Photodynamic treatment of the RIF-1 tumor with Verteporfin with online monitoring of tissue oxygen using electron paramagnetic resonance oximetry

In this study, treatment of the RIF-1 tumor was examined with photodynamic therapy using Verteporfin (formerly benzoporphyrin derivative, BPD). The effects of two different optical dose rates were examined, with no detectable difference in the tumor regrowth time. Oxygen consumption during PDT could reliably be monitored with electron paramagnetic resonance (EPR) oximetry using an implanted paramagnetic material within the tumor. A reduction of the tumor pO₂ was detected in the animals that were followed after treatment, suggesting that there was a compromise to the tumor vasculature that persisted throughout the measurements. At high total doses some of the tumors did not regrow. Altogether these results are indicative of the tumor destruction being caused by destruction of the blood vessels from the treatment.