Improving accuracy of MR-Linac arterial spin labelling for imaging dynamics of highly-perfused tumour regions in glioblastoma

Motivation: MRI-linear accelerator arterial spin labelling shows low absolute cerebral blood flow (CBF) values, which impedes the accurate definition of highly-perfused tumour regions in glioblastoma for adaptive dose-escalation. Goal(s): Correct CBF values by measuring labelling efficiency and characterize highly-perfused region dynamics. Approach: Labelling efficiency was determined in five subjects, then used to adjust CBF values. The dynamics of high-CBF regions were determined in 47 glioblastoma patients during radiotherapy. Results: MR-Linac labelling efficiency is low (0.59) compared to the literature-recommended value (0.85). High-CBF regions extend outside the enhancing tumour (~47% of the volume) and shrink during chemoradiation by ~30-70%. Impact: Accurate cerebral blood flow measurements from MR-Linac arterial spin labelling are possible by using the measured labelling efficiency. To target highly-perfused glioblastoma regions with dose-escalation, targeting enhancing tumour is insufficient and adaptation is required.