Narrow Pencil Beam Research Articles

Galaxy clustering measurements out to redshift z ˜ 8 from Hubble Legacy Fields

ABSTRACT We present a novel approach for measuring the two-point correlation function of galaxies in narrow pencil beam surveys with varying depths. Our methodology is utilized to expand high-redshift galaxy clustering investigations up to z ∼ 8 by analysing a comprehensive sample consisting of Ng = 160 Lyman break galaxy candidates obtained through optical and near-infrared photometric data within the CANDELS GOODS data sets from the Hubble Space Telescope Legacy Fields. For bright sources with MUV < −19.8, we determine a galaxy bias of b = 9.33 ± 4.90 at $\overline{z} = 7.7$ and a correlation length of r0 = 10.74 ± 7.06 $h^{-1}\, \mathrm{Mpc}$. We obtain similar results for the XDF, with a galaxy bias measurement of b = 8.26 ± 3.41 at the same redshift for a slightly fainter sample with a median luminosity of MUV = −18.4. By comparing with dark-matter halo bias and employing abundance matching, we deduce a characteristic halo mass of Mh ∼ 1011.5 M⊙ and a duty cycle close to unity. To validate our approach for variable-depth data sets, we replicate the analysis in a region with near-uniform depth using a standard two-point correlation function estimator, yielding consistent outcomes. Our study not only provides a valuable tool for future utilization in JWST data sets but also suggests that the clustering of early galaxies continues to increase with redshift beyond z ≳ 8, potentially contributing to the existence of protocluster structures observed in early JWST imaging and spectroscopic surveys at z ≳ 8.

Very high-energy electron dose calculation using the Fermi-Eyges theory of multiple scattering and a simplified pencil beam model.

Very high-energy electrons (VHEE) radiotherapy, in the energy range of 100-200 MeV is currently considered a promising technique for the future of radiation therapy and could benefit from the promises of ultra-high dose rate FLASH therapy. However, to our knowledge, no analytical calculation models have been tested for this type of application and the approximations proposed for multiple scattering with electron beams have not been extensively evaluated at these high energies. In this work, we discuss the derivation of a simple and fast algorithm based on the Fermi-Eyges theory of multiple Coulomb scattering for fast dose calculation for VHEE beams (up to 200 MeV). Similar to the Gaussian pencil beam models used for electron or proton beams, this pencil beam kernel is separated into a central and an off-axis term. Monte Carlo simulations are performed to compare the analytical calculations with simulations and to determine the parametrizations used in the model at the highest electron energies. The normalized electron planar fluence distribution is described in water according to the Fermi-Eyges theory of multiple Coulomb scattering and a double Gaussian distribution model. The main quantities used in the model and their calculation (mass angular scattering power, mean energy, range straggling) are discussed and tested for electron energies up to 200 MeV. The TOPAS/Geant4 Monte Carlo (MC) toolkit is used to compare analytical calculations with MC simulations for a theoretical pencil beam irradiation and to find the best parameters describing the range straggling. The model is then tested on a realistic simulation of a pencil beam scanning beamline with treatment field dimensions up to 15×15cm2 and for deep-seated targets. Radial dose distributions of a pencil beam in water were calculated with the model and compared with the results of a complete Monte Carlo simulation. A good agreement (within 2%/2mm gamma passing rate superior to 90%, and a mean deviation between calculated and simulated pencil beam radial spread smaller than 0.6mm) was observed between analytical dose distributions and simulations for energies up to 200 MeV and field sizes up to 15×15cm2 . A parameterization of an electron source and an analytical pencil beam model were proposed in this work, thereby allowing a suitable reproduction of the lateral fluence of a VHEE beam and good agreement between calculations and simulated data. Further improvement of the method would require the consideration of a model describing the large-angle scattering of the electrons. The results of this work could support future research into VHEE radiotherapy and might be of interest for use together with VHEE broad beams produced by scanned narrow pencil beams.

