Program Information
A Factor for Converting Dose to a Gold Nanoparticle Mixture to a Biologically-Relevant Dose
B Koger1,2*, C Kirkby1,3 , (1) University of Calgary, Calgary, AB, (2) Tom Baker Cancer Centre, Calgary, AB, (3) Jack Ady Cancer Centre, Lethbridge, AB
Presentations
SU-E-T-30 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Monte Carlo studies of gold nanoparticle (GNP) dose enhancement on macroscopic scales in radiotherapy have modeled GNPs in tissue as a homogeneous mixture of gold and tissue. Using an explicit model of GNPs randomly positioned in a small volume (1 μm³) of tissue, this study aims to quantify the dose to the biologically relevant component of a gold-tissue mixture, enabling a conversion from macroscopically-scored dose.
Methods: Using the PENELOPE Monte Carlo code with the penEasy package, we modeled a 1 μm³ volume containing either a tissue-gold mixture or GNPs suspended in ICRU 4-component tissue at various gold concentrations (0, 5, 10, and 15 mg Au/g tissue) and GNP diameters (20, 30, 40, 50 nm). The volume was irradiated with monoenergetic photon and electron beams, ranging from 110 eV to 6 MeV. Interaction forcing was utilized to increase simulation efficiency. Energy deposition was scored in the tissue for each case and was converted to dose. For each scenario, we calculated a conversion factor, the ratio of dose-to-tissue to dose-to-mixture as a function of energy.
Results: The conversion factor was plotted as a function of energy for both photons and electrons. For electrons, the conversion factor was relatively unaffected by any of the parameters, including energy, ranging between 0.98 - 1.02. For photons, the factor was very energy dependent, with a range of 0.49 – 1.02. The factor was lowest for 10 – 100 keV photons. The conversion factor generally decreased with increasing GNP concentration and increasing GNP size.
Conclusions: With a large variation in the conversion factor with incident energy, dose deposition is dependent on the spectrum incident on a volume. By scoring the energy spectrum in a given volume, one can provide a scenario-specific conversion factor, allowing fast, detailed Monte Carlo simulations without the need for explicit GNP-definition.
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