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

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.

SUBMITTER: Cordova JS

PROVIDER: S-EPMC5241103 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Abstract The standard of care for glioblastoma is neurosurgical resection followed by radiation therapy (RT) and temozolomide (TMZ) chemotherapy. Although RT is effective for glioblastoma, attempts to improve survival using RT dose escalation above 60 Gy have been largely unsuccessful. This may be because prior attempts have been targeted to resection cavity or enhancing tumor, which may not accurately predict areas at highest recurrence risk. To overcome the limitations of standard T1 and T2-weighted MRI in predicting tumor recurrence, we have shown that supplementation with 3D high-resolution spectroscopic MRI (sMRI) identifies actively proliferating tumor beyond areas of T1-enhancement by measuring endogenous metabolites and their ratios. Previously, we demonstrated that the choline to N-acetylaspartate ratio (Cho/NAA) best correlates with tumor cellularity in surgically resected tissue (?=0.82, p< 0.001) and, most importantly, areas of sMRI metabolic abnormalities predate disease recurrence in those same areas (Cordova et al, Neuro-Oncology 2016). Therefore, we seek to identify whether sMRI can be used by radiation oncologists to choose the optimal regions to target for RT dose escalation. To assess its feasibility and safety, we developed a web-based imaging platform designed specifically to incorporate sMRI into the RT planning clinical workflow and are using it in a multisite sMRI-guided dose escalation trial (NCT03137888; Emory, Johns Hopkins, U. Miami). Recently, we have completed full enrollment including 30 patients treated with sMRI-guided dose escalated RT across three institutions. We have demonstrated successful integration of sMRI into the RT planning workflow, and we have delivered sMRI-guided dose escalated RT plans to glioblastoma patients without severe adverse events to date. Follow-up data will be analyzed for overall and progression-free survival. Based on the feasibility and safety of this technique in the current trial, we plan to assess the efficacy of sMRI-guided dose-escalated RT on patient outcomes in a NCTN clinical trial.

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

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