Ultrahigh Rate Research Articles

Facile access to highly functionalized polyacrylamide with ultra-high molecular weight: Multicomponent initiators-based free radical polymerization

We report a novel multicomponent initiators-based copolymerization strategy for synthesizing of acrylamide (AM) and 2-acrylamide-2-methylpropane sulfonic acid (AMPS) copolymers, denoted by P(AM-co-AMPS), with an ultra-high content of AMPS (≥ 50 mol%) and an ultra-high molecular weight (> 107 g/mol), while achieving a high conversion rate of monomer (∼100.0%). The multicomponent initiators contain a redox couple, an azo compound, and a catalyst. Our investigation into the mechanism suggested that the synergistic effect in different rate constant for initiator decomposition between redox and azo initiators was responsible for actualizing ultra-high molecular weight copolymers with high conversion rates of monomer. Moreover, copolymers with 75 mol% and 100 mol% of AMPS were synthesized to verify the advantage of the multicomponent initiators-based strategy, both of which exhibited ultra-high molecular weight and ultra-high monomer conversion rates. This study fills a long-standing gap in research on the polyacrylamide family by providing highly functionalized P(AM-co-AMPS) with an ultra-high molecular weight. Moreover, it reveals how multicomponent initiators reconcile the contradiction between the ultra-high molecular weight and the high conversion rate in copolymerization.

RBIO-02. DEVELOPMENT OF FLASH-CAR RADIOIMMUNOTHERAPY FOR PEDIATRIC BRAIN TUMORS

Abstract Pediatric brain tumors including medulloblastoma and high-grade glioma are generally refractory to T cell-based immunotherapy, largely due to an immune-hostile microenvironment infiltrated extensively with immunosuppressive macrophages. Ultra-high dose rate (FLASH) radiotherapy holds promise for treating solid tumors, given the potential lower toxicity in normal tissues and possible favorable impact on tumor immunity. Using a genetically engineered mouse model of medulloblastoma and glioma, we show that FLASH radiation stimulates pro-inflammatory polarization in tumor macrophages. Single-cell transcriptome analysis shows that FLASH proton beam radiation skews macrophages towards proinflammatory phenotypes and increases T cell infiltration in the medulloblastoma model. Further bulk transcriptome analyses reveal that FLASH radiation reduces peroxisome proliferator-activated receptor (PPAR)-γ and arginase-1 expression and inhibits immunosuppressive macrophage polarization under stimulus-inducible conditions. Mechanistically, FLASH radiation abrogates lipid oxidase expression and oxidized low-density lipid (oxLDL) generation to reduce PPARγ activity, while standard radiation induces reactive oxygen species (ROS)-dependent PPARγ activation in macrophages. Notably, FLASH radiotherapy improves infiltration and activation of chimeric antigen receptor (CAR) T cells and sensitizes tumors to GD2 CAR T immunotherapy in the autochthonous medulloblastoma and syngeneic glioma models. These findings suggest that FLASH radiotherapy may reprogram macrophage lipid metabolism to reverse tumor immunosuppression and that combination FLASH-CAR radioimmunotherapy may offer exciting opportunities for treatment of pediatric brain tumor.

RBIO-03. A SMALL ANIMAL RADIATION RESEARCH PLATFORM (FLASH-SARRP) TO MEASURE IMMUNOLOGICAL EFFECT OF ULTRA HIGH DOSE RATE (FLASH) RADIOTHERAPY

