Supratentorial glioblastoma multiforme (GBM) is a lethal malignancy. Subtotal surgical resection and post operative external beam radiotherapy palliate symptoms and prolong survival, but very few patients survive more than 3 years following diagnosis.‘,3,20*32,43,46,48*5’*58,66 Whereas the probability of survival of supratentorial anaplastic astrocytoma (AA) is slightly better, most patients will still succumb to the tumor.58-60*66 The resistance of these neoplasms to conventional therapies has prompted many physicians to undertake new clinical and laboratory investigations. These have included the use of chemotherapy,44 immunotherapy,40 multiple-fraction-perday radiotherapy,2’,34,49 radiotherapy with chemical radiosensitizers,6’ and neutron radiotherapy.45 As interest in the biology and treatment of malignant gliomas has increased, many conceptual verities have been proposed to guide therapeutic investigations, These include the significance of the cellular heterogeneity of AA and GBM,‘2,24 the presence of the blood-brain-barrier (BBB) as a functional obstruction to chemotherapy, and the local nature of these tumors. In this editorial, we focus on the last of these premises. We have selected this issue because of its major implications for any treatment that is directed at a specific portion of the brain rather than the whole brain: BBB disruption, intracarotid drug administration, and brain brachytherapy. Interstitial brachytherapy is used for primary and recurrent GBM and AA. The technique consists of the stereotactic computed tomography (CT) or magnetic resonance imaging (MRI) guided placement of coaxial catheters within and around the tumor. Radioactive sources are after-loaded into the catheters to deliver continuous low-dose rate irradiation. After a specified dose is delivered, the system is removed.22~27~28~39~45 Interstitial hyperthermia generated by implanted microwave antennae may be administered in conjunction with the radiation.52 One of the justifications invoked for brachytherapy is the concept of malignant gliomas as localizedlesions. Allusions to this concept abound in the literature. “Most malignant gliomas are localized to a single area of the brain, central nervous system (CNS) metastases from these tumors are uncommon and systemic metastases are rare.“29 “Since an astrocytoma is almost invariably a nonmetastatizing single mass, ideally it should lend itself best to regional treatment.“** “Because a primary brain tumor is most often a localized disease, hyperthermia, intratumoral chemotherapy, and interstitial irradiation, the stereotactic placement of radioactive sources directly into brain tumors, have been suggested as possible local treatments for brain tumors.“*’