Program Information
Application of Diffusion Weighted MRI for Target Delineation in Radiotherapy for Glioblastoma
O Morin*, M Held , M Wahl , S Braunstein , University of California San Francisco, San Francisco, CA
Presentations
TU-AB-601-2 (Tuesday, August 1, 2017) 7:30 AM - 9:30 AM Room: 601
Purpose: Recent studies of glioblastoma (GBM) patients with MGMT methylated tumors reveal a 30-40% rate of marginal or distant failure. GBM invades predominantly along large white matter pathways within the brain, but this information has not been incorporated into radiotherapy planning. We investigate the use of diffusion-weighted MRI (dwMRI), which non-invasively measures the orientation of major white matter tracts, to inform target delineation for GBM.
Methods: 31 patients were retrospectively identified who had undergone 55-direction dwMRI-HARDI at the time of treatment planning. Diffusion tractography was performed using the physician contoured GTV as a seed, and used to automatically generate anisotropic CTV expansions (CTVdwMRI), encompassing all surrounding white matter up to a threshold tract length from the GTV. Simulated replanning was also performed to determine the effect of anisotropic expansion on dosimetric parameters.
Results: At the time of submission, a pilot set of 5 patients had been analyzed, all of whom experienced disease recurrence. All recurrences were encompassed within the CTVdwMRI, while the conventional CTV encompassed the recurrence in only 80% of the cases. Furthermore, the target volume for radiotherapy was significantly reduced in a majority of patients using the dwMRI-based CTV (median CTV volume change of 26.7%, range [-35.4, +9.0]%). Critical structures such as the hippocampus and the fornix had significant reduction in mean and maximum doses for the 5 cases analyzed. The results for all 31 patients will be available at the time of presentation.
Conclusion: We have demonstrated the feasibility of incorporating white matter track information in the target delineation process for GBM patients. Our preliminary data demonstrates that our dwMRI-based approach can be used to define target volumes that may provide superior coverage of areas at highest risk of tumor spread, without increased risk for long-term toxicity from treatment.
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