Oxygen Enhancement Research Articles

Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Modelling oxygen effects on the in- and out-of-field radiosensitivity of cells exposed to intensity-modulated radiation fields

Objective. The delivery of intensity-modulated radiation fields has improved the conformity of dose to tumour targets during radiotherapy (RT). Previously, it has been shown that intercellular communication between cells positioned in- and outside of the radiation field impacts cellular radiosensitivity under hypoxic and normoxic conditions. However, the mechanism of intercellular communication in hypoxia remains to be fully understood. In this study, the cell-killing effects of intercellular communication in hypoxia were modelled in an effort to better understand the underlying mechanisms of response. Approach. By irradiating a 50% area of the culture dish (half-field exposure), experimental dose-response curves for cell survival and residual DNA double-strand breaks (DSBs) were generated in prostate (DU145) and non-small cell lung cancer (H1299) cells. The oxygen enhancement ratio (OER) was determined from early DSB yields (corresponding to relative direct damage) and used to model the in- and out-of-field radiosensitivity. Main results. The developed integrated microdosimetric-kinetic (IMK) model successfully predicted the experimental dose responses for survival and lethal lesions, and provides a mechanistic interpretation that the probability of hits for releasing cell-killing signals is dependent on oxygen. This experimental and modelling study also suggests that residual DSBs correspond to logarithmic survival fraction (meaning lethal lesions) for in- and out-of-field cells. Our data suggest that the OER value determined using uniform-field exposure can be applied to predict the in- and out-of-field radiosensitivity of cells following exposure to intensity modulated beams. Significance. The developed IMK model facilitates a more precise understanding of intercellular signalling following exposure to intensity-modulated radiation fields.

Modeling of the FLASH effect for ion beam radiation therapy

PurposeNormal tissue sparing has been shown in preclinical studies under the ultra-fast dose rate condition, so-called FLASH radiotherapy. The preclinical and clinical FLASH studies are being conducted with various radiation modalities such as photons, protons, and heavy ions. The aim of this study is to propose a model to predict the dependency of the FLASH effect on linear energy transfer (LET) by quantifying the oxygen depletion. MethodsWe develop an analytical model to examine the FLASH sparing effect by incorporating time-varying oxygen depletion equation and oxygen enhancement ratios according to LET. The variations in oxygen enhancement ratio (OER) are quantified over time with different dose rate (Gy/s) and LET (keV/μm). The FLASH sparing effect (FSE) is defined as the ratio of DFLASH/Dconv where Dconv is the reference absorbed dose delivered at the conventional dose rate, and DFLASH is the absorbed dose delivered at a high dose rate that causes the same amount of biological damage. ResultsOur model suggests that the FLASH effect is significant only when the oxygen amount is at an intermediate level (10 ∼ 100 mmHg). The FSE is increased as LET decreases, suggesting that LET less than 100 keV/μm is required to induce FLASH sparing effects in normal tissue. ConclusionsOxygen depletion and recovery provide a quantitative model to understand the FLASH effect. These results highlight the FLASH sparing effects in normal tissue under the conditions with the intermediate oxygen level and low-LET region.

Elemental and chemical depth profiling of high-build single-component (1K) polyester-polyurethane coil coatings

The interior structure and chemistry of single-component (1K) polyester-polyurethane (PU) coil coatings, which find preferred application in the construction industry, was comprehensively investigated by energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS). Fabrication of extended tapers in the millimetre-range through a double-layered coating system with a total dry film thickness of 50 μm was achieved by cryo-ultra-low-angle microtomy (cryo-ULAM). The linearity and surface topography of shallow angle ULAM cuts created at different preparation conditions were examined at mesoscopic and microscopic scale by coherence scanning interferometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). EDX mappings recorded on the exposed sections enabled to determine the elemental structure and the distribution of embedded fillers at plane-view. Focal plane array (FPA) FTIR spectroscopy in attenuated total reflection (ATR) mode was used to acquire high-resolution chemical data from the fabricated taper, revealing the clustering of nitrogen-containing groups. Compositional depth profiling of the investigated high-build PU coating system was achieved by performing XPS line scans on the exposed sections. Depth analysis at a chemical level was obtained by means of evaluating the high-resolution carbon C1s spectra, which showed an enhancement of nitrogen and oxygen containing functionalities near the primer/substrate interface. All methods of this correlative work of analysis consistently indicate the presence of chemical gradients related to the cross-linking agent.

