Variation Of Spot Size Research Articles

Effects of spot size errors in DynamicARC pencil beam scanning proton therapy planning.

Spot size stability is crucial in pencil beam scanning (PBS) proton therapy, and variations in spot size can disrupt dose distributions. Recently, a novel proton beam delivery method known as DynamicARC PBS scanning has been introduced. The current study investigates the dosimetric impact of spot size errors in DynamicARC proton therapy for head and neck (HNC), prostate, and lung cancers.
Approach: Robustly optimized DynamicARC proton therapy plans were created for HNC (n=4), prostate (n=4), and lung (n=4) cancer patients. Spot size errors of ±10%, ±15%, and ±20% were introduced, and their effects on target coverage (D95% and D99%), homogeneity index (HI), and organ-at-risk (OAR) doses were analyzed across different cancer sites.
Main Results: HNC and lung cancer plans showed greater vulnerability to spot size errors, with reductions in target coverage of up to 4.8% under -20% spot size errors. Dose homogeneity was also more affected in these cases, with HI degrading by 0.12 in lung cancer. Prostate cancer demonstrated greater resilience to spot size variations, even under errors of ±20%. For spot size errors ±10%, the oral cavity, parotid glands, and constrictor muscles experienced Dmean deviations within ±1.2%, while deviations were limited to ±0.5% for D10% of the bladder and rectum and ±0.3% for V20Gy(RBE) of the lungs. The robustness analysis indicated that lung cancer plans were most susceptible to robustness reductions caused by spot size errors, while HNC plans demonstrated moderate sensitivity. Conversely, prostate cancer plans demonstrated high robustness, experiencing only minimal reductions in target coverage.
Significance: While the ±10% spot size tolerance is appropriate in the majority of the cases, lung cancer plans may require more stringent criteria. As DynamicARC becomes clinically available, measuring spot size errors in practice will be essential to validate these findings and refine tolerance thresholds for clinical use.

Guiding properties of Bessel–Gaussian and super-Gaussian pulses in inhomogeneous parabolic plasma channels

The guidance and stable propagation of laser pulses over many Rayleigh lengths are crucial for the plasma electron acceleration in the laser wakefield accelerators. Using plasma channels with specific characteristics can lead to the proper guidance of the laser pulse. Here, quasi-three-dimensional particle-in-cell (PIC) simulations are performed to investigate the guidance of Bessel–Gaussian pulse (BGP) of zeroth order and super-Gaussian pulse (SGP) of 3rd and 4th orders in an axially and radially inhomogeneous plasma channel. The effects of the channel radius and depth, the laser wavelength and initial spot size, and the plasma channel inhomogeneity on the guidance of the laser pulse are also examined. The results indicate that the guidance of a laser pulse in the plasma channel depends on the pulse profile, and under certain conditions, the pulses can be guided with the least variation of spot size in the inhomogeneous plasma channel. It is shown that the channel depth and the initial laser spot size are very effective in pulse guiding, as the values of these parameters increase, the pulse guidance is done better. In addition, the results show that the guidance of laser pulse is dependent on the type of plasma inhomogeneity represented by three different kinds of initial conditions, as considering the nonlinear-axial inhomogeneity in the parabolic plasma channel can lead to more convergence than the axially homogeneous and linear-axially plasma density profiles.

Dephasingless laser wakefield acceleration in the bubble regime

Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space–time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space–time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse.

Bumblebee responses to variation in pollinator-attracting traits of Vicia faba flowers.

Adaptations that attract pollinators to flowers are central to the reproductive success of insect-pollinated plants, including crops. Understanding the influence of these non-rewarding traits on pollinator preference is important for our future food security by maintaining sufficient crop pollination. We have identified substantial variation in flower shape, petal size, corolla-tube length, petal spot size and floral volatile compounds among a panel of 30 genetically distinct lines of Vicia faba. Using this variation, we found that Bombus terrestris was able to distinguish between natural variation in petal spot size, floral volatile emissions and corolla-tube length. Foragers showed some innate preference for spotted flowers over non-spotted flowers and preferred shorter corolla-tube lengths over longer tubes. Our results suggest that some floral traits may have significant potential to enhance pollinator attraction to V. faba crops, particularly if paired with optimised rewards.

