Modelling of Light Propagation in Tissue

One of the main factors affecting the efficacy of PDT is the light dose delivered to the target and the surrounding normal tissue. Due to the complex nature of biological tissue, the propagation of light through this medium cannot be directly calculated for realistic scenarios. While analytical approximations exist, these require a set of assumptions that limit their applicability. Monte Carlo (MC) simulation is therefore often used to simulate light propagation in tissue. MC simulation of light propagation treats light as a series of photons or photon packets that undergo absorption, scattering, and transmission and reflection at boundaries.  Each of these phenomena is handled statistically, based on the optical properties of the sample.  If enough photons are run, MC simulation can provide very accurate results.

We have developed a Monte Carlo modelling space that can represent complex, three-dimensional samples based on a patient’s CT images. This MC model incorporates a number of fiber geometries, including a more physically accurate representation of cylindrical diffusing fibers. These diffuser fibers are used for interstitial PDT, and our model has been used to perform treatment planning for patients with head and neck cancer. We have implemented this model using graphics processing units (GPUs), to allow for near real-time simulation.

Related publications:

Z. Li, L. Nguyen, D.A. Bass, and T.M. Baran. Effects of patient-specific treatment planning on eligibility for photodynamic therapy of deep tissue abscess cavities: Retrospective Monte Carlo simulation study. Journal of Biomedical Optics 27, 083007 (2022).

T.M. Baran, H.W. Choi, M.J. Flakus, and A.K. Sharma. Photodynamic therapy of deep tissue abscess cavities: Retrospective image-based feasibility study using Monte Carlo simulation. Medical Physics 46, 3259-3267 (2019).

T.M. Baran and T.H. Foster. Comparison of flat cleaved and cylindrical diffusing fibers as treatment sources for interstitial photodynamic therapy. Medical Physics 41, 022701 (2014).

T.M. Baran and T.H. Foster. New Monte Carlo model of cylindrical diffusing fibers illustrates axially heterogeneous fluorescence detection: simulation and experimental validation. Journal of Biomedical Optics 16, 085003 (2011).