1. Department of Radiology; Sloan Kettering Institute for Cancer Research; New York New York 10065 USA
2. Department of Cell Biology; Sloan Kettering Institute for Cancer Research; New York New York 10065 USA
3. Department of Medical Physics; Sloan Kettering Institute for Cancer Research; New York New York 10065 USA
4. Department of Materials Science & Engineering; Cornell University; Ithaca New York 14853 USA