95 Temporal diffusion ratio as a potential biomarker of treatment response to stereotactic radiosurgery in human brain metastases

Abstract Introduction The temporal diffusion ratio (TDR) is a model free technique which uses diffusion MRI data to create contrast between voxels with and without restricted diffusion, and has previously been used to inform on cell sizes (typically, larger TDR implies larger cell size). In this study, we hypothesise that TDR may be used to predict treatment response to stereotactic radiosurgery (SRS) with the same sensitivity as ‘Response assessment in neuro-oncology brain metastases (RANO-BM)’ criteria, as early as 1 month after treatment. Methods 26 patients with brain metastases received diffusion-MRI scans at baseline, 1 month and 3 month timepoints. Patients received SRS between baseline and 1 month. TDR was estimated voxelwise in the metastasis regions of interest (ROIs), and mean TDR in the ROI was calculated. Treatment response was assessed using RANO-BM criteria at the 3 month timepoint. Results Excluding one patient, in the ‘good’ treatment response group (RANO-BM=1,2), the percentage change from baseline of mean TDR varied between +43.6% and +98.3% at 1 month, and +6.8% and +149.9% at 3 months. In the ‘poor’ treatment response group (RANO-BM=3,4), the percentage change of mean TDR varied between -4.9% and -2227.1% at 1 month, and -6.2% to -679.2% at 3 months. The difference in the percentage change of mean TDR between the ‘good’ and ‘poor’ response groups was statistically significant. Conclusion Excluding 1 patient at each timepoint, the positivity/negativity of the change in mean TDR from baseline at 1 month and 3 months was associated with the RANO-BM assessment at 3 months. This indicates that mean TDR may help predict treatment response to SRS as early as 1 month after treatment. Future work will examine this technique in a larger patient cohort.