Comparison of finite element modeling and Monte Carlo simulations for interstitial photodynamic therapy (Conference Presentation)

Abstract

Background and Objectives: Finite Element Methods (FEM) and Monte Carlo (MC, FullMonte) simulations are employed to compute light propagation during interstitial photodynamic therapy. FullMonte models the light source as a fixed number of photons emitted from the center of the catheter. In the FEM, the light source is modeled as a flux of photons emitted from the outside diameter of the catheter. The objective of this study was to compare the FEM and MC computed light fluence rate distributions. Methods: A solid phantom with tissue optical properties was used to compare MC simulations conducted using FullMonte and FEM using COMSOL Multiphysics. A tetrahedral mesh of approximately 400,000 elements was created to mimic experiments in the phantom with one central 2 cm cylindrical diffuser fiber, and five IP85 detector fibers were inserted 5, 10, 15, 20, and 25 mm from the light source. FEM and FullMonte simulations were conducted for 50 and 100 mW/cm source power, and the resulting fluence rates were compared, at the detector locations. Results: Initially, the computed fluence rates differed significantly between the MC and FEM simulations. However, the light gradient was comparable between both methods. Changing the FEM boundary conditions such that the light source was modeled as a flux of photons emitted from inside the catheter approximately 0.6 mm from the outside diameter resulted in a better agreement (16% difference). Conclusions: The light source boundary condition is a major contributor to the difference between FEM and FullMonte computed light distributions. Acknowledgements: This work was supported in part by National Cancer Institute of the National Institutes of Health under Award Number R01CA193610 to G. Shafirstein