Radiation therapy is a key component of the control and eradication of malignant disease. Adequate tumoricidal doses may, however, result in damage to surrounding healthy tissue. Therapeutic radiation injuries to non-target tissues can be divided into acute, sub-acute, and delayed complications. Acute injuries are considered a direct cellular toxicity, self-limiting, and in most cases successfully managed symptomatically. Sub-acute injuries are typically identifiable in only a few organ systems, e.g., radiation pneumonitis. These, too, are generally limited but occasionally evolve to late complications. Late changes occur several months to many years after completing radiotherapy.