Hyperthermia as a supplement to radiotherapy
Different mechanisms are responsible for the supra-additive effect of hyperthermia when used in conjunction with radiotherapy. The additive, complementary effect of hyperthermia is due to the higher heat sensitivity of cells in the hypoxic and low-pH range, as well as the sensitivity of cells in the S phase, both of which are relatively radio-resistant.
Moderate hyperthermia can also cause increased blood flow and thus increased tissue oxygenation, which results in increased radio-sensitivity. Though this effect is strongest within short succession of radiation, it can last as long as a few days, albeit in a milder form (PET-CT: Lüdemann et al IntJHT 2009)
Hyperthermia increases cytotoxic radiation effects, particularly by interfering with the cellular repair system as a result of the denaturing of the DNA. According to literature, hyperthermia can boost the effect of radiotherapy by a factor of 1.2 to 5.
In summary, according to Horseman/ Overgaard (IntJHT 2008), hyperthermia is probably the most potent radio-sensitising method currently known.