HSV-tk + Valacyclovir + SBRT + Chemotherapy for Recurrent GBM

This trial is testing a gene therapy approach combined with radiation and chemotherapy for people whose brain tumor (glioblastoma or a related aggressive brain cancer) has come back after previous treatment. The gene therapy involves injecting a viral gene into the tumor, then giving an antiviral drug that turns the gene into a cancer-killing agent. **You may be eligible if...** - You have been diagnosed with recurring glioblastoma (GBM) or anaplastic astrocytoma, confirmed by biopsy or imaging - Your cancer has returned and shows up on scans as a single, localized area (not in multiple spots) - You are in good general health (ECOG 0-1) - It has been at least 3 weeks since your last surgery, radiation, or systemic treatment - You have a life expectancy of at least 12 weeks **You may NOT be eligible if...** - Your tumor has spread to multiple areas or involves the brainstem - You are pregnant - You have had recent major surgery within the last 3 weeks - Your general health is poor Talk to your doctor to see if this trial is right for you.