MC Calculations Research Articles

Commissioning an ultra-high-dose-rate electron linac with end-to-end tests

Objective. The FLASH effect can potentially be used to improve the therapeutic ratio of radiotherapy (RT) through delivery of Ultra-high-dose-rate (UHDR) irradiation. Research is actively being conducted to translate UHDR-RT and for this purpose the Mobetron is capable of producing electron beams at both UHDR and conventional dose rates for FLASH research and translation. This work presents commissioning of an UHDR Mobetron with end-to-end tests developed for preclinical research. Approach. UHDR electron beams were commissioned with an efficient approach utilizing a 3D-printed water tank and film to fully characterize beam characteristics and dependences on field size, pulse width (PW) and pulse repetition frequency (PRF). This commissioning data was used to implement a beam model using the GAMOS Monte Carlo toolkit for the preclinical research. Then, the workflow for preclinical FLASH irradiation was validated with end-to-end tests delivered to a 3D-printed mouse phantom with internal inhomogeneities. Main results. PDDs, profiles and output factors acquired with radiochromic films were precisely measured, with a PRF that showed little effect on the UHDR beam energy and spatial characteristics. Increasing PW reduced the D max and R50 by 2.08 mm µs−1 and 1.28 mm µs−1 respectively. An end-to-end test of the preclinical research workflow showed that both profiles in head-foot and lateral directions were in good agreement with the MC calculations for the heterogeneous 3D printed mouse phantom with Gamma index above 93% for 2 mm/2% criteria, and 99% for 3 mm/3%. Significance. The UHDR Mobetron is a versatile tool for FLASH preclinical research and this comprehensive beam model and workflow was validated to meet the requirements for conducting translational FLASH research.

Simulation of ordering and diffusion in CrxMoNbTaVW alloys within the framework of the N-body approach when specifying interatomic interactions

Purpose. Development of interatomic potentials for atomistic simulation of alloys based on refractory metals of the V-Cr-Nb-Mo-Ta-W system and atomistic simulation using these ordering and diffusion potentials in CrxMoNbTaVW alloys. Methods. The development of the interatomic potentials of the V-Cr-Nb-Mo-Ta-W system was carried out within the framework of the 𝑁-body approach; To optimize the parameters of the potentials, the results of calculations within the framework of the electron density functional theory using the VASP software package were used as target values; the simulations of ordering and diffusion was carried out using methods of molecular dynamics and the developed We have previously used the combined method of molecular dynamics and the Monte Carlo method (MD+MK). Results. Within the framework of the 𝑁-body approach, potentials are constructed that complement the V-Nb-Mo-W potential system that we built earlier to the V-Cr-Nb-Mo-Ta-W system. The constructed potentials predict the characteristics of alloys in good agreement with experimental data, CALPHAD data and density functional theory data. Using these potentials by the MD+MC method, CrxMoNbTaVW alloys were modeled, where 𝑥 = 0, 0.5, 1, 2 and 3, in the temperature range from 500 ºC to 2300 ºC. The MD+MC calculations and CALPHAD data agreed in the temperature and concentration regions containing one phase of BCC. At a temperature of 1000ºC, MD + MC calculations show the presence of a single BCC phase, which contradicts CALPHAD data, but is consistent with experimental data. The simulation showed that the atomic structure of the CrMoNbTaVW model alloy is self-sufficient to realize the diffusion of components without artificial introduction of vacancies. The absolute values of the diffusion coefficients of the components and the values of the effective activation energy of diffusion in a solid solution of CrMoNbTaVW were calculated for the first time by the method of molecular dynamics. Analysis of the calculated diffusion characteristics indicates that a diffusion mechanism is implemented in the CrMoNbTaVW alloy, which includes coordinated movement of atoms of various grades. Conclusion. The development of methods for atomistic simulations of alloys based on refractory metals of the V-Cr-Nb-Mo-Ta-W system and the results of atomistic simulation of ordering and diffusion in CrxMoNbTaVW alloys have shown their importance for explaining and predicting heat resistance caused by diffusion processes in multicomponent alloys at high temperatures.

