DIGITAL RADIATION THERAPY Radiation therapy is one of the most effective cancer management approaches. In external beam radiation treatment, a lethal radiation dose is delivered through precisely conformed external radiation to the tumor while sparing the adjacent healthy tissues. However, the current paradigm is based on an assumption that both tumor location and shape are known and remain unchanged during the course of radiation delivery. Such a favorable rigid-body relationship does not exist in anatomical sites such as the thoracic cavity and the abdomen, owing predominantly to respiratory motions. When the tumor-bearing normal organs move during radiation therapy, discrepancies between planned and actually delivered radiation doses can be quite significant. As a result, although higher radiation doses have shown better local tumor control, organ motions have unfortunately required less aggressive treatment strategies having relatively large dose margin to tolerate potential targeting errors. To overcome this problem we are developing physics-based, 4D motion-simulating virtual-human models to study complex radiation interactions in tissues and dose distribution patterns for various radiation delivery strategies using advanced Monte Carlo simulations. PROJECTS Virtual lung model  SPONSORS       NIH/NLM R01 LM009362: Physically Realistic Virtual Surgery (2006-2010) INVESTIGATORS     George Xu     Suvranu De