Abstract Patients who undergo radiation therapy (RT), particularly fractionated courses, often develop lymphopenia. Clinical outcome for various cancer types, including brain tumors, identifies lymphopenia as a negative prognostic factor. The mechanism for RT induced lymphopenia is unclear. Simulated models suggest the volume of blood flowing through a radiation field could play a crucial role in death of radiosensitive lymphocytes. FLASH RT is ultrahigh dose rate administration of RT, >100 times faster dose rate than standard RT that has been observed to improve the therapeutic ratio in preclinical models by preferential normal tissue sparing. Hypothesized mechanisms include chemical reactions depleting oxygen in well oxygenated normal cells creating radioresistance, differing pro-inflammatory signaling impacting tumor and normal tissue, and less impact on circulating immune cells consequent to decreased proportion exposed during a treatment session which may enhance antineoplastic response. We designed the novel FLASH kV x-ray cabinet system for preclinical laboratory research (FLASH-SARRP) to deliver ultra-high dose rates up to 100 Gy/s as well as conventional dose rates of 1.0 Gy/s to facilitate comparative studies. A custom designed docking system was developed to reproducibly position and immobilize mouse for stereotactic radiation of the brain. Dose and dose rate measurements were performed with calibrated Gafchromic EBT3 film in solid water with 0.025 mm additional copper filter. FLASH-SARRP system delivered kV x-rays at an average dose-rate of 79.2±2.1Gy/s corresponding to 10 mm depth in the immobilized mouse brain. For the delivery of 15 Gy, treatment duration was 0.2 seconds for FLASH RT administration whereas it was 244 seconds for conventional dose rate. We successfully designed a high-precision platform to study partial brain x-ray FLASH effects in mice and studies are ongoing to assess differential impact on normal brain tissue, circulating cytokines, and immune cell populations for single dose and fractionated administration of FLASH and standard radiotherapy.

Oxygen consumption measurements at ultra-high dose rate over a wide LET range.

The role of radiolytic oxygen consumption for the in-vitro "Ultra-High Dose Rate" (UHDR) sparing and in-vivo FLASH effect is subject to active debate, but data on key dependencies such as the radiation quality are lacking. The influence of "dose-averaged Linear Energy Transfer" (LETd) and dose rate on radiolytic oxygen consumption was investigated by monitoring the oxygen concentration during irradiation with electrons, protons, helium, carbon, and oxygen ions at UHDR and "Standard Dose Rates" (SDR). Sealed "Bovine Serum Albumin" (BSA) 5% samples were exposed to 15Gy of electrons and protons, and for the first time helium, carbon, and oxygen ions with LETd values of 1, 5.4, 14.4, 65, and 100.3keV/µm, respectively, delivered at mean dose rates of either 0.3-0.4Gy/s for SDR or approximately 100Gy/s for UHDR. The Oxylite (Oxford Optronics) system allowed measurements of the oxygen concentration before and after irradiation to calculate the oxygen consumption rate. The oxygen consumption rate was found to decrease with increasing LETd from 0.351mmHg/Gy for low LET electrons to 0.1796mmHg/Gy for high LET oxygen ions at SDR and for UHDR from 0.317 to 0.1556mmHg/Gy, respectively. A higher consumption rate for SDR irradiation compared to the corresponding UHDR irradiation persisted for all particle types. The measured consumption rates demonstrate a distinct LETd dependence. The obtained dataset, encompassing a wide range of LETd values, could serve as a benchmark for Monte Carlo simulations, which may aid in enhancing our comprehension of oxygen-related mechanisms after irradiations. Ultimately, they could help assess the viability of different hypotheses regarding UHDR sparing mechanisms and the FLASH effect. The found LETd dependence underscores the potential of heavy ion therapy, wherein elevated consumption rates in adjacent normal tissue offer protective benefits, while leaving tumor regions with generally higher "Linear Energy Transfer" (LET) vulnerable.

Noninvasive Early Detection of Systemic Inflammatory Response Syndrome of COVID-19 Inpatients Using a Piezoelectric Respiratory Rates Sensor

In 2020, 20% of patients with COVID-19 developed severe complications, including life-threatening pneumonia with systemic inflammatory response syndrome (SIRS). We developed a preliminary SIRS monitor that does not require blood sampling, is noninvasive, and can collect data 24 h per day. The proposed monitor comprises a piezoelectric respiratory sensor located beneath the patient’s mattress and a fingertip pulse sensor that determines ultra-high accuracy respiratory rate (mode of a 40-min frequency distribution of respiratory rates (M40FD-RR)). We assessed the clinical performance of the M40FD-RR preliminary SIRS monitor in 29 patients (12 female, 17 male, aged 15–90 years) hospitalized at Suwa Central Hospital with COVID-19, which was confirmed by a positive polymerase chain reaction test. SIRS was evaluated by logistic regression analysis using M40FD-RR, heart rate, age, and sex as explanatory variables. We compared the results of 109 examinations of 29 COVID-19 inpatients with SIRS against those determined by the proposed monitor. The proposed monitor achieved 75% sensitivity and 83% negative predictive value, making it a promising candidate for future 24 h noninvasive preliminary SIRS tests.

