Abstract #0485

Dynamics of hypercellular glioma regions identified with diffusion-weighted imaging for adaptive radiotherapy on an MR-Linac

Liam S. P. Lawrence^1,2, Rachel W. Chan¹, James Stewart³, Mark Ruschin³, Aimee Theriault³, Sten Myrehaug³, Jay Detsky³, Pejman J. Maralani⁴, Chia-Lin Tseng³, Greg J. Stanisz^1,2,5, Arjun Sahgal³, and Angus Z. Lau^1,2

¹Physical Sciences Platform, Sunnybrook Research Institute, Toronto, ON, Canada, ²Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, ³Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁵Department of Neurosurgery and Paediatric Neurosurgery, Medical University, Lublin, Poland

Synopsis

For radiotherapy of high-grade glioma, dose escalation to hypercellular tumour could improve local control, but changes during treatment might necessitate target volume adaptation. Since hypercellular tumour causes low apparent diffusion coefficient (ADC) values, volumetric changes in low-ADC regions were quantified using near-daily MR-Linac imaging to evaluate adaptation necessity. Low-ADC regions increased in volume (median extremal change: 12.2%) and changed rapidly for certain patients (maximum growth/shrinkage rate: 7.1/9.1% per day). Low-ADC regions changed more in magnitude and grew more rapidly for resected tumours than intact ones. These findings imply that adaptation may be required for dose escalation to hypercellular glioma regions.

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