The control of photosensitizer in tissue during photodynamic therapy by means of absorption spectroscopy.

The data about absorption spectra properties of the photosensitized tumor tissues in vivo are very important for the evaluation photosensitizer concentration and influence of the chemical environment on photosensitizer properties in tissue. This information will help one in the appropriate choosing of irradiation light dose and wavelength in the photodynamic therapy (PDT) treatment. The interaction of photosensitizer with tumor tissue may change its absorption spectrum. Moreover the light irradiation during PDT treatment can also affect the photosensitizer chemical structure and hence change its absorption spectrum. The simple technique based on the measurement of reflection spectra try means of fiber optic spectrometer has been developed This method allows one to evaluate the contribution to the tissue absorption properties due to the presence of photosensitizer in it. The absorption spectra of photosensitized normal and tumor tissues presented in this paper has been obtained during PDT sessions of head and neck tumors. The photosensitizer - sulphanated aluminum phthalocyanine (Photosence) (NIOPIC, Russia) has been injected intravenously in doses 0.5 - 2 mg per kg of body weight. It has been observed that absorption properties of this photosensitizer are not changed significantly in tissue as compared to that of in solution. The absorption spectra widening and red shift (4 nm) has been noticed The qualitative pharmocokinetic of photosensitizer based on absorption spectra measurements is presented.