Technical Note: Film‐based measurement of gold nanoparticle dose enhancement for ¹⁹²Ir

Abstract

Purpose-The purpose of this work is to introduce a simple yet accurate technique to measure the dose enhancement factor (DEF) of a citrate-capped gold nanoparticle (GNP) solution using EBT3 film in an 192 Ir setup.Methods-DEF is the ratio of absorbed dose in a solution compared to absorbed dose in water, assuming identical irradiation parameters. Citrate-capped GNPs were synthesized. An acrylic apparatus was constructed such that the EBT3 film was placed in charged particle equilibrium within the GNP solution with 0.28%, 0.56%, and 0.77% gold by mass. Sets of 12 dose measurements were collected for each GNP concentration as well as for water. The expected value of DEF was also calculated with the effective mass absorption coefficient of the GNP solution and water for an 192 Ir spectrum. Furthermore, Burlin cavity correction factors were calculated and experimentally verified. Experimental verification of the cavity correction was performed by measuring DEF using stacks of 1, 3, and 5 sheets of film and extrapolating the DEF to 0 sheets of film.Results-Experimental cavity corrections agreed with those calculated with the Burlin cavity formalism. The calculated DEF was 1.013, 1.027, and 1.037 for the 0.28%, 0.56%, and 0.77% gold by mass GNP solutions, respectively. The corresponding uncorrected DEF measurement values were 1.013±0.006, 1.024±0.010, and 1.032±0.006, respectively. When applying the Burlin cavity formalism, the final corrected DEF measurement values were 1.016±0.006, 1.029±0.010, and 1.039±0.006, respectively. Conclusion-The experimental cavity correction results agreed with the theoretical Burlin calculations, which allowed for the Burlin corrections to be performed for all GNP concentrations and measured DEF values. The adjusted DEF values agreed with the theoretical calculations. Thus, these results indicate that a Burlin cavity calculation can be applied to correct film-based DEF measurements for 192 Ir.

Multiscale Monte Carlo simulations of gold nanoparticle dose‐enhanced radiotherapy I: Cellular dose enhancement in microscopic models

“…A frequently cited GNP concentration is 7 mg/g, 4,7,27,28 which is well within the range of concentrations considered in this work. Further examples from MC studies include Bahreyni Toossi et al 29 who studied 10, 20, and 30 mg/g, Koger and Kirkby 20 who studied 5-30 mg/g, Brivio et al 21 who studied 10-66 mg/g, Bassiri et al 22 who studied 7, 18, and 50 mg/g, and Moradi et al 30 who studied 5-20 mg/g. For in vitro and in vivo studies, observed tumor gold concentrations also tend to vary, and depend strongly on GNP size, shape, any attached ligands, and more.…”

“…who studied 10, 20, and 30 mg/g, Koger and Kirkby 20 who studied 5–30 mg/g, Brivio et al 21 . who studied 10–66 mg/g, Bassiri et al 22 . who studied 7, 18, and 50 mg/g, and Moradi et al 30 .…”

“…These concentrations are consistent with previous MC studies (e.g., see Refs. 19,20,21 ) and gold concentration is discussed in Section IV.. All gold is assumed to be taken up by the cell (i.e., no gold in extracellular medium) and the total mass of gold per cell is chosen such that the average gold concentration of the overall medium remains the same.…”

A detailed Monte Carlo evaluation of 192Ir dose enhancement for gold nanoparticles and comparison with experimentally measured dose enhancements

“…All experimental measurements were performed using an acrylic measurement apparatus developed in house at UT Health Mays Cancer Center as previously described in Bassiri et al (2019). The apparatus was designed to house an Ir-192 source placed inside a steel vaginal cylinder applicator.…”

“…Monte Carlo N-Particle code, version 6.2 (MCNP6.2, Los Alamos National Laboratory) was utilized to model the dose enhancement to a volume of GNPs placed below an Ir-192 seed. Experimental validation was performed using a previously-described dose measurement apparatus (Bassiri et al 2019) developed and built in-house. Herein we provide a full description of our MCNP6 model, including the source and nanoparticle-containing phantom and the important parameters used.…”