Four-dimensional dose evaluation for the liver stereotactic body radiotherapy with lipiodol retention after transcatheter arterial chemoembolization

PurposeTo evaluate the effect of lipiodol on the four-dimensional accumulated dose of liver stereotactic body radiotherapy (SBRT) after transcatheter arterial chemoembolization (TACE). Material and methodsTen patients who underwent liver SBRT with lipiodol retention after TACE were retrospectively analyzed. Free-breathing three-dimensional (3D) computed tomography (CT) and respiration-based four-dimensional (4D) CT scans were used. The tumor tissue and lipiodol region were delineated within the gross tumor volume (GTV). Volumetric modulated arc therapy plans were created using the X-ray Voxel Monte Carlo (XVMC), a fast MC algorithm. For 4D accumulated dose assessments, the dose was recalculated after copying the plan into each CT phase, and a deformable registration was used with the 3D CT as a reference. Additionally, dose variation due to tumor irradiation at the lipiodol location through motion was simulated by density override of planning target volume using tumor tissue density followed by dose recalculation. ResultsDose to the lipiodol region increased after density override with tumor density. In eight out of ten patients, 4D doses covering 98% of the GTV and tumor tissue increased compared to 3D doses. Notably, for both 3D and 4D cases, doses to the tumor tissue exceeded those of the GTV. Attention to GTV coverage in 3D planning for liver SBRT without considering lipiodol was deemed sufficient. The similar 19.2 Gy-liver volume for 3D and 4D allowed for liver evaluation using the 3D plan as a quick substitute. ConclusionsIn liver SBRT cases involving lipiodol after TACE, the XVMC planning system revealed higher 4D doses to tumor tissue compared to GTV, with 4D doses surpassing 3D. However, results were limited by XVMC accuracy, unable to reflect lipiodol's dose enhancement. For precise CT-based dose calculations involving lipiodol in the GTV, incorporating lipiodol's material information in the MC calculations is crucial.

A comprehensive open-access database of electron backscattering coefficients for energies ranging from 0.1KeV to 15MeV.

The characterization of electron backscattering is essential in medical physics for accurately assessing dose deposited around inhomogeneities where backscattering alters the spatial energy distribution pattern and for determining Monte-Carlo code's ability to effectively describe electron scattering and does calculation in a target volume. Recent machine learning advances have provided physicists with powerful tools for effectively extracting information and trends from extensive experiment observations if sufficiently sizeable datasets are available for data mining. We report on the development of a publicly accessible database on electron backscattering coefficients for solid targets. The first database on electron-solid interactions was assembled in 1995. Data for bulk materials, limited to normal incidence and energies up to 100keV, were primarily focusing on electron microscopy. To accommodate broad high-energy applications and include the most recent publications we have created a comprehensive database of electron backscattering coefficients, listed as a function of target atomic number and thickness, electron energy, and incidence angle. These additions resulted in a database of 3566 data points, compared to the previous database of 1430. The data collection includes only published experimental observations (no calculations or results fitting) with no attempt to judge their accuracy or quality. A limited number of data points were compared to recently published Monte-Carlo results. The presented database provides values of electron backscattering coefficients for 50 elements and 19 compounds at electron energies ranging from 0.1keV to 15MeV, presented in ASCII files. Each file contains the electron energy and backscattering coefficient with target thickness or electron incidence angle included where available, and the reference number shown in the last column. Additionally, the presented data were shown in the graphs for better visualization. The online database can be accessed from the website https://doi.org/10.5281/zenodo.7810951. The database provides the most up-to-date source of experimentally obtained electron backscattering coefficients that can be used in theoretical and MC calculations and modeling validations. The data availability is still very limited for many solids and almost non-existent for compounds. Novel machine learning methods should be well adapted to predict these unknown values for various targets, thicknesses, energies, and incident angles utilizing the presented cleaned dataset.

Volatility Measurements of Individual Components in Organic Aerosol Mixtures Using Temperature-Programmed Desorption-Direct Analysis in Real Time-High Resolution Mass Spectrometry.

