Thermotolerance and radiation sensitizing effects of long duration, mild temperature hyperthermia

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Abstract
Clinical application of long duration hyperthermia at temperatures in vitro. Thermotolerance developed during 41°C heating with or without concurrent low dose-rate irradiation. Thermotolerance reached a maximum within 6 h during 41°C heating and remained stable for at least 24 h. When cells were returned to 37°C after heating at 41°C for 6 h, thermotolerance remained stable for at least 12 h. The time course of thermotolerance development correlated with that of induction of 41°C radiation sensitization. Radiation sensitization, on the other hand, was shown to be independent of thermotolerance because the protein synthesis inhibitor cycloheximide prevented thermotolerance induction but had no effect on radiation sensitization. We conclude that thermotolerance development during concurrent clinical application of long duration mild temperature hyperthermia and low dose-rate irradiation should not be a factor in altering treatment outcome.