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Abstract #4747

Towards an understanding of radiation-induced R1 changes in irradiated water on an MR linear accelerator

Brandon T. T. Tran1,2, Liam S. P. Lawrence1,2, Shawn Binda3, Ryan T. Oglesby4, Brige P. Chugh3, and Angus Z. Lau1,2,3
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, 2Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, 3Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 4Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins Medicine, Baltimore, MD, United States

Synopsis

Keywords: Novel Contrast Mechanisms, Relaxometry

Motivation: Absorbed radiation dose can be directly imaged on an MR-Linac using T1 mapping, hypothesized to result from depletion of paramagnetic dissolved oxygen. However, it is unclear whether T1 changes are solely caused by this effect.

Goal(s): To determine whether radiochemical oxygen depletion is solely responsible for radiation-induced R1 changes.

Approach: Water phantoms with different dissolved gas compositions were irradiated and T1 mapping was acquired on an MR-Linac. Dissolved oxygen was measured using a polarographic probe.

Results: Oxygen depletion explains 54% of radiation-induced R1 change in the atmospheric gas phantom. R1 change in the nitrogen-bubbled phantom was caused only by oxygen depletion.

Impact: An understanding of the mechanism behind radiation-induced R1 changes could determine if radiation beam effects can be imaged in other systems and in vivo.

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Abstract

Keywords