Improvement of tumor oxygenation status by mild temperature hyperthermia alone or in combination with carbogen

The effects of mild temperature hyperthermia (MTH) on the oxygenation and radioresponse in rodent tumors were investigated. FSall tumors grown in the legs of C3H mice and R3230 AC tumors grown in the legs of Fischer rats were heated with a water bath and the partial pressure of oxygen (pO2) was determined using the microelectrode method. In FSall tumors, the pO2 measured immediately after heating at 41.5 degrees C for 1 hour was markedly higher than that in the control tumors, whereas heating at higher temperatures for 1 hour decreased the tumor oxygenation. In R3230 AC tumors, heating at 41.5 degrees C for 1 hour caused a moderate increase in the pO2 and heating at 42.5 degrees or 43.5 degrees C for 30 minutes markedly increased the pO2. However, heating at 42.5 degrees C or higher temperatures for 1 hour decreased the pO2 in the R3230 AC tumors. The improvement of oxygenation in FSall tumors by heating at 41.5 degrees C for 1 hour increased the radiation-induced cell death in these tumors. The combination of carbogen breathing with MTH was far more potent than carbogen breathing or MTH alone in increasing tumor oxygenation and potentiating the radiation effect in FSall tumors.