A Single-Layer Dual-Band Array at Low-Frequency Ratio With Concurrent Broad Fan Beam and Narrow Pencil Beam

A Single-Layer Dual-Band Array at Low-Frequency Ratio With Concurrent Broad Fan Beam and Narrow Pencil Beam

Anomalous Beam Transport through Gabor (Plasma) Lens Prototype

An electron plasma lens is a cost-effective, compact, strong-focusing element that can ensure efficient capture of low-energy proton and ion beams from laser-driven sources. A Gabor lens prototype was built for high electron density operation at Imperial College London. The parameters of the stable operation regime of the lens and its performance during a beam test with 1.4 MeV protons are reported here. Narrow pencil beams were imaged on a scintillator screen 67 cm downstream of the lens. The lens converted the pencil beams into rings that show position-dependent shape and intensity modulation that are dependent on the settings of the lens. Characterisation of the focusing effect suggests that the plasma column exhibited an off-axis rotation similar to the m=1 diocotron instability. The association of the instability with the cause of the rings was investigated using particle tracking simulations.

Al2O3:C optically stimulated luminescence dosimeters (OSLDs) for ultra-high dose rate proton dosimetry

The response of Al2O3:C optically stimulated luminescence detectors (OSLDs) was investigated in a 250 MeV pencil proton beam. The OSLD response was mapped for a wide range of average dose rates up to 9000 Gy s−1, corresponding to a ∼150 kGy s−1 instantaneous dose rate in each pulse. Two setups for ultra-high dose rate (FLASH) experiments are presented, which enable OSLDs or biological samples to be irradiated in either water-filled vials or cylinders. The OSLDs were found to be dose rate independent for all dose rates, with an average deviation <1% relative to the nominal dose for average dose rates of (1–1000) Gy s−1 when irradiated in the two setups. A third setup for irradiations in a 9000 Gy s−1 pencil beam is presented, where OSLDs are distributed in a 3 × 4 grid. Calculations of the signal averaging of the beam over the OSLDs were in agreement with the measured response at 9000 Gy s−1. Furthermore, a new method was presented to extract the beam spot size of narrow pencil beams, which is in agreement within a standard deviation with results derived from radiochromic films. The Al2O3:C OSLDs were found applicable to support radiobiological experiments in proton beams at ultra-high dose rates.

Radiation Properties of a 2-D Periodic Leaky-Wave Antenna

A study of the radiation characteristics of a 2-D periodic leaky-wave antenna (LWA) [i.e., one that radiates from higher order space harmonics (Floquet waves) instead of the fundamental one] is presented here for the first time, and an optimization to produce maximum radiation at broadside is discussed. The structure consists of a 2-D periodic arrangement of narrow rectangular patches on a grounded dielectric substrate, excited by a simple source such as a slot in the ground plane. A 2-D periodic LWA can be designed to radiate a narrow pencil beam pattern at broadside by adjusting its geometric parameters. The main beam at broadside is narrower in the E-plane than in the H-plane, and there are also grating lobes introduced due to the periodicity. The structure has been analyzed theoretically using the periodic spectral-domain immittance (periodic SDI) method. The proposed antenna has also been simulated using both FEM and method of moments methods and a fabricated design has been measured. A good correlation is observed between the theoretical, simulated, and measured radiation patterns.

Dual-Band Antenna Array With Superdirective Elements for Short-Distance Ballistic Tracking

This paper describes an innovative architecture of dual-band planar array for short-range tracking radar applications. The proposed antenna consists of two integrated patch arrays and it works in the L-band and Ka-band. The structure is characterized by compact size and lightweight, thanks to the concept of sharing the same PCB and mechanical chassis for dual-band operation. One of the key aspects, besides the interoperability of the two patch arrays, is the use of dielectric rods that increase the realized gain while minimizing the required number of elements. As a consequence, the beamforming network is simplified, and the reliability of the module is significantly improved. The proposed dual-band array provides a gain higher than 28 dBi with low sidelobes and controlled narrow pencil beam, making it ideal for highly accurate radar tracking.

