The relationship between heating time and temperature: its relevance to clinical hyperthermia

It is well known that for a given level of damage to either cells in vitro or tissues in situ the relationship between temperature and time of application undergoes a transition in the range 42-43 degrees C and that above this temperature a change of 1 degree C is equivalent to a change in heating time by a factor of two. The present study has concentrated on establishing the relationship between time and temperature over a wide range. The investigation is in two parts, i.e. a review of the literature and an experimental study in which the endpoint used was necrosis in the tail of the baby rat. The aim is to provide information which might help solve a major clinical problem, namely the lack of a satisfactory means of relating treatments given with different temperatures for different lengths of time. The difficulty arises because there is no satisfactory definition of heat dose, in this context. The results confirm the relationship given above for temperatures above the transition. However, below the transition a change of 1 degree C is equivalent to a change in heating time by a factor of six. It is suggested that these relationships provide a means of monitoring a treatment in which the temperature does not remain constant and may vary within a heated volume. The method may also be used to compare treatments from different centres. An indication of the considerable uncertainties of the procedure is given.(ABSTRACT TRUNCATED AT 250 WORDS)