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

Michael G. Nichols, Thomas H. Foster

Research output: Contribution to journalConference articlepeer-review

7 Scopus citations


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 comprising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-il photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steadystate 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. Timedependent 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.

Original languageEnglish (US)
Pages (from-to)260-271
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Jul 19 1994
Externally publishedYes
EventOptical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III 1994 - Los Angeles, United States
Duration: Jan 23 1994Jan 29 1994

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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