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Proceedings Paper

In vivo determination of the absorption and scattering spectra of the human prostate during photodynamic therapy
Author(s): Jarod C. Finlay; Timothy C. Zhu; Andreea Dimofte; Diana C. Hsiung Stripp; S. Bruce Malkowicz; Richard Whittington; Jeremy Miles; Eli Glatstein; Stephen M. Hahn
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Paper Abstract

A continuing challenge in photodynamic therapy is the accurate in vivo determination of the optical properties of the tissue being treated. We have developed a method for characterizing the absorption and scattering spectra of prostate tissue undergoing PDT treatment. Our current prostate treatment protocol involves interstitial illumination of the organ via cylindrical diffusing optical fibers (CDFs) inserted into the prostate through clear catheters. We employ one of these catheters to insert an isotropic white light point source into the prostate. An isotropic detection fiber connected to a spectrograph is inserted into a second catheter a known distance away. The detector is moved along the catheter by a computer-controlled step motor, acquiring diffuse light spectra at 2 mm intervals along its path. We model the fluence rate as a function of wavelength and distance along the detector’s path using an infinite medium diffusion theory model whose free parameters are the absorption coefficient μa at each wavelength and two variables A and b which characterize the reduced scattering spectrum of the form μ’s = Aλ-b. We analyze our spectroscopic data using a nonlinear fitting algorithm to determine A, b, and μa at each wavelength independently; no prior knowledge of the absorption spectrum or of the sample’s constituent absorbers is required. We have tested this method in tissue simulating phantoms composed of intralipid and the photosensitizer motexafin lutetium (MLu). The MLu absorption spectrum recovered from the phantoms agrees with that measured in clear solution, and μa at the MLu absorption peak varies linearly with concentration. The µ’s spectrum reported by the fit is in agreement with the known scattering coefficient of intralipid. We have applied this algorithm to spectroscopic data from human patients sensitized with MLu (2 mg kg-1) acquired before and after PDT. Before PDT, the absorption spectra we measure include the characteristic MLu absorption peak. Using our phantom data as a calibration, we have determined the pre-treatment MLu concentration to be approximately 2 to 8 mg kg-1. After PDT, the concentration is reduced to 1 to 2.5 mg kg-1, an indication of photobleaching induced by irradiation. In addition, absorption features corresponding to the oxygenated and deoxygenated forms of hemoglobin indicate a reduction in tissue oxygenation during treatment.

Paper Details

Date Published: 14 June 2004
PDF: 11 pages
Proc. SPIE 5315, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIII, (14 June 2004); doi: 10.1117/12.528968
Show Author Affiliations
Jarod C. Finlay, Univ. of Pennsylvania (United States)
Timothy C. Zhu, Univ. of Pennsylvania (United States)
Andreea Dimofte, Univ. of Pennsylvania (United States)
Diana C. Hsiung Stripp, Univ. of Pennsylvania (United States)
S. Bruce Malkowicz, Univ. of Pennsylvania (United States)
Richard Whittington, Univ. of Pennsylvania (United States)
Jeremy Miles, Univ. of Pennsylvania (United States)
Eli Glatstein, Univ. of Pennsylvania (United States)
Stephen M. Hahn, Univ. of Pennsylvania (United States)

Published in SPIE Proceedings Vol. 5315:
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIII
David Kessel, Editor(s)

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