Analysis of the heat and radiation interaction

The amount and type of interaction between heat and radiation are evaluated for several sets of experiments using Chinese hamster ovary cells, subline HA-1, through the interaction coefficient derived by Roti Roti and Henle. As the duration of postradiation heat treatment is increased from 15 min to 2 h, the amount of interaction increases linearly with heating time from 15 to 60 min. From 60 to 120 min the amount of interaction remains relatively constant. For a given heat treatment the amount of interaction increases linearly with radiation dose over four decades of survival when the X-ray treatment immediately follows the heat treatment. The additivity of heat and radiation is also analyzed by use of the envelope of additivity method suggested by Steel and Peckham. The results imply that heat and radiation are not superadditive which suggests that this analysis is inapplicable to the interaction of these two modalities. Several possible reasons for the failure of this analysis are discussed.