Implementation of planar proton minibeam radiation therapy using a pencil beam scanning system: A proof of concept study.

Proton minibeam radiation therapy (pMBRT) is an innovative approach that combines the advantages of minibeam radiation therapy with the more precise ballistics of protons to further reduce the side effects of radiation. One of the main challenges of this approach is the generation of very narrow proton pencil beams with an adequate dose-rate to treat patients within a reasonable treatment time (several minutes) in existing clinical facilities. The aim of this study was to demonstrate the feasibility of implementing pMBRT by combining the pencil beam scanning (PBS) technique with the use of multislit collimators. This proof of concept study of pMBRT with a clinical system is intended to guide upcoming biological experiments. Monte Carlo simulations (TOPAS v3.1.p2) were used to design a suitable multislit collimator to implement planar pMBRT for conventional pencil beam scanning settings. Dose distributions (depth-dose curves, lateral profiles, Peak-to-Valley Dose Ratio (PVDR) and dose-rates) for different proton beam energies were assessed by means of Monte Carlo simulations and experimental measurements in a water tank using commercial ionization chambers and a new p-type silicon diode, the IBA RAZOR. An analytical intensity-modulated dose calculation algorithm designed to optimize the weight of individual Bragg peaks composing the field was also developed and validated. Proton minibeams were then obtained using a brass multislit collimator with five slits measuring 2cm×400μm in width with a center-to-center distance of 4mm. The measured and calculated dose distributions (depth-dose curves and lateral profiles) showed a good agreement. Spread-out Bragg peaks (SOBP) and homogeneous dose distributions around the target were obtained by means of intensity modulation of Bragg peaks, while maintaining spatial fractionation at shallow depths. Mean dose-rates of 0.12 and 0.09Gy/s were obtained for one iso-energy layer and a SOBP conditions in the presence of multislit collimator. This study demonstrates the feasibility of implementing pMBRT on a PBS system. It also confirms the reliability of RAZOR detector for pMBRT dosimetry. This newly developed experimental methodology will support the design of future preclinical research with pMBRT.

Design of a QA method to characterize submillimeter-sized PBS beam properties using a 2D ionization chamber array

Pencil beam scanning (PBS) periodic quality assurance (QA) programs ensure the beam delivered to patients is within technical specifications. Two critical specifications for PBS delivery are the beam width and position. The aim of this study is to investigate whether a 2D ionization chamber array, such as the MatriXX detector (IBA Dosimetry, Schwarzenbruck, Germany), can be used to characterize submillimeter-sized PBS beam properties. The motivation is to use standard equipment, which may have pixel spacing coarser than the pencil beam size, and simplify QA workflow.The MatriXX pixels are cylindrical in shape with 4.5 mm diameter and are spaced 7.62 mm from center to center. Two major effects limit the ability of using the MatriXX to measure the spot position and width accurately. The first effect is that too few pixels sample the Gaussian shaped pencil beam profile and the second effect is volume averaging of the Gaussian profile over the pixel sensitive volumes. We designed a method that overcomes both limitations and hence enables the use of the MatriXX to characterize sub-millimeter-sized PBS beam properties. This method uses a cross-like irradiation pattern that is designed to increase the number of sampling data points and a modified Gaussian fitting technique to correct for volume averaging effects. Detector signals were calculated in this study and random noise and setup errors were added to simulate measured data.With the techniques developed in this work, the MatriXX detector can be used to characterize the position and width of sub-millimeter, σ = 0.7 mm, sized pencil beams with uncertainty better than 3% relative to σ. With the irradiation only covering 60% of the MatriXX, the position and width of σ = 0.9 mm sized pencil beams can be determined with uncertainty better than 3% relative to σ. If one were to not use a cross-like irradiation pattern, then the position and width of σ = 3.6 mm sized pencil beams can be determined with uncertainty better than 3% relative to σ. If one were to not use a cross-like pattern nor volume averaging corrections, then the position and width of σ = 5.0 mm sized pencil beams can be determined with uncertainty better than 3% relative to σ.This work helps to simplify periodic QA in proton therapy because more routinely used ionization chamber arrays can be used to characterize narrow pencil beam properties.

