There appears to be a dose-dependent increase in tumor immunogenicity and radiation dose size per fraction. Higher dose size per fraction results in greater infiltration of tumors by CD8+ T cells as well as higher levels of ICAM, Fas, and MHC-I with loaded tumor antigen expressed on the tumor cells surface. These higher levels of expression, as a function of higher radiation dose size, correlate with improved antitumor immune-directed killing. APC, antigen-presenting cell; ICAM, intercellular adhesion molecule; MHC I, major histocompatibility complex type I; MDSC, myeloid-derived suppressor cell.