Room: Karl Dean Ballroom C
Purpose: To develop a framework for assessing voxel-wise dose-correlated changes in key magnetic resonance (MR) biomarkers and apply this framework to a cohort of patients with brain metastases (BM) treated with stereotactic radiosurgery (SRS). Specifically, we investigated apparent diffusion coefficient (ADC) and dynamic contrast-enhanced (DCE) MRI parameters within a common coordinate system with dose and contours.
Methods: To enable spatially-registered voxel-wise analyses with dose, we created a registration pipeline to perform image registration steps and visualize registration results using Python interacting with 3D Slicer. We also employed an in-house-developed 4-D temporal dynamic analysis approach to extract the contrast transfer coefficient (Ktrans) and volume of extracellular extravascular space (ve) from dynamic DCE-MRI time courses. For our clinical study, we processed prospective MRI data collected from 18 patients (29 BM, 5 with imaging-diagnosed radionecrosis) at day 0, 3 and 20 following 15â€“21 Gy SRS. For each voxel, we computed Î”ADC, Î”Ktrans and Î”ve for day 3 and 20 post-SRS relative to day 0 both within the GTV and the surrounding >12 Gy dose level. We performed linear regression analyses for Î”MR biomarker versus dose at day 3 and 20.
Results: Across all subjects, we observed significant negative correlations between Î”Ktrans and Î”ve with dose at day 20 within the GTV and >12 Gy region (r = -0.04 to -0.16, p<0.001). In contrast, for radionecrotic BMs we found significant positive dose-correlated Î”ADC increases only in the GTV (r = 0.11 to 0.19, p<0.001).
Conclusion: We provide a framework for investigating voxel-wise MR biomarker changes that may aid delineation of local control, subclinical normal brain injury and radionecrosis. Our results demonstrated weak but significant dose-correlated reductions in Ktrans and ve at 20 days following SRS both within the GTV and the surrounding >12 Gy region, an indication of radiation-induced vascular changes.