 The hypothesis underlying this research is that repeated measurements of tissue oxygen levels can be used to optimize cancer therapy, including combined therapy, and to minimize normal tissue side effects or complications. Because studies have found that tumors vary both in their initial levels of oxygen and exhibit changing patterns during growth and treatment, we propose to monitor oxygen levels in tumors and their responsiveness to hyperoxygenation procedures. Such knowledge about oxygen levels in tumor tissues and their responsiveness to hyper-oxygenation could potentially be used to select subjects for particular types of treatment, or otherwise to adjust routine care for patients known to have hypoxic but unresponsive tumors in order to improve their outcomes. 