Investigating ultra-high dose rate water radiolysis using the Geant4-DNA toolkit and a Geant4 model of the Oriatron eRT6 electron linac

Ultra-high dose rate FLASH radiotherapy, a promising cancer treatment approach, offers the potential to reduce healthy tissue damage during radiotherapy. As the mechanisms underlying this process remain unknown, several hypotheses have been proposed, including the altered production of radio-induced species under ultra-high dose rate (UHDR) conditions. This study explores realistic irradiation scenarios with various dose-per-pulse and investigates the role of pulse temporal structure. Using the Geant4 toolkit and its Geant4-DNA extension, we modeled the Oriatron eRT6 linac, a FLASH-validated electron beam, and conducted simulations covering four distinct dose-per-pulse scenarios – 0.17 Gy, 1 Gy, 5 Gy, and 10 Gy – all featuring a 1.8 µs pulse duration. Results show close agreement between simulated and experimental dose profiles in water, validating the eRT6 model for Geant4-DNA simulations. We observed important changes in the temporal evolution of certain species, such as the earlier fall in hydroxyl radicals (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{ \\bullet } \ ext{O}\ ext{H}$$\\end{document}) and reduced production and lifetime of superoxide (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{O}}_{2}^{{\\bullet\\:}-}$$\\end{document}) with higher dose-per-pulse levels. The pulse temporal structure did not influence the long-term evolution of species. Our findings encourage further investigation into different irradiation types, such as multi-pulse configurations, and emphasize the need to add components in water to account for relevant cellular processes.

Study of a gel dosimeter based on Ag nanoparticles for applications in radiation therapy with synchrotron X-rays at ultrahigh dose rate compared to 60Co γ-rays

A silver nitrate (AgNO3) gel was developed and evaluated as a dosimeter for synchrotron X-ray-based studies in microbeam radiation therapy (MRT) and FLASH radiation therapy. The gel was irradiated at the European Synchrotron Radiation Facility (ID17 Biomedical beamline) with a continuous X-ray spectrum in the 50–600 keV range and a dose rate of 11.6 kGy/s. The spectrophotometric response after irradiation at this beamline was compared with the response at a conventional 60Co γ-ray source providing a dose rate of 0.27 Gy/s. Ag + ions in the gel dosimeter undergo reduction to Ago nanoparticles, as detected at 450 nm, which is a surface plasmon resonance band. The intensity of this band increased linearly with increasing absorbed dose up to 100 Gy, and improved with the addition of glycerol. The gel dosimeter exhibited the lowest detectable dose (LDD) of 75.9% lower and a dose deposition of 76% higher for ID17 beamline irradiation than for 60Co irradiation. The theoretical relative response HQ,Qo for the gel irradiated at the synchrotron was 1.70, which is in close agreement with the experimental relative response FQ,Qo = 1.76. These results confirm the dose enhancement in the gel irradiated with orthovoltage X-rays. The good properties of the silver nitrate gel, together with its increased sensitivity to orthovoltage X-ray irradiation and modest overall uncertainty of 5.8% (2σ), confirm that the gel is a valid dosimeter for measurements at ultrahigh dose rates for synchrotron radiotherapy. The dosimeter is also a promising candidate for dose enhancement factor measurements in nanoparticle-based radiotherapy techniques.

Characterizing devices for validation of dose, dose rate, and LET in ultra high dose rate proton irradiations.

