Bragg peak position monitoring using silicon and titanium nanoparticles as prompt-gamma tracers

Spherical silicon and rods-like titanium oxide nanoparticles (NPs) have been analyzed for use in the proton range verification method in proton therapy (main goal), as well as radiosensitizers (second goal) in this therapy due to their physical and biological properties. The method involved the use of tracers emitting prompt-gamma radiation during irradiation with protons. The basic assumption of the method is to selectively deliver the tracer in form of NPs to the tumor. The cytotoxicity of the obtained nanomaterials was also checked against normal and cancer cells.

Correlation between the Bragg peak (BP) position in the PMMA phantom and the signal emitted by the analyzed tracers were determined on the basis of simulations carried out using the Geant4 toolkit. To determine the cytotoxicity of nanosilicone and nanotitanium, as well as their radiosensitizing properties a classic MTS test and a modified multiple MTS test were performed. The location of both types of NPs was determined using holotomographic microscopy.

For silicon NPs, a signal was observed when the BP was located entirely in the structure imitating a tumor and decreased when the BP was entirely outside the structure. In the case of titanium NPs, the signal did not correlate with the position of the structure mimicking a tumor. Both types of NPs at low concentrations turned out to be non-toxic to both cell lines. It has been shown that both types of nanoparticles have promising radiosensitizing properties, in particular towards cancer cells.

When it comes to physical properties, silicon appears to be an optimal candidate for use in proton therapy monitoring. Moreover, the silica NPs turned out to be slightly more effective radiosensitizers than titanium NPs.