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 language | English |
|---|---|
| Title of host publication | Proceedings of SPIE - The International Society for Optical Engineering |
| Editors | Thomas J. Dougherty |
| Pages | 141-151 |
| Number of pages | 11 |
| Volume | 2392 |
| State | Published - 1995 |
| Externally published | Yes |
| Event | Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy IV - San Jose, CA, USA Duration: Feb 4 1995 → Feb 5 1995 |
Other
| Other | Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy IV |
|---|---|
| City | San Jose, CA, USA |
| Period | 2/4/95 → 2/5/95 |
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All Science Journal Classification (ASJC) codes
- Electrical and Electronic Engineering
- Condensed Matter Physics
Cite this
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 proceeding › Conference contribution
}
TY - GEN
T1 - Oxygen sensitivity of PDT determined from time-dependent electrode measurements in spheroids
AU - Foster, Thomas H.
AU - Nichols, Michael G.
PY - 1995
Y1 - 1995
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0029452582&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029452582&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:0029452582
SN - 0819417394
SN - 9780819417398
VL - 2392
SP - 141
EP - 151
BT - Proceedings of SPIE - The International Society for Optical Engineering
A2 - Dougherty, Thomas J.
ER -