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98increasing depth under the tissue surface for some PSs. The PSs from the group (SiNc, SiPc,TiPc, ZnS 3 Pc) absorb within the region of 670-800 nm which is within the therapeutic window.Typical normalized absorption spectra of the investigated PSs measured with a UV-Vis-NIRspectrophotometerCary-5E-Varian are shown in Fig.2. Propagation of a collimated circularlaser beam is modeled at wavelength corresponding to maximum absorption of the tested PS.Optical properties (absorption and scattering coefficients, µ a and µ s , anisotropy factor) of thehealthy and tumor tissue are chosen from the literature. A Henyey-Greenstein scattering phasefunction and refractive index of 1.37 are accepted throughout all types of tissue. A Beer-Lambert propagation is assumed inside the tumor with the PS’s absorption coefficient µ PS .Efficiency of the PSs is compared at a given concentration of the drug on the basis of theradiant exposure (J/cm 2 ) required to achieve necrosis at increasing depth inside the tumor.[1] R.M. Ion, Porphyrins for tumor destruction in photodynamic therapy, Current Topics inBiophysics, 24 (1),21–34 , 2000.[2] R. R Allison, G. H Downie, R. Cuenca, Xin-Hua Hu, C. JH Childs, C. H Sibata,Photosensitizers in clinical PDT, Photodiagnosis and Photodynamic Therapy (2004) 1,27-423. DETERMINATION OF PHOTOSENSITIZER REFRACTIVE INDEX FOR ANEFFICIENT photodynamic therapyMihaela Antonina Calin 1 , Rodica Mariana Ion 2 , Nicoleta Herascu 11National Institute of Research and Development for Optoelectronics INOE 2000, Bucharest2INCDCP – ICECHIM, Splaiul Independentei 202, 060021-BucharestPhotodynamic therapy is a local treatment modality of cancer, based on theadministration of photosensitizer, which is selectively retained al tumoral level, which after theoptical radiations exposure lead to the tumoral tissue destruction.The application of the photodynamic therapy in clinical practice presentes certainproblems about: choice of the photosensitizer type, establishment of it administration,modalities of drug preparation (depending of administration), determination of therapeuticconcentration of photosensitizer, establishment the expecting period of time from thephotosensitizer administration moment till the laser irradiation of the tumor, choice of the lasersource (continuous or pulsed emission), establishment of the laser radiation parameters