A dynamic model for ALA-PDT of skin: analysis of the correlation of fluorescence and singlet oxygen luminescence to spatial distribution of singlet oxygen
2011
Both photosensitizer fluorescence photobleaching and singlet oxygen luminescence (SOL) have been measured
during ALA-PDT of skin in attempts to estimate PDT dose. However, the relationship of these detected signals
to singlet oxygen ( 1 O 2 ) dose in a given volume and to its depth distribution are not well understood and difficult
to verify experimentally because of the temporal and spatial variations of the essential parameters in PDT. A
model for ALA-PDT of normal human skin was developed to simulate the dynamic progress of PDT. The model
incorporates Monte Carlo simulations of excitation light fluence and both SOL and PpIX fluorescence signals,
1 O 2 -mediated photobleaching mechanism, ground-state oxygen ( 3 O 2 ) diffusion and perfusion, a cumulative 1 O 2 -dependent threshold vascular response and any initial distribution of PpIX. The simulated
time-resolved evolution
of the instantaneous PpIX fluorescence photobleaching and cumulative SOL signals are examined as functions
of irradiance and related to both the time-resolved distribution of cumulative 1 O 2 production at various depths
and the average dose in the dermis. The simulations used a green light source at 523 nm. The correlation of SOL
signals with the average dose was found to be less
irradiance-dependent than that of fluorescence photobleaching,
which indicates the great potential of SOL as a clinical dosimetric tool in PDT.
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