From Localized Mild Hyperthermia to Improved Tumor Oxygenation: Physiological Mechanisms Critically Involved in Oncologic Thermo-Radio-Immunotherapy.

(1) Background: Mild hyperthermia (mHT, 39-42 °C) is a potent cancer treatment modality when delivered in conjunction with radiotherapy. mHT triggers a series of therapeutically relevant biological mechanisms, e.g., it can act as a radiosensitizer by improving tumor oxygenation, the latter generally believed to be the commensurate result of increased blood flow, and it can positively modulate protective anticancer immune responses. However, the extent and kinetics of tumor blood flow (TBF) changes and tumor oxygenation are variable during and after the application of mHT. The interpretation of these spatiotemporal heterogeneities is currently not yet fully clarified. (2) Aim and methods: We have undertaken a systematic literature review and herein provide a comprehensive insight into the potential impact of mHT on the clinical benefits of therapeutic modalities such as radio- and immuno-therapy. (3) Results: mHT-induced increases in TBF are multifactorial and differ both spatially and with time. In the short term, changes are preferentially caused by vasodilation of co-opted vessels and of upstream normal tissue vessels as well as by improved hemorheology. Sustained TBF increases are thought to result from a drastic reduction of interstitial pressure, thus restoring adequate perfusion pressures and/or HIF-1α- and VEGF-mediated activation of angiogenesis. The enhanced oxygenation is not only the result of mHT-increased TBF and, thus, oxygen availability but also of heat-induced higher O2 diffusivities, acidosis- and heat-related enhanced O2 unloading from red blood cells. (4) Conclusions: Enhancement of tumor oxygenation achieved by mHT cannot be fully explained by TBF changes alone. Instead, a series of additional, complexly linked physiological mechanisms are crucial for enhancing tumor oxygenation, almost doubling the initial O2 tensions in tumors.

Methanol promotes the biodegradation of 2,2′,3,4,4′,5,5′-heptachlorobiphenyl (PCB 180) by the microbial consortium QY2: Metabolic pathways, toxicity evaluation and community response

As one of the most frequently detected PCB congeners in human adipose tissue, 2,2′,3,4,4′,5,5′-heptachlorobiphenyl (PCB 180) has attracted much attention. However, PCB 180 is difficult to be directly utilized by microorganisms due to its hydrophobicity and obstinacy. Herein, methanol (5 mM) as a co-metabolic carbon source significantly stimulated the degradation performance of microbial consortium QY2 for PCB 180 (51.9% higher than that without methanol addition). Six metabolic products including low-chlorinated PCBs and chlorobenzoic acid were identified during co-metabolic degradation, denoting that PCB 180 was metabolized via dechlorination, hydroxylation and ring-opening pathways. The oxidative stress and apoptosis induced by PCB 180 were dose-dependent, but the addition of methanol effectively promoted the tolerance of consortium QY2 to resist unfavorable environmental stress. Additionally, the significant reduction of intracellular reactive oxygen species (ROS) and enhancement of cell viability during methanol co-metabolic degradation proved that the degradation was a detoxification process. The microbial community and network analyses suggested that the potential PCB 180 degrading bacteria in the community (e.g., Achromobacter, Cupriavidus, Methylobacterium and Sphingomonas) and functional abundance of metabolic pathways were selectively enriched by methanol, and the synergies among species whose richness increased after methanol addition might dominate the degradation process. These findings provide new insights into the biodegradation of PCB 180 by microbial consortium.

