Evaluation of changes in oxygen tension as indicators of RIF-1 tumor response to Nd:YAG laser heating

Heat-induced oxygen tension changes in RIF-1 tumors in C3H male mice were analyzed in an attempt to correlate these changes with tumor response to Nd:YAG laser heating. A low power, microprocessor-controlled Nd:YAG laser was used to superficially heat 250-300 mm3 tumors to base temperatures of 44, 45, 46, or 48 degrees C for 30 minutes via a flexible 600 microns quartz fiberoptic with a terminating microlens. A glass, Clark-style microelectrode was inserted into the center of each tumor allowing real time measurement of the tumor's oxygenation status before, during, and after heating. Results showed that heating at 44 degrees C caused a greater than 2-fold increase in oxygen tension during heating, while a temperature of 48 degrees C caused a brief initial increase in oxygen tension followed by a decrease to below pretreatment values. There was a significant correlation (P < 0.05) between relative tumor oxygen tension during and post-heating and tumor growth delay. A significant correlation (P < 0.05) was also seen between tumor base temperature during heating and tumor growth delay. It appears from our initial data that single point oxygen tension measurements in small RIF-1 tumors may be useful indicators of this model's response to Nd:YAG laser heating. This result may allow for modification of heating parameters (temperature/time) during treatment to optimize thermal response.