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Photodynamic therapy (PDT) elicits significant molecular and host responses, which are understood to be important to long-term tumor control. We demonstrate the ability to image these responses using confocal fluorescence in superficial tumors in vivo.

Raman spectra were obtained from single mouse tumor cells before and after treatment with photodynamic therapy. We are presently investigating pure chemicals to illuminate differences observed in the spectra of treated and untreated cells.

We examine the bleaching kinetics of the photosensitizer Photofrin® using spectrally-resolved fluorescence measurements in optical sections of multicell tumor spheroids during photodynamic therapy. The results suggest that Photofrin photodegrades via two simultaneous bleaching mechanisms, and their relative importance is dependent on the initial Photofrin concentration.