1.4 Hyperthermia It is reported that hyperthermia is effective in S phase, Low partial oxygen pressure (pO2), acidic condition, and low perfusion site which are known as radio-resistant. Because of these characteristics, it considered as the most valuable radiosensitizer in cancer treatment, theoretically. Furthermore ,mild hyperthermia (41 to 41.5 ºC) can promote tumor reoxygenation.