Response to pulsed dose rate irradiation with and without mild hyperthermia using tumour and normal cell lines

To determine whether pulsed dose rate irradiation in combination with mild hyperthermia could radiosensitize cells in comparison to pulsed dose rate irradiation alone, human ovarian carcinoma (A2780s, cisplatin- and radiation-sensitive, and A2780cp, cisplatin- and radiation-resistant) and human fibroblast (AG1522) cell lines were used. Cells were irradiated in vitro using two fraction sizes, 0.53 Gy given every hour and 1.6 Gy given every 3h, with an overall average dose rate of 0.53 Gy/h. The data showed that 40 degrees C hyperthermia did not radiosensitize any of the cell lines for the 0.53 Gy every 1 h fractionation scheme. In addition, mild hyperthermia radiosensitized both carcinoma cell lines when using the 1.6 Gy fraction size for all doses tested in the A2780s and at higher doses in the A2780cp, but not the normal cell line. These results suggest a potential clinical advantage when using the 1.6 Gy fraction size with 40 degrees C mild hyperthermia, since hyperthermia radiosensitized the carcinoma cells but not the normal cells.