Enhancement of acidic sites in layered MnO2 for the highly efficient selective catalytic oxidation of gaseous ammonia

Ammonia (NH3), as a typical harmful gaseous pollutant in atmosphere, poses a serious threat to human health and ecological environment. It is of great significance to develop the cost-effective catalysts with both excellent selective catalytic oxidation (SCO) activity and N2 selectivity. In this study, the acidic sites of layered MnO2 were regulated and its NH3-SCO performance was investigated. The enhancement of acidic sites in layered MnO2 significantly improved the SCO of NH3, and the resulting MnO2 could achieve complete conversion of NH3 at as lower as 100 °C, even better than the reported noble-metal catalysts. Furthermore, the improvement in NH3-SCO activity can be attributed to the abundant active oxygen species and enhancement of acidic sites (especially stronger Brønsted acidic sites). On the one hand, more active oxygen species can enhance the catalytic oxidation of NH3. On the other hand, Brønsted acidic sites acted not only as adsorption sites but also reaction sites, the increase in the content and strength of acidic sites facilitated the adsorption and activation of NH3. This research reveals the functional role of acidic sites in NH3-SCO, and provides a suggestive for the rational design of catalysts with excellent N2 selectivity and low-temperature NH3-SCO activity.

A simple mathematical model of cyclic hypoxia and its impact on hypofractionated radiotherapy.

There is evidence that the population of cells that experience fluctuating oxygen levels ("acute," or, "cyclic" hypoxia) are more radioresistant than chronically hypoxic ones and hence, this population may determine radiotherapy (RT) response, in particular for hypofractionated RT, where reoxygenation may not be as prominent. A considerable effort has been devoted to examining the impact of hypoxia on hypofractionated RT; however, much less attention has been paid to cyclic hypoxia specifically and the role its kinetics may play in determining the efficacy of these treatments. Here, a simple mathematical model of cyclic hypoxia and fractionation effects was worked out to quantifythis. Cancer clonogen survival fraction was estimated using the linear quadratic model, modified to account for oxygen enhancement effects. An analytic approximation for oxygen transport away from a random network of capillaries with fluctuating oxygen levels was used to model inter-fraction tissue oxygen kinetics. The resulting survival fraction formula was used to derive an expression for the iso-survival biologically effective dose (BED), BEDiso-SF . These were computed for some common extra-cranial hypofractionated RTregimens. Using relevant literature parameter values, inter-fraction fluctuations in oxygenation were found to result in an added 1-2 logs of clonogen survival fraction in going from five fractions to one for the same nominal BED (i.e., excluding the effects of oxygen levels on radiosensitivity). BEDiso-SF 's for most ultra-hypofractionated (five or fewer fractions) regimens in a given tumor site are similar in magnitude, suggesting iso-efficacy for common fractionationschedules. Although significant, the loss of cell-killing with increasing hypofractionation is not nearly as large as previous estimates based on the assumption of complete reoxygenation between fractions. Most ultra-hypofractionated regimens currently in place offer sufficiently high doses to counter this loss of cell killing, although care should be taken in implementing single-fractionregimens.

Cover Image, Volume 140, Issue 8

The cover image designed by Shamila Hamdani and Muhammad Rabnawaz depicts the paper coating process for the enhancement of oxygen and water vapor barrier properties. The paper has the potential to offer viable alternatives to single-use plastics. DOI: 10.1002/app.53440

Handelin Reduces Ultraviolet A-Induced Photoaging by Inhibiting Reactive Oxygen Species Generation and Enhancing Autophagy.

