The Relationship between Heating Time and Temperature for Inhibition of Growth in Baby Rat Cartilage by Combined Hyperthermia and X-rays

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Abstract
The relationship between the thermal enhancement ratio (TER) for X-ray damage and time of heating was investigated in epiphyseal rate cartilage. The TER at each temperature rose steeply with increasing heating time. Various heat treatments with 8 Gy [gray] of X-rays were analyzed by the stunting rate, as measured by the slope of the dose-effect curve obtained for each temperature. The rate of stunting per unit heating time, induced by thermally enhanced X-ray damage was compared with the rate of stunting induced by only heat. The 2 were similar, having an activation energy of .apprx. 550 kJ/mol with the Arrhenius equation. Halving the heating time required a 1.degree. C temperature increase to achieve the same degree of thermal enhancement of X-ray damage. Damage caused by heat alone was similar. Over a range of 42.degree.-45.degree. C, the threshold heating time to cause direct thermal injury fell within the range of times used to enhance X-ray damage. A component of damage due to direct thermal injury, indistinguishable from radiation damage and thermally enhanced radiation damage, apparently contributes to TER assessments in some systems.