Atmospheric organic aerosols (OA) have profound effects on air quality, visibility, and radiative forcing of climate. Quantitative assessment of gas-particle equilibrium of OA components is critical to understand formation, growth, distribution, and evolution of OA in the atmosphere. This study presents a novel ambient pressure measurement approach developed and tested for untargeted screening of individual components in complex OA mixtures, followed by targeted chemical speciation of identified species and assessment of their physicochemical properties such as saturation vapor pressure and enthalpies of sublimation/evaporation. The method employs temperature-programmed desorption (TPD) experiments coupled to "direct analysis in real time" (DART) ionization source and high resolution mass spectrometry (HRMS) detection. Progression of the mass spectra is acquired in the TPD experiments over a T = 25-350 °C temperature range, and extracted ion chromatograms (EIC) of individual species are used to infer their apparent enthalpies of sublimation/evaporation (ΔHsub*) and saturation vapor pressure (pT*, Pa, or CT*, μg m-3) as a function of T. We validate application of this method for analysis of selected organic compounds with known ΔHsub and CT values, which showed excellent agreement between our results and the existing data. We then extend these experiments to interrogate individual components in complex OA samples generated in the laboratory-controlled ozonolysis of α-pinene, limonene, and β-ocimene monoterpenes. The abundant OA species of interest are distinguished based on their accurate mass measurements, followed by quantitation of their apparent ΔHsub* and CT* values from the corresponding EIC records. Comparison of C298K* values derived from our experiments for the individual OA components with the corresponding estimates based on their elemental composition using a "molecular corridors" (MC) parametrization suggests that the MC calculations tend to overestimate the saturation vapor pressures of OA components. Presented results indicate very promising applicability of the TPD-DART-HRMS method for the untargeted analysis of organic molecules in OA and other environmental mixtures, enabling rapid detection and quantification of organic pollutants in the real-world condensed-phase samples at atmospheric pressure and without sample preparation.

On the field size definition and field output factors in small field dosimetry.

There is a major conceptual difference between small-field and large field dosimetry that is, different definition of the field size. The dosimetry protocol IAEA TRS-483 recommends the use of the field size defined by measured dose profiles (full-width half maximum, FWHM) that is significantly different from conventional field size definition by the geometric field opening of MLC/Jaw at the isocenter. The application of the effective field size concept, Sclin , was introduced by Cranmer-Sargison etal. (DOI:10.1016/j.radonc.2013.10.002) as a reporting mechanism for field output factors of rectangular fields. The study by Das etal. (DOI:10.1002/mp.15624) indicated the limitations of obtaining the field size by experimentally measuring FWHM, for example, the measured FWHM is smaller than beam geometric size, which is contradictory to what is expected as a result of partial occlusion of the primary photon source by the collimating devices. Cranmer-Sargison etal. and Das et al suggested that additional investigations are needed to evaluate its limitations. This study investigates the validity of the field size definition by FWHM and by MLC/Jaw opening and finds the pros and cons between these two methods to resolve the controversial issue. The FWHM can be obtained by measuring or calculating dose profiles. Using Monte Carlo simulations this study compares the field size obtained by FWHM and by field geometric field opening. The EGSnrc system is used to simulate 6 MV beam to generate square and rectangular fields from 5-30mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 30mm). The calculated FWHM and output factors are compared with measurements obtained by a microSilicon detector. The results show that field width (FWHM) derived from MC calculations generally agrees with machine geometric field width within 0.5mm for square or rectangular fields with a minimum field width of ≥8mm. For the extremely small fields with a minimum field width of 5mm the discrepancies are up to 1.6mm. The field width (FWHM) obtained by measuring dose profiles are unreliable for small fields due to the measurement uncertainties for an extremely small field. The effect of partial occlusion of the primary photon source by the jaws on the beam axis is clearly observed in the calculated dose profiles. For the extremely small field width of 5mm, Monte Carlo predicted up to 10% exchange factor differences which are confirmed by the measurements. The field size defined by the geometric opening of the beam-defining system, is still valid for small fields. The field size defined by geometric opening is independent of measurement uncertainties, independent of machine design, and highly reproducible. It is feasible to accurately tabulate the output factors as a function of geometric field opening thus eliminating user and detector choice for FWHM measurements. The field output factor of a small rectangular field cannot be related to an equivalent field size without considering the exchange factor due to partial occlusion of the photon source.

