Measurement and modelling of protoporphyrin IX photo-oxidation during superficial PDT

D J Robinson, M R Stringer, W R Crum, P Collins

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

Abstract

The oxidation of photosensitisers during photodynamic therapy (PDT) has important implications for their therapeutic and diagnostic potential. The reduction in sensitiser concentration during illumination progressively reduces the effectiveness of therapy and ultimately, limits the destruction of the host tissue. In the course of our studies of the effects of PDT upon superficial skin disorders, following topical application of 5-aminolaevulinic acid (ALA), we routinely record the surface fluorescence emission of protoporphyrin IX (PpIX) before, during, and after therapy, in order to monitor the sensitiser photo-oxidation. It is important, therefore, to establish that measurements made in this way are representative of the variation in sensitiser concentration throughout the illuminated volume.

We have developed a time-dependent Monte-Carlo model to simulate PpIX photooxidation during either low intensity laser (488 nm) or white light irradiation of plaque psoriasis. We have assessed the effect of differences in the optical properties of tissue at sites on different patients prior to treatment and the effect of these variations on the surface fluorescence signal detected during treatment, at sites within the same plaque.

The results show that the PpIX fluorescence intensity recorded from plaque psoriasis is an accurate indicator of the relative concentration of the sensitiser and can be used as a direct comparison between different sites and different patients. Also, the reduction in fluorescence emission during PDT is an effective measure of the depletion in sensitiser concentration throughout the illuminated volume. These results illustrate that the light dose required to achieve significant PpIX photo-oxidation is significantly lower than that often adopted for the treatment of superfacial skin conditions.

Original languageEnglish
Title of host publicationPHOTOCHEMOTHERAPY: PHOTODYNAMIC THERAPY AND OTHER MODALITIES II, PROCEEDINGS OF
EditorsSB Brown, B Ehrenberg, J Moan, A Katzir
Place of PublicationBELLINGHAM
PublisherSPIE - INT SOC OPTICAL ENGINEERING
Pages31-39
Number of pages3
ISBN (Print)0-8194-2326-2
DOIs
Publication statusPublished - 1996
EventConference on Photochemotherapy - Photodynamic Therapy and Other Modalities II - VIENNA
Duration: 7 Sept 19968 Sept 1996

Conference

ConferenceConference on Photochemotherapy - Photodynamic Therapy and Other Modalities II
CityVIENNA
Period7/09/19968/09/1996

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