Source model for Immunostimulating Interstitial Laser Thermotherapy dosimetry

Abstract: A common tool for tissue ablation is the use of heat. For the imILT technique investigated in this project, the heat is induced by the usage of laser light. The light is absorbed by the tissue and is thus turned into heat, the amount absorbed depends on the optical properties of the tissue, such as absorption and scattering. In imILT such as in other laser based ablation techniques, optical fibers are used to deliver the laser light to the treatment volume. The main aim of this project was to develop a source model for the imILT technique using COMSOL Multiphysics. This was done in three steps, first ray tracing inside the different fiber models, then light distribution in tissue and last heat distribution in tissue due to the introduced laser light. A second aim of this project was to simulate the heat induced in the different fiber layers during an imILT treatment for the different fiber designs as well as comparing two fibers of the same design but of different thicknesses. The two fiber designs used were bare end and radial. The results from the developed simulation model are in large, in agreement with the validation experiments performed. The intensity profiles of the bare end fiber is approximately the same for both simulation and experiment, but differs slightly for the radial fibers. The results from the heat distribution simulation models does agree with the validation experiments but overall, the temperatures received in the simulation may be lower than for the validations. This is most likely due to the main source of error in the simulations, the optical properties of the simulated tissue. When comparing the two fibers of the same model but different thicknesses, it was concluded that different parameters limit the maximum power and treatment time that can be used for the different fiber thicknesses.