Accelerated calculation of configurational free energy using a combination of reverse Monte Carlo and neural network models: Adsorption isotherm for 2D square and triangular lattices

We demonstrate the application of artificial neural network (ANN) models to reverse Monte Carlo based thermodynamic calculations. Adsorption isotherms are generated for 2D square and triangular lattices. These lattices are considered because of their importance to catalytic applications. In general, configurational free energy terms that arise from adsorbate arrangements are challenging to handle and are typically evaluated using computationally expensive Monte Carlo simulations. We show that a combination of reverse Monte Carlo (RMC) and ANN model can provide an accurate estimate of the configurational free energy. The ANN model is trained/constructed using data generated with the help of RMC simulations. Adsorption isotherms are accurately obtained for a range of adsorbate-adsorbate interactions, coverages and temperatures within few seconds on a desktop computer using this method. The results are validated by comparing to MC calculations. Additionally, H adsorption on Ni(100) surface is studied using the ANN/RMC approach.

THE IMPACT OF THE PCE MC CORRECTION VALUE USING MODIFIED AVERAGE TIME HEADWAY METHOD TO ROAD PERFORMANCE (CASE STUDY: VETERAN STREET, MALANG CITY)


 
 
 
 Passenger Car Equivalent (PCE) is a conversion factor of various types of vehicles compared to passenger cars or other light vehicles concerning their impact on traffic behavior. The PCE value used in calculating the performance of urban roads refers to Manual Kapasitas Jalan Indonesia (MKJI 1997) as an Indonesian Highway Capacity Manual. There have been many changes in traffic behavior nowadays compared to in 1997. The calculation of the PCE MC value using the average time headway method does not match the actual conditions. Therefore, modifications are needed by calculating the vehicle dimension factors to obtain the PCE value. The result of the PCE MC calculation using the modified average time headway method shows 0.17. This value is smaller than the value of the PCE MC set by the MKJI 1997, which shows 0.25. Based on the analysis of traffic conditions for ten years, the DS value using the PCE MC according to the MKJI 1997 obtains DS>1. Meanwhile, the DS value calculated based on the corrected PCE MC has DS<1. The difference in the value of PCE MC has implications for road performance. As a result, it affects traffic maintenance management in the form of maintenance costs and decision-making.
 
 
 

Critical Properties of 2D Anisotropic Ising Model with More Than Nearest Neighbor Interaction

Using the finite cluster approximation (FCA) based on a single-site cluster theory and Monte Carlo simulation (MCS) under the Metropolis algorithm, we study the critical properties of two-dimensional (2D) spins-½ system by analyzing the effect of the anisotropic parameter [Formula: see text] and next-nearest-neighbor (NNN) interaction [Formula: see text] on the critical temperature [Formula: see text] of the 2D anisotropic square lattice. It is found that the MCS is more reliable than the FCA method in the resolution of the Ising model. Moreover, MC calculations reveal that [Formula: see text] is strongly correlated with the external magnetic field [Formula: see text], [Formula: see text], and [Formula: see text], where the competition between these parameters can generate several rich phase diagrams.

A 3-D Neutron Distribution Reconstruction Method Based on the Off-Situ Measurement for Reactor

Understanding the core neutron distribution is an indispensable condition to ensure the safe operation and effective burn-up of reactor fuel. It has become one of the new ways for reactor monitoring to use ex-core monitoring signals to calculate the in-core information recently. In this paper, an FCN-based architecture was implemented, where the 2D and 3D fully convolutional neural networks were used to reconstruct the space-and energy-dependent 3D neutron distribution of the reactor core through the off-situ measurement directly. The new method has been validated in the H. B. Robinson reactor. The differences between reconstruction results of neutron flux distribution and MC calculation were mostly less than 2%. The average relative deviation of reconstructing the neutron density kept in 5%. It was demonstrated that the provided method was applicable to monitor the reactor core theoretically and would provide strong support for the subsequent research on the real-time monitoring for an operating reactor, safety and operational testing for new reactor designs, and evaluation of source term information in a nuclear emergency.