Photoaging is mainly caused by the exposure of the skin to ultraviolet (UV) radiation. Among them, damage to human dermal fibroblast (HDF) cells caused by ultraviolet A (UVA) is the main cause of skin aging. Researchers have dedicated to identifying natural compounds from plants to fight against UV radiation-induced photoaging. We previously found that extracts from wild chrysanthemum could prevent acute damage and photoaging induced by UV irradiation. As one of the most abundant ingredients in wild chrysanthemum extract, handelin was hypothesized to have the potential to prevent UVA-induced photoaging of skin fibroblast. In the present study, we report the great potential of handelin in combating UVA-induced photoaging of fibroblasts. We firstly demonstrated that handelin was safe for skin fibroblast as high as a concentration of 0.0125 μM, showing no toxicity on the cells and improved cell viability. Furthermore, handelin can reduce UVA-induced cellular senescence, indicated by a reduced proportion of senescence-associated beta-galactose positive cells and the expression of P21. We then verified that handelin pretreatment markedly attenuated the production of reactive oxygen species (ROS) generation after UVA irradiation. Meanwhile, we found that handelin enhances autophagy after UVA irradiation, and autophagy is involved in the quality control of intracellular proteins after UV-induced damage (partially indirectly via ROS). Therefore, these results suggest that handelin has a very high potential as an effective ingredient against UVA-induced skin aging. Moreover, this provides an important basis for further research on the photoprotective mechanism of handelin.

Feasibility Study on the nIORT® Adjuvant Treatment of Glioblastoma Multiforme through the Irradiation Field of Fast Neutrons Produced by a Compact Generator

The glioblastoma multiforme (GBM) is the most malignant glial brain tumour with average survival time of 6÷18 months. Emerging evidence suggests that GBM cells appears to reprogram their tumour microenvironment, which is a highly heterogeneous and complex system, so that an efficient GBM radiotherapy (RT) should cover both the cells of the GBM and those of its microenvironment. Relying on a 5-year collaborative research study on the intra-operative radiotherapy (IORT) with fast neutrons - the so-called neutron-IORT (nIORT®) technique - the authors think that this objective could be achieved by using an ionizing radiation field of fast neutrons that behave in the biological tissues as a “foam field” hitting both the GBM cancer cells and the neighbouring microenvironment. The nIORT® research activities - conducted by TheranostiCentre Srl, Berkion Technology LLC and ENEA - led to the fabrication of the first prototype of a compact neutron generator (CNG) that, through the deuterium-deuterium fusion reaction, produces neutrons of 2.45 MeV energy having: i) high linear energy transfer; ii) very high relative biological effectiveness (RBE), about 16 times higher than X-rays (and electrons) used in standard RT and IORT treatments; iii) reduced oxygen enhancement ratio, and hence resulting be very effective in cancer cells necrosis and apoptosis. The CNG is self-shielded, limited in size and weight (~120 kg) and manageable remotely by a robotic arm. A new prototype equipped by a cylindrical applicator to be inserted in the surgical cavities is currently under construction, with some technical advancements making possible its installation in an operating room dedicated to nIORT® treatments without posing any safety and environmental concern. In this article the nIORT® potentiality was investigated in the view of the GBM treatment, but the study is however generalisable for the neutron irradiation of other brain cancer pathologies. Accurate Monte Carlo simulations, modelling the CNG equipped with a couple of cylindrical applicators of 4 and 6 cm in diameter inserted in the brain surgical cavity after craniotomy, demonstrated that the nIORT® device operated at 100 kV-10 mA DC supplies a neutron flux ~108 cm-2 s-1 and can deliver equivalent dose rates ~5 Gy (RBE)/min in the centre of the tumour bed. Thus, it could administer the clinical endpoints foreseen by the standard IORT protocols (~10-20 Gy (RBE)) in treatment times of few minutes, by providing a sort of “switching on and off neutron brachytherapy tool” without using needles of radioisotopes (e.g., 252Cf). The near isotropic neutron emission allows to irradiate the tumour bed margins, normally filled by potential quiescent cancer cells, with lower (but still significant) dose levels. This should improve the local control of the tumour through the reduction of local recurrences and metastasis in the tumour microenvironment, and at the same time to avoid adverse effects of the administered neutron radiation field on the surrounding brain central nervous system. Also, the rapid decrease in tissue depth of the dose gradient (within few centimetres) should avoid any adverse effect on normal brain tissues and the neighbouring organs.

