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Proceedings Paper

How photobleaching affects dosimetry and fluorescence monitoring of PDT in turbid media
Author(s): Steven L. Jacques; Rachel Joseph; Gary Gofstein
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Paper 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.

Paper Details

Date Published: 18 June 1993
PDF: 12 pages
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
Show Author Affiliations
Steven L. Jacques, Univ. of Texas M.D. Anderson Cancer Ctr. (United States)
Rachel Joseph, Univ. of Texas M.D. Anderson Cancer Ctr. (United States)
Gary Gofstein, Univ. of Texas M.D. Anderson Cancer Ctr. (United States)


Published in SPIE Proceedings Vol. 1881:
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy II
Thomas J. Dougherty, Editor(s)

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