A new hybrid next-event estimator for photon-based Monte Carlo dose rate calculations

This work describes the implementation of a deterministic-like straight-line transport routine inside the \(\hbox {TRIPOLI-4}^{\circledR }\) Monte Carlo code, aimed at developing a hybrid estimator that can speed up the MC calculation while retaining its precision. The algorithm is based on the exponential track length estimator or eTLE, a next-event estimator that has already been investigated for medical applications. In this implementation, the eTLE is paired with a forced detection algorithm. We describe the implementation of the method in \(\hbox {TRIPOLI-4}^{\circledR }\), then we present the first results obtained over some test cases and compare them with the classic track-length estimator already implemented in \(\hbox {TRIPOLI-4}^{\circledR }\). These results show that the forced detection technique drastically improves the eTLE performance.

NanoDot™ OSLDs in verifying radiotherapy dose calculations in the presence of metal implants: A Monte Carlo assisted research

The goal of this work is to evaluate the dosimetric accuracy of nanoDot optically stimulated luminescence dosimeters (OSLDs) for small field sizes both at phantom-implant interfaces and deeper depths of a phantom. The central axis percentage depth-dose (PDD) curves were obtained by 6 MV flattening-filter-free (FFF) photon beams in conjunction with the homogeneous and nonhomogeneous RW3 slab phantoms with aluminum (Al), titanium alloy grade 5 (Ti5), and stainless steel grade 316 L (SS) implant material sheets inserted into, in small fields: 2 × 2 cm2 and 4 × 4 cm2. Three different depths were defined within the heterogeneous phantoms created to compare the measured and calculated doses: The soft tissue/metal implant upper interface (level I), metal implant/soft tissue lower interface (level II), and deeper depth from the implant (level III). The assessment of OSLDs was performed at defined depths comparing by Monte Carlo simulation (EGSnrc-based DOSXYZnrc/BEAMnrc) and Acuros XB (AXB) algorithm with GafChromic™ EBT3 film and PTW 31014 pinpoint ion chamber (IC) measurements. The PDDs using OSLDs were compared to those predicted by MC, and AXB, and those measured by EBT3 and IC and found to agree with uncertainty (<3%) in a homogeneous medium. The mean relative differences between OSLD and MC simulation at the level I interface of the Al, Ti5, and SS implants were analyzed as 2.5%, 5.6%, and 9.8% for 2 × 2 cm2 and 3.0%, 5.2%, and 8.8% for 4 × 4 cm2, respectively. When using implant material with lower electron density such as Al, the OSLD measurement values were found to agree with each measurement and calculation technique. At level II, the relative doses measured using OSLDs were similar to those of MC calculations for both field sizes. The maximum difference was found at 3.2% for SS implant. Except for the vicinity of the metal implant/RW3 phantom slab interfaces, the OSLD relative dose values were similar to those of PDD measurements in homogeneous media at depths away from the implant material. The OSLDs present a high capacity for radiotherapy dosimetry in homogeneous medium.But we can not adequately consider the dose to the interface between tissue and high Zeff materials in the case of the Ti5 and SS implant materials for small fields using OSLDs.

