Dynamic relaxations play an important role in understanding the nature of glass. The conventional methods to explore dynamic relaxations rely on the measurement of mechanical and thermic properties, while new methods that may provide a new perspective to probe dynamic relaxation are desperately required. Here, we show that the β-relaxation of metallic glasses (MGs) can be unveiled by electrical resistivity (ER). Irreversible β-relaxation leads to an increment in electrical resistivity, which can be fitted by the Kohlrausch–Williams–Watts equation well. In contrast, the ER results of the initialized sample only exhibit a negligible change during annealing, which indicates that the reversible β-relaxation change cannot be manifested by ER testing. This work provides the ER measurement as a new means to explore the dynamic relaxation of MGs, which may offer a new insight into the understanding of β-relaxation in glass materials.

INTRODUCTION: The continued reliance upon the traditional biologically effective dose (BED T ) formalism of BED T = nd(1 + d/( alpha/ beta)) may be one possible contributor to the poor clinical outcomes observed with single-fraction 19-20 Gy prescriptions in prostate high-dose-rate (HDR) brachytherapy because BED T does not consider intrafraction sublethal damage repair (iSLDR). This, along with low alpha/ beta and repair half-times comparable to delivery time, could reduce the biological effect predicted using BED T .METHODS AND MATERIALS: BED was recalculated with a model accounting for iSLDR, using time-averaged uniform dose rate (BED g1 ) patterns and time-variable dose rate (BED gss ) patterns inherent to stepping-source delivery. An assortment of two-pulse delivery sequences assuming 19 Gy in 972 s was analyzed. Calculations were repeated for 17470 and 61050 U to investigate source strength dependence.RESULTS: BED g1 and BED gss was/were lower than BED T by 16.9% and 11.1%-21.1%, respectively, for 40700 U. For 17470 U, BED g1 and BED gss was/were lower than BED T by 32.5% and 21.5%-37.1%, respectively. For 61050 U, BED g1 and BED gss was/were lower than BED T by 11.9% and 7.8%-15.3%, respectively. BED gss was most dependent on pulse spacing with milder dependence on pulse onset time. BED g1 served as a lower bound approximation of BED gss for fast effective delivery time.CONCLUSIONS: Even for points with the same calculated dose, the biological dose was significantly reduced by iSLDR (as much as 37.1%). While BED gss explicitly addressed the temporallyvariable dose rate inherent to a stepping-source delivery, calculations were cumbersome. Under certain conditions, BED g1 may serve as an approachable method to quickly assess "worst-case scenario" BED. (c) 2023 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

PURPOSE:Total skin electron therapy (TSET) has proven to be one of the most effective treatments for advanced-stage cutaneous T-cell lymphoma. Two most used techniques are the Stanford six-field and rotational techniques. This study compares patient skin dose distributions as a function of depth between these two techniques. METHODS:The EGSnrc system was used to simulate electron beams and calculate patient dose distributions. The calculations assumed the same patient standing on a platform, and the patient's different postures were ignored for the Stanford technique in the comparison of dose distributions. The skin doses were analyzed as a function of skin depth-dose coverage and evaluated using dose-volume-histograms (DVH). The comparisons were performed in three realistic clinical settings in which dual-field were used for patients treated at extended distances of 316 and 500 cm, and a single field was used at 700 cm. In all cases the realistic patient treatment beam delivery geometry was simulated. RESULTS:Although small dose differences were observed in some local areas, no clinically significant differences were found in the patient 3D dose distributions between the Stanford and rotational techniques. Virtually the same DVH curves between two the techniques were observed for mean dose to skin depth of 0-5, 5-10, and 10-15 mm from the skin surface, respectively. It is found that the skin depth dose coverage is 2 mm shallower for patient treatment at 500 cm compared to at 316 cm due to the additional air attenuation. However, very similar dose coverage and uniformity can be achieved at these two different extended treatment distances by adjusting the thickness of acrylic scatter plate. Adequate thickness of a scattering plate improves the skin dose uniformity. CONCLUSION:Both the Stanford and rotational techniques deliver very similar skin dose coverage in DVH plots, and only small differences are seen in local areas. It is worth to emphasize that the DVH is a graphical representation of the distribution of dose within a structure, and it does not contain spatial information. Therefore, comparison of entire skin dose using DVH may mask some variations at different locations of the surface area. In addition, the comparison did not consider different patient postures of the Stanford technique. Including the different patient postures in the calculation may affect the result of doses to the limbs.