Investigation of the Relationship between Aperture Use for Treating Small and Shallow Brain Lesions in Proton Therapy with Different Spot Size Variations in Three Proton Therapy Systems

To compare plan quality among standard vs. aperture-based Intensity-Modulated Proton Therapy (IMPT) using cyclotron-generated proton beams (CPB), linear accelerator proton beams (LPB), and linear accelerator proton minibeams (LPMB) for multiple brain metastases. Fifty-five brain lesions from twenty patients were planned with three different spot size ranges using CPBs (σ: 2.7-7.0 mm) and compared against LPBs (σ: 2.9-5.5 mm), and LPMBs (σ: 0.9-3.9 mm). Apertures with a diameter of 0.3 cm were applied to beams irradiating all tumors < 1 cm3 in volume and any tumor < 2.5 cm depth in the patient and compared against the same patient plans containing no apertures. All plans were optimized with the multi-field optimization (MFO) technique using the Monte Carlo algorithm. Dose coverage to each lesion for each proton plan was set to 99% of the GTV receiving the prescription (Rx) dose for all plans. Robustness with ±2 mm setup uncertainty and ±2% range uncertainty was included in robust evaluation using V100%Rx > 95% of the GTV. Conformity index (CI) and gradient index (GI) were used to analyze the effect of apertures vs. no apertures (standard) for each IMPT plan type. CI was defined as the volume of the 100% isodose line divided by the volume of the GTV + 2 mm expansion to account for robust planning. The Wilcoxon signed rank test was utilized to determine the statistical significance of dosimetric results compared between aperture-based and standard IMPT plans. When apertures were implemented in the treatment planning for all shallow and small brain lesions, shallow brain tumors showed the most prominent improvement in conformity and gradient index. A 6.7% difference in average conformity was calculated for standard vs. aperture-based plans for LPMBs, followed by a 5.3% improvement for CPBs. Improvement in gradient index for standard vs. aperture-based plans was significant for both shallow and deeper tumors for CPB and LPB plan types, as shown in Table 1 below. CPB and LPB plan gradient indices were statistically significant for comparing aperture-based vs. standard IMPT plans. We successfully quantified plan quality and evaluated results for aperture- vs. standard IMPT plans using CPBs, LPBs, and LPMBs for brain metastases. Plan quality improves the greatest with apertures applied to beams irradiating shallow tumors. Apertures may not be necessary for small, deeper tumors with IMPT.

Experimental Revelation of Surface and Bulk Lattices in Faceted Cu2 O Crystals.

Semiconductor crystals have generally shown facet-dependent electrical, photocatalytic, and optical properties. These phenomena have been proposed to result from the presence of a surface layer with bond-level deviations. To provide experimental evidence of this structural feature, synchrotron X-ray sources areused to obtain X-ray diffraction (XRD) patterns of polyhedral cuprous oxide crystals. Cu2 O rhombic dodecahedra display two distinct cell constants from peak splitting. Peak disappearance during slow Cu2 O reduction to Cu with ammonia borane differentiates bulk and surface layer lattices. Cubes and octahedra also show two peak components, while diffraction peaks of cuboctahedra are comprised of three components. Temperature-varying lattice changes in the bulk and surface regions also show shape dependence. From transmission electron microscopy (TEM) images, slight plane spacing deviations in surface and inner crystal regions are measured. Image processing provides visualization of the surface layer with depths of about 1.5-4nm giving dashed lattice points instead of dots from atomic position deviations. Close TEM examination reveals considerable variation in lattice spot size and shape for different particle morphologies, explaining why facet-dependent properties are emerged. Raman spectrum reflects the large bulk and surface lattice difference in rhombic dodecahedra. Surface lattice difference can change the particle bandgap.