Influence of heat treatment on H2S gas sensing features of NiO thin films deposited via thermal evaporation technique

In this study, NiO thin films are prepared on Ni foil using thermal evaporation method and the effect of deposition conditions on structural, morphological and H2S gas sensing properties of NiO thin films is investigated. Structural analysis of the NiO films are conducted by means of X-ray diffraction (XRD), and the films are found to have the FCC phase with preferred (111) and (200) Bragg reflections. Based on XRD and scanning electron microscopy results, it is shown that the crystallite size and the size of homogeneous nanoclusters on the surface of the films increase after increasing oxidation temperature. Also, the EDS patterns of NiO films demonstrate a rise in the intensity of O peak upon increasing the oxidation temperature due to the enhancement of oxygen in the NiO films. The Raman spectrum of NiO thin films several bands correspond to Ni–O vibrations. The obtained gas sensing results demonstrate the sensing response to 20 ppm of hydrogen sulfide at 700 °C. Upon increasing the amount of hydrogen sulfide gas to more than 20 ppm, the fabricated sensors show no significant change in their response, indicating that no additional active sites were exist to interplay with hydrogen sulfide molecules for the higher concentration of hydrogen sulfide. The response of the sensors, recorded 10 s after H2S gas exposure, depended on the deposition temperature. The current study shows that NiO thin films-based sensors prepared by a simple thermal evaporation method are potentially useful for the detection of H2S gas.

NIMG-70. MAGNETIC RESONANCE HYPOXIA IMAGING FOR RADIATION TREATMENT GUIDANCE IN GLIOBLASTOMA MULTIFORME - A DIAGNOSTIC/PROGNOSTIC CLINICAL IMAGING STUDY

Abstract Local recurrence in glioblastoma (GBM) patients is caused by the ability of tumour cells to develop treatment resistance mechanisms. Hypoxia, which is present in subregions of GBM tumours, is the leading cause of resistance to radiotherapy and is associated with worse clinical outcomes in GBM. Current standard of care treatment does not account for tumour hypoxia. The ability to image tumour hypoxia at various stages of treatment offers opportunities to personalise and improve treatment for GBM patients. Preoperative imaging of tumour hypoxia offers the opportunity for supramarginal resections in surgical planning beyond current neurosurgical standard of care guidelines. Imaging hypoxia prior to radiotherapy enables selective dose escalation strategies to radioresistant tumour regions, increasing the likelihood of local control. Identifying hypoxic tumour regions harbouring progression at follow up is key to intervening at an early stage of tumour recurrence and personalising therapy tailored to the tumour response to treatment. Imaging of tumour hypoxia in routine clinical practice is challenging, as it requires 18FMISO PET, which is not available in most clinical centres. In this clinical imaging study, we aim to investigate the role of oxygen enhanced (OE) and blood-oxygen level dependent (BOLD) MRI as imaging biomarkers of hypoxia in GBM. Aiming to recruit 20 GBM patients, this study involves the addition of OE/BOLD MRI and 18FMISO PET imaging at several timepoints during the course of treatment. The primary objective is to investigate the ability of OE/BOLD MRI to map tumour hypoxia on preoperative scans using 18FMISO PET as the ground truth. Secondary objectives include evaluating the role of hypoxia imaging biomarkers for dose-painting radiotherapy planning and treatment response assessment in GBM. Overall, by validating the role of MRI biomarkers of hypoxia we ought to provide a non-invasive and more accessible means to more effective, personalised treatment to GBM patients.

Study of sewage oxygenation treatment based on gas magnetization mechanism.

