Anisotropic scattering in photothermal therapy and beyond: a detailed evaluation of transport approximation for gold nanoshells and nanospheres

Abstract Photothermal therapy (PTT) utilizes thermal radiation to heat a targeted tissue for cancer treatment. Nanoparticles can be embedded in tissue regions to enhance radiation absorption, a practice known as plasmonic photothermal therapy (PPTT). This study focuses on computational simulations of heat transfer in PTT, particularly on the role of scattering phase functions of nanoparticles and the evaluation of the widely employed transport approximation. Mie phase functions of gold nanospheres and nanoshells are detailed taken into account in Monte Carlo simulations, and the heat equation is solved to provide the transient temperature distribution. Results are compared to those obtained using the transport approximation. Two transport approximation approaches are considered: the first approach disregards the asymmetry associated with the phase function of nanoparticles, as is common in PTT applications, while the second takes it into account. For nanoparticles within the 50 to 100 nm range, ideal for PPTT, results confirm the approximation is accurate. However, when the first approach led to inaccuracies, these were significantly reduced by the second. The study also investigated the impacts of size variability, resulting from imperfect synthesis processes of nanoparticles, on the phase function. This variability was effectively managed by the second approach. Overall, with the aid of the second approach, the findings demonstrate that transport approximation can accurately simulate PPTT and suggest considerable accuracy for imaging applications, significantly simplifying modeling.