INTRAVASCULAR OXYGEN DISTRIBUTION IN SUBCUTANEOUS 9L TUMORS AND RADIATION SENSITIVITY

Phosphorescence quenching was evaluated as a technique for measuring P o-2 in tumors and for determining the effect of increased Po-2 on sens itivity of the tumors to radiation. Suspensions of cultured 9L cells o r small pieces of solid tumors from 9L cells were injected subcutaneou sly on the hindquarter of rats, and tumors were grown to between 0.2 a nd 1.0 cm in diameter. Oxygen-dependent quenching of the phosphorescen ce of intravenously injected Pd-meso-tetra-(4-carboxyphenyl) porphine was used to image the in vivo distribution of Po-2 in the vasculature of small tumors and surrounding tissue. Maps (512 x 480 pixels) of tis sue oxygen distribution showed that the Po-2 within 9L tumors was low (2-12 Torr) relative to the surrounding muscle tissue (20-40 Torr). Wh en the rats were given 100% oxygen or carbogen (95% O-2-5% CO2) to bre athe, the Po-2 in the tumors increases significantly. This increase wa s variable among tumors and was greater with carbogen compared with 10 0% oxygen. Based on irradiation and regrowth studies, carbogen breathi ng increased the sensitivity of the tumors to radiation. This is consi stent with the measured increase in Po-2 in the tumor vasculature. It is concluded that phosphorescence quenching can be used for noninvasiv e determination of the oxygenation of tumors. This method for oxygen m easurements has great potential for clinical application in tumor iden tification and therapy.