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

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.

<p>Gold Nanoparticles as Radiosensitizers in Cancer Radiotherapy</p>

“…Monte Carlo simulation, as a theoretical calculation method, is often used to evaluate the dose distribution and dose enhancement ratio (DER) of GNPs. 179 , 180 However, based solely on physical dose enhancement, the radiosensitization of GNPs is significant at KV energy levels, but not at MV levels. 179 Interestingly, the radiation dose enhancement ratio calculated using the biological model of MV radiation is significantly higher than the predicted theoretical Monte Carlo simulation values.…”

“… 179 , 180 However, based solely on physical dose enhancement, the radiosensitization of GNPs is significant at KV energy levels, but not at MV levels. 179 Interestingly, the radiation dose enhancement ratio calculated using the biological model of MV radiation is significantly higher than the predicted theoretical Monte Carlo simulation values. The differences between theoretical predictions and experimental data reveal the existence of biological enhancement.…”

Impact of the Spectral Composition of Kilovoltage X-rays on High-Z Nanoparticle-Assisted Dose Enhancement

“…The NP concentration in water was equal to 10 mg/mL, according to [ 47 ]. Concentrations of this order are widely studied in theoretical works [ 32 , 48 ] and are also relevant to in vitro and in vivo conditions [ 49 ]. The values of the photon mass energy-absorption coefficients were obtained using the XMuDat software [ 50 ], based on the data by Hubell J.H.…”

Application of Nanomaterials in Biomedical Imaging and Cancer Therapy

“…Image-guided radiotherapy can improve cancer outcomes significantly [ 169 , 170 , 171 ]. A theranostic platform and a combination of bismuth and gadolinium were proposed for onsite radiosensitization and image contrast enhancement.…”