Feasibility of selective nanoparticle-assisted photothermal treatment for an embedded liver tumor.

Using the finite volume method, the present work numerically explored the feasibility of extending nanoparticle-assisted photothermal therapy (PPTT) from treating subcutaneous tumors to treating organ tumors, particularly tumors growing in the clearance organ liver. To serve this purpose, a superficially embedded liver tumor and its immediate surrounding medium were selected as the study object. A 633-nm laser beam of 1- W/cm(2) intensity externally irradiated the tumor. The matching gold-silica nanoshell with a 16-nm silica core and a 5-nm-thick gold shell was used as the photothermal agent. The nanoshell retention ratio was varied to simulate different levels of nanoshell tumor discriminations. Laser light distributions, conversions from photon energy to heat, and tissues' thermal responses to the generated heat within the study object were analyzed. It was found that although nanoshells have enhanced the thermal transportation, they also restricted the optical transportation of PPTT. This indicates that laser delivery is more demanding for PPTT than for the conventional laser therapy. For the investigated case, when the nanoshell retention ratio was in the range of 2/1-4/1, the therapeutic effects were optimal: a confined medium temperature hyperthermia (47-55 °C) was achieved in the liver tumor while impacts on the surrounding health liver tissues were only marginal. When then nanoshell retention ratio was 8/1 or higher, about half of the liver tumor was ablated. However, some of the surrounding healthy liver tissues were sacrificed as well. The therapeutic effects of PPTT depend nonlinearly on the nanoshell tumor discriminations. Better tumor discriminations do not necessarily result in better PPTT therapeutic effects.