The Influence of Pre-treatment Temperature on the Thermal Sensitivity of a Mouse Tumour

Summary

The response of tumours to hyperthermia was tested by giving graded heat treatments and assessing local control at 90 days. Mice were divided into three groups which were pre-treated for 3 days in ambient temperatures of 4, 21 or 35°C. This enabled the mean tumour resting temperature to be varied by up to 11°C, before subsequent heat treatment. For the heat treatments, the tumours were clamped in order to eliminate blood flow, resulting in uniform temperature distributions and hence more uniform thermal sensitivity. TCD₅₀ values were used to construct Arrhenius plots. For all three pre-treatment temperatures, these plots demonstrated a factor of 1·6 increase in heating time per degree Celcius reduction in heating temperature. However, tumours kept in a 4°C environment before treatment were more thermally sensitive than those kept in 21°C conditions, while those in a 35°C environment were more resistant. Pretreatment at 4°C was equivalent to an increase of either 0·5°C in heating temperature or 28 per cent in heating time, compared with pre-treatment at 21°C. Pre-treatment at 35°C was equivalent to a reduction of either 0·6°C in heating temperature or 25 per cent in heating time. These data indicate that the pre-treatment tumour temperature is an important parameter, but the effect of heat treatment is more closely related to absolute heating temperature rather than to the increase in temperature above the normal resting level.

• hyperthermia
• tumuor cure
• adaptation temperature