Comment: Radiosensitization and the Selective Effect

The ideal in the treatment of malignant disease is achieved when the cancer is completely eradicated and the surrounding normal tissue shows no evidence of structural or functional injury. In clinical practice, this ideal selective effect is seldom achieved; a certain degree of residual damage must be accepted as a sequel to the destruction of a lethal tumor. The extent of alterations of normal tissues that is acceptable varies in different anatomic settings, but the integrity of the vital structures must be maintained. This ideal has been described as the "selective effect" when it is applied to radiation therapy. One of the major frontiers of radiation biologic research is to make irradiation more selective. The term, "radiosensitization" has been used to describe the modification of the radiation response by agents; it broadly includes mechanisms of enhancement, such as additivity, synergism, or time dose modification. No specific radiation effect that is