Ground-based x-ray calibration of the Astro-H/Hitomi soft x-ray telescopes

We present the summary of the on-ground calibration of two soft x-ray telescopes (SXT-I and SXT-S), developed by NASA’s Goddard Space Flight Center (GSFC), onboard Astro-H/Hitomi. After the initial x-ray measurements with a diverging beam at the GSFC 100-m beamline, we performed the full calibration of the x-ray performance, using the 30-m x-ray beamline facility at the Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency in Japan. We adopted a raster scan method with a narrow x-ray pencil beam with a divergence of ∼15″. The on-axis effective area (EA), half-power diameter, and vignetting function were measured at several energies between 1.5 and 17.5 keV. The detailed results appear in tables and figures in this paper. We measured and evaluated the performance of the SXT-S and the SXT-I with regard to the detector-limited field-of-view and the pixel size of the paired flight detector, i.e., SXS and the SXI, respectively. The primary items measured are the EA, image quality, and stray light for on-axis and off-axis sources. The accurate measurement of these parameters is vital to make the precise response function of the ASTRO-H SXTs. This paper presents the definitive results of the ground-based calibration of the ASTRO-H SXTs.

A clumpy and anisotropic galaxy halo at redshift 1 from gravitational-arc tomography.

Every star-forming galaxy has a halo of metal-enriched gas that extends out to at least 100 kiloparsecs, as revealed by the absorption lines that this gas imprints on the spectra of background quasars. However, quasars are sparse and typically probe only one narrow beam of emission through the intervening galaxy. Close quasar pairs and gravitationally lensed quasars have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circumgalactic medium remains poorly constrained. As a result, our understanding of the physical processes that drive the recycling of baryons across the lifetime of a galaxy is limited. Here we report integral-field (tomographic) spectroscopy of an extended background source-a bright, giant gravitational arc. We can thus coherently map the spatial and kinematic distribution of Mg ɪɪ absorption-a standard tracer of enriched gas-in an intervening galaxy system at redshift 0.98 (around 8 billion years ago). Our gravitational-arc tomography unveils a clumpy medium in which the absorption strength decreases with increasing distance from the galaxy system, in good agreement with results for quasars. Furthermore, we find strong evidence that the gas is not distributed isotropically. Interestingly, we detect little kinematic variation over a projected area of approximately 600 square kiloparsecs, with all line-of-sight velocities confined to within a few tens of kilometres per second of each other. These results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow.

RADIOTHERAPY PROTON BEAM PROFILOMETRY WITH scCVD DIAMOND DETECTOR IN SINGLE PARTICLE MODE.

Proton radiotherapy requires precise knowledge of the volumetric dose distribution. In proton beam delivery systems, based on narrow pencil beams, a contribution from small doses in low-intensity regions, consisting mainly of scattered protons, may have not negligible influence on total dose delivered to patient. Insufficient information about dose profile can cause underestimation of dose and potential delivery of inflated dose during hadrontherapy treatment. Presented work aims to verify applicability of diamond detectors, produced by Chemical Vapor Deposition method, for therapeutic proton beam profilometry at large fields. This requires the capability of measuring the core of the beam intensity profile (wide dynamic range) as well as its lateral spread (very high sensitivity) with a single device.

Transmit Beampattern Design in Range and Angle Domains for MIMO Frequency Diverse Array Radar

The frequency diverse array (FDA) has a range-angle-dependent transmit beampattern, which can provide the potential capability for novel radar application. However, the basic FDA's beampattern is periodic in range and coupled in range and angle dimensions, which limits the application of FDA in radar field. In this letter, we propose a novel FDA model with nonmonotone increasing frequency offset to form a narrow pencil beam, which eliminates the range periodicity and coupling of range and angle domains. Combining this new FDA with multiple-input–multiple-output radar, not only can multiple narrow pencil beams be formed to track multiple targets simultaneously, but also a flat-top transmit beampattern for targets searching can be synthesized. Simulation results show the effectiveness and outperformance of the proposed scheme compared to the existing Log-FDA, which uses the logarithmically increasing frequency offset.

