Thermal distributions in a water bath heated mouse tumor

In the past several years numerous investigators have employed various mouse tumor systems and a variety of heating methods to examine the effects of hyperthermia in vivo. These studies have led, in some cases, to different results in tumor response in what appear to be similar experiments. Our results indicate that these discrepancies may in part be attributable to variations in intratumor temperature and depend strongly upon the method and conditions of heating employed. In all cases, we have employed the C3H mammary carcinoma tumor system with the tumor implanted in the right hind limb of the mouse. All tumors were 7-9 mm in diameter at the time of the experiments. Water bath heating was employed with the animals under one of four possible conditions: the presence or absence of anesthesia, and the use or lack of core cooling. Thermometry was performed with an array of multiple microthermocouples, each less than 150 micron in diameter, implanted in the tumor in a grid-like pattern. Significant variations (1.0 degrees C for no anesthesia, p less than .01; 1.3 degrees C for Thorazine/Ketamine, p less than .001) in intratumor temperature were found across the tumor in the unperturbed state. These variations were essentially eliminated under all hyperthermic conditions. Control of core (rectal) temperature (with or without anesthesia) reduced the intratumor temperatures even though the water bath temperature was held constant resulting in variations between water bath and tumor temperatures of from 0.1-0.8 degrees C.