Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy

Michael G. Nichols; Thomas H. Foster

doi:10.1117/12.179983

19 July 1994 Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy

Michael G. Nichols, Thomas H. Foster

Author Affiliations +

Proceedings Volume 2133, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III; (1994) https://doi.org/10.1117/12.179983
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

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.

Citation Download Citation

Michael G. Nichols and Thomas H. Foster "Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy", Proc. SPIE 2133, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III, (19 July 1994); https://doi.org/10.1117/12.179983

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