Simulation-based correction of dose enhancement factor values in photon brachytherapy with metal nanoparticle targeting
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Simulation-based correction of dose enhancement factor values in photon brachytherapy with metal nanoparticle targeting Slobodan Milutinovic´1,2 • Milosˇ Vujisic´1
Received: 9 July 2020 / Revised: 11 September 2020 / Accepted: 17 September 2020 China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, Chinese Nuclear Society and Springer Nature Singapore Pte Ltd. 2020
Abstract The purpose of this study is to investigate and quantify the influence of nanoparticle composition, size, and concentration on the difference between dose enhancement values derived from Monte Carlo simulations with homogeneous and structured geometrical representations of the target region in metal nanoparticle-enhanced photon brachytherapy. Values of the dose enhancement factor (DEF) were calculated for Pd-103, I-125, and Cs-131 brachytherapy sources with gold, silver, or platinum nanoparticles acting as targeting agents. Simulations were performed using the Geant4 toolkit with condensed history models of electron transport. Stringent limits were imposed on adjustable parameters that define secondary electron histories, so that simulations came closest to true event-byevent electron tracking, thereby allowing part of the nanoparticle-laden volume used for calculating the dose to be represented as a structured region with uniformly distributed discrete nanoparticles. Fine-tuned physical models of secondary radiation emission and propagation, along with the discrete geometrical representation of nanoparticles, result in a more realistic assessment of dose enhancement. The DEF correction coefficient is introduced as a metric that quantifies the absorption of secondary
The work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia under contracts TR-37021 and 171007. & Milosˇ Vujisic´ [email protected] 1
School of Electrical Engineering, University of Belgrade, Belgrade, Serbia
2
Vincˇa Institute of Nuclear Sciences - National Institute of tht Republic of Serbia, University of Belgrade, Belgrade, Serbia
radiation inside the nanoparticles themselves, a phenomenon disregarded when the target region is treated as a homogeneous metal–tissue mixture, but accounted for by discrete nanoparticle representation. The approach applied to correcting DEF values both draws from and expands upon several related investigations published previously. Comparison of the obtained results to those found in relevant references shows both agreement and deviation, depending on nanoparticle properties and photon energy. Keywords Monte Carlo Brachytherapy Nanoparticles Dose enhancement Geant4
1 Introduction For the past two decades, the use of metal nanoparticles (MNPs) as selective radiosensitizers in photon radiotherapy has been investigated extensively. Owing to their high atomic number and density, MNPs absorb more X-rays or gamma rays than the surrounding tissue. When introduced selective
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