The role of gamma knife radiosurgery in the treatment of primary and metastatic brain tumors.

With the widespread diffusion of stereotactic radiosurgical procedures, GKR treatments have gained considerable momentum as a major therapeutic option for patients harboring primary or metastatic brain tumors. Present results in high grade gliomas indicate a potential palliative role of this technique. The overall low radiosensitivity of these oncotypes and their infiltrative nature-with the resulting problems in properly defining the tumor target-are still a major obstacle to further development of the approach. In this regard, useful contributions are expected from advances in molecular neurobiology and functional neuroimaging as shown by preliminary investigations with MR spectroscopy. Surgery maintains a dominant role in the therapeutic armamentarium for low grade gliomas. However, in unfavorable cases (unresectable tumors, recurrences), GKR seems to be an effective alternative to conventional radiochemotherapy. In grade 2 astrocytomas and specifically in grade 1 pilocytic forms, short-to-mid-term reported studies have documented encouraging 70 to 93% local tumor control rates, with minimal cerebral toxicity. Finally, during the last decade, GKR has become a primary treatment choice for patients harboring small-to-medium-size brain metastases, with reasonable life expectancy and no impending intracranial hypertension. Focal tumor responses are consistently elevated, even in the most radioresistant oncotypes (melanoma, renal carcinoma); median and actuarial survival rates are far better than with conventional radiation treatments and are comparable to those observed in accurately selected surgical-radiation series.