Dynamics of Hermite–Gaussian laser beam in plasma and terahertz generation

In the present work, the dynamical study of a Hermite–Gaussian (HG) laser beam propagating through plasma with relativistic nonlinearity has been carried out. Furthermore, the dependency of THz generation on the HG laser dynamics has also been investigated. Self-focusing of laser beam inside plasma is achieved due to the modification in electron’s rest mass due to their motion at relativistic velocities. The coupled differential equations obtained using the method of moment determines the variation in spot size of laser beam and have been solved numerically. The laser beam propagating through plasma excites the plasma wave and the nonlinear coupling of HG beam and plasma wave generates THz radiation. It has been observed that THz generation strongly depends upon the variation of spot size, TEM modes, plasma density and intensity of laser beam. Furthermore, the self-trapping of HG laser beam has also been studied.

Tungsten oxide nanoparticle and aggregate formation through direct femtosecond laser ablation in air

In this work, we report the generation of tungsten oxide (WO3) nanoparticles and aggregate structures through direct femtosecond laser ablation in air. The nanoparticle morphology is studied utilizing Raman spectroscopy and TEM analysis, showing the generation of nanorods in the monoclinic phase with an average width and length of 70 and 168 nm, respectively. A range of laser fluences (0.8 to 4.2 J/cm 2) were during the ablation process, demonstrating control over the spread and density of the aggregate structures. Moreover, through variation of the laser spot size we demonstrate controlled aggregate formation, creating structures ranging from a high-density web-like structure with high area coverage to longer wire-like structures with lengths above 100μm.

Genome-wide association analysis reveals that EDNRB2 causes a dose-dependent loss of pigmentation in ducks

BackgroundBirds have various plumage color patterns, and spot is a common phenotype. Herein, we conducted genome-wide association studies (GWAS) in a population of 225 ducks with different sized black spots to reveal the genetic basis of this phenomenon.Results First, we quantified the black spot phenotype within the duck population. The results showed that the uncolored area of the body surface first appeared on the ventral side. With increasing duck age, the area of the black spots was highly conserved across the whole body surface. The GWAS results identified a 198 kb (Chr4: 10,149,651 bp to 10,348,068 bp) genetic region that was significantly associated with the black spot phenotype. The conditional GWAS and linkage disequilibrium (LD) analysis further narrowed the ultimate candidate region to 167 kb (Chr4: 10,180,939 bp to 10,348,068 bp). A key gene regulating melanoblast migration and differentiation, EDNRB2 (Endothelin B receptor-like), was found in the candidate region and having significant mRNA expression level changes in embryonic duck skin tissue with different spot sizes. The significant SNPs (single nucleotide polymorphisms) associated with the EDNRB2 gene were annotated, and two mutations (Chr4: 10,180,939 T > C and Chr4: 10,190,671 A > T) were found to result in the loss of binding sites for two trans-factors, XBP1 and cMYB. The phenotypic effect of these two mutations suggested that they can regulate the size of black spots in a dose-dependent manner, and Chr4: 10,180,939 T > C was the major allele locus.ConclusionsOur results revealed that EDNRB2 was the gene responsible for the variation in duck body surface spot size. Chr4: 10,180,939 T > C was the major allele that explained 49.5 % (dorsal side) and 32.9 % (ventral side) of the variation in duck body surface spot size, while 32.1 % (dorsal side) and 19.1 % (ventral side) of the variation could be explained by Chr4: 10,190,671 A > T. The trans-factor prediction also suggested that XBP1 and cMYB have the potential to interact with EDNRB2, providing new insights into the mechanism of action of these genes.

Broadband X-ray ptychography using multi-wavelength algorithm.

Ptychography is a rapidly developing scanning microscopy which is able to view the internal structures of samples at a high resolution beyond the illumination size. The achieved spatial resolution is theoretically dose-limited. A broadband source can provide much higher flux compared with a monochromatic source; however, it conflicts with the necessary coherence requirements of this coherent diffraction imaging technique. In this paper, a multi-wavelength reconstruction algorithm has been developed to deal with the broad bandwidth in ptychography. Compared with the latest development of mixed-state reconstruction approach, this multi-wavelength approach is more accurate in the physical model, and also considers the spot size variation as a function of energy due to the chromatic focusing optics. Therefore, this method has been proved in both simulation and experiment to significantly improve the reconstruction when the source bandwidth, illumination size and scan step size increase. It is worth mentioning that the accurate and detailed information of the energy spectrum for the incident beam is not required in advance for the proposed method. Further, we combine multi-wavelength and mixed-state approaches to jointly solve temporal and spatial partial coherence in ptychography so that itcan handle various disadvantageous experimental effects. The significant relaxation in coherence requirements by our approaches allows the use of high-flux broadband X-ray sources for high-efficient and high-resolution ptychographic imaging.

