Role of optical coefficients and healthy tissue-sparing characteristics in gold nanorod-assisted thermal therapy

Abstract

Purpose: This study seeks to define parameters for gold nanorod assisted thermal therapy, to achieve the thermal ablation temperature (50-60°C) in the tumour region and spare healthy tissue surrounding the tumour. Also, a criterion for size selection of gold nanorods is described based on the role of optical coefficients. Theory and methods: In this study a tissue domain (comprising a 3mm tumour and 7mm of surrounding healthy tissue) embedded with gold nanorods is irradiated with electromagnetic radiation within the therapeutic wavelength band. Optical interaction is captured using light scattering theory (Mie-electrostatic approach). The resulting temperature field is evaluated using Penne's bioheat model. The effect of key parameters, namely irradiation intensity, irradiation duration and volume fraction, on tissue temperature is also modelled numerically. Results: With increasing nanorod diameter-from 5nm to 15nm-the scattering coefficient increases ∼76 times as compared to a 1.7-fold increase in absorption coefficient. Scattering is considerably minimised by having smaller gold nanorods of 5nm diameter. For this study, gold nanorods of 5nm diameter and volume fraction 0.001%, irradiated with 50W/m2-nm for 250s ablated the tumour as well as spare healthy tissue 2mm beyond the tumour region. Conclusion: Overall it may be concluded that tumour ablation as well as surrounding healthy tissue-sparing (within millimetres immediately adjacent to the tumour) can be achieved through a combination of specified parameters, namely diameter and volume fraction of gold nanorods, irradiation intensity and duration.