Monte Carlo simulation of enhanced laser absorption in tumors with gold nanorods inclusions

Laser ablation is a widely used technology in medicine as a surgical tool for cutting and removing tissue. In cancer treatment via temperature elevations in tumor by laser energy absorption, the challenge is how to deliver laser to deep-seated tumors and how to confine laser energy to targeted region. Recently, laser photothermal therapy utilizing gold nanoshells or nanorods has attracted a lot of attention due to its ability of concentrating laser energy to tumor region with minimal collateral thermal damage to the surrounding healthy tissue. In this thesis research, the focus is on the near infrared (NIR) laser propagation in tumor tissue and the resulted specific absorption rate (SAR) distribution in tumors enhanced by nanorod absorption of laser energy. We have developed a computational algorithm of Monte Carlo simulation of laser photon propagation in a two-layer spherical tumor, mimicking a tumor with an intratumoral nanorod injection at the tumor center. It has been found that the presence of nanorods in the tumor not only concentrates the majority of the laser, but also shifts the laser absorption towards the upper half of the tumor. Parametric studies are also performed to test the effects of radiation properties of the nanorod region on the resulted energy absorption distribution. It is confirmed that the absorption coefficient acts similarly as that suggested by the Beer's law, however, the scattering coefficient greatly enhances photon energy escaping from the upper boundary of the simulated domain. We conclude that the Monte Carlo method is a powerful tool to understand photon propagation in multi-layer tissue and it is supposed to be more accurate than the simple Beer's law even with an effective attenuation coefficient combining absorption and scattering coefficients. The computational algorithm can be used in the future to extract radiation properties of nanorod region, as well as to improve simulation accuracy in designing optimal treatment protocols in cancer treatment using laser photothermal therapy.