Dosimetry investigation of a prototype of 169Yb seed brachytherapy for use in circular stapler

This study aims to investigate dosimetry parameters for the new design of 169Yb seed in the form of a surgical staple for circular staplers commonly used in the abdominal incision and the esophageal and gastric surgery, which facilitates the precise placement. This seed includes a titanium tube with the inner diameter and outer diameter 0.68 mm and 2.2 mm, respectively, and length of 0.8 mm. Both sides of the tube are closed by titanium wires with the thickness of 0.65 mm by the laser. Natural ytterbium oxide is used after the thermal neutron activation; it is necessary for cooling time of 40 days. The dosimetry parameters were calculated based on the TG-43U1 using Monte Carlo MCNP5 code. The experimental dosimetry was performed by EBT3 radiochromic film to determine 2D dosimetry at near distance of the source and validate the MC code. The dose rate constant of MC calculation was obtained at 1.39cGyh-1U-1 ± 4% with the difference of 5% compared to another study. The dose distribution was symmetrical along the Z-axis and Y-axis (around the seed) and there was a uniform activity inside the tube. The distinction of dose rate was not noticeable at the 90 and 270 degrees on the Z-axis, which indicated a slight effect on staple legs in the matter of delivery dose. However, to understand dose distribution and introduce this source in a pre-clinical study, 3D dosimetry as well as further studying the heterogeneous function is required.

Radiosensitization by Au-nanofilm at micrometer level using confocal Raman spectroscopy.

To measure the radiosensitization by an Au-nanofilm (GNF) at a micrometer level on a radiochromic film (RCF) using confocal Raman spectroscopy (CRS). Unlaminated radiochromic films were irradiated by 200kVp x-ray from 0.3 to 50Gy to obtain a calibration curve. Raman spectra of these films were measured by positioning the postirradiated RCF perpendicular to the CRS monochromatic beam and reading a depth profile of the film along the lateral axis. The Raman peak corresponding to the C≡C peak was obtained from a region of interest of 100×5µm2 . To investigate the radiosensitization by GNF, two sets of RCF, one attached to a 100-nm thick GNF and the other without GNF were irradiated at 0.5Gy by 50 and 120kVp X-rays. The spatial resolution of the CRS on the RCF was quantified by the modulation transfer function method (MTF). Thus, in the spatial resolution determined by MTF, the doses deposited on the films were evaluated. The dose enhancement factor (DEF) was obtained in the measurable micro-size by comparing doses deposited on the RCFs with and without GNF. To verify the experimental results, Monte Carlo simulations following the experimental set up were performed using Geant4. In addition, analytical calculations for the radiosensitization by GNF were carried out. The confocal Raman spectroscopy on the RCF achieved a spatial resolution of ~6μm. An experimental DEF within the first 6μm depth from the surface of RCF was found to be 17.9 for 50kVp and 14.7 for 120kVp. The DEF for the same depth obtained by MC and analytical calculations was 13.53 and 9.75 for 50kVp, and 10.63 and 6.67 for 120kVp, respectively. The experimental DEF as a function of the distance from GNF was consistent with data from previous studies and the MC simulations, supporting that CRS in conjunction with the RCF is a feasible micrometer-resolution dosimeter.

Zinc oxide nanoclusters and nanoparticles as a drug carrier for cisplatin and nedaplatin anti-cancer drugs, insights from DFT methods and MC simulation

ABSTRACT In this work, we study the ability of (Zno) n (n = 2–5 and 12) nanoclusters and ZnO nanoparticles to act as a drug carrier for cisplatin and nedaplatin drugs by DFT methods and MC simulation. Binding energies in both gas and water phases are calculated, the bonds formed between (ZnO)n (n = 2–5 and 12) and cisplatin and nedaplatin drugs are studied and computed using QMAIM. The binding energy in water is lower than that in gas, which supports that the partially covalent and partially electrostatic bonding nature. Also, binding energies in the state of (ZnO) n -cisplatin complexes are lower than those in the (ZnO) n -nedaplatin complexes in both gas and water phases. Also, the adsorption of cisplatin and nedaplatin drugs on ZnO nanoparticles surface (different sizes and shapes) was studied by Monte Carlo simulation. We find that increasing the ZnO size dose not significantly influences on the adsorption energies of cisplatin and nedaplatin drugs for all studied nanoparticles shapes. All adsorption energies obtained by MC calculations are negative which revealed that the adsorption of the cisplatin and nedaplatin molecules on ZnO surfaces is exothermic, spontaneously and energetically favourable. So, ZnO nanoclusters and nanoparticles can act as a drug carrier for cisplatin and nedaplatin anticancer drugs. Abbreviations: Density Functional Theory; MC simulation: Monte Carlo simulation; QMAIM: quantum mechanics atoms in molecules

