Recovery kinetics from the damage by step-up and step-down heatings in combination with radiation in Chinese hamster cells.

The recovery kinetics from the synergistic damage resulting from the combination treatments of X-irradiation (3 Gy), and 42°C (60 min) and 44°C (15 min) hyperthermia were analized in Chinese hamster V-79 cells. Recovery time was less than about 8 hr when the first treatment was hyperthermia [42°C (60 min) or 44°C (15 min)] alone, X-irradiation alone, the combined treatments with the both, or the combined hyperthermia of 42 → 44°C sequence. However, when the combined hyperthermia of 44 → 42°C sequence was given as the first treatment, the survival of cells did not attain to the additive level within a 24 hr interval at 37°C. From these results, it is suggested that the damage induced by the combined hyperthermia of 44 → 42°C sequence was retained partially in the cells during at least a 24 hr interval at 37°C, and may interact synergistically with the damage by the subsequent X-irradiation.