The concept of thermal dose.
1. In the ideal but theoretical situation, where hyperthermia is defined to be at a specific, constant temperature, duration of heating is a perfectly acceptable and satisfactory method of describing thermal dose. 2. In the real situation, the dose is far from constant. Time will be required to reach the desired temperature and to cool afterwards. During hyperthermia the temperature is variable. We are thus obliged to use a biologically equivalent thermal dose to account for these variations. 3. Various attempts have been made to solve this problem, but at present, the most feasible approach appears to be the integration of the biological isoeffect relationship (Dewey formula) over the whole treatment. 4. This method provides a practical and reasonable method of comparing hyperthermal treatments under conditions likely to be met in practice, i.e. moderate variation about a fairly steady temperature. However, the formula would certainly be inaccurate if there were a sudden reduction in temperature resulting in a significant effect of step-down sensitisation or a long treatment resulting in the development of thermotolerance. Also, it must be emphasised that the formula does not account for absolute differences in sensitivity among tissues. Nor does it address the problem of varying sensitivity throughout a course of fractionated heat treatments. 5. Less is known about the applicability of such a formula to the combination of heat and ionizing radiation when the two treatment modalities interact. The parameters are fairly similar to those for heat alone, although the transition appears to be lowered to 41.5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Field
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MRC Cyclotron Unit, Hammersmith Hospital, London, Great Britain.
D006979:Hyperthermia, Induced; D008962:Models, Theoretical