Simulating the Effect of Spectroscopic MRI as a Metric for Radiation Therapy Planning in Patients with Glioblastoma

J Scott Cordova; Shravan Kandula; Saumya Gurbani; Jim Zhong; Mital Tejani; Oluwatosin Kayode; Kirtesh Patel; Roshan Prabhu; Eduard Schreibmann; Ian Crocker; Chad A Holder; Hyunsuk Shim; Hui-Kuo Shu

doi:10.18383/j.tom.2016.00187

Simulating the Effect of Spectroscopic MRI as a Metric for Radiation Therapy Planning in Patients with Glioblastoma

Tomography. 2016 Dec;2(4):366-373. doi: 10.18383/j.tom.2016.00187.

Authors

Affiliations

¹ Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia.
² Department of Radiation Oncology, Emory University School of Medicine, Atlanta, Georgia; Florida Hospital Medical Group, Radiation Oncology Associates, Orlando, Florida.
³ Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia; Department of Biomedical Engineering, GA Institute of Technology, Atlanta, Georgia.
⁴ Department of Radiation Oncology, Emory University School of Medicine, Atlanta, Georgia.
⁵ SE Radiation Oncology Group, Levine Cancer Institute, Charlotte, North Carolina.
⁶ Department of Radiation Oncology, Emory University School of Medicine, Atlanta, Georgia; Winship Cancer Institute, Atlanta, Georgia.
⁷ Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia; Department of Radiation Oncology, Emory University School of Medicine, Atlanta, Georgia; Winship Cancer Institute, Atlanta, Georgia; Department of Biomedical Engineering, GA Institute of Technology, Atlanta, Georgia.

Abstract

Due to glioblastoma's infiltrative nature, an optimal radiation therapy (RT) plan requires targeting infiltration not identified by anatomical magnetic resonance imaging (MRI). Here, high-resolution, whole-brain spectroscopic MRI (sMRI) is used to describe tumor infiltration alongside anatomical MRI and simulate the degree to which it modifies RT target planning. In 11 patients with glioblastoma, data from preRT sMRI scans were processed to give high-resolution, whole-brain metabolite maps normalized by contralateral white matter. Maps depicting choline to N-Acetylaspartate (Cho/NAA) ratios were registered to contrast-enhanced T1-weighted RT planning MRI for each patient. Volumes depicting metabolic abnormalities (1.5-, 1.75-, and 2.0-fold increases in Cho/NAA ratios) were compared with conventional target volumes and contrast-enhancing tumor at recurrence. sMRI-modified RT plans were generated to evaluate target volume coverage and organ-at-risk dose constraints. Conventional clinical target volumes and Cho/NAA abnormalities identified significantly different regions of microscopic infiltration with substantial Cho/NAA abnormalities falling outside of the conventional 60 Gy isodose line (41.1, 22.2, and 12.7 cm³, respectively). Clinical target volumes using Cho/NAA thresholds exhibited significantly higher coverage of contrast enhancement at recurrence on average (92.4%, 90.5%, and 88.6%, respectively) than conventional plans (82.5%). sMRI-based plans targeting tumor infiltration met planning objectives in all cases with no significant change in target coverage. In 2 cases, the sMRI-modified plan exhibited better coverage of contrast-enhancing tumor at recurrence than the original plan. Integration of the high-resolution, whole-brain sMRI into RT planning is feasible, resulting in RT target volumes that can effectively target tumor infiltration while adhering to conventional constraints.

Keywords: glioblastoma; magnetic resonance spectroscopy; metabolic regions-of-interest; radiation therapy planning; spectroscopic MRI.

Abstract

Grants and funding