In the process of sewage treatment, the sewage usually needs to be aerated, so the oxygenation efficiency is an important indicator for the aerator. The general oxygenation technique is to inject large amount of natural air into the aeration tank over long time, which has lower efficiency and leads to dramatic waste of energy. Based on the gas-liquid fusion mass transfer model and combined the oxygen enrichment mechanism by magnetization of the gas into the aerator, a novel method to improve the efficiency of wastewater oxygenation is proposed. This method is based on the fact that oxygen and nitrogen exhibit completely different magnetic characteristics in gradient magnetic fields, and then the special shaped permanent magnets can be used to build a target gradient magnetic field to increase the oxygen content as the gas is injected into the sewage by the aerator, which reaches the oxygenation enhancement effect. Through theoretical analysis and experiments, it is concluded that the efficiency of sewage oxygenation treatment is dramatically improved with the permanent magnet oxygen enrichment technique.

Application effect of different oxygenation methods with mulched drip irrigation system in Xinjiang

When crop roots are in a low oxygen environment for a long time, it will lead to a series of problems. To improve soil oxygen conditions, a method of oxygenation irrigation is increasing the dissolved oxygen (DO) concentration in irrigation water. However, its application effect in a mulched drip irrigation system is not clear. In this study, a field experiment was conducted in Xinjiang to investigate the actual effect of oxygenation irrigation in field planting. We set up mechanical oxygenation (AO), venturi oxygenation (VO), and four chemical oxygenations with different DO concentrations (CO1–4). The results showed that physical oxygenation (AO, VO) was limited by the saturated DO of irrigation water. Compared with venturi oxygenation, mechanical oxygenation could reach the saturated DO faster and had higher stability of DO concentration during single irrigation. The chemical oxygenation was not limited by the saturated DO. The maximum DO in irrigation water would also increase with the increase in the amount of oxygen enhancer, but it needed more reaction time than the physical oxygen to reach a stable state. The oxygenated water would be affected by water temperature and delivery distance in the mulched drip irrigation system, resulting in the continuous decline of DO during the irrigation process. For those oxygenated water with saturated DO under different oxygenation methods (AO, VO, and CO1), when they entered the soil, there was no significant difference in the changing trend of DO. In an irrigation process, with the increase of DO, the actual oxygenation efficiency in the soil also increased. The DO concentration of irrigation water was increased from 3.9 mg L−1 to 9.1 mg L−1, and 10 times of irrigation was carried out during the crop growth period, then soil oxygen could be increased by an average of 6.72∼6.89%. By increasing the DO of irrigation water, the soil oxygen condition of mulched drip irrigation can be improved. Under the condition of saturated DO, each oxygenation irrigation had no significant impact on the soil physical and chemical properties. After two years of irrigation, the chemical oxygenation using sodium percarbonate had increased the soil EC, pH, and Na+ content, which means slightly intensified the soil salinization.

Evaluation of Riboflavin as an enhancer for X-ray and EBeam irradiation treatment of Tulane virus

Ionizing technologies rely on high doses of irradiation to achieve 5-log reduction of foodborne viruses. We hypothesized that riboflavin (vitamin B2), a singlet oxygen enhancer could synergize the virucidal effects of electron beam (eBeam) and X-ray doses by using Tulane virus as a model virus. Concentrations of up to 1% w/v riboflavin were evaluated against 1 kGy X-ray treatments. Also 0.1% riboflavin was evaluated against eBeam treatments up to 10 kGy. The results showed that riboflavin did not enhance the sensitivity of Tulane virus to either eBeam or X-ray treatments.

Hypoxia adapted relative biological effectiveness models for proton therapy: a simulation study

