Diffusion Tensor MRI to Distinguish Brain Tumor Recurrence From Radiation Necrosis

The most common major side effect of radiation therapy for the treatment of primary brain tumors is the necrosis of normal brain tissues (radiation necrosis). Radiation necrosis typically occurs weeks to months following treatment. The diagnosis is suspected when patients have new areas of gadolinium enhancement on magnetic resonance imaging (MRI) scans. Tumor recurrence can also occur within weeks to months following treatment and is represented by new areas of gadolinium enhancement as well. As the management options for radiation necrosis and tumor recurrence are significantly different, distinguishing the two is of critical importance. Conventional MRI, diffusion-weighted MRI (DW-MRI), MR spectroscopy, SPECT, and PET imaging have all been used to try to make this distinction, but the sensitivity and specificity of these techniques have not been clinically useful. Most patients must therefore undergo a risky diagnostic surgical procedure. Diffusion tensor MRI (DT-MRI) is an imaging technique that provides information regarding both the diffusive properties of water as well as the directionality of water movement. A modification of DT-MRI, referred to as two-compartment DT-MRI, appears to be more sensitive than other variations of MRI for the diagnosis of selected types of brain abnormalities. Objective: We plan to conduct a feasibility study to determine if two-compartment DT-MRI can distinguish tumor recurrence from radiation necrosis. Study Population: Patients aged greater than or equal to twenty one years old with a prior diagnosis of primary brain tumor and history of radiation treatment who develop new areas of gadolinium enhancement on conventional MRI scans and who require surgery for diagnostic or therapeutic purposes will be evaluated for enrollment in this study. Ten patient controls will also undergo DT-MRI scans for the purpose of obtaining normative data for this quantitative study. Design: Patients who meet eligibility criteria will undergo a two compartment DT-MRI scan. Regions of abnormality will be identified and surgical biopsies will be obtained of these regions. The radiographic and histologic characteristics of the samples will be correlated. Volunteers will undergo DT-MRI scans only. Outcome Measure: The primary outcome measure of this study is the degree of agreement between the radiographically predicted diagnosis of tumor recurrence or radiation necrosis using two-compartment DT-MRI and the histologic diagnosis of such. This outcome will be measured as the proportion of instances in which the two modalities identify a particular lesion as being tumor recurrence or as being radiation necrosis. The information gathered from this study will allow for the implementation of a larger study with more patients if there is a high degree of agreement between the two compartment DT-MRI and histologic diagnoses of surgical biopsy specimens. The long range goal of the larger study is to radiographically diagnose tumor recurrence or radiation necrosis with a high enough level of sensitivity and specificity to avoid a diagnostic surgical procedure with its attendant risks.