Microdosimetric Evaluation on the Metallic Nanoparticle-Mediated Dose Enhancement in Radiotherapeutic Proton Irradiation

Monte Carlo simulations are performed on the dosimetric effect of metallic nanoparticles in a clinical proton irradiation.With an in-water hitting model of a single nanoparticle,the secondar.y electrons dose,deposited around the particle surface,is calculated for the proton irradiations in a typical spread-out Bragg peak.The dose enhancement,as the ratio of electron doses from the target particle and background water,is evaluated for the dependence on the depth of hitting,particle size,elements,coating material and thickness.The results indicate a significant dose enhancement on the particle surface within-200 nm,but a fast decay in further distance.The dose enhancement presents a consistency along the spread-out Bragg peak,a positive dependence on both the particle size and electron density,but a strong attenuation by surface coating.Particle cluster may increase the incdividual dose enhajncement by electron crossfire,but is only noticeable in a compact case.The dose enhancement potentiates a radiosensitization use of metallic nanoparticles in clinical proton therapy,but challenqging meanwhile with the narrow ranqge of enhancement effect.

Simulation-based correction of dose enhancement factor values in photon brachytherapy with metal nanoparticle targeting

The purpose of this study is to investigate and quantify the influence of nanoparticle composition,size,and concentration on the difference between dose enhancement values derived from Monte Carlo simulations with homogeneous and structured geometrical representations of the target region in metal nanoparticle-enhanced photon brachytherapy.Values of the dose enhancement factor(DEF)were calculated for Pd-103,I-125,and Cs-131 brachytherapy sources with gold,silver,or platinum nanoparticles acting as targeting agents.Simulations were performed using the Geant4 toolkit with condensed history models of electron transport.Stringent limits were imposed on adjustable parameters that define secondary electron histories,so that simulations came closest to true event-byevent electron tracking,thereby allowing part of the nanoparticle-laden volume used for calculating the dose to be represented as a structured region with uniformly distributed discrete nanoparticles.Fine-tuned physical models of secondary radiation emission and propagation,along with the discrete geometrical representation of nanoparticles,result in a more realistic assessment of dose enhancement.The DEF correction coefficient is introduced as a metric that quantifies the absorption of secondary radiation inside the nanoparticles themselves,a phenomenon disregarded when the target region is treated as a homogeneous metal–tissue mixture,but accounted for by discrete nanoparticle representation.The approach applied to correcting DEF values both draws from and expands upon several related investigations published previously.Comparison of the obtained results to those found in relevant references shows both agreement and deviation,depending on nanoparticle properties and photon energy.

Radiation dose enhancement in skin therapy with nanoparticle addition: A Monte Carlo study on kilovoltage photon and megavoltage electron beams

AIMTo investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage (kV) photon and megavoltage (MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness.METHODSClinical kV photon beams (105 and 220 kVp) and MV electron beams (4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe2O3 nanoparticles with concentrations ranging from 3 to 40 mg/mL. The dose enhancement ratio (DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness.RESULTSIt was found that among all nanoparticles, Au had the highest DER (5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 kVp photon beam but it was for 105 kVp beam for Au nanoparticle concentrations higher than 18 mg/mL. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER (1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams.CONCLUSIONIn nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 kVp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as kV photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams.

Effect of ionizing radiation on dual 8-bit analog-to-digital converters (AD9058) with various dose rates and bias conditions

The radiation effects on several properties （reference voltage, digital output logic voltage, and supply current） of dual 8-bit analog-to-digital （A/D） converters （AD9058） under various biased conditions are investigated in this paper. Gamma ray and 10-MeV proton irradiation are selected for a detailed evaluation and comparison. Based on the measurement results induced by the gamma ray with various dose rates, the devices exhibit enhanced low dose rate sensitivity （ELDRS） under zero and working bias conditions. Meanwhile, it is obvious that the ELDRS is more severe under the working bias condition than under the zero bias condition. The degradation of AD9058 does not display obvious ELDRS during 10-MeV proton irradiation with the selected flux.

Estimation of enhanced low dose rate sensitivity mechanisms using temperature switching irradiation on gate-controlled lateral PNP transistor

The mechanisms occurring when the switched temperature technique is applied,as an accelerated enhanced low dose rate sensitivity(ELDRS)test technique,are investigated in terms of a specially designed gate-controlled lateral PNP transistor(GLPNP)that used to extract the interface traps(Nit)and oxide trapped charges(Not).Electrical characteristics in GLPNP transistors induced by ^(60)Co gamma irradiation are measured in situ as a function of total dose,showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP.Based on the analysis of the variations of Nit and Not,with switching the temperature,the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation.Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup.In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP,which provides us with a new insight into the test technique for ELDRS.