UC Irvine

Transcutaneous oxygen electrodes are used to non-invasively measure tissue oxygen tension during photodynamic therapy (PDT). Measurements are performed on VX-2 skin carcinomas in rabbit ears. The degree of tumor oxygen tension reduction is proportional to the applied light dose. In the absence of irradiation, oxygen tension returns to pre-irradiation levels until a 'damage threshold' has been reached. For 50mW/cm2 irradiations of Photofrin II (at 630 nm) and tetraphenylporphine tetrasulfonate (at 657 nm), the cumulative dose required to irreversibly deplete tumor transcutaneous oxygen was approximately 300 kJ/m2 and 600 kJ/m2, respectively.