Thermodynamic analysis and simulation for gas baffle entrance collimator of EAST-NBI system based on thermo-fluid coupled method

The world's first full Experimental Advanced Superconducting Tokamak(EAST) is designed with the auxiliary heating method of neutral beam injection(NBI)system. Beam collimators are arranged on both sides of the beam channel for absorbing the divergence beam during the beam transmission process in the EAST-NBI system.The gas baffle entrance collimator(GBEC) is a typical high-heat-flux component located at the entrance of gas baffle. An efficient and accurate analysis of its thermodynamic performance is of great significance to explore the working limit and to ensure safe operation of the system under a high-parameter steady-state condition. Based on the thermo-fluid coupled method, thermodynamic analysis and simulation of GBEC is performed to get the working states and corresponding operating limits at different beam extraction conditions. This study provides a theoretical guidance for the next step to achieve long pulse with highpower experimental operation and has an important reference to ensure the safe operation of the system.

Neutron Radiography System Collimator Design via Monte Carlo Calculation

Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron radiography system that utilizes 241Am-Be neutron source. Many different arrangements have been simulated to obtain a neutron flux with higher amplitude and more uniform distribution in the collimator outlet, next to image plane. In the final arrangement the specifications of neutron filter, Gamma-ray shield and beam collimator has been determined. Simulations has been carried out for a 5Ci 241Am-Be neutron source. In this case 43.8 n/cm2s thermal neutron flux has been achieved at a distance of 35 cm from neutron source.

Assessment of Modeling Collimator Designs for Gamma-Ray Transmission of Uranium Oxide Spectrometry Using HPGe Detectors

Many scientific domains use gamma-ray spectrometry, but non-destructive gamma scanning and gamma emission tomography of radioactive fuel in particular. In the experimental setting, a collimator is frequently employed to focus on a particular location of interest in the fuel. Predictive models for the transmitted gamma-ray intensity through the collimator are required for both the optimization of instrument design and the planning of measurement campaigns. Gamma-ray transport accuracy is frequently predicted using Monte Carlo radiation transport methods, but using these tools in low-efficiency experimental setups is challenging due to the lengthy computation times needed. This study focused on the full-energy peak intensity that was transmitted through several collimator designs, including rectangle and cylinder. The rate of photons arriving at a detector on the other side of the collimator was calculated for anisotropic source of SNM (U3O8). Some geometrical assumptions that depended on the source-to-collimator distance and collimator dimensions (length, radius or length, height, and width) were applied to achieve precise findings.

CT机Collimator详析

X -CT的品牌、型号较多,但不管是什么厂家什么型号的CT ,其Collimator的结构都是大同小异,本文将详细剖析单层CT机的Collimator的结构,讨论一些常见故障,并提出相应解决方法。

Dosimetric evaluation of VMAT radiation therapy technique for breast cancer after conservative surgery based on three different types of multileaf collimators

Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The purpose of this study was to investigate the dosimetric effects of different multileaf collimators(MLC) on VMAT radiotherapy plans for treating breast cancer.Methods Fifteen breast cancer patients who were treated using a conventional technique in our department were selected to participate in this retrospective analysis. VMAT plans based on three types of Elekta MLCs [Beam Modulator(BM) with 4-mm leaf width, Agility with 5-mm leaf width and MLCi2 with 10-mm leaf width] were independently generated for each patient. Plan comparisons were performed based on dose-volume histogram(DVH) analysis including dosimetric parameters such as the homogeneity index(HI), conformity index(CI), Dmax, Dmin, and Dmean for the planning treatment volume(PTV), in addition to dose-volume parameters for the organs at risk(OARs). The delivery efficiency of the three types of MLCs was compared in terms of the beam delivery time and the monitor units(MUs) per fraction for each plan. Results Both target uniformity and conformity were improved in plans for Agility and BM MLC compared with the plan using MLCi2. The mean HI decreased from 1.14 for MLCi2 to 1.13 for BM and 1.10 for Agility, while the mean CI increased from 0.68 for MLCi2 to 0.73 for BM and 0.75 for Agility. Furthermore, at both low and high dose levels, smaller volumes of ipsilateral lung, heart, contralateral lung, and breast were irradiated with Agility MLC than with the other two types of MLCs. The delivery time with Agility MLC was reduced by 10.8% and 32.1%, respectively, compared with that for MLCi2 and BM.Conclusion Our results indicate that the Agility MLC exhibits a dosimetric advantage and a significant improvement in delivery efficiency for the treatment of breast cancer using VMAT.

