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 w ere analyzed in an attempt to correlate these changes with tumor respo nse to Nd:YAG laser heating. A low power, microprocessor-controlled Nd :YAG laser was used to superficially heat 250-300 mm3 tumors to base t emperatures of 44, 45, 46, or 48-degrees-C for 30 minutes via a flexib le 600 mum quartz fiberoptic with a terminating microlens. A glass, Cl ark-style microelectrode was inserted into the center of each tumor al lowing 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 heati ng, while a temperature of 48-degrees-C caused a brief initial increas e in oxygen tension followed by a decrease to below pretreatment value s. There was a significant correlation (P<0.05) between relative tumor oxygen tension during and post-heating and tumor growth delay. A sign ificant correlation (P<0.05) was also seen between tumor base temperat ure during heating and tumor growth delay. It appears from our initial data that single point oxygen tension measurements in small RIF-1 tum ors 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.