Hyperthermia

Abstract

Though its use has waned and conventional heat treatments alone are only used to treat some types of cancer at a few clinics in the United States, there is still some interest in the use of hyperthermia as an adjuvant to radiotherapy, since it can often work synergistically with ionizing radiation to enhance tumor control. There are several methods by which heat may be delivered to a tumor, but with the general exception of some superficial tumors, hyperthermia remains technically difficult to accurately and uniformly administer, and monitoring of the heat doses remains problematic. Also, the development of thermotolerance is a barrier to its use as a stand-alone therapy, and also precludes the use of multiple heat treatments when used as an adjuvant to fractionated radiotherapy. While radiation typically induces death via damage to DNA, heat is believed to induce cell death through denaturation and aggregation of proteins. Hyperthermia may be effective at killing radio-resistant tumor cells, including S-phase, nondividing, hypoxic, or poorly vascularized cells. When combined with radiation, there may be a synergistic effect through vasodilation (reducing hypoxia) and inhibition of DNA repair (double-strand breaks). After a heat dose, thermotolerance may develop due to expression of heat-shock proteins. While interest in conventional hyperthermia has waned, thermal ablation (using temperatures >50 C) may produce good long-term results.