Design and verification of the HXI collimator on the ASO-S mission

A space-borne hard X-ray collimator,comprising 91 pairs of grids,has been developed for the Hard X-ray Imager(HXI).The HXI is one of the three scientific instruments onboard the first Chinese solar mission:the Advanced Space-based Solar Observatory(ASO-S).The HXI collimator(HXI-C)is a spatial modulation X-ray telescope designed to observe hard X-rays emitted by energetic electrons in solar flares.This paper presents the detailed design of the HXI-C for the qualification model that will be inherited by the flight model.Series tests on the HXI-C qualification model are reported to verify the ability of the HXI-C to survive the launch and to operate normally in on-orbit environments.Furthermore,results of the X-ray beam test for the HXI-C are presented to indirectly identify the working performance of the HXI-C.

Systematic study on visible light collimation by nanostructured slits in the metal surface

We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove-groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.

The Precise Methods for the Measurement of Collimator Hole Angulation and Center of Rotation of SPECT by Adaptive Quality Control Phantom

The Adaptive Quality Control Phantom (AQCP) is a computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce a spatial distribution of gamma rays to perform QC Tests such as the Collimator Hole Angulation (CHA) and the Center of Rotation (COR) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for six collimators was measured using a point source and a computer-controlled cylindrical positioning system. In this method, the displacement of the image of a point source was examined as the AQCP was moving point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS and LEUHR collimators of SMV dual heads camera and LEGP, MEGP and HEGP of GE Millennium MG were evaluated to be 0.290°, 0.292°, 0.208°, 0.154°, 0.220° and 0.202°, respectively. It is to be added in this connection that the evaluated RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface ±1 mm has been varied ±0.04 degree. A new method for the center of rotation assessment by AQCP is introduced and the results of this proposed method as compared with the routine QC test and their differences are discussed in detail. We defined and measured a new parameter called Dynamic Mechanical Error (DME) for applying the gantry motion correction.

Thermal analysis and tests of W/Cu brazing for primary collimator scraper in CSNS/RCS

To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators.Given the material properties and power deposition distribution,the beam scraper of the primary collimator is a0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm x 20 mm.The heat is transferred to the outside by a φ34 mm copper rod.In this paper,for minimizing brazing thermal stress,we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size.We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block.This innovation contributes to the successful R&D of the primary collimator.And this study may be of help for working out a brazing plan of similar structures.

Direct simulation Monte Carlo study of metal evaporation with collimator in e-beam physical vapor deposition

The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article.Collimators are used to achieve the desired vapor beam and deposition rate profile in some applications.This increases the difficulty measuring boundary conditions and the size of the liquid metal pool inside the collimators.It is accordingly hard to obtain accurate results from numerical calculations.In this article, two-dimensional direct simulation Monte Carlo(DSMC) codes are executed to quantify the influence of uncertainties of boundary conditions and pool sizes.Then, three-dimensional DSMC simulations are established to simulate cerium and neodymium evaporation with the collimator.Experimental and computational results of substrate deposition rate profile are in excellent agreement at various evaporation rates and substrate heights.The results show that the DSMC method can assist in metal evaporation with a collimator.

Methods for Setting up a Three-Dimensional Industrial Surveying System of “Building Blocks Type”

This paper is to advance some relevant techniques to set up a three-dimensional industrial surveying system of “building blocks type”, making use of the electronic theodolite, standard ruler and portable computer.