Ultra high dose rate (UHDR) radiotherapy using ridge filter is a new treatment modality known as conformal FLASH that, when optimized for dose, dose rate (DR), and linear energy transfer (LET), has the potential to reduce damage to healthy tissue without sacrificing tumor killing efficacy via the FLASH effect. Clinical implementation of conformal FLASH proton therapy has been limited by quality assurance (QA) challenges, which include direct measurement of UHDR and LET. Voxel DR distributions and LET spectra at planning target margins are paramount to the DR/LET-related sparing of organs at risk. We hereby present a methodology to achieve experimental validation of these parameters. Dose, DR, and LET were measured for a conformal FLASH treatment plan involving a 250-MeV proton beam and a 3D-printed ridge filter designed to uniformly irradiate a spherical target. We measured dose and DR simultaneously using a 4D multi-layer strip ionization chamber (MLSIC) under UHDR conditions. Additionally, we developed an "under-sample and recover (USRe)" technique for a high-resolution pixelated semiconductor detector, Timepix3, to avoid event pile-up and to correct measured LET at high-proton-flux locations without undesirable beam modifications. Confirmation of these measurements was done using a MatriXX PT detector and by Monte Carlo (MC) simulations. MC conformal FLASH computed doses had gamma passing rates of>95% (3mm/3% criteria) when compared to MatriXX PT and MLSIC data. At the lateral margin, DR showed average agreement values within 0.3% of simulation at 100Gy/s and fluctuations ∼10% at 15Gy/s. LET spectra in the proximal, lateral, and distal margins had Bhattacharyya distances of<1.3%. Our measurements with the MLSIC and Timepix3 detectors shown that the DR distributions for UHDR scenarios and LET spectra using USRe are in agreement with simulations. These results demonstrate that the methodology presented here can be used effectively for the experimental validation and QA of FLASH treatment plans.

Ultra-High Rate and Long Cycle Life Sodium-Based Dual-Ion Batteries Enabled by Li2TiO3-Modified Cathode-Electrolyte-Interphase

Ultra-High Rate and Long Cycle Life Sodium-Based Dual-Ion Batteries Enabled by Li2TiO3-Modified Cathode-Electrolyte-Interphase

Proton FLASH Irradiation Using a Synchrotron Accelerator: Differences by Irradiation Positions.

To establish an ultra-high dose rate (UHDR) radiation system using a synchrotron proton beam accelerator and to compare the effects by irradiation positions on cultured cells and chick embryos. Protons for UHDR were obtained by applying high-frequency power at much higher levels than usual to extract all protons within approximately 50 ms. Subsequently, monitoring with a Faraday cup was performed immediately after synchrotron extraction and the waveform was adjusted accordingly. Four cultured tumor lines, two normal cell lines, and chick embryos were used. Ultra-high dose-rate radiation (UHDR-RT) at 6-18 Gy (200-300 Gy/s, single exposure) and conventional dose-rate radiation (Conv-RT) at 6-18 Gy (3 Gy/s) were administered to the 1-cm spread-out Bragg peak (SOBP) and the plateau region preceding SOBP. Following irradiation, disparities in cell growth rates and cell cycle progression were assessed, and cell survival was evaluated via colony assay. Chick embryos were also examined for survival. UHDR-RT was achieved at a range of 40 to 800 Gy/s, encompassing both plateau and peak phases. In vitro studies demonstrated similar cell-killing effects between UHDR-RT and Conv-RT in cancer cells. Significant apoptotic effects and G2 arrest were observed during the cell cycle under peak UHDR-RT conditions. The FLASH effect was not observed in normal single cells under normal atmospheric conditions. Stronger cell-killing effects were noted in V79 spheroids exposed to peak UHDR-RT than peak Conv-RT. Moreover, in chick embryos, an increase in survival rate, indicative of the FLASH effect, was observed. The FLASH effect was also achieved with UHDR-RT using a synchrotron proton beam accelerator in chick embryos. The cell-killing effects in cancer cells were higher with peak UHDR-RT which may be due to the higher linear energy transfer at the SOBP.

Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

An ultra-high strain rate (104 s-1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650°C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

Grain size effect on stress-induced martensite in a metastable β-Ti alloy with ultrahigh strength and strain hardening rate

In the present work, the influence of β grain size on stress-induced martensite (SIM) was investigated in a metastable β-Ti alloy (Ti-4Mo-3Cr-1Fe-1Al). Samples with varying grain sizes were prepared by cold rolling and annealing. The triggering stress for SIM decreases with the grain size increase from 44 μm to 180 μm. Meanwhile, the yield strength increases with decreasing grain size, consistent with the Hall-Petch effect. Fine-grained samples formed a greater number of martensitic bands during deformation compared to coarse-grained samples, resulting in an ultra-high strain-hardening rate ∼4320 MPa. The deformation mechanism of the Ti-4Mo-3Cr-1Fe-1Al alloy consists of the ω to β transformation, SIM, martensite deformation twinning ({110}cc < 1–10>α" and {130}<-310>α" twins), reorientation of martensite and dislocation slip. Both the 44 μm and 59 μm samples exhibit ultra-high true tensile strengths (>1200 MPa), with a large work-hardening interval of nearly 600 MPa relative to the yield strength. This significant work-hardening capability is attributed to interfacial and dislocation strengthening arising from the dynamic formation of martensitic bands during deformation.

Synergistic chemical traction and pre-intercalation strategies enable high-quality MnO2 composites for efficient ammonium capture

The δ-MnO2 exhibits an ideal capacitive deionization (CDI) electrode for the efficient removal of ammonium ions (NH4+), owing to its unique layered structure that facilitates effective insertion and extraction of ions. However, MnO2 is constrained by self-aggregation, inadequate electrical conductivity, and sluggish reaction kinetics in practical applications, leading to subpar ammonium removal performance. Here, the polyaniline (PANI) intercalated MnO2 and carbon nanotubes (CNTs) composites (P/M-C-X) were synthesized by a straightforward and swift one-step inorganic/organic interface reaction using the chemical traction effect of aniline. The synergistic effect of the increased layer spacing and the introduced oxygen vacancy after PANI intercalated and the 1D/2D conductive interconnect structure constructed by CNTs can effectively improve the electrical conductivity, promote ions/electrons diffusion, and enhance the charge reaction kinetics. As results, P/M-C-50 exhibits excellent NH4+ removal performance, including the maximum salt adsorption capacity (SAC) (160.0 mg g−1), ultra-high salt adsorption rate (SAR) (1.07 mg g−1 s−1), and good cyclic stability. Furthermore, the comprehension of NH4+ storage mechanism has been enhanced through structural characterization, electrochemical analysis, and theoretical calculation. This study shows that P/M-C-50 has broad potential as a CDI ammonium removal electrode, and lays a solid foundation for the effective recovery and reuse of ammonium resources.

Precise regulation of layered-to-rock structure of spent Li-ion cathodes achieving ultrahigh lithium recovery rate

With the rapid development of electric vehicles and digital devices, the accumulated spent lithium-ion batteries (LIBs) cause severe anxiety about lithium resources and environmental safety. However, the low capture rate of Li+ and the high chemical consumption of the existing recovery methods lead to high Li loss, treatment costs and disposal fees. Herein, we propose a universal strategy of spent LIBs recovery via precise directional regulating structures (from layered to rock) to achieve ultrahigh lithium recovery rate with super-low chemical and energy consumption. Experimental characterization and theoretical calculations reveal the dissociation of structure, reorganization of Li–O bonds and phase transformation of the cathode materials in the limited-domain reduction process, realizing the complete recovery of Li+ without consuming acid leaching agent. This process realizes an extra-high Li separation index (19154) and extra-long cycle half-life (173 cycles) which are far superior to those of traditional methods (9–191 and 7 cycles). Besides, ecological and economic analysis shows that the consumptions of chemicals and energy are only 9 % and 9.7 % those of the existing literature, respectively, providing a bright pathway for industrializable lithium batteries recycling.

