18 June 1993 How photobleaching affects dosimetry and fluorescence monitoring of PDT in turbid media
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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, Pth, 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.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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); doi: 10.1117/12.146307; https://doi.org/10.1117/12.146307
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