MODELING OF PHOTOSENSITIZER FLUORESCENCE EMISSION AND PHOTOBLEACHING FOR PHOTODYNAMIC THERAPY DOSIMETRY

Photon diffusion theory was used to model photobleaching and tissue ne crosis resulting from broad-beam therapeutic light irradiation of tiss ue containing a photosensitizer. The photosensitizer fluorescence sign al at the tissue surface was simulated with both broad-beam and pencil -beam excitation. The relationship between the decreasing fluorescence signal and the increasing depth of tissue photodynamic damage during treatment was examined. By analyzing spatially resolved fluorescence m easured at the tissue surface in terms of an equivalent virtual point or planar source of fluorescence within the tissue, predictions of nec rosis depth that are insensitive to a range of initial treatment param eters were shown to be possible. Preliminary measurements in tissue-si mulating phantoms supported the main theoretical findings. The potenti al value and feasibility of this technique for photodynamic therapy do simetry are discussed. (C) 1998 Optical Society of America. OCIS codes : 170.5180, 170.5280, 170.6280.