Feasibility study of Compton cameras for x-ray fluorescence computed tomography with humans

X-ray fluorescence imaging is a promising imaging technique able to depict the spatial distributions of low amounts of molecular agents in vivo. Currently, the translation of the technique to preclinical and clinical applications is hindered by long scanning times as objects are scanned with flux-limited narrow pencil beams. The study presents a novel imaging approach combining x-ray fluorescence imaging with Compton imaging. Compton cameras leverage the imaging performance of XFCT and abolish the need for pencil beam excitation. The study examines the potential of this new imaging approach on the base of Monte-Carlo simulations. In the work, it is first presented that the particular option of slice/fan-beam x-ray excitation has advantages in image reconstruction in regard of processing time and image quality compared to traditional volumetric Compton imaging. In a second experiment, the feasibility of the approach for clinical applications with tracer agents made from gold nano-particles is examined in a simulated lung scan scenario. The high energy of characteristic x-ray photons from gold is advantageous for deep tissue penetration and has lower angular blurring in the Compton camera. It is found that Doppler broadening in the first detector stage of the Compton camera adds the largest contribution on the angular blurring; physically limiting the spatial resolution. Following the analysis of the results from the spatial resolution test, resolutions in the order of one centimeter are achievable with the approach in the center of the lung. The concept of Compton imaging allows one to distinguish to some extent between scattered photons and x-ray fluorescent photons based on their difference in emission position. The results predict that molecular sensitivities down to 240 pM l−1 for 5 mm diameter lesions at 15 mGy for 50 nm diameter gold nano-particles are achievable. A 45-fold speed up time for data acquisition compared to traditional pencil beam XFCT could be achieved for lung imaging at the cost of a small sensitivity decrease.

Experimental Validation of an Efficient Fan-Beam Calibration Procedure for &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$k$&lt;/tex&gt;&lt;/formula&gt;-Nearest Neighbor Position Estimation in Monolithic Scintillator Detectors

Monolithic scintillator detectors can achieve excellent spatial resolution and coincidence resolving time. However, their practical use for positron emission tomography (PET) and other applications in the medical imaging field is still limited due to drawbacks of the different methods used to estimate the position of interaction. Common statistical methods for example require the collection of an extensive dataset of reference events with a narrow pencil beam aimed at a fine grid of reference positions. Such procedures are time consuming and not straightforwardly implemented in systems composed of many detectors. Here, we experimentally demonstrate for the first time a new calibration procedure for $k$ -nearest neighbor ( $k$ -NN) position estimation that utilizes reference data acquired with a fan beam. The procedure is tested on two detectors consisting of $16~\hbox{mm} \times 16~\hbox{mm} \times 10~\hbox{mm}$ and $16~\hbox{mm} \times 16~\hbox{mm} \times 20~\hbox{mm}$ monolithic, Ca-codoped LSO:Ce crystals and digital photon counter (DPC) arrays. For both detectors, the spatial resolution and the bias obtained with the new method are found to be practically the same as those obtained with the previously used method based on pencil-beam irradiation, while the calibration time is reduced by a factor of $\sim 20$ . Specifically, a FWHM of $\sim 1.1~\hbox{mm}$ and a FWTM of $\sim 2.7~\hbox{mm}$ were obtained using the fan-beam method with the 10 mm crystal, whereas a FWHM of $\sim 1.5~\hbox{mm}$ and a FWTM of $\sim 6~\hbox{mm}$ were achieved with the 20 mm crystal. Using a fan beam made with a $\sim 4.5~\hbox{MBq}\quad ^{22}{\rm Na}$ point-source and a tungsten slit collimator with 0.5 mm aperture, the total measurement time needed to acquire the reference dataset was $\sim 3$ hours for the thinner crystal and $\sim 2$ hours for the thicker one.

