The effects of hyperthermia on biological structures are pleiotropic and complex. Apart from relying on technology, they also depend on the temperature, the duration of the application, the heating time, the form, type and size of tissue, the blood flow and the homogeneity of temperature distribution, and affect the denaturation of cellular and subcellular elements.
General effective mechanisms of hyperthermia (depending on the temperature):
1. Direct tumour necrosis by means of heat application
2. Nutrient and oxygen deficiency of the tumour tissue
3. Apoptosis (progr. cell death) due to the anaerobic metabolism
4. Sensitisation of radiotherapy and chemotherapy (synergistic effect)
5. Breaking through chemotherapy and radiotherapy resistance
6. Reducing the pain
7. Increasing the quality of life
Hyperthermia in addition to radiotherapy:
Different mechanisms are responsible for the supra-additive effect of hyperthermia in combination with radiotherapy. Hyperthermia can furthermore cause an augmented blood flow which increases the oxygenisation of the tissue and results in increased radiosensitivity. In-vivo studies have shown that the effect of radiotherapy can be increased by hyperthermia by the factor 1.2 to 5.
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Hyperthermia in addition to chemotherapy:
The countereffects of hyperthermia and cyostatic drugs can be independent, additive or supra-additive (synergistic). An increased intra-tumour concentration of medication as well as an augmented intra-cellular medication metabolism, among others, are the most important mechanisms leading to an interactive effect with cyostatic drugs. Synergy effects can however also result from changes in the tissue and the altered metabolism of cyostatic drugs caused by the heat.