Low dimensional materials especially carbon materials hold high promise in the fields of water purification, mineral separation, energy harvesting/conversion, and so on. The fluidic devices fabricated by direct synthesis, lithography, or selfassembly of low dimensional materials provide opportunities for exploring the novel properties and applications of nanoconfined transport. Here, continuous filling of water and acetone molecules into a graphene nanochannel is investigated. A stairlike nonlinear dependence of the number of filling water molecules on interlayer distance d is found when d < 1 nm due to the existence of outplane layered and in-plane ordered monolayer structure, while near-linear dependence is found for acetone because of the freely rotating configurations along with varying d during the filling process. The entropy, potential energy, and free energy of the confined system during the continuous filling are analyzed to understand the structural evolution of water. The energy-costs are discussed depending on the structure evolution of water during the filling, which is crucial to understanding the swelling and capillary condensation widely existing in the angstrom/nanometer-scale separation membranes.

The Monte Carlo (MC) method is widely used to solve various problems in radiotherapy. There has been an impetus to accelerate MC simulation on GPUs whereas thread divergence remains a major issue for MC codes based on acceptance-rejection sampling. Inverse transform sampling has the potential to eliminate thread divergence but it is only implemented for photon transport. Here, we report a MC package Particle Transport in Media (PTM) to demonstrate the implementation of coupled photon-electron transport simulation using inverse transform sampling. Rayleigh scattering, Compton scattering, photo-electric effect and pair production are considered in an analogous manner for photon transport. Electron transport is simulated in a class II condensed history scheme, i.e., catastrophic inelastic scattering and Bremsstrahlung events are simulated explicitly while subthreshold interactions are subject to grouping. A random-hinge electron step correction algorithm and a modified PRESTA boundary crossing algorithm are employed to improve simulation accuracy. Benchmark studies against both EGSnrc simulations and experimental measurements are performed for various beams, phantoms and geometries. Gamma indices of the dose distributions are better than 99.6% for all the tested scenarios under the 2%/2 mm criteria. These results demonstrate the successful implementation of inverse transform sampling in coupled photon-electron transport simulation.

As a promising additive manufacturing technique, selective laser melting (SLM) provides the possibility of fabricating metallic glassy components free of the constraints of geometrical complexity and dimensions. However, unexpected crystallization greatly affects the microstructure and degrades the mechanical performance of SLM-fabricated metallic glasses (MGs). To clarify the crystallization mechanism and the effect of laser processing on the crystallization, we investigate the atomic-level crystallization in the SLM Zr90Cu10 MG by using molecular dynamics simulations. The results show that crystallization highly related to scan speed lies in the atomic-level cluster changes. Lower scan speed leads to a dramatically increased fraction of the BCC crystal phase, accompanied by the nucleation of a few HCP and FCC crystal phases. As scan speed increases, more icosahedron-like clusters are formed, leading to the formation of the MG, while the nucleation of the crystal phase is suppressed. The suppression of crystallization is further attributed to a higher average temperature variation rate induced by higher scan speed, which reduces the relaxation time, preventing the nucleation and growth of crystal phases. This work contributes to the understanding of the crystallization in MGs during the SLM process at the atomic level, providing guidance to suppress the crystallization in the SLM process of desired metallic glassy components.

