Assessment of singlet oxygen dosimetry concepts in photodynamic therapy through computational modeling

Publication date: Available online 29 December 2017
Source:Photodiagnosis and Photodynamic Therapy
Author(s): Georgios Kareliotis, Sofia Liossi, Mersini Makropoulou
BackgroundIn photodynamic therapy (PDT) oxygen plays vital role in killing tumor cells and therefore its dosimetry is being thoroughly studied.MethodsLight distribution into tissue is modelled for radiation-induced fibrosarcoma (RIF) and nodular basal cell carcinoma (nBCC), in order to study the influence of blood flow on singlet oxygen concentration effectively leading to cell death ([¹O2]rx) on PDT, within this light distribution. This is achieved through initial oxygen supply rate (g0) and initial molecular oxygen concentration ([³O2]0) calculations. Monte Carlo simulations and mathematical models are used for spatial and temporal distributions of [¹O2]rx. Hypoxia conditions are simulated by minimizing [³O2]0 and g0. Furthermore, an optimization algorithm is developed to calculate minimum initial molecular oxygen concentration needed ([³O2]0,min) for constant [¹O2]rx, when blood flow changes.ResultsOur results validate that in initially well-oxygenated scenarios with normal blood flow maximum [¹O2]rx values are significantly higher than corresponding values of hypoxic scenarios both for RIF and nBCC models, with maximum oxygen supply rate percentage variations being independent from g0. Moreover, [¹O2]rx appears to be more affected by an increase of g0 than of [³O2]0 values. For low blood flow there is a linear relationship between [³O2]0,min and g0, while for better oxygenated areas high blood flow reduces [³O2]0,min needed in exponential manner.ConclusionsBlood flow appears to be able to compensate for oxygen consumption. Finally, the developed optimization protocol on oxygen dosimetry offers the suitable combination of [³O2]0,min and g0 to achieve constant [¹O2]rx, despite possible blood flow variations.



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