Te rapidly changing concepts in radiation oncology with the development of more precise - strumentation for delivery of radiation therapy and a greater emphasis on hypofractionation technologies require a very intimate knowledge of tumor biology and the infuence of various biologic factors on dose distribution within the tumor in terms of homogeneity as well as prev- tion of any late efects on normal tissue surrounding the tumor itself. Not only are these major factors in clinical practice but also the known factors of inhomogeneity of cancer cells, the impact of microenvironment in terms of...