Commissioning and beam characterization of the first gantry-mounted accelerator pencil beam scanning proton system.

To present and discuss beam characteristics and commissioning process of the first gantry-mounted accelerator single room pencil beam scanning (PBS) proton system. The Mevion HYPERSCAN employs a design configuration with a synchrocyclotron mounted on the gantry to eliminate the traditional beamline and a nozzle that contains the dosimetry monitoring chambers, the energy modulator (Energy Selector (ES)), and an Adaptive Aperture (AA). To characterize the beam, we measured the integrated depth dose (IDDs) for 12 energies, from highest energy of 227MeV down to 28MeV with a range difference~2cm between the adjacent energies, using a large radius Bragg peak chamber; single-spot profiles in air at five locations along the beam central axis using radiochromic EBT3 film and cross compared with a scintillation detector; and determined the output using a densely packed spot map. To access the performance of AA, we measured interleaf leakage and the penumbra reduction effect. Monte Carlo simulation using TOPAS was performed to study spot size variation along the beam path, beam divergence, and energy spectrum. This proton system is calibrated to deliver 1Gy dose at 5cm depth in water using the highest beam energy by delivering 1 MU/spot to a 10×10 cm2 map with a 2.5mm spot spacing. The spot size in air varies from 4mm to 26mm from 227MeV to 28MeV at the isocenter planewith the nozzle retracted 23.6 cm from isocenter. The beam divergence of 28MeV beam is~52.7 mrad, which is nearly 22 times that of 227MeV proton beam. The binary design of the ES has resulted in shifts of the effective SSD toward the isocenter as the energy is modulated lower. The peaks of IDD curves have a constant 80%-80% width of 8.4mm at all energies. The interleaf leakage of the AA is less than 1.5% at the highest energy; and the AA can reduce the penumbra by 2mm to 13mm for the 227 and 28MeV energies at isocenter plane in air. The unique design of the HYPERSCAN proton system has yielded beam characteristics significantly different from that of other proton systems in terms of the Bragg peak shapes, spot sizes, and the penumbra sharpening effect of the AA. The combination of the ES and AA has made PBS implementation possible without using beam transport line and range shifter devices. Different considerations may be required in treatment planning optimization to account for different design and beam characteristics.

Remote vibrometry recognition of nonlinear eigen-states for object coverage of randomly large size

For objects of “large” vibration size such as waves on the sea surface, the choice of measurement method can create different understandings of system behavior. In one case, laser vibrometry measurements of a vibrating bar in a controlled laboratory setting, variation in probe spot size can omit or uncover crucial structural vibration mode coupling data. In another case, a finite element simulation of laser vibrometry measures a nonlinearly clattering armor plate system of a ground vehicle. The simulation shows that sensing the system dynamics simultaneously over the entire structure reveals more vibration data than point measurements using a small diameter laser beam spot, regardless of the variation of footprint (coverage) boundaries. Furthermore, a simulation method described herein allows calculation of transition probabilities between modes (change-of-state). Wideband results of both cases demonstrate the 1/f trend explained within – that the energy of discrete structural vibration modes tends to decrease with increasing mode number (and frequency), and why. These results quantify the use of less expensive non-imaging classification systems for vehicle identification using the remote sensing of surface vibrations while mitigating spectral response distortion due to coverage variation on the order of the structural wavelength (spectral reduction or elimination).

Drosophila suzukii wing spot size is robust to developmental temperature.

