MRI Relaxometry for Glioblastoma Response Assessment During Radiation Therapy on a 0.35 T MRI Linear Accelerator.

Background And Purpose: The integration of MRI and linear accelerator (MRI-Linac) enables daily imaging during radiation therapy (RT). This study implements MRI-Linac relaxometry to evaluate quantitative imaging changes in glioblastoma patients during RT and identify associations with disease progression and survival outcomes.

Materials And Methods: Thirty-eight glioblastoma patients were treated on a 0.35T MRI-Linac with Strategically Acquired Gradient Echo (STAGE) and T2 multi-echo acquisitions every other day. Per voxel changes in tumor T2, T2*, and T1 values were assessed by parametric response mapping comparing each treatment fraction with pre-RT baselines. Statistical analyses included the Wilcoxon test for group comparisons and Cox proportional hazards models for survival associations.

Results: Progressors had higher proportions of voxels with increased T2 values at week 2 (49% vs. 40%, p = 0.008) and week 6 (58% vs. 43%, p = 0.012) and higher T2* values at week 1 (47% vs. 43%, p = 0.016), week 2 (48% vs. 43%, p = 0.016), week 3 (50% vs. 44%, p = 0.012), and the final week (53% vs. 43%, p = 0.021). Cox modelling linked increased T2 values at week 4 with overall survival (HR = 4.72, 95% CI: 1.24-12.9) and progression-free survival (HR = 9.26, 95% CI: 1.88-24.5). Increased T2* values at weeks 2 and 3 correlated with progression-free survival (HR = 5.02, 95% CI: 1.44-17.6; HR = 6.04, 95% CI: 1.59-22.9) and overall survival at week 3 (HR = 3.09, 95% CI: 0.94-10.1).

Conclusion: Quantitative changes in T2 and T2* values during RT, particularly in weeks 3-4, were associated with progression and survival outcomes. Early detection of poor responders may enable therapy adaptation, improving glioblastoma treatment outcomes.