ESTRO 2024 - Abstract Book

S2881

Interdiscplinary - Other

ESTRO 2024

Radiosensitization mechanisms of gold nanoparticles in radiotherapy: a Monte Carlo simulation study

Joana Antunes 1,2 , Jorge Miguel Sampaio 1,2 , Filipa Mendes 3 , António Paulo 3

1 LIP, Dosimetry, Lisbon, Portugal. 2 FCUL, Physics, Lisbon, Portugal. 3 IST, C2TN, DECN, Lisbon, Portugal

Purpose/Objective:

Gold nanoparticles (AuNPs) are promising radiosensitizers with the potential to enhance radiotherapy, principally due to two mechanisms, physical and chemical. In the first one, the presence of AuNPs leads to an increase in the production of secondary particles, such as Auger electrons, that deposit their energy locally, contributing to a higher deposited dose in the tumoral cells. In the chemical mechanism, the interactions between AuNPs and radiation induce the production of more free radicals and reactive oxygen species (ROS). These highly reactive species can play a crucial role because they cause DNA damage and cell death in the tumor cells. Each mechanism contribution depends on the type of radiation used and their role in the enhancement effect is not clear yet [1].

The main objective of this work is to simulate the temporal distribution of ROS produced and the radial dose produced by a single AuNP irradiated with different beam sources ( ɣ -rays, X-rays, and protons).

Material/Methods:

Monte Carlo simulations were performed using TOPAS [2] and TOPAS-nBio [3] toolkits. The simulation consisted of irradiating one NP with a Co-60 beam, 160 kVp X-rays, and a proton beam (18 MeV), to obtain the spatial distribution of ROS for different times during the chemical stage of water radiolysis, the number of chemical species produced as a function of time, and the radial dose (RD) per ionization. The ROS enhancement factor across time in the surrounding of the NP and the RD enhancement time as function of the distance from the NP surface were also obtained. Both enhancement factors correspond to the ratio of the quantity in study (number of chemical species or radial dose) produced by an AuNP and the one produced when a water nanoparticle (WNP) was simulated instead. The simulation setup used to obtain both quantities was divided into three steps. First, a water cylinder was irradiated with each one of the source beams and a phase-space file was obtained at 1 mm depth. This file was shrunk to the dimension of a single nanoparticle (NP), and it was used as a source to irradiate an AuNP. A second phase-space file was recorded on the NP surface to score the outgoing electrons, and then it was used as a source in the center of a water volume.

Results:

The ROS enhancement factor obtained for the three sources simulated is illustrated in figure 1 and the RD enhancement factor in figure 2. For the case of the protons, despite an increase of the total deposited dose, a more significant increase was verified in the production of ROS. In turn, when a 160 kVp X-ray source was used to irradiate the NP, a much modest increase in the ROS enhancement factor was verified. When the primary radiation was set to the Co-60 source, the results showed that there was neither an increase in the production of chemical species nor in the deposited dose.