Clinical studies have demonstrated that tumour vascular can increase during the course of radiation therapy, consistent with re-oxygenation and that this is suggestive of a better outcome. Tumours that become less hypoxic during the course of therapy have an increased likelihood of response to the given treatment. However, response to tirapazamine may be reduced. In order to assess both the vascular change that may occur directly because of tirapazamine infusion, as well as any increase in tumour vascularity and perhaps increase in tumour oxygenation during the course of therapy, we plan to assess these tumours during the course of therapy. Assessment of tumour perfusion and vessel permeability after 10 radiation treatments (on day 12) of chemo-radiation therapy will be performed via T1 weighted dynamic contrast enhanced MRI (DCMRI).