Laser-ablated silicon nanoparticles in tumor treatment via hyperthermia: numerical calculations
Hyperthermia is a promising technique for cancer treatment based on selective tumor heating resulting in tumor cells death. Embedding nanoparticles into the tumor is a convenient approach to localization of the heat generation. Among various nanoparticles, the silicon ones are characterized by low toxicity and biodegradability together with relatively high optical absorption, indicating their potential for hyperthermia.
We report on the results of numerical study on tumor hyperthermia with silicon nanoparticles as absorbing and scattering agents selectively delivered to a tumor. Embedding the nanoparticles modifies tumor optical properties, which results in a local increase in absorption efficiency. In our simulations, we considered silicon nanoparticles obtained by means of porous silicon laser ablation in liquids  with particle sizes less than 100 nm embedded into tumor and irradiated by red and near-infrared continuous-wave laser radiation. For calculations we employed previously measured optical properties of the nanoparticles suspensions  assuming that nanoparticles concentration of tumor may reach as high as 10-fold as compared to concentration in suspension due to buffer liquid removal. The laser intensity considered in the hyperthermia simulation varied in the range of 200 - 500 mW/cm2, the beam cross section was 1 cm2. Absorption volume distribution was calculated by Monte-Carlo technique both for tumor only and for tumor with embedded nanoparticles; in the latter case the absorption increased for up to 2 times at depths less than 1 mm. To obtain temperature values the bioheat equation  was solved, with the distributed heat source obtained as a Monte-Carlo simulated absorption map. We demonstrated that the presence of silicon nanoparticles ablated in water within a tumor in concentration of 5 mg/mL leads to 2– 5 K increase in maximum temperature in comparison with the tumor without nanoparticles depending on the illumination wavelength and type of ablation target in the course of the nanoparticles fabrication. Simulations indicate that the temperatures required for hyperthermia (~ 42°C) can be reached at laser intensities 200 and 250 mW/cm2 for illumination wavelengths 633 and 800 nm, respectively.
To conclude, Monte Carlo simulations of the laser-induced heating of tumors with embedded silicon nanoparticles formed by laser ablation of porous silicon indicate their huge potential in tumor hyperthermia.
This work was supported by Russian Science Foundation grant no. 19-12-00192.
 S.V,Zabotnov, A.V. Skobelkina, D.A. Kurakina, A.V. Khilov, F.V. Kashaev, T.P. Kaminskaya, D. E. Presnov, P.D. Agrba, D.V. Shuleiko et al., Nanoparticles Produced via Laser Ablation of Porous Silicon and Silicon Nanowires for Optical Bioimaging//Sensors, 10(17), 4874(2020);
 H.H. Pennes, Analysis of tissue and arterial temperatures in the resting human forearm// J. Appl. Physiol., 1, 93(1948);
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Physics Dept., Lomonosov Moscow State University
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