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Proceedings Paper

Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy
Author(s): Michael G. Nichols; Thomas H. Foster
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Paper Abstract

We have previously reported results of experiments in which EMT6/Ro spheroids were subjected to Photofrin-PDT consisting of a fixed incident fluence (60 J-cm-2) delivered at 200, 50, and 25 mW-cm-2. Surviving fractions from treated spheroids decreased as the incident fluence rate was lowered over this range. We have interpreted these data using a model wherein the cells compromising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-II photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steady-state measurements of 3O2 gradients in and around metabolizing spheroids allow determination of the 3O2 diffusion constant and the rate of metabolic 3O2 consumption within a spheroid. Time-dependent measurements obtained at a single spatial location during laser irradiation are fit to numerical solutions of a pair of time-dependent diffusion with consumption equations. Fits allow a determination of the rate of PDT-induced 3O2 consumption. Based on these fits, it is possible to calculate the spatial and temporal distributions of oxygen within a spheroid undergoing PDT.

Paper Details

Date Published: 19 July 1994
PDF: 12 pages
Proc. SPIE 2133, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III, (19 July 1994); doi: 10.1117/12.179983
Show Author Affiliations
Michael G. Nichols, Univ. of Rochester School of Medicine and Dentistry (United States)
Thomas H. Foster, Univ. of Rochester School of Medicine and Dentistry (United States)


Published in SPIE Proceedings Vol. 2133:
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III
Thomas J. Dougherty, Editor(s)

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