Phenotypic plasticity is an important mechanism allowing adaptation to new environments and as such it has been suggested to facilitate biological invasions. Under this assumption, invasive populations are predicted to exhibit stronger plastic responses than native populations. Drosophila suzukii is an invasive species whose males harbor a spot on the wing tip. In this study, by manipulating developmental temperature, we compare the phenotypic plasticity of wing spot size of two invasive populations with that of a native population. We then compare the results with data obtained from wild‐caught flies from different natural populations. While both wing size and spot size are plastic to temperature, no difference in plasticity was detected between native and invasive populations, rejecting the hypothesis of a role of the wing‐spot plasticity in the invasion success. In contrast, we observed a remarkable stability in the spot‐to‐wing ratio across temperatures, as well as among geographic populations. This stability suggests either that the spot relative size is under stabilizing selection, or that its variation might be constrained by a tight developmental correlation between spot size and wing size. Our data show that this correlation was lost at high temperature, leading to an increased variation in the relative spot size, particularly marked in the two invasive populations. This suggests: (a) that D. suzukii's development is impaired by hot temperatures, in agreement with the cold‐adapted status of this species; (b) that the spot size can be decoupled from wing size, rejecting the hypothesis of an absolute constraint and suggesting that the wing color pattern might be under stabilizing (sexual) selection; and (c) that such sexual selection might be relaxed in the invasive populations. Finally, a subtle but consistent directional asymmetry in spot size was detected in favor of the right side in all populations and temperatures, possibly indicative of a lateralized sexual behavior.

Angular dependency of the polarization rotation in a coherent atomic medium

The dependency of polarization rotation with electromagnetically induced transparency (PREIT) in 87Rb vapor on the angular mismatch between the probe and the pump beams has been studied experimentally and theoretically for a V-type configuration. We have observed a nonlinear variation of the PREIT angle with the angular mismatch. The angular mismatch enhanced the residual Doppler broadening effect, as well as diminishes the two photon coherence contribution, in the medium. We have also systematically studied the effect of optical depth (OD) and the pump beam spot size variations to understand how the number of interacting atoms affect the two photon coherence contribution of the polarization rotation. The value of group velocity of the probe beam has been calculated from the experimentally observed spectrum. We have modeled a three-level V-type system to explain the experimentally observed phenomena by considering the effect of OD and spot size with angular mismatch in the medium. We have considered two-dimensional Maxwell–Boltzmann distribution to calculate the susceptibilities for all atoms of all velocity components. The characteristic variation of the angle of PREIT with the angular mismatch matches well with the experimentally observed result.

Low-frequency Raman spectrophotometer with wide laser illumination on the sample: A tool for pharmaceutical analytical analysis.

This work describes an optical configuration for a Raman spectrophotometer, which permits variation of the laser spot size from 3 to 3000μm, maintaining a high Raman photons throughput and allowing acquisitions with a short integration time. In addition, the instrument can acquire spectra from the low to middle frequency vibrational range (10 to 2000cm-1), on the Stokes and anti-Stokes sides. One of the features of this new optical configuration is the non-use of beam splitters to redirect the scattered light to the detector, which would sacrifice the laser power. The quantitative and qualitative analytical performances of the Raman spectrophotometer were evaluated using chemometric models to predict the concentrations of different active pharmaceutical ingredients (APIs) in mixtures with polymorphs and excipients, as well as by analysis of an API mixture employing hyperspectral imaging. This new optical configuration was shown to be versatile for pharmaceutical purposes and could be used in applications such as the characterization of new drugs or the quality control of raw materials and processes, using normal Raman measurements or SERS (surface-enhanced Raman scattering).

Geometrical-optics approach to measure the optical density of bacterial cultures using a LED-based photometer.

We develop a suitable geometrical-optics approach and demonstrate that it is possible to measure the optical density (OD) of bacterial cultures using a light emitting diode (LED)-based photometer. We measure both attenuation and spot-size variation, and we compensate for diffraction and stray-light impairment related to the incoherent source and large detection area. The approach is validated for different concentrations of two bacterial species, Escherichia coli and Staphylococcus aureus, that present different shapes and clustering organization.

Statistical properties of dynamic speckles in application to laser focusing systems.

