A standard treatment for glioblastoma is a combination of radiation and the drug temozolomide. This combination sometimes causing swelling (inflammation) of the brain tissue. When standard monitoring with MRI or CT scans is done within a few months of finishing treatment, it may be hard to tell if the scans are showing post-treatment brain inflammation or tumor growth and worsening of disease. Currently the only way to definitively distinguish inflammation from tumor growth is biopsy.