The debate on necessity of CT in brachytherapy planning has recently been revisited. As with many clinics, our vaginal cylinder cases are planned using both CT and MR for the majority of vaginal cylinder cases. The main advantages to including CT in treatment planning are its spatial resolution, spatial integrity, and inherent electron density information. We examined the feasibility of an MR-exclusive workflow with applicator in situ for our custom vaginal cylinders.

Auxetic materials are promising structural and functional candidates due to their unique lateral expansion when stretched, however, bulk metallic glasses (MGs) could not show any auxeticity because of their intrinsic isotropic nature. Here we construct chiral Cu50Zr50 metallic glass nanolattices with cavities, and investigate their auxeticity and underlying mechanism with molecular dynamics simulations. It is found that, compared to monolithic MGs, all the chiral metallic glass nanolattices (CMGNs) exhibit improved auxeticity and lower density. For CMGNs with cavities, the negative Poisson's ratio and ultimate tensile strength (UTS) increase first and then decrease with increasing cavity radius, with the cavity radius of 2.5 nm being the most favorable for auxeticity and enhanced UTS. The auxetic mechanism is attributed to the competition between rotation behavior and non-affine deformation under tension. Our study not only reveals the mechanism of auxeticity in CMGNs having cavities but also provides a feasible method to optimize their auxetic performance and density by structure designing of MGs.

In present work, the glass-forming ability of Cu-Zr and Cu-Al systems has been estimated by utilizing a monolayer two-dimensional model. The structure of 2D Cu-Zr MGs can be simply characterized by three kinds of Voronoi polygons, i.e. pentagon, hexagon and heptagon, and the structural translational symmetry is broken down by the strong coupling effect between pentagon and heptagon, promoting the formation of MGs. Moreover, the larger bond lengths of Cu-Zr and Zr-Zr pairs are found responsible for the outstanding GFA of Cu-Zr system. The 2D model provides a promising avenue for accurately predicting the GFA of alloys of interest, which is important both in theoretical research and engineering.

OBJECTIVE:To evaluate the benefits of adaptive imaging with automatic correction compared to periodic surveillance strategies with either manual or automatic correction.METHODS:Using Calypso trajectories from 54 patients with prostate cancer at 2 institutions, we simulated 5-field intensity-modulated radiation therapy and dual-arc volumetric-modulated arc therapy with periodic imaging at various frequencies and with continuous adaptive imaging, respectively. With manual/automatic correction, we assumed there was a 30/1 second delay after imaging to determine and apply couch shift. For adaptive imaging, real-time "dose-free" cine-MV images during beam delivery are used in conjunction with online-updated motion pattern information to estimate 3D displacement. Simultaneous MV-kV imaging is only used to confirm the estimated overthreshold motion and calculate couch shift, hence very low additional patient dose from kV imaging.RESULTS:Without intrafraction intervention, the prostates could on average have moved out of a 3-mm margin for ∼20% of the beam-on time after setup imaging in current clinical situation. If the time interval from the setup imaging to beam-on can be reduced to only 30 seconds, the mean over-3 mm percentage can be reduced to ∼7%. For intensity-modulated radiation therapy simulation, with manual correction, 110 and 70 seconds imaging periods both reduced the mean over-3 mm time to ∼4%. Automatic correction could give another 1% to 2% improvement. However, with either manual or automatic correction, the maximum patient-specific over-3 mm time was still relatively high (from 6.4% to 12.6%) and those patients are actually clinically most important. In contrast, adaptive imaging with automatic intervention significantly reduced the mean percentage to 0.6% and the maximum to 2.7% and averagely only ∼1 kV image and ∼1 couch shift were needed per fraction. The results of volumetric-modulated arc therapy simulation show a similar trend to that of intensity-modulated radiation therapy.CONCLUSIONS:Adaptive continuous monitoring with automatic motion compensation is more beneficial than periodic imaging surveillance at similar or even less imaging dose.

