Dose Enhancement for the Flattening-Filter-Free and Flattening-Filter Photon Beams in Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Study.

Stefano Martelli,James C L Chow

doi:10.3390/nano10040637

Abstract

Monte Carlo simulations were used to predict the dose enhancement ratio (DER) using the flattening-filter-free (FFF) and flattening-filter (FF) photon beams in prostate nanoparticle-enhanced radiotherapy, with multiple variables such as nanoparticle material, nanoparticle concentration, prostate size, pelvic size, and photon beam energy. A phantom mimicking the patient’s pelvis with various prostate and pelvic sizes was used. Macroscopic Monte Carlo simulation using the EGSnrc code was used to predict the dose at the prostate or target using the 6 MV FFF, 6 MV FF, 10 MV FFF, and 10 MV FF photon beams produced by a Varian TrueBeam linear accelerator (Varian Medical System, Palo Alto, CA, USA). Nanoparticle materials of gold, platinum, iodine, silver, and iron oxide with concentration varying in the range of 3–40 mg/ml were used in simulations. Moreover, the prostate and pelvic size were varied from 2.5 to 5.5 cm and 20 to 30 cm, respectively. The DER was defined as the ratio of the target dose with nanoparticle addition to the target dose without nanoparticle addition in the simulation. From the Monte Carlo results of DER, the best nanoparticle material with the highest DER was gold, based on all the nanoparticle concentrations and photon beams. Smaller prostate size, smaller pelvic size, and a higher nanoparticle concentration showed better DER results. When comparing energies, the 6 MV beams always had the greater enhancement ratio. In addition, the FFF photon beams always had a better DER when compared to the FF beams. It is concluded that gold nanoparticles were the most effective material in nanoparticle-enhanced radiotherapy. Moreover, lower photon beam energy (6 MV), FFF photon beam, higher nanoparticle concentration, smaller pelvic size, and smaller prostate size would all increase the DER in prostate nanoparticle-enhanced radiotherapy.

Highlights

There are three major methods of treating tumors, namely, radiotherapy, chemotherapy, and surgery
The relationships between the dose enhancement ratio (DER) and nanoparticle concentration for different materials of gold, platinum, iodine, silver, and iron oxide, irradiated by the FFF and FF photon beams are shown in Figure 1a,b for beam energy equal to 6 and 10 MV
The relationships between the DER and the gold nanoparticle concentration for the 6 MV FFF, 6 MV FF, 10 MV FFF, and 10 MV FF photon beams are shown in Figure 4 in which the prostate and pelvic size were equal to 3.5 cm and 25 cm, respectively

Summary

Introduction

There are three major methods of treating tumors, namely, radiotherapy, chemotherapy, and surgery. Many studies focused on the development of radiosensitizers such as heavy-atom nanoparticles in radiotherapy [3,4,5,6,7,8]. These nanomaterials aggregate in the cell because of the interactions with glutathione present in cytosol. Having a higher DER allows for a better local tumor control by increasing the dose to the cancerous target, while exposing the healthy surrounding tissues to a lower and more tolerable dose. Nanoparticles having a high atomic number and a low energy photon irradiation will increase the probability of absorption to the target with nanoparticle addition [12,13]

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Conclusion