One-Step Fabrication of 2.5D CuMoOx Interdigital Microelectrodes Using Numerically Controlled Electric Discharge Machining for Coplanar Micro-Supercapacitors

With the increasing market demands for wearable and portable electronic devices, binary metal oxides (BMOs) with a remarkable capacity and good structure stability have been considered as a promising candidate for fabricating coplanar micro-supercapacitors (CMSCs), serving as the power source. However, the current fabrication methods for BMO microelectrodes are complex, which greatly hinder their further development and application in BMO CMSCs. Herein, the one-step fabrication of 2.5D CuMoOx-based CMSCs (CuMoCMSCs) has been realized by numerically controlled electric discharge machining (NCEDM) for the first time. In addition, the controllable capacity of CuMoCMSCs has been achieved by adjusting the NCEDM-machining voltage. The CuMoCMSCs machined by a machining voltage of 60 V (CuMoCMSCs60) showed the best performance. The fabricated CuMoCMSCs60 with binary metal oxides could operate at an ultra-high scanning rate of 10 V s−1, and gained a capacity of 40.3 mF cm−2 (1.1 mA cm−2), which is more than 4 times higher than that of MoOx-based CMSCs (MoCMSCs60) with a single metal oxide. This is because CuMoOx BMOs materials overcome the poor electroconductivity problem of the MoOx single metal oxide. This one-step and numerically controlled fabrication technique developed in this research opens a new vision for preparing BMO materials, BMO microelectrodes, and BMO microdevices in an environmental, automatic, and intelligent way.

Thermally tunable add-drop filter based on valley photonic crystals for optical communications

Abstract Valley photonic crystals (VPCs) provide an intriguing approach to suppress backscattering losses and enable robust transport of light against sharp bends, which could be utilized to realize low-loss and small-footprint devices for on-chip optical communications. However, there are few studies on how to achieve power-efficient tunable devices based on VPCs, which are essential for implementing basic functions such as optical switching and routing. Here, we propose and experimentally demonstrate a thermally tunable add-drop filter (ADF) based on VPCs operating at telecommunication wavelengths. By leveraging the topological protection of the edge state and the distinct property of negligible scattering at sharp bends, a small footprint of 17.4 × 28.2 μm2 and a low insertion loss of 2.7 dB can be achieved for the proposed device. A diamond-shaped microloop resonator is designed to confine the light and enhance its interaction with the thermal field generated by the microheater, leading to a relatively low power of 23.97 mW needed for switching the output signal from one port to the other. Based on the thermally tunable ADF under the protection of band topology, robust data transmission is implemented with an ultrahigh data rate of 132 Gb/s. Our work shows great potential for developing high-performance topological photonic devices with the thermally tunable silicon-based VPCs, which offers unprecedented opportunities for realizing topologically protected and reconfigurable high-speed datalinks on a chip.

On the acceptance, commissioning, and quality assurance of electron FLASH units.

FLASH or ultra-high dose rate (UHDR) radiation therapy (RT) has gained attention in recent years for its ability to spare normal tissues relative to conventional dose rate (CDR) RT in various preclinical trials. However, clinical implementation of this promising treatment option has been limited because of the lack of availability of accelerators capable of delivering UHDR RT. Commercial options are finally reaching the market that produce electron beams with average dose rates of up to 1000Gy/s. We established a framework for the acceptance, commissioning, and periodic quality assurance (QA) of electron FLASH units and present an example of commissioning. A protocol for acceptance, commissioning, and QA of UHDR linear accelerators was established by combining and adapting standards and professional recommendations for standard linear accelerators based on the experience with UHDR at four clinical centers that use different UHDR devices. Non-standard dosimetric beam parameters considered included pulse width, pulse repetition frequency, dose per pulse, and instantaneous dose rate, together with recommendations on how to acquire these measurements. The 6- and 9-MeV beams of an UHDR electron device were commissioned by using this developed protocol. Measurements were acquired with a combination of ion chambers, beam current transformers (BCTs), and dose-rate-independent passive dosimeters. The unit was calibrated according to the concept of redundant dosimetry using a reference setup. This study provides detailed recommendations for the acceptance testing, commissioning, and routine QA of low-energy electron UHDR linear accelerators. The proposed framework is not limited to any specific unit, making it applicable to all existing eFLASH units in the market. Through practical insights and theoretical discourse, this document establishes a benchmark for the commissioning of UHDR devices for clinical use.

Major contributors to FLASH sparing efficacy emerge from murine skin studies: dose rate, total dose per fraction, anesthesia and oxygenation.