In proton therapy, a constant relative biological effectiveness (RBE) factor of 1.1 is applied although the RBE has been shown to depend on factors including the Linear Energy Transfer (LET). The biological effectiveness of radiotherapy has also been shown to depend on the level of oxygenation, quantified by the oxygen enhancement ratio (OER). To estimate the biological effectiveness across different levels of oxygenation the RBE-OER-weighted dose (ROWD) can be used. To investigate the consistency between different approaches to estimate ROWD, we implemented and compared OER models in a Monte Carlo (MC) simulation tool. Five OER models were explored: Wenzl and Wilkens 2011 (WEN), Tinganelli et al 2015 (TIN), Strigari et al 2018 (STR), Dahle et al 2020 (DAH) and Mein et al 2021 (MEI). OER calculations were combined with a proton RBE model and the microdosimetric kinetic model for ROWD calculations. ROWD and OER were studied for a water phantom scenario and a head and neck cancer case using hypoxia PET data for the OER calculation. The OER and ROWD estimates from the WEN, MEI and DAH showed good agreement while STR and TIN gave higher OER values and lower ROWD. The WEN, STR and DAH showed some degree of OER-LET dependency while this was negligible for the MEI and TIN models. The ROWD for all implemented models is reduced in hypoxic regions with an OER of 1.0–2.1 in the target volume. While some variations between the models were observed, all models display a large difference in the estimated dose from hypoxic and normoxic regions. This shows the potential to increase the dose or LET in hypoxic regions or reduce the dose to normoxic regions which again could lead to normal tissue sparing. With reliable hypoxia imaging, RBE-OER weighting could become a useful tool for proton therapy plan optimization.

Effect of diffusion oxygen enrichment on soot formation in coflow diffusion flames of gasoline-surrogate fuel doped with ethanol

• Combined effect of diffusion oxygen enrichment and ethanol addition to gasoline on soot was investigated numerically. • The dominant mechanism of particle mass growth after ethanol addition does not change with the increasing oxygen concentration. • Inhibition of ethanol addition and promotion of diffusion oxygen enrichment on soot attribute to PAH condensation and HACA, respectively. • Coupling effect between oxygenated fuel and diffusion oxygen is strongest in the surface growth. • Ethanol addition and diffusion oxygen enrichment have opposite effect on particle oxidation. The combined effect of ambient oxygen enhancement and oxygenated fuel addition is expected to improve combustion efficiency and control soot formation. In this work, the effect of diffusion oxygen enrichment on soot formation and the particle dynamics mechanism in coflow diffusion flames of gasoline-surrogate doped with ethanol were investigated numerically. The results showed that the peak temperature and SVF of ethanol-gasoline flames increase linearly with the increase of diffusion oxygen concentration, while the ethanol addition reduces the peak temperature and SVF. The action mechanism of diffusion oxygen enrichment on final soot formation is the result of the competition between residence time and particle dynamics, while the action mechanism of ethanol addition is the combined effect of residence time and particle dynamics. From the perspective of particle dynamics, the dominant mechanism of particle growth in gasoline flame changes with the increase of diffusion oxygen concentration. When the oxygen concentration exceeds 25%, HACA gradually replaces PAH condensation as the main mechanism of particle mass growth. However, after adding ethanol, HACA is always the dominant mechanism of particle mass growth and does not change with the increasing oxygen concentration. The inhibition of ethanol addition on soot is mainly achieved by reducing the PAH condensation rate, while the promotion of diffusion oxygen enrichment on soot is largely attributed to the increasing temperature and HACA rate. In addition, there is a coupling effect between the oxygenated fuel addition and the diffusion oxygen enrichment on the inhibition of particle dynamics. The coupling effect is strongest in the surface growth of particles, and is further enhanced with the increasing ethanol ratio and oxygen concentration. Ethanol addition and diffusion oxygen enrichment do not change the dominant role of O 2 oxidation in particle oxidation, but they have opposite effect on particle oxidation.

