How photobleaching affects dosimetry and fluorescence monitoring of PDT in turbid media

Steven L. Jacques; Rachel Joseph; Gary Gofstein

doi:10.1117/12.146307

18 June 1993 How photobleaching affects dosimetry and fluorescence monitoring of PDT in turbid media

Steven L. Jacques, Rachel Joseph, Gary Gofstein

Proceedings Volume 1881, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy II; (1993) https://doi.org/10.1117/12.146307
Event: OE/LASE'93: Optics, Electro-Optics, and Laser Applications in Scienceand Engineering, 1993, Los Angeles, CA, United States

Abstract

The observation of photobleaching is affected by the tissue optics. The apparent time constant for photobleaching at a particular irradiance of light is related to the true photobleaching constant, D, in J/cm² by a factor which depends on the tissue optical properties, especially at the wavelength used to excite fluorescence. We report in vivo experimental measurements of protoporphyrin IX (PPIX) photobleaching in subcutaneous rat tumors which suggest tentative values for D of about 105 +/- 23 J/cm² during 630 nm irradiation. The effect of such a photobleaching constant on the photodynamic dose, P, in photons/cm³ absorbed by PPIX, was calculated. We estimate that an initial PPIX concentration of about 0.2 (mu) g/ml is required such that P reaches twice the toxic threshold photodynamic dose, P_th, which is assumed to be similar to the 8.6 X 10¹⁷ value cited for PhotofrinII. The above estimates are subject to further investigation. This paper presents the mathematics underlying the process of photobleaching and its observation based on fluorescence monitoring.

Citation Download Citation

Steven L. Jacques, Rachel Joseph, and Gary Gofstein "How photobleaching affects dosimetry and fluorescence monitoring of PDT in turbid media", Proc. SPIE 1881, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy II, (18 June 1993); https://doi.org/10.1117/12.146307

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