Imaging
All patients underwent MRI of the brain on 1.5 or 3 Tesla systems (Skyra, Aera, Biograph mMR, Siemens Healthcare; Discovery 750w, Signa HDxt, GE Healthcare, Milwaukee, WI), pre- and post-treatment. MRI sequences included axial T1-weighted (repetition time/echo time [TR/TE]: 550-700 milliseconds/7-10 milliseconds, 3-5 mm slice thickness) or 3-dimensional T1 SPACE (TR/TE: 600-700 milliseconds/11-19 milliseconds, 120 degree flip, 1 mm slice thickness), axial T2 (TR/TE: 3,200-4,000 milliseconds/93-98 milliseconds, 5 mm slice thickness), and axial T2 fluid attenuation inversion recovery (FLAIR) or 3- dimensional T2 FLAIR (TR/TE: 6,300-8,500 milliseconds/394- 446 milliseconds, 120 degree flip, 1 mm slice thickness). Axial diffusion-weighted sequences were obtained (TR/TE: 6,280-9,000 milliseconds/78-103 milliseconds, 90- or 180- degree flip, 5 mm slice thickness) with ADC maps. Additionally, T1-weighted DCE perfusion MRI was performed (TR = 4 milliseconds, TE = 1-2 milliseconds, flip angle: 13 degrees, slice thickness: 3 mm, 44 slices to cover the entire lesion volume, 24 phases with 4 phases before and 20 phases after intravenous bolus administration of 0.1 mL/kg gadopentetate).
Olea Medical 3.0 software (La Ciotat, France) was used for DCE perfusion MRI processing and histogram analysis. Histogram analysis was performed on volumes-of-interest that included the entire enhancing tumor volume, encompassing all voxels with enhancing tumor, pre- and post- treatment. Blood-brain barrier permeability metrics, including median, mean, and 90th percentile of the plasma volume (Vp) and volume transfer constant (Ktrans) were derived from the histogram analysis from the volumes-of-interest. Diffusion metrics, including median, mean, and 10th percentile of the ADC were derived from the histogram analysis from the volume-of-interest. All values were normalized utilizing the contralateral normal white matter.