A robust optimization method for weighted-layer-stacking proton beam therapy

The layer-stacking method can provide three-dimensional conformal dose distributions to the target based on a passive scattering method using mini-spread-out Bragg peak (SOBP). The purpose of this work is to demonstrate the effectiveness of a new weight optimization algorithm that can enhance the robustness of dose distributions against layer depth variation in layer-stacking proton beam therapy.In the robustness algorithm, the upper limit of the layer’s weight was adapted to the conventional algorithm and varied for 620 weight set evaluations. The optimal weight set was selected by using an analytical objective function based on Gaussian function with σ = 3 mm for WED variation. Then, we evaluated the stabilities of the one-dimensional depth dose distribution against WED variation generated by Gaussian samples. Three-dimensional dose distributions in the water phantom were also evaluated using the Monte-Carlo dose calculation. The variation of dose as well as dose volume histograms for the spherical target and the organ at risk (OAR) were evaluated.The robustness algorithm reduced the change of the dose distribution due to the WED variation by a factor of almost 3/4 compared to those with the conventional procedure. The rate of 91.8% in total samples was maintained within 5% change of the maximum dose, compared with the rate of 64.9% in the conventional algorithm. In the MC calculation, the high dose-volume in the OAR was reduced around the lateral penumbra and distal falloff region by the robustness algorithm.The stability of depth dose distributions was enhanced under the WED variation, compared to the conventional algorithm. This robust algorithm in layer-stacking proton therapy may be useful for treatment in which the sharpness of the distal falloff along the depth distribution needs to be maintained to spare the organ at risk and keep the dose coverage for the target tumor.

Dosimetric Issues Associated with Percutaneous Ablation of Small Liver Lesions with 90Y

The aim of the present paper is twofold. Firstly, to assess the absorbed dose in small lesions using Monte Carlo calculations in a scenario of intratumoral injection of 90Y (e.g., percutaneous ablation). Secondly, to derive a practical analytical formula for the calculation of the absorbed dose that incorporates the absorbed fractions for 90Y. The absorbed dose per unit administered activity was assessed using Monte Carlo calculations in spheres of different size (diameter 0.5–20 cm). The spheres are representative of tumor regions and are assumed to be uniformly filled with 90Y. Monte Carlo results were compared with the macrodosimetric approach used for dose calculation in liver radioembolization. The results of this analysis indicate that the use of the analytic model provides dose overestimates below 10% for lesions with diameter larger than approximately 2 cm. However, for lesions smaller than 2 cm the analytic model is likely to deviate significantly (&gt;10%) from Monte Carlo results, providing dose overestimations larger than 50% for lesions of 0.5 cm diameter. In this paper an analytical formula derived from MC calculations that incorporates the absorbed fractions for 90Y is proposed. In a scenario of intratumoral injection of microspheres, the proposed equation can be usefully employed in the treatment planning of spherical lesions of small size (down to 0.5 cm diameter) providing dose estimates in close agreement with Monte Carlo calculations (maximum deviation below 0.5%).

Boron nitride nanoclusters, nanoparticles and nanotubes as a drug carrier for isoniazid anti-tuberculosis drug, computational chemistry approaches

