Combining phosphatidylserine (PS)-targeting monoclonal antibodies with radiation therapy can potentially enhance treatment efficacy. Oxygenation is important in radiation therapy response and could influence future treatment design. Oxygen enhanced MRI was used to examine changes in oxygenation in orthotopic lung tumors in rats treated by radiation or radiation plus a PS-targeting antibody. Orthotopic tumors were well oxygenated and responsive to oxygen breathing challenges before and after treatment. Combination therapy appeared to be more effective in tumor control than radiation alone.