Brain imaging: Assessing therapy responses using quantitative imaging biomarkers

Neuroimaging is essential for both the diagnosis and evaluation of the therapeutic response of intracranial tumors. Measurement of structural changes in tumor morphology after institution of therapy using magnetic resonance imaging (MRI) serves as the current gold standard for monitoring therapeutic response; however, information of prognostic value cannot be obtained until weeks after the initiation of treatment. Positron emission tomography (PET) using radiolabled ligands that trace physiologic processes offers promise as a method for early therapy response assessment, although to date the neuro-oncologic utility of PET imaging has not been good enough to replace the current gold standard. This chapter first reviews some of the current methods in which MR is used to evaluate physiologic changes in tumor environment after therapy (e.g. spectroscopy and diffusion-weighted imaging). The chapter then surveys several PET tracers that are either currently in clinical use (e.g. FDG) or under investigation (e.g. FLT) and discusses their use for therapeutic response assessment.