Fluorescence Quantum Yield of Verteporfin is Independent of Oxygen

Photodynamic therapy dosimetery and treatment planning is affected by the concentration of photosensitizer in a given tissue, and these values are often estimated based on measurements of fluorescence in the region to be treated. Some studies with benzoporphyrin derivate monoacid ring a (BPD-MA) showed a significant increase in fluorescence quantum yield with deoxygenation of the solution, indicating a possible oxygen sensitive switch in intersystem crossing or reverse intersystem crossing. The experiments done in this paper show that at oxygenation levels found in vivo the variation in fluorescence quantum yield of liposomal BPD-MA (verteporfin) is negligible for changes in solution oxygenation. The results from all of the experiments show that it is not necessary to measure the oxygenation of tissues when calculating the concentration of verteporfin from fluorescence measurements, so that dosimetry calculations based upon photosensitizer levels would not be affected by the tissue oxygenation. This greatly simplifies the dosimetry process with verteporfin.