Oxygen Enhanced-MRI for Hypoxia Imaging in Head and Neck Cancer

<h3>Purpose/Objective(s)</h3> Hypoxia is an important predictor of treatment efficacy in head and neck (H&N) cancer. Oxygen-enhanced (OE)-MRI is a non-invasive method for mapping and quantifying the extent of regional hypoxia, by identifying tumor regions that are perfused but refractory to oxygen change (termed perfused oxygen refractory, or pOxy-R). The aim of this work was to develop OE-MRI in H&N carcinoma and measure pOxy-R during (chemo)radiotherapy ((C)RT) and to then translate OE-MRI onto an MRI-Linac (MRL), with a longer term aim of using the technique for biologically adaptive radiotherapy. We hypothesized that pOxy-R proportion would reduce during the treatment course, suggesting a reduction in regional tumor hypoxia. <h3>Materials/Methods</h3> The study received ethics approval. Imaging was performed on a 1.5 T MRI-RT simulator (MRSim) and a 1.5 T MRL system. OE-MRI gas delivery was administered during a dynamic series: scans 1-25 (21% O₂), 26-70 (100% O₂) and 71-91 (21% O₂). A low-flow gas blender ensured 15 L/min flow via a high concentration mask. In patients, DCE-MRI was acquired after OE-MRI, at the 8^th dynamic measurement (gadoterate meglumine, 0.1 mol/kg at 3 ml/s). The protocol was initially run in 6 healthy volunteers, each imaged twice on the MRSim. Next, 8 patients with H&N carcinoma (15 lesions in total, including primary tumor and lymph nodes) were imaged on the MRSim 1-2 times pre-treatment and then during standard-of-care (C)RT at weeks 2 and/or 4. Finally, 3 additional patients were imaged on the MRL system. <h3>Results</h3> The technique developed in 6 volunteers identified the nasal conchae as a suitable reference tissue to confirm oxygen delivery, as signals changed between air and 100% O₂ breathing (all p<0.001). In the 8 patients recruited to date (table 1), we observed a significant reduction in median cohort pOxy-R proportion at week 2 (41% to 25%, p<0.01, N=14 lesions, 7 patients). pOxy-R proportion was reduced at week 4 (43% to 31%, p=0.06, N=5 lesions, 3 patients). Coefficient of variation (wCV), was found to be 24% (N=6 lesions). Technique feasibility was demonstrated on the MRL, with all tumors showing signal change between air and 100% O₂ breathing (all p<0.001). <h3>Conclusion</h3> OE-MRI can identify and map oxygen refractory regions in patients with H&N carcinoma and may detect cohort-wide hypoxia modification induced by (C)RT. The technique can also be translated onto an MRL system, suggesting the potential feasibility of using OE-MRI for online adaptive radiotherapy.

A mechanistic consideration of oxygen enhancement ratio, oxygen transport and their relevancies for normal tissue sparing under FLASH irradiation

Our study investigated the role of oxygen in mediating the FLASH effect. This effect, which was first reported in vitro in the 1950s and in vivo in the 1970s, recently gained prominence with a number of publications showing differential sparing between normal tissues and tumors. Oxygen depletion (and subsequent induction of transient hypoxia) is the oldest and most prominent hypothesis to explain this effect. To better understand how the oxygen depletion hypothesis and oxygen enhancement ratio (OER) are relevant for interpreting FLASH benefits, an analytical model was proposed to estimate the sparing factor. The model incorporated factors such as OER, oxygen partial pressure (pO2), loco-regional oxygen diffusion/metabolism, total dose and dose rate. The sparing factor, was used to quantify the sparing of normal tissue (initially physoxic). The radiosensitivity parameters of two cell types (V79 Chinese hamster cells and T1 human kidney cells) were selected. Furthermore, the transient behavior of OER during finite time intervals was modeled, for both without and with the presence of oxygen transport using a diffusion model. For tissues with an oxygen consumption rate of 20 mmHg/s and a distance of 60 μm away from blood vessels, the sparing factor demonstrates an increase from 1.03/1.06 (V79/T1) at 2.5 Gy/s up to 1.28/1.72 (V79/T1) at 100 Gy/s (total dose: 10 Gy). For normal tissues of initial pO2 between 1.5 and 8 mmHg, the benefit from pushing the dose rate above 100 Gy/s is found to be marginal. Preliminary animal experiments have been conducted for validation. Overall, our study predicts that the dose rate associated with maximum normal tissue protection is between 50 Gy/s and 100 Gy/s. Other than the postulation of the hypoxic stem cell niches in normal tissues, we believe that a framework based upon the oxygen depletion hypothesis and OER is not able to efficiently interpret differential responses between normal and tumor tissue under FLASH irradiation.