In popular gynecological applicators, such as the tandem-and-ovoid (TO) or tandem-and-ring (TR) designs, a tandem is paired with two ovoids or a single ring, respectively. Removal of TO and TR may be difficult for patients with narrow vaginal canals. Furthermore, lateral extension of CTV is difficult to address in a pear-shaped distribution without excess dose delivery to normal tissue with the classic intracavitary applicators. We propose a novel vendor-neutral “virtual ring” applicator to overcome these challenges.

Many US institutions have high dose rate (HDR) brachytherapy licenses for Ir-192 sources which are limited by licensure to a maximum activity of 10 Ci. Considering the half-life of 73.8 days for Ir-192, treatment times are more than doubled (2.3x) when using a 90-day source exchange cycle. Total dwell times for an individual single delivery fraction can routinely exceed 20 minutes for procedures such as HDR prostate monotherapy. This study investigates the theoretical radiobiological impact of using an Ir-192 source with an initial activity of 15 Ci compared to a 10 Ci source on 90- and 60-day exchange cycles.

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Porous metallic glass (MG) structures are good candidates for structural and functional applications due to their light weight, enhanced ductility and specific surface area. Motivated by the improvement of mechanical properties of MGs, we perform molecular dynamics simulations on uniaxial tensile strain of monatomic Ta MG with nanoscale porous structures, focusing on the effects of pore stacking, size, as well as the strain rate on deformation behaviors. Obvious atomic level fracture from necking to shear sliding or accompanied with a network of multiple SBs are observed, and relating deformation transition from brittle to ductile is declared. It is found that: (i) AB pore stacking results in an improved ductility contrary to AA pore stacking with weakened ductility, and pore stacking inclining at 45° with respect to the loading direction may not necessarily deteriorate the ductility; (ii) Ultimate tensile stress decreases with the pore diameter, due to increasing porosity; and (iii) Better ductility is shown under higher strain rate for nanoporous MG structures due to the formation of the network of multiple SBs. This study is expected to shed light on the modulation of mechanical properties by designing the pore stacking and size in metallic glasses.

Brachytherapy has advanced dramatically in the last decade due largely to improvements in applicators, imaging, treatment planning, and use of clinical trials. In addition, current research in brachytherapy technology continues to change how we deliver this treatment modality. The future of brachytherapy lies in the ability of new technologies to overcome real or perceived barriers. The focus for this manuscript is on specific tools that have or are near to being introduced in the clinic. First, we explore the impact electromagnetic tracking technologies can have on brachytherapy implants and planning workflow. This is followed by an overview of the use of 3D printing and its ability to help tailor brachytherapy implants. Next, we discuss advances in self-shielded applicators and intensity-modulated brachytherapy technology. The manuscript closes out with 2 sections on treatment planning. First is a discussion of biological optimization and its potential as compared with current techniques (eg, based on physical dosimetry). And lastly, a section on optimization treatment planning efficiencies in which we explore the potential for machine learning in brachytherapy. As recent clinical evidence continues to show excellent outcomes, this is an exciting time to practice brachytherapy. With the new technologies presented here, the future is even brighter.

Combined application of thermal and pressure are effective to obtain structure excited metallic glass with high energy state. This work studied the thermal-pressure effects on energy state, atomic level structure and tensile behavior during each separate fabrication stage (heating, equilibrating, and quenching) of Cu50Zr50 metallic glasses by dynamic simulation. It is found that quenching under pressure is the most effective approach obtaining high energy state Cu50Zr50 metallic glass among 4 designed methods. For the effective approach, the potential energy increases and the atomic volume decreases with pressure for Cu50Zr50 metallic glass when the pressure is below 30 GPa, and the latter reaches its minimum at 30 GPa. Moreover, Cu-centered full icosahedron <0, 0, 12, 0> plays a dominant role in the formation of high energy structure, and Cu50Zr50 metallic glass fabricated by method 3 under 30 GPa shows the most improved plasticity.