Abstract
Singlet oxygen direct dosimetry and photosensitizer fluorescence photobleaching are being investigated and applied as dosimetric tools during 5-aminolevulinic acid (ALA)-induced protophorphyrin IX (PpIX) photodynamic therapy (PDT) of normal skin and skin cancers. The correlations of photosensitizer fluorescence and singlet oxygen luminescence (SOL) emission signals to distribution and cumulative dose are difficult to interpret because of the temporal and spatial variations of three essential components (light fluence rate, photosensitizer concentration and oxygen concentration) in PDT. A one-dimensional model is proposed in this paper to simulate the dynamic process of ALA-PDT of normal human skin in order to investigate the time-resolved evolution of PpIX, ground-state oxygen and distributions. The model incorporates a simplified three-layer semi-infinite skin tissue, Monte Carlo simulations of excitation light fluence and both PpIX fluorescence and SOL emission signals reaching the skin surface, -mediated photobleaching mechanism for updating PpIX, and distributions after the delivery of each light dose increment, ground-state oxygen supply by diffusion from the atmosphere and perfusion from blood vessels, a cumulative -dependent threshold vascular response, and the initial non-uniform distribution of PpIX. The PpIX fluorescence simulated using this model is compared with clinical data reported by Cottrell et al (2008 Clin. Cancer Res. 14 4475–83) for a range of irradiances (10–150 mW cm−2). Except for the vascular response, one set of parameters is used to fit data at all irradiances. The time-resolved depth-dependent distributions of PpIX, and at representative irradiances are presented and discussed in this paper, as well as the PDT-induced vascular response at different depths. Tissue hypoxia and shutdown of oxygen supply occur in the upper dermis, where PpIX is also preserved at the end of treatment.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
