STEREOTAXIC RADIOSURGERY

Radiosurgery aims at the precise destruction of small, defined volumes of tissue by employing ionizing radiation energy. Its methodologies m ay be subdivided into closed-skull, external focussed beam radiosurger y, and interstitial radiosurgery (brachytherapy). Focussed beam stereo tactic radiosurgery has been used successfully for over two decades to treat cerebral arteriovenous malformations. Complete obliteration ran ges from 30 % to 50 % after one year. After two years, obliteration is observed in up to 90 % of patients. Outcome, however, is influenced b y patient selection. In the treatment of acoustic neurinomas, follow-u p data of larger series show that radiosurgery performed under local a nesthesia on an out-patient basis is competitive with microsurgery dat a. Using multiple isocenters and magnetic resonance localization, tumo r growth control is achieved in more than 90 % of patients with preser vation of hearing in approximately 50 %. Pituitary tumors with Cushing 's syndrome, acromegaly, Nelson's syndrome, prolactinomas and non-secr eting adenomas have been treated. Only a small subgroup of patients wi th low-grade gliomas are candidates for interstitial radiosurgery, nam ely those with circumscribed tumors with limited spread of tumor cells into the periphery. For this subgroup, which usually comprises not mo re than 25 % of all low-grade gliomas, interstitial radiosurgery compe tes with surgical resection. Local, single high-dose treatment remains controversial for highly malignant infiltrative tumors, and a signifi cant treatment benefit remains to be demonstrated. Radiosurgery can be used to effectively treat solitary brain metastases (less than or equ al to 3 cm diameters) with less invasiveness, and dissection of normal tissue; it may be performed with lower morbidity and with less expens e in comparison with open surgery.