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Dose and Timing of the First Light Fraction in Two‐fold Illumination Schemes for Topical ALA‐mediated Photodynamic Therapy of Hairless Mouse Skin ¶
Author(s) -
Robinson Dominic J.,
Bruijn Henriëtte S.,
Star Willem M.,
Sterenborg Henricus J. C. M.
Publication year - 2003
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2003)0770319datotf2.0.co2
Subject(s) - hairless , photodynamic therapy , protoporphyrin ix , fluence , kinetics , fluorescence , chemistry , photosensitizer , fraction (chemistry) , nuclear medicine , optics , photochemistry , medicine , chromatography , physics , biochemistry , ion , organic chemistry , quantum mechanics
A fractionated illumination scheme in which a cumulative fluence of 100 J cm −2 is delivered in two equal light fractions separated by a dark interval of 2 h has been shown to considerably increase the efficacy of 5‐aminolevulinic acid (ALA)–photodynamic therapy (PDT). The efficacy of such a scheme is further increased if the fluence of the first light fraction is reduced to 5 J cm −2 . We have investigated the relationship between the PDT response and the kinetics of protoporphyrin IX (PpIX) fluorescence in the SKH1 HR hairless mouse for first fraction fluences below 5 J cm −2 delivered 4 h after the application of ALA and 10 J cm −2 delivered 2 h after the application of ALA. Illumination is performed using 514 nm at a fluence rate of 50 mW cm −2 . Reducing the fluence of the first fraction to 2.5 J cm −2 does not result in significantly different visual skin damage. The PDT response, however, is significantly reduced if the fluence is lowered to 1 J cm −2 , but this illumination scheme (1 + 99 J cm −2 ) remains significantly more effective than a single illumination of 100 J cm −2 . A first light fraction of 10 J cm −2 can be delivered 2 h earlier, 2 h after the application of ALA, without significant reduction in the PDT response compared with 5 + 95 J cm −2 delivered 4 and 6 h after the application of ALA. The kinetics of PpIX fluorescence are consistent with those reported previously by us and do not explain the significant increase in PDT response with a two‐fold illumination scheme. Histological sections of the illuminated volume showed a trend toward increasing extent and depth of necrosis for the two‐fold illumination scheme in which the first light fraction is 5 J cm −2 , compared with a single illumination scheme.