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating,accelerating and guiding protons,using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism.In addition,the problems involved are studied by using two-dimensional particle-in-cell simulations.The results show that the proton beam can be collimated,accelerated and guided effectively through this type of target.Theoretically,a formula is derived for the combined electric field of accelerating protons.Compared with a proton beam without a beam collimator,the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10%respectively.Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field,and that the beam collimator plays a role in focusing energy.In addition,the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I.The more prominent point is that the proton number of type II is 2.2 times higher than that of type I.This kind of target has important applications in many fields,such as fast ion ignition in inertial fusion,high energy physics and proton therapy.

Derivation of General Formula for Coupling Loss of Single-mode Fiber Collimators with Gradient-index Rod Lenses

Gradient-index rod lens (GRIN-lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for determining the coupling loss with axes mismatch, radial mismatch, and angular mismatch is derived by use of the Gaussian field approximation and mode-field coupling theory. The experimental results are in good agreement with the theory prediction. It indicates that these formulas are suitable to analyze the gradient-index rod lens coupling system with pigtail fiber.

Dosimetric comparison of different multileaf collimators in volumetric modulated arc therapy for malignant pleural mesothelioma

Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulated arc therapy （VMAT） planning for malignant pleural mesothelioma. Methods VMAT for ten patients with inoperable malignant pleural mesotheliomas was retrospectively planned with the sMLC and mMLC. Histogram-based dose-volume parameters of the planning target vol- ume （PTV） [conformity index （CI） and homogeneous index （HI）] and organs-at-risk were compared for VMAT plans with sMLC （sMLC-VMAT） and mMLC （mMLC-VMAT）. Results The mMLC-VMAT plans were more efficient （average delivery time： 2.67±1.49 min） than the sMLC-VMAT plans （average delivery time： 4.21 ± 2.03 min; P 〈 0.05）. Moreover, compared to the sMLC plans, the mMLC plans demonstrated advantages in the dose coverage of the PTV （CI 0.75 ± 0.08 vs 0.73± 0.09; HI 1.09 ±0.02 vs 1.10± 0.02）, although the difference was not statistically significant （P 〉 0.05）. In addition, significant dose sparing in the fraction of the ipsilateral lung volume receiving 〉 20 Gy （V20; 54.72± 27.08 vs 58.52 ± 29.30） and 〉 30 Gy （V30; 42.74 ± 27.86 vs 46.86± 31.49） radiation, respectively, was observed for the mMLC plans （P 〈 0.05）. Conclusion Comparing sMLC-VMAT and mMLC-VMAT not only demonstrated the higher efficiency and better optimal target coverage of mMLC-VMAT, but also considerably improved the dose sparing of the ipsilateral lung in the VMAT plans for mali qnant pleural mesothelioma.

Portable two linearly polarized beams absorption biometric system

The purpose of this paper is to design a portable two linearly polarized beams absorption biometric system (PTLPBABS) that measures the amount of absorption of the visible collimated beam passing by the sample to know the absorbance of the sample. The measured object in the system is the gold colloid that the sample produces after a biochemical reaction. After measuring the absorbance of the gold colloid we can obtain the concentrations of the waiting-measured sample and further obtain the concentration of chemical solution contained in the sample. The two linearly polarized beams device can be used to enhance rejection of ambient light and causes PTLPBABS to have excellent data stability measured. The process of the double optical path method increases the opportunities that the visible collimated beam is absorbed, which raise the detection sensitivity of the system to a sensitivity of 0.1%.

Results of the Measurement of the Collimator Hole Angulation for Different Collimators of SPECT with Adaptive Quality Control Phantom

The Adaptive Quality Control Phantom (AQCP) is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce any spatial distribution of gamma rays to perform the QC Tests such as the Collimator Hole Angulation (CHA) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for seven collimators were measured with the method by using a point source and computer-controlled cylindrical positioning. In this method the displacement of the image of a point source examined as the AQCP move point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS, LEUHR, MEGP-250, MEGP-300, MEGP-360 and HEPH collimators of SMV dual heads camera were measured to be 0.290°, 0.292°, 0.208°, 0.194°, 0.181°, 0.177°, 0.150°, respectively. The Root Mean Square (RMS) of CHA for LEGP, MEGP and HEGP collimators of GE Millennium MG were measured to be 0.154°, 0.220° and 0.202° respectively. It is to be added in this connection that the measured RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface +/– 1 mm has been varied +/– 0.04 degree.

