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Abstract #0366

Optimizing early response assessment in glioblastoma using diffusion imaging on a 1.5T MR-Linac

Liam S. P. Lawrence1, Brige Chugh2,3, James Stewart2, Mark Ruschin2, Aimee Theriault2, Jay Detksy2, Sten Myrehaug2, Pejman J. Maralani2, Chia-Lin Tseng2, Hany Soliman2, Mary Jane Lim-Fat4, Sunit Das5, Greg J. Stanisz1,6,7, Arjun Sahgal2, and Angus Z. Lau1,6
1Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, 2Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 3Department of Physics, Toronto Metropolitan University, 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, 6Physical Sciences Platform, Sunnybrook Research Institute, Toronto, ON, Canada, 7Department of Neurosurgery and Paediatric Neurosurgery, Medical University, Lublin, Poland

Synopsis

Keywords: Tumors (Post-Treatment), Cancer, Glioblastoma, apparent diffusion coefficient, response assessment

Motivation: Early response assessment for glioblastoma may be possible using regions of low apparent diffusion coefficient (low-ADC) during MRI-linear accelerator (MR-Linac) treatment, but low-ADC definition has not been optimized.

Goal(s): Optimize definition of low-ADC for correlation with progression-free survival.

Approach: We defined low-ADC regions from near-daily diffusion-weighted imaging and weekly contrast-enhanced T1-weighted imaging for 41 glioblastoma patients during MR-Linac treatment (3-6 weeks). We compared correlation strength across b-values (800 versus 2000s/mm2) and ADC thresholds (0.7 to 2.0μm2/ms).

Results: The optimal b-value/threshold combination was b=800s/mm2 and 1.2μm2/ms (correlation for weeks 2-6).

Impact: We showed that early response assessment in glioblastoma during radiotherapy is possible with weekly acquisition of ADC maps and contrast-enhanced T1-weighted imaging on MR-Linacs. Low-ADC regions could serve as targets for radiotherapy dose escalation to potentially extend patient survival.

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Abstract

Keywords