Abstract #1575

High b-value diffusion-weighted imaging of glioblastoma on an MR-Linac

Liam S. P. Lawrence¹, Rachel W. Chan¹, James Stewart², Mark Ruschin², Aimee Theriault², Sten Myrehaug², Jay Detsky², Pejman J. Maralani³, Chia-Lin Tseng², Hany Soliman², Mary Jane Lim-Fat⁴, Sunit Das⁵, Greg J. Stanisz^1,6, Arjun Sahgal², and Angus Z. Lau¹

¹Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ²Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ³Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Division of Neurology, Department of Medicine, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁵Department of Surgery, St. Michael's Hospital, Toronto, ON, Canada, ⁶Department of Neurosurgery and Paediatric Neurosurgery, Medical University, Lublin, Poland

Synopsis

Keywords: Tumors, RadiotherapyHyperintense regions on high b-value DWI (HRDs) may reflect hypercellular tumour and are of interest for radiotherapy dose escalation. However, the extent to which diffusion restriction versus prolonged T₂ creates these hyperintensities is not known. Additionally, the dynamics of HRDs during radiotherapy are not fully characterized. In 35 glioblastoma patients treated on a 1.5T MR-Linac, we found HRDs shrank during treatment and extended beyond the gross tumour volume. Apparent diffusion coefficient was reduced and T₂ was elevated in HRD compared to the remainder of the clinical target volume, implying that both diffusion restriction and prolonged relaxation are responsible for HRDs.

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