Contrast Enhancement for Portal Imaging in Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Evaluation Using Flattening-Filter-Free Photon Beams.

Aniza Abdulle,James C L Chow

doi:10.3390/nano9070920

Abstract

Our team evaluated contrast enhancement for portal imaging using Monte Carlo simulation in nanoparticle-enhanced radiotherapy. Dependencies of percentage contrast enhancement on flattening-filter (FF) and flattening-filter-free (FFF) photon beams were determined by varying the nanoparticle material (gold, platinum, iodine, silver, iron oxide), nanoparticle concentration (3–40 mg/mL) and photon beam energy (6 and 10 MV). Phase-space files and energy spectra of the 6 MV FF, 6 MV FFF, 10 MV FF and 10 MV FFF photon beams were generated based on a Varian TrueBeam linear accelerator. We found that gold and platinum nanoparticles (NP) produced the highest contrast enhancement for portal imaging, compared to other NP with lower atomic numbers. The maximum percentage contrast enhancements for the gold and platinum NP were 18.9% and 18.5% with a concentration equal to 40 mg/mL. The contrast enhancement was also found to increase with the nanoparticle concentration. The maximum rate of increase of contrast enhancement for the gold NP was equal to 0.29%/mg/mL. Using the 6 MV photon beams, the maximum contrast enhancements for the gold NP were 79% (FF) and 78% (FFF) higher than those using the 10 MV beams. For the FFF beams, the maximum contrast enhancements for the gold NP were 53.6% (6 MV) and 53.8% (10 MV) higher than those using the FF beams. It is concluded that contrast enhancement for portal imaging can be increased when a higher atomic number of NP, higher nanoparticle concentration, lower photon beam energy and no flattening filter of photon beam are used in nanoparticle-enhanced radiotherapy.

Highlights

External beam radiotherapy is a comprehensive term that describes the use of high-energy ionizing radiation to treat cancer
It should be noted that zero percentage contrast enhancement means no nanoparticle was added to the tumour, because the contrast ratio does not change with variations of nanoparticle addition
Monte Carlo simulation was carried out to predict the dependencies of contrast enhancement for portal imaging on FF and FFF photon beams with various nanoparticle materials and concentrations

Summary

Introduction

External beam radiotherapy is a comprehensive term that describes the use of high-energy ionizing radiation to treat cancer. Since the level of GSH is much higher than that in normal cells, more gold NP are found to be accumulated in the tumour compared to the normal tissue This increases the efficiency of radiotherapy, which is decreased significantly in tumours due to multiple drug resistance and the actions of antiapoptotic protein survivin [9,10]. During treatment when the photon beam irradiates the tumour, NP inside the tumour interact with photons to emit more secondary electrons [11,12,13] These electrons contribute further damage to cancer cells close to the NP and increase the dose absorbed by the tumour. These ionized water molecules would further damage the DNA in the same way as the liberated electrons

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