Evaluating Tumor Pseudoprogression With FLT-PET and MRI

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. However, biopsy is an invasive procedure that is associated with risks. Having a non-invasive method to distinguish post-treatment inflammation from tumor growth can help improve care for patients with glioma. For the PET scans in this research study, the investigators are using a radioactive substance called FLT (3'-deoxy-3'-\[F-18\] fluorothymidine), instead of the standard substance FDG (fluorodeoxyglucose). FLT gets absorbed by cancer cells but not by areas of inflammation. Because of that FLT may be better than FDG in differentiating cancer cells from inflammation. An MRI scan will also be done at the same time as each of the 2 FLT-PET scans done for this research study. The two MRI scans performed will also help give more information about the patient's tumor that is not routinely provided with a routine clinical scan, such as blood flow through the tumor or metabolic activity in the tumor. The information from these special MRI scans may provide more information about the blood supply to the tumor and how this changes in response to treatment. In addition, the MRI scans along with the FLT-PET scans may help how to distinguish inflammation due to radiation therapy from tumor growth.