Simulation of the Dependence of Spatial Fluence Profiles on Tissue Optical Properties

摘要

Medical laser applications are promoted as safe, effective treatments for a multiplicity of concerns, ranging from hyperthermal skin rejuvenation to subcutaneous tumor ablation. Chromophore and structural protein concentration and distribution within a patient's tissue vary from patient to patient and dictate the interaction of incident radiative energy of a specific wavelength with the target tissue. Laser parameters must be matched to tissue optical and thermal properties in order to achieve the desired therapeutic results without inducing unnecessary tissue damage, although accurate tissue optical properties are not always measured prior to and during laser therapies. A weighted variable step size Monte Carlo simulation of laser irradiation of skin tissue was used to determine the effects of variations in absorption (μ_a) and scattering coefficients (μ_s) and the degree of anisotropy (g) on the radiant energy transport per mm in response to steady-state photon propagation. The three parameters were varied in a factorial experimental design for the ranges of 0.25/mm ≤ μ_a≤ 2.0/mm, 30.0/mm ≤ μ_s≤ 140.0/mm, and 0.65 ≤ g≤ 0.99 in order to isolate their impacts on the overall fluence distribution. Box plots of the resulting fluence profiles were created and compared to identify ranges in which optical property variance could be considered to significantly impact the spatial variance of fluence within the simulation volume. Results indicated that accurate prediction of the fluence profiles that will be achieved by any given medical laser treatment is unlikely without pre-treatment assessment of the tissue optical properties of individual patients.