Normal tissue sparing from radiation damage upon ultra-high dose rate irradiation, known as the FLASH effect with an equivalent tumor response, has been widely reported in murine skin models, and translation of this type of radiotherapy to humans has already begun, with skin sparing being a primary outcome expected. This study reviews the status of the field, focusing on the proposed mechanisms and skin response assays, outlining what has become known in terms of input parameters that might control the magnitude of the FLASH effect. Murine studies have largely focused on acute damage responses, developing over 3-8 weeks, to single doses of FLASH versus conventional dose rate (CDR), suggesting that at dose rates above tens of Gray per second, with a total dose of more than 20 Gy, the FLASH effect is induced. Fractionated delivery appears to be possible, although fraction sizes >17 Gy appear to be needed for sparing efficacy. The interplay between the dose rate and total dose per fraction remains to be fully elucidated. Oxygen is a modulator of efficacy, with both hypoxia and hyperoxia diminishing the effect of FLASH. Measurement of transient changes in oxygen levels is possible and may be a marker of treatment efficacy. Taken together, murine skin data provide important information for translational studies, despite the associated limitations. Studies of later-term sparing effects, as well as studies on pig skin, are needed to take the next step in assessing translational FLASH efficacy. The control of biological factors, such as tissue oxygenation, may be required to understand and control the response.

Dosimetric saturation effect study and correction calculation method of ionization chamber at ultra-high dose rate (FLASH)

Backgroundand Purpose: FLASH radiotherapy has aroused strong interest among researchers, but how to monitor dose in real time and lack of generally accepted ion correction model are one of the challenges. This study is based on previous research work, the dosimetric verification of FLASH ionization chamber was performed using a 200 keV electron beam irradiation platform at an ultra-high dose rate. At the same time, the finite element program is written to analyze and calculate the ion correction factor. In addition, the results are compared with the calculation results of Boag model. MethodsIn this study, the pressure of the sensitive volume in the detector was adjusted to 16 mbar for the purpose of dosimetry of dose rates in excess of 100 Gy/s. In order to monitor the response of the detector, the beam frequency and pulse width were adjusted accordingly. However, due to the saturation effect of the ionization chamber, the processes of electron ion pair drift, attachment, recombination and diffusion in the sensitive volume were modelled on the basis of the relevant physical principles. Finally, the correction factor was calculated by the finite element analysis. ResultsThe experimental results demonstrate that the FLASH ionization chamber is capable of meeting the requirements of dose measurement and beam monitoring of the electron beam at ultra-high dose rates. Furthermore, the analytical model is able to more accurately describe the saturation effect and calculate the correction factor. ConclusionIn this paper, the method of reducing air pressure is employed for the purpose of monitoring the dose of ultra-high dose rate. Simultaneously, the finite element method was employed to analyze the physical process of electron–ion pairs within the chamber and to calculate the ion correction factor analytically. A comparison with the Boag model indicates that the proposed approach is effective. However, the results exhibit a certain degree of divergence from experimental outcomes. This discrepancy may be attributed to the influence of the input parameters, which require further calibration to enhance the accuracy and the robustness of the model.

Design of dual-defective polymeric carbon nitride with compact interlayer stacking for boosting photocatalytic H2O2 production: Insight of various configurations

Polymeric carbon nitride (PCN) is an environmentally friendly photocatalyst for solar-driven H2O2 production, but the activity of original PCN is still not satisfactory. The main limitation is the sluggish exciton dissociation leading to slow generation and conversion of superoxide radical (•O2−) intermediate. Herein, the PCN with dual defect sites and compact interlayer is rationally designed for H2O2 photosynthesis with an ultrahigh rate of 3930.9 μmol g−1h−1 and rapid •O2− yield rate of 1.92 min−1. The enhanced activity is attributed to effective exciton dissociation during interlayer and intralayer process. Moreover, nitrogen vacancies change the oxygen adsorption configuration (formation of C − O − O − C bridge mode), thus promoting O2 adsorption and activation. A well-matched linear relationship was established between the concentration of nitrogen vacancies and •O2−/H2O2 production. This work not only provides in-depth insights for the photocatalytic H2O2 generation mechanism, but also offers a new paradigm for designing efficient PCN-based photocatalysts for energy conversion.