Temperature-dependent changes in physiologic parameters of spontaneous canine soft tissue sarcomas after combined radiotherapy and hyperthermia treatment

Purpose: The objectives of this study were to evaluate effects of hyperther mia on tumor oxygenation, extracellular pH (pHe), and blood flow in 13 dogs with spontaneous soft tissue sarcomas prior to and after local hyperthermi a. Methods and Materials: Tumor pO(2) was measured using an Eppendorf polarogr aphic device, pHe using interstitial electrodes, and blood flow using contr ast-enhanced magnetic resonance imaging (MRI), Results: There was an overall improvement in tumor oxygenation observed as an increase in median pO(2) and decrease in hypoxic fraction (% of pO(2) me asurements < 5 mmHg) at 24-h post hyperthermia. These changes were most pro nounced when the median temperature (T-50) during hyperthermia treatment wa s less than 44 degrees C, Tumors with T-50 > 44 degrees C were characterize d by a decrease in median pO(2) and an increase in hypoxic fraction. Simila r thermal dose-related changes were observed in tumor perfusion. Perfusion was significantly higher after hyperthermia, Increases in perfusion were mo st evident in tumors with T-50 < 44 degrees C, With T-50 > 44 degrees C, th ere was no change in perfusion after hyperthermia. On average, pHe values d eclined in all animals after hyperthermia, with the greatest reduction seen for larger T-50 values. Conclusion: This study suggests that hyperthermia has biphasic effects on t umor physiologic parameters. Lower temperatures tend to favor improved perf usion and oxygenation, whereas higher temperatures are more likely to cause vascular damage, thus leading to greater hypoxia, While it has long been r ecognized that such effects occur in rodent tumors, this is the first repor t to tie such changes to temperatures achieved during hyperthermia in the c linical setting. Furthermore, it suggests that the thermal threshold for va scular damage is higher in spontaneous tumors than in more rapidly growing rodent tumors. (C) 2000 Elsevier Science Inc.