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 1O2 dose deposition and comparing these amounts with the 5 × 10 18 molecules cm−3 threshold of reacting 1O2, simulation results demonstrate that fractionated illumination with alternating light and dark periods of 60 s improved the tumor response further for PpIX-mediated PDT.

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