Abstract #2201

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

Liam S. P. Lawrence¹, Brige Chugh^2,3,4, James Stewart², Mark Ruschin², Aimee Theriault², Jay Detsky², Sten Myrehaug², Pejman J. Maralani⁵, Chia-Lin Tseng², Hany Soliman², Mary Jane Lim-Fat⁶, Sunit Das⁷, Arjun Sahgal², and Angus Z. Lau^1,2

¹Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ³Department of Physics, Toronto Metropolitan University, Toronto, ON, Canada, ⁴Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ⁵Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁶Division of Neurology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁷Department of Surgery, St. Michael's Hospital, Toronto, ON, Canada

Synopsis

Keywords: MR-Guided Radiotherapy, Arterial spin labelling, MR-Linac, Quantitative imaging, 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.

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