Type II photodynamic therapy (PDT) is used for cancer treatment based on the combined action of a photosensitizer, a
special wavelength of light, oxygen (3O2) and generation of singlet oxygen (1O2). Intra-patient and inter-patient
variability of oxygen concentration ([3O2]) before and after the treatment as well as photosensitizer concentration and
hemodynamic parameters such as blood flow during PDT has been reported. Simulation of these variations is valuable,
as it would be a means for the rapid assessment of treatment effect. A mathematical model has been previously
developed to incorporate the diffusion equation for light transport in tissue and the macroscopic kinetic equations for
simulation of [3O2], photosensitizers in ground and triplet states and concentration of the reacted singlet oxygen ([1O₂]rx)
during PDT. In this study, the finite-element based calculation of the macroscopic kinetic equations is done for 2-(1-
Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH)-mediated PDT by incorporating the information of the
photosensitizer photochemical parameters as well as the tissue optical properties, photosensitizer concentration, initial
oxygen concentration ([3O2]0), blood flow changes and Φ that have been measured in mice bearing radiation-induced
fibrosarcoma (RIF) tumors. Then, [1O2]rx calculated by using the measured [3O2] during the PDT is compared with
[1O2]rx calculated based on the simulated [3O₂]; both calculations showed a reasonably good agreement. Moreover, the
impacts of the blood flow changes and [3O2]0 on [1O2]rx have been investigated, which showed no pronounced effect of
the blood flow changes on the long-term 1O2 generation. When [3O2]0 becomes limiting, small changes in [3O₂] have
large effects on [1O2]rx.
Rozhin Penjweini, Michele M. Kim, Jarod C. Finlay, and Timothy C. Zhu, "Investigating the impact of oxygen concentration and blood flow variation on photodynamic therapy," Proc. SPIE 9694, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXV, 96940L (Presented at SPIE BiOS: February 14, 2016; Published: 1 March 2016); https://doi.org/10.1117/12.2211120.
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