Abstract
Radiation therapy (RT) targeted by conventional MRI may not fully identify the tumor profile of (GBM), which may in part account for high recurrence rates. Identifying the extent of GBM margins remains a challenging task due to the infiltrative nature of these tumors and limitations in current standard imaging methods. Multiple studies have demonstrated that MR spectroscopic imaging, or spectroscopic MRI (sMRI), can detect areas of infiltrating tumor with a high degree of sensitivity, and could be an essential tool in targeting tumor margins. sMRI enables the identification of non-enhancing, infiltrating cells that are marked by increased Choline/N-Acetylaspartate ratio (Cho/NAA), including regions undetected by standard MRI and therefore left untreated. sMRI shows considerable promise for improving the efficacy of RT and may delay recurrence. In this study, we correlated pre-treatment sMRI metabolite maps with recurrence patterns to validate that sMRI could provide coverage for untreated regions that later recurred, and provide support for its adjunctive use in tumor contouring for RT planning. In an ongoing NCI-funded trial (U01CA172027), metabolite and their ratio maps were obtained pre-chemoradiation and normalized to the patient’s normal-appearing contralateral white matter (NAWM) and then compared to contrast-enhancing recurrence patterns with at least 6 months follow-up. A Cho/NAA ratio of twice the NAWM mean was used to identify regions of potential infiltration in our patients, and the resulting planning target volumes were compared with actual treated target volumes based on conventional MRI. For 9 out of 11 cases, the addition of sMRI data expanded RT volumes to better encompass regions of tumor recurrence, which were not completely covered by the CTV60. Thus, RT planning for GBMs augmented by sMRI could reduce recurrence rates. A multi-institutional clinical trial has been initiated to prospectively assess potential for sMRI to guide RT and assess treatment response (R01CA214557).