In this work, the ability of B12N12 fullerene-like nanoclusters as a drug carrier for isoniazid anti-tuberculosis drug has been studied by DFT methods. Binding energies in both gas and water phases are reported. The formed bonds between B12N12-FLN and Iso drug are studied and computed using QMAIM method. NPA is computed to obtain the total charges transferred in the B12N12-FLN-Iso drug complexes, NPA obtained values suggested that the cluster may oxidize the coordinated of Iso drug. The charge-transfer energy values are also computed and confirmed that the charges were transferred from the non-bonding lone-pair (n) of N and O atoms orbitals to the σ* orbitals of B and N atoms of B12N12-FLN. Also, the adsorption of Iso drug on BN nanoparticles surface (different sizes and shapes) and BN nanotubes was studied by Monte Carlo simulation. We found that increasing the BN size did not affect significantly on the adsorption energies of Iso drug for all various BN nanoparticles shapes. All adsorption energies obtained by MC calculations are negative values which revealed that the adsorption of the Iso drug molecule on BN surfaces is exothermic, spontaneous and energetically favourable. Also, the stability of B12N12-FLN-Iso drug complex in water explicitly was studied by MD simulations. MD simulation confirmed that iso-B12N12-FLN complexes are stable in the presence of water molecules. So, finally, we deduced that B12N12 fullerene-like nanoclusters can be acted as a drug carrier for isoniazid anti-tuberculosis drug. Communicated by Ramaswamy H. Sarma

Preliminary evaluation of the production of non-carrier added 111Ag as core of a therapeutic radiopharmaceutical in the framework of ISOLPHARM_Ag experiment

Research in the field of radiopharmaceuticals is increasingly promoted by the widespread and growing interest in applying nuclear medicine procedures in both disease diagnosis and treatment. The production of radionuclides of medical interest is however a challenging issue. Along with the conventional techniques other innovative approaches are being investigated and, among those, the ISOLPHARM project is being developed at INFN-LNL (Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Legnaro). Such technique foresees the employment of the SPES ISOL facility to produce isobarically pure Radioactive Ion Beams (RIBs), obtained thanks to electromagnetic mass separation and collected on appropriate substrates. The latter are successively recovered and dissolved, allowing thus the chemical separation and harvesting of the nuclides of interest, free from any isotopic contaminant. Although ISOLPHARM can be potentially employed for most of the routinely used medical radioisotopes, its innovation potential is better expressed considering its capability to provide carrier free unconventional nuclides, difficult to produce with state-of-art techniques, such as 111Ag, a β— emitter potentially interesting for therapeutic applications. Thus, in the framework of ISOLPHARM, INFN supported a two-years experiment, called ISOLPHARM_Ag, aimed at evaluating the feasibility of the production of a111Ag labelled radiopharmaceutical. The ISOL production yields are estimated by computing intensive Monte Carlo codes, that require an appropriate custom Information Technology infrastructure. The presented work is focused on the first part of the production chain including the capability to extract, ionize, and collect stable Ag beams with SPES technologies. MC calculations were used to estimate the expected 111Ag in-target yields, whereas experiments with stable Ag were performed to test the ionization, transport and collection of Ag beams.

Monte carlo model and output factors of elekta infinity™ 6 and 10 MV photon beam.

This study aimed to commission the Elekta Infinity™ working in 6 and 10 MV photon beam installed in Concord International Hospital, Singapore, and compare the OFs between MC simulation and measurement using PTW semiflex and microDiamond detector for small field sizes. There are two main steps in this study: modelling of Linac 6 and 10 MV photon beam and analysis of the output factors for field size 2 × 2-10 × 10 cm2. The EGSnrc/BEAMnrc-DOSXYZnrc code was used to model and characterize the Linac and to calculate the dose distributions in a water phantom. The dose distribution and OFs were compared to the measurement data in the same condition. The commissioning process was only conducted for a 10 × 10 cm2 field size. The PDD obtained from MC simulation showed a good agreement with the measurement. The local dose difference of PDDs was less than 2% for 6 and 10 MV. The initial electron energy was 5.2 and 9.4 MeV for 6 and 10 MV photon beam, respectively. This Linac model can be used for dose calculation in other situations and different field sizes because this Linac has been commissioned and validated using Monte Carlo simulation. The 10 MV Linac produces higher electron contamination than that of 6 MV. The Linac model in this study was acceptable. The most important result in this work comes from OFs resulted from MC calculation. This value was more significant than the OFs from measurement using semiflex and microDiamond for all beam energy and field sizes because of the CPE phenomenon.