Simulation of fractionated and continuous irradiation in photodynamic therapy: study the differences between photobleaching and singlet oxygen dose deposition.

This study aims to compare the continuous irradiation with fractionated irradiation for photodynamic therapy (PDT) of solid tumors with intraperitoneally administered 5-aminolaevulinic acid (ALA). Therefore, considering the complex physiology of solid tumors and in order to inform simulations well, we did experiments on Balb/c mice using non-invasive fluorescence spectroscopy to have a feedback of protoporphyrin IX (PpIX) concentration in tumor just before irradiation and during treatment. PDT simulations were performed based on delivery of 36 J cm(-2) total laser energy (630 nm) at the fluence rate of 40 mW cm(-2) either for continuous or fractionated illumination. Based on the calculated amounts of (1)O(2) dose deposition and comparing these amounts with the 5 × 10 (18) molecules cm(-3) threshold of reacting (1)O(2), simulation results demonstrate that fractionated illumination with alternating light and dark periods of 60 s improved the tumor response further for PpIX-mediated PDT.