Comparison of radiosensitization by 41 degrees C hyperthermia during low dose rate irradiation and during pulsed simulated low dose rate irradiation in human glioma cells

Purpose: Long duration mild hyperthermia has been shown to be an effective radiosensitizer when given concurrently with low dose rate irradiation, Pul sed simulated low dose rate (PSLDR) is now being used clinically, and we ha ve set out to determine whether concurrent mild hyperthermia can be an effe ctive radiosensitizer for the PSLDR protocol, Materials and Methods: Human glioma cells (U-87MG) were grown to plateau ph ase and treated in plateau phase in order to minimize cell cycle redistribu tion during protracted treatments. Low dose rate (LDR) irradiation and 41 d egrees C hyperthermia were delivered by having a radium irradiator inside a temperature-controlled incubator. PSLDR was given using a 150 kVp X-ray un it and maintaining the cells at 41 degrees C between irradiations. The dura tion of irradiation and concurrent heating depended on total dose and exten ded up to 48 h, Results: When 41 degrees C hyperthermia was given currently with LDR or PSL DR, the thermal enhancement ratios (TER) were about the same if the average dose rate for PSLDR was the same as for LDR. At higher average dose rates for PSLDR the TERs became less. Conclusions: Our data show that concurrent mild hyperthermia can be an effe ctive sensitizer for PSLDR, This sensitization can be as effective as for L DR if the same average dose rate is used and the TER increases with decreas ing dose rate. Thus mild hyperthermia combined with PSLDR may be an effecti ve clinical protocol. (C) 1999 Elsevier Science Inc.