[Hyperthermia as cytotoxic and radiosensitizing agent: cellular effects--a review]

Some aspects of the effect of hyperthermia on mammalian cells are presented. Hyperthermia is an efficient means to kill cells or to reinforce the action of radiation. These effects depend on temperature. Between both effects exists a steep temperature gradient, making necessary an exact measurement of temperature. The cytotoxic effect prefers radioresistant cells such as hypoxic cells or cells in the late DNA synthesis phase. A combination will be favorable because both therapy methods supplement each other, but produce no interaction. If one wishes to take advantage of the radiosensitizing effect, hyperthermia intervenes in the processes of recovery after the radiation insult. It is therefore indicated especially in case of tumors presenting a great capacity of cells recovery. Here, a real interaction between hyperthermia and radiotherapy takes place at the same target. Cellular death after hyperthermia and radiotherapy is caused by different mechanisms. All these data suggest the following recommendations for clinical practice: The temperature should be chosen higher or lower than 42 degrees C depending on the desired effect (cytotoxic or radiosensitizing effect). Under the point of view of recovery, radiotherapy should be followed by hyperthermia. In order to avoid an induction of resistance against hyperthermal treatment, hyperthermia should be combined as often as possible with radiotherapy.