The influence of pre-treatment temperature on the thermal sensitivity of a mouse tumour

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 pre-treated for 3 days in ambient temperatures of 4, 21 or 350C, enabling the mean tumour resting temperature to be varied by up to 110C, before subsequent heat treatment. 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, plots demonstrated a factor of 1.6 increase in heating time per degree Celcius reduction in heating temperature. Tumours kept in a 40C environment before treatment were more thermally sensitive than those kept in 210C conditions, while those in a 350C environment were more resistant. Pre-treatment at 40C was equivalent to an increase of either 0.50C in heating temperature or 28% in heating time, compared with pre-treatment at 210C. Pre-treatment at 350C was equivalent to a reduction of either 0.60C in heating temperature or 25% in heating time. (author)