptember 1994, has rapidly gained recognition. 184 patients have been treated by 30 April 1997. An average follow-up period of 15 months is much too short for analysis of patients treated by radiosurgery. Howev er, our series of benign tumors shows stabilization of volume in the f irst few months followed by a slow reduction of the tumor volume, in a ll but two cases. The gamma knife represents the treatment of choice f or recurrent and unsuccessfully operated patients with endocrine activ e pituitary adenomas. With brain metastases, a rapid reduction in tumo r volume is seen in the first few weeks in the majority of cases. The tumor volume may then remain stable or reduce further until complete d isappearance. In the case of arteriovenous malformations complete obli teration of the nidus is not seen, on average, for 2-3 years. Individu al patient follow-up studies illustrate these results. To date our res ults have shown zero morbidity and mortality. International statistics from 58 766 cases (as of December 1996) from 77 gamma knife centers d emonstrate the value of this technique as a complement or, depending o n the indication, an alternative to classical microsurgery.