Hypofractionated stereotactic body radiation therapy, a new radiation treatment scheme, may be particularly susceptible to tumor hypoxia. We applied oxygen enhanced MRI together with DCE MRI to observe tumor physiological changes induced by a radiation fraction in a human lung cancer xenograft rat model. This study showed reduced vascular oxygenation 24 hours after the first fraction of 12 Gy, as indicated by the significant decrease in T2* compared to baseline, but no significant response in dynamic contrast enhanced MRI. DCE parametric maps revealed a multinodular structure in the tumor as confirmed by histology.
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