Dynamic speckles, which carry information about beam parameters of a diffuse object, are produced by a moving diffuse object under illumination of a Gaussian beam. In this paper, we consider that the diffuse object moves in a plane with constant velocity and discuss the statistical properties of dynamic speckles for estimating the variation of focusing spot size. The space-time statistical properties of dynamic speckle have been revealed by analyzing the space-time cross-correlation function of speckle intensity fluctuations detected at two points in the receiving plane. We discuss the influence of the distance between two point detectors on the detection results by simulation analyses, and the theoretical analysis results are verified by experiment. This method, which applies feedback of the dynamic speckle fields for estimating the variation of focusing spot size, will help a laser focusing system optimize focusing performance.

Overall Optical Design of LED Surgical Luminaires of Variable Light Spot

The surgical luminaires play a very important role in surgical operation and diagnostics. Its overall optical design is the most important component in the design of the surgical luminaires. The wide variable range of the spot size makes the luminaires adaptable to multiple occasions, and the variability is an important indicator for high-grade surgical luminaires. However, it is difficult to keep the uniformity of illumination when the size of the light field changes. One of the reasons why there are few new surgical lamps with wide range of spot size variation in the market is the lack of theoretical analysis. In this paper, we analyze the relationship between the optics of surgical luminaries and the variable light spot by examining a hypothetical surgical lamp composed of 7 LEDs, 6 of which can move radially to create the total spot variable. An improved multivariate Gaussian function will be used to simulate the variable illumination field. Several important optical parameters describing the light field in IEC standard are carefully selected as the independent variables of the Gaussian function. By adding seven improved Gaussian functions of single-spot, a mathematical function of all-spot illumination distribution is established. By this way, it is easy to find in what manner the illumination distribution of surgical luminaires varies with independent variables under the condition of meeting the requirements of international standards. From the calculated results, the important parameters for overall optical design are determined, such as the illumination distribution, the amount of spot movement, the maximum variation range of the light field and the uniformity of illumination. The graphical representation of the results are also given in this paper. The original calculations provided in this article can be used in overall optical design of surgical luminaires with any range of light field change.

Impact of spot size variations on dose in scanned proton beam therapy

BackgroundIn scanned proton beam therapy systematic deviations in spot size at iso-center can occur as a result of changes in the beam-line optics. There is currently no general guideline of the spot size accuracy required clinically. In this work we quantify treatment plan robustness to systematic spot size variations as a function of spot size and spot spacing, and we suggest guidelines for tolerance levels for spot size variations. MethodsThrough perturbation of spot size in treatment plans for 7 patients and a phantom, we evaluated the dose impact of systematic spot size variations of 5% up to 50%. We investigated the dependence on nominal spot size by studying scenarios with small, medium and large spot sizes for various inter-spot spacings. To come to tolerance levels, we used the Γ passing rate and dose-volume-histograms. ResultsLimits on spot size accuracy were extracted for 8 sites, 3 different spot sizes and 3 different inter-spot spacings. While the allowable spot size variation strongly depends on the spot size, the inter-spot spacing turned out to be only of limited influence. ConclusionsPlan robustness to spot size variations strongly depend on spot size, with small spot plans being much more robust than larger spots plans. Inter-spot spacing did not influence plan robustness. Combining our results with existing literature, we propose limits of ±25%, ±20% and ±10% of the spot width σ, for spots with σ of 2.5, 5.0 and 10 mm in proton therapy spot scanning facilities, respectively.

Effects of spot size variation on the laser induced breakdown spectroscopy analysis of Cu(In,Ga)Se2 solar cell

The effects of spot size variation on the results of laser induced breakdown spectroscopy (LIBS) analysis of Cu(In,Ga)Se2 (CIGS) thin film solar cell using a scanning laser beam (λ = 532 nm, τ = 5 ns, top-hat spatial profile) are reported. The spot diameter of laser beam was reduced from 150 μm to 35 μm, below the laser P2 scribing pattern width, at the fixed laser fluence of about 4.5 J/cm2 and overlap ratio of 79%. The results showed that the measured LIBS signal intensity ratio rather than intensity could be nearly independent of laser spot diameter if the spectral lines are properly selected. It is demonstrated that the concentration ratio of CIGS layer can be predicted within 5% error from the average concentration ratio measured by inductively coupled plasma optical emission spectroscopy by LIBS analysis with a spot diameter of 50 μm.