Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids

Thomas H. Foster, Michael G. Nichols

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Citations (Scopus)

Abstract

We have previously reported on a microelectrode technique for mapping spatial and temporal distributions of oxygen in and around individual photosensitized multicell tumor spheroids. Steady-state and time-resolved measurements have been analyzed using diffusion theory ad have yielded estimates of the oxygen diffusion coefficient in the spheroid, the rate of metabolic oxygen consumption, and the fluence-rate-dependent rate of photochemical oxygen depletion. We have recently modified the theoretical treatment of the time-resolved measurements to include the oxygen dependence of the rate of therapy-induced oxygen consumption. The oxygen consumption term in the diffusion equation is now derived from kinetics of type II photochemistry. This expression contains the ration of two rate constants' the photosensitizer triplet decay rate (k p) and the bimolecular rate for collisional triplet-quenching interactions with oxygen (k ot). From fits of numerical solutions of the diffusion equation to microelectrode measurements of PDT-induced oxygen transients, k p/k ot, may be obtained for a photosensitizer in a multicell environment. The ration plays an important role in direct cell photosensitization by defining the concentration at which singlet oxygen formation is limited by the availability of oxygen. In a multicell environment where oxygen supply is diffusional, extremely low values of k p/k ot exacerbate the oxygen depletion problem. Recent experiments and analysis indicate that in some cases photosensitizer bleaching rates may also be determined from microelectrode measurements in spheroids.

Original languageEnglish
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
EditorsThomas J. Dougherty
Pages141-151
Number of pages11
Volume2392
StatePublished - 1995
Externally publishedYes
EventOptical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy IV - San Jose, CA, USA
Duration: Feb 4 1995Feb 5 1995

Other

OtherOptical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy IV
CitySan Jose, CA, USA
Period2/4/952/5/95

Fingerprint

spheroids
Electrodes
Oxygen
electrodes
sensitivity
oxygen
oxygen consumption
Photosensitizers
Microelectrodes
rations
Time measurement
depletion
time measurement
temporal distribution
diffusion theory
Oxygen supply
bleaching
Photochemical reactions
photochemical reactions
decay rates

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering
  • Condensed Matter Physics

Cite this

Foster, T. H., & Nichols, M. G. (1995). Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids. In T. J. Dougherty (Ed.), Proceedings of SPIE - The International Society for Optical Engineering (Vol. 2392, pp. 141-151)

Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids. / Foster, Thomas H.; Nichols, Michael G.

Proceedings of SPIE - The International Society for Optical Engineering. ed. / Thomas J. Dougherty. Vol. 2392 1995. p. 141-151.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Foster, TH & Nichols, MG 1995, Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids. in TJ Dougherty (ed.), Proceedings of SPIE - The International Society for Optical Engineering. vol. 2392, pp. 141-151, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy IV, San Jose, CA, USA, 2/4/95.
Foster TH, Nichols MG. Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids. In Dougherty TJ, editor, Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2392. 1995. p. 141-151
Foster, Thomas H. ; Nichols, Michael G. / Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids. Proceedings of SPIE - The International Society for Optical Engineering. editor / Thomas J. Dougherty. Vol. 2392 1995. pp. 141-151
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