Stereotactic radiotherapy (radiosurgery). Methods, indications, results

Background: Stereotaxy is a method to determine a point in the patient's bo dy by an external coordinate system which is attached to the patient. Radio surgery uses this method for precise delivery of a high single radiation do se to the patient. The aim is to destroy the tissue in the target and to sp are surrounding unaffected normal tissue by a steep dose gradient. Methods: Three techniques of percutaneous radiosurgery are available: radio surgery with ion beams with a cyclotron, spherical arrangement of cobalt-60 sources, the so-called Gamma-knife, and an adapted linear accelerator. The availability and the good clinical experience lead to a wide spread use of linear accelerator for radiosurgery in recent years. A subsequent developm ent is fractionated stereotactic radiotherapy which combines the precision of radiosurgery with the radiobiological advantage of fractionation. Results: Only a few indications for radiosurgery are proven by statisticall y valid studies. One of these is the treatment of small arteriovenous malfo rmation, where obliteration rates of 80% to 100% are reported with only min or toxicity. However, the obliteration rate is reduced significantly in lar ge arteriovenous malformations. A local control rate of 90% is obtained aft er radiosurgery of brain metastases which is comparable to the results of m icrosurgical resection followed by adjuvant whole brain radiotherapy. An on going EORTC study evaluates the role of adjuvant whole brain radiotherapy a fter radiosurgery. The survival of the patients with brain metastases is li mited by the existence of progressive extracerebral disease. The role of ra diosurgery in the treatment of benign tumors is currently evaluated in clin ical studies which include: vestibular schwannomas, meningeomas, chordomas and chondrosarcomas and pituitary adenomas. Most of the published studies i nclude only small tumors because radiosurgery is limited by the risk of rad ionecrosis of adjacent normal tissue, which shows a steep dose volume respo nse relationship. Recent developments of stereotactic radiotherapy include the use of mini-multileaf-collimators and clinical studies on stereotactic radiotherapy of extracranial targets. Conclusions: Stereotactic irradiation is a well established treatment techn ique for intracranial tumors and arteriovenous malformations. Methods are a vailable that allow optimization of dose distributions to irregularly shape d tumors for single dose as well as fractionated stereotactic irradiations by linear accelerator. Therefore the therapeutic potential of this techniqu e has increased and enables also the extracerebral application in controlle d clinical studies.