Design and test of the motion system for HEPS storage ring horizontal collimator

Background Collimators in the storage ring of high-energy photon source(HEPS)are used to localize the beam loss,making it possible to set local radiation shields.The motion system of the collimator is used to adjust the position of the movable jaws for controlling the beam loss precisely.Moreover,dump mode of the collimator increases the risk of jaw damage from beam heat deposition.According to the requirements of motion accuracy and the severe working condition of the collimators,a new design of a two-axis motion system for the movable jaws is proposed,realizing high-precision control and extending the lifetime.Purpose The purpose of this paper is to introduce the designing scheme of the motion system for HEPS storage ring horizontal collimators,including the analyses of the key components,the structure design of the motion system and test results of the prototype.Method Temperature excursions of the movable jaw are calculated theoretically and analyzed by ANSYS,respectively.The motion accuracy of the system is measured by coordinate measuring machine.Result The temperature excursion is simulated as 1883 K while using graphite as the absorbing material at dump mode.The motion system consists of a mobile slide for aperture adjustment and a manual wedge jack for vertical adjustment.The average coupled deviation in horizontal direction of the wedge jack is 0.031 mm,while the maximum positioning deviation of the slide is 0.014 mm,both having good repeatability and being compensable.Conclusion Test results of the prototype indicate that the new design of the motion system is applicable to the horizontal collimator in HEPS storage ring.The problem of the jaw rotation in the horizontal movement is found,and the solution is given.

Assessment of Monitor Units and Gamma Pass Rate for 6 MV and Flattening Filter Free (FFF) Beams in Volumetric Modulated Arc Therapy (VMAT)

Background: In linear accelerators, the treatment field’s uniform intensity is achieved by including a flattening filter in the beam. However, to produce more conformal dose distributions, contemporary radiotherapy practice now frequently uses fluence and aperture modifying techniques, such as volumetric modulated arc therapy. In these circumstances, the flattening filter in the beam manufacturing process is no longer required. It is therefore necessary to compare the monitor units of 6 MV and flattening filter free plans and how it influences the gamma pass rates to determine which is best for treating cervical cancer with pelvic lymph node metastasis. Methods: VMAT plans for fifteen patients with cervical cancer with pathological pelvic lymph node metastasis were included in this study. Each patient had two VMAT plans using conventional 6 MV beam with flattening filter and one with flattening filter free beam (FFF). The VMAT plans were made using two arcs, and then recalculated to give the planned dose distribution to the detectors in a Delta4 phantom. The VMAT plans were irradiated on the Delta4 phantom using an Elekta linear accelerator (6 MV). Results: The mean monitor unit for the 6 MV plans was 506.3 MU and a standard deviation of 48.6 while that of the FFF plans had a mean MU of 701.5 with a standard deviation of 87.6. The total monitor units (MUs) for the FFF plans were significantly greater than the 6 MV plans (p = 6.1 × 10-5). Conclusion: Flattening filter free (FFF) plans require more numbers of monitor units in comparison to conventional 6 MV filtered beams for external radiation of cervical cancer with pelvic lymph nodes involvement.

瓦里安21EX直线加速器多叶准直器维护与维修

0引言 配备多叶准直器（mulli-leaf collimator,MLC）系统的直线加速器能使照射野最大限度地接近肿瘤形状,从而达到最大限度地杀死肿瘤细胞,同时最小程度影响正常组织的目的[1]。由于MLC比挡铅的操作方法更简单快速[2],目前配有MLC的直线加速器在全国各地的放疗科应用越来越广泛[3]。因多叶准直器被安装在医用电子直线加速器的照射机头上,所以部件受辐射比较严重,