Comparison of the charge sharing effect in two hybrid pixel detectors of different thickness

Advances in semiconductor technologies, enable the design of hybrid pixel detectors with ever smaller pixel sizes while maintaining good performance of analogue circuits. Along with the decrease in the size of pixels new, previously unaddressed phenomena are beginning to play an important role. One such phenomenon is the charge sharing effect, where the charge generated by a particle in the vicinity of the pixel's border is collected by two or more different detector electrodes and processed in part by two or more independent pixels. In systems operating in the single photon counting (SPC) mode which compares the amplitude of the recorded signal with a predetermined threshold, this may reduce or increase the number of photons counted. In systems which measure the amplitude of the signal recorded, this phenomenon can lead to incorrect results of the amplitude measurements. In order to investigate the effect of charge sharing, measurements were conducted using silicon pixel detectors with the thickness of 300 μ m and 1 mm, 100 μ m × 100 μ m pixel size, connected to the PXD18k ASIC. The pixel array was scanned with 16 keV narrow pencil beam. The measurement setup and the results of the measurements are presented in the article.

Transfer line scattering model of therapeutic hadron beams and applications to nozzle and gantry optimization

The field of hadron therapy is growing rapidly with several facilities currently being planned, under construction or in commissioning worldwide. In the ``active scanning'' irradiation technique, the target is irradiated using a narrow pencil beam that is scanned transversally over the target while the penetration depth is altered with the beam energy. Together, the target dose can thereby be conformed in all three dimensions to the shape of the tumor. For applications where a sharp lateral beam penumbra is required in order to spare critical organs from unwanted dose, beam size blowup due to scattering in on-line beam diagnostic monitors, air gaps and passive elements like the ripple filter must be minimized. This paper presents a model for transverse scattering of therapeutic hadron beams along arbitrary multislab geometries. The conventional scattering formulation, which is only applicable to a drift space, is extended to not only take beam optics into account, but also non-Gaussian transverse beam profiles which are typically obtained from the slow resonant extraction from a synchrotron. This work has been carried out during the design phase of the beam delivery system for MedAustron, an Austrian hadron therapy facility with first patient treatment planned for the end of 2015. Irradiation will be performed using active scanning with proton and carbon ion beams. As a direct application of the scattering model, design choices for the MedAustron proton gantry and treatment nozzles are evaluated with respect to the transverse beam profile at the focal point; in air and at the Bragg peak.

First experimental-based characterization of oxygen ion beam depth dose distributions at the Heidelberg Ion-Beam Therapy Center

Over the last decades, the application of proton and heavy-ion beams to external beam radiotherapy has rapidly increased. Due to the favourable lateral and depth dose profile, the superposition of narrow ion pencil beams may enable a highly conformal dose delivery to the tumour, with better sparing of the surrounding healthy tissue in comparison to conventional radiation therapy with photons. To fully exploit the promised clinical advantages of ion beams, an accurate planning of the patient treatments is required. The clinical treatment planning system (TPS) at the Heidelberg Ion-Beam Therapy Center (HIT) is based on a fast performing analytical algorithm for dose calculation, relying, among others, on laterally integrated depth dose distributions (DDDs) simulated with the FLUKA Monte Carlo (MC) code. Important input parameters of these simulations need to be derived from a comparison of the simulated DDDs with measurements. In this work, the first measurements of 16O ion DDDs at HIT are presented with a focus on the determined Bragg peak positions and the understanding of factors influencing the shape of the distributions. The measurements are compared to different simulation approaches aiming to reproduce the acquired data at best. A simplified geometrical model is first used to optimize important input parameters, not known a priori, in the simulations. This method is then compared to a more realistic, but also more time-consuming simulation approach better accounting for the experimental set-up and the measuring process. The results of this work contributed to a pre-clinical oxygen ion beam database, which is currently used by a research TPS for corresponding radio-biological cell experiments. A future extension to a clinical database used by the clinical TPS at HIT is foreseen. As a side effect, the performed investigations showed that the typical water equivalent calibration approach of experimental data acquired with water column systems leads to slight deviations between the experimentally determined and the real Bragg peak positions. For improved accuracy, the energy dependence of the stopping power, and herewith the water equivalent thickness, of the material downstream of the water tank should be considered in the analysis of measured data.

