Radiation Dosimetry in the Presence of Gold Nanoparticles
Abstract
The use of gold nanoparticles (GNPs) to enhance the dose due to radiation, through increased photoelectric effect interactions, has shown promise in vivo and in vitro. Monte Carlo studies have worked towards quantifying the dose enhancement and the dosimetry surrounding GNPs. This thesis investigates the dosimetry in the presence of GNPs for several scenarios using PENELOPE Monte Carlo simulations.
Accurate simulation of GNPs can be challenging due to the large number of particles present in realistic scenarios – up to 10^15 particles/cm^3. Because of this, many Monte Carlo studies have approximated GNPs in tissue as a homogeneous mixture of tissue and gold. However, such models ignore details of energy deposition on nanoscopic scales, including absorption of dose within the GNPs. In this thesis, we first quantified the dosimetric impact of this assumption, finding dose differences up to 31% for the scenarios investigated, and enabling fast, accurate simulation of macroscopic dose enhancement.
The eventual clinical application of GNP-enhanced radiation therapy will rely on enhancement at macroscopic scales. We next investigated the general feasibility of using GNP-enhanced arc radiation therapy (GEART) to treat deep-seated tumours using kilovoltage photon beams. Applying the method established above, we quantified the quality of GEART treatments compared to conventional 6 MV treatments for a variety of tumour sizes and depths. We recommended those sites for which further investigation should be undertaken.
In vivo and in vitro, GNPs are often coated with polyethylene glycol (PEG), a polymer that enables functionalization and biocompatibility. Monte Carlo studies, however, typically do not model these coatings, which may lead to dosimetric errors. We quantified the dose lost to PEG coatings for a variety of GNP sizes, coating thicknesses, and photon beam energies. Dose losses of up to 7.5% and 34% were seen on microscopic and nanoscopic scales, respectively.
Through this work we aim to provide a basis for future studies examining clinical implementation of GNP dose enhancement, adding to the base of knowledge that can be drawn upon if GNP dose enhancement is to be brought into clinical use. Further research is needed to evaluate the radiobiological impact of the effects studied here.
Description
Keywords
Biophysics--Medical, Physics, Physics--Radiation
Citation
Koger, B. (2017). Radiation Dosimetry in the Presence of Gold Nanoparticles (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27518