Monitoring oxygen concentration during photodynamic therapy using prompt photosensitizer fluorescence.

A novel technique is described that uses either time-resolved or steady state prompt photosensitizer fluorescence to measure local oxygen concentration. Solution experiments conducted with Al(III) phthalocyanine chloride tetrasulfonic acid confirmed that the steady state fluorescence signal is dependent on the oxygen concentration and fluence rate. A relationship between prompt sensitizer fluorescence and sensitizer triplet quenching efficiency is derived which does not require knowledge of the Stern-Volmer constant. Similar relationships are also derived for sensitizer delayed fluorescence and phosphorescence. An explicit photodynamic therapy (PDT) dose metric that incorporates light dosimetry, sensitizer dosimetry, and triplet quenching efficiency is introduced. All components of this metric can be determined by optical measurements.