SU-GG-T-590: Delta-Functional Multi Segmented Pencil Beam Algorithm for Highly Accurate Proton Dose Calculation in Heterogeneous Body

Purpose: A pencil beam algorithm (PBA), which is the most widely used dose calculation method for proton therapy, could make a considerable error in the case of complicated structure. This is because it utilizes the one‐dimensional density scaling along the central axis of the pencil beam and neglects the off‐axis density heterogeneity. In order to obtain accurate dose distribution in heterogeneous materials in a patient body, we have developed a novel dose calculation algorithm, delta‐functional multi segmented pencil beam algorithm (DMS‐PBA). In this study, the superiority of DMS‐PBA to conventional PBA was verified by using phantom experiment. Method and Materials: An L‐shaped polyethylene block, representing lateral heterogeneity, was set above polyethylene plates. Three dimensional dose distributions were measured with a simulated using two algorithms: DMS‐PBA and conventional PBA. The accuracy of the calculation was evaluated by comparing the measured and calculated dose distributions. Results: In the measurement, hot and cold spots were detected at z = 123, 142, 162 mm‐WEL. Conventional PBA method could reproduce none of these spots. The difference between PBA results and the measured dose amounted to 12 %. On the other hand, DMS‐PBA and the measured dose generally agreed well. The hot and cold spots may be produced by the proton trajectories in different angles around the border between polyethylene and air. DMS‐PBA could reproduce the detour and overreaching of proton by using “narrow” pencil beams with laterally delta‐functional initial beam emittance. In addition, the computing time by DMS‐PBA method in this situation was reasonable due to the less overlapped narrow pencil beams. Conclusions: We showed that our proposed method, DMS‐PBA, could improve the accuracy of dose calculation for treatment planning of proton therapy.

WE‐E‐AUD B‐07: EGSnrc Benchmarking Against High‐Precision Angular Electron Scattering Data Through Thin Foils

Purpose: The EGSnrc Monte Carlo code was benchmarked against newly measured angular scattering distributions of electron beams through thin materials. Method and Materials: The BEAMnrc user code was used for the simulation of the experimental setup. The geometry, beam and material properties were implemented in BEAMnrc, while the DOSXYZnrc user code was used to score the absorbed dose up to angles of 10°. The electron beam was generated using the National Research Council of Canada (NRC) Vickers linear accelerator, which allows for the production of narrow pencil beams of electrons with well known energies. Six materials: Be, C, Al, Ti, Cu, Ta and Au, were used as scattering foils and measurements were made at two energies — 13 MeV and 20 MeV. Great care was taken to obtain high accuracy experimental data for comparison with the results of the simulations. Results: The obtained angular distributions were fitted with a Gaussian and the characteristic angle (the angle at which the absorbed dose decreases by 1/e) was used to compare the measured and simulated distributions. The discrepancy between the measured and the EGSnrc characteristic angles is on average about 1.5%. A careful error estimation was performed on the measured data, that resulted in a value of about 1%. The EGSnrc code shows an agreement with the measured data at the 2σ level. In general, the EGSnrc predicts narrower distributions. The full distributions were also compared and the shapes were found to be very similar even at large angles. Conclusion: The present study shows that the EGSnrc code predicts electron angular scattering distributions in agreement with the measured data at the 2% level. It is intended to make the experimental data available to the user community to be used for benchmarking of other Monte Carlo codes.Partial support from NIH R01 CA104777‐01A2.