Background: The most common glial tumor is the glioblastoma, and the prognosis remains dismal despite a multimodal therapeutic approach. The role of radiosurgery for the treatment of glioblastomas has been evaluated in several studies with some benefit at the recurrent stage. We evaluate the results of the protocol administered at the Gamma Knife unit administering radiosurgery as a boost to metabolic active parts of the tumor after the patient had completed traditional external beam radiotherapy (XBRT) as part of the Stupp protocol for high-grade gliomas. Methods: This is a retrospective analysis of seven patients with newly diagnosed glioblastomas who were treated with Gamma Knife radiosurgery as a boost after receiving XBRT as part of the Stupp protocol. The target of radiation was determined according to the findings of the C-methionine PET scan in relation to magnetic resonance images. The primary end point of this study was to determine the progression-free survival (PFS) from the time of diagnosis. Results: The median age of patients was 48.8 years and the mean Karnofsky performance score was 92.8%. The median PFS was 12.4 months. No radiation adverse effects were documented. Conclusion: Stereotactic radiosurgery is safe to use in the upfront treatment for these patients and appears to have a beneficial role in improving the PFS. This beneficial role seems to be conditioned not only by the time the treatment is administered but also where the radiation dose is targeted to.