基于蒙特卡罗方法的XHA600D医用电子直线加速器的入射电子束参数研究

使用蒙特卡罗方法研究入射电子束参数对XHA600D医用电子直线加速器产生的剂量分布的影响,并确定优化的入射电子束参数。根据厂商提供的XHA600D加速器治疗头的几何、材料参数,使用蒙特卡罗程序EGSnrc对不同的入射电子束参数进行模拟并记录其在水模体中产生的剂量分布,将模拟结果与测量结果进行比较。模拟的入射电子束参数包括平均能量、径向强度分布、角度展宽和能量展宽;实验测量数据包括4 cm×4 cm、10 cm×10 cm、30 cm×30 cm射野条件下的百分深度剂量与离轴剂量。结果表明当入射电子束的平均能量为6 MeV、径向强度的半高宽(Full Width at Half Maximum, FWHM)为0.25 cm、角度展宽为0.15°时,模拟结果和测量结果吻合非常好。这些参数可以作为建立适用于XHA600D加速器的TPS(Treatment Planning System)剂量计算模型的基础参数。     

发散型准直器限束孔应用于被动散射质子放疗可行性研究

被动散射质子放疗（Passive Scattering Proton Therapy,PSPT）是质子治疗的主要技术之一,束流通过准直器限束孔（Aperture）时因边缘散射效应导致患者体内剂量分布偏离理想状态。使用蒙特卡洛软件TOPAS（TOol for PArticle Simulation）对质子束流经过发散型与传统型准直器限束孔后进入水模体中的过程建模,分析两种准直器的边缘散射效应对剂量及中子能谱分布的影响,分别测试70,110,160,200,230,250 MeV能量下的质子束流,发现传统Aperture在70 MeV的质子束下边缘散射效应最明显,在距水箱表面0.5 cm深度处横向剂量曲线平坦度、均匀度分别达到4.63%,108.05%,随着深度增加边缘散射效应逐渐减弱,在布拉格峰位置处接近消失。使用发散型准直器限束孔后,在70 MeV下平坦度、均匀度分别降至1.28%,101.31%,对于100,160,200 MeV质子束均有不同程度改善。对于能量接近250 MeV的质子束,发散型准直器限束孔设置下横向剂量曲线并无优势。边缘散射效应导致的剂量不均随水深增加而减弱,对于各个能量质子,使用发散型准直器限束孔后次级中子减少。研究结果表明,发散型准直器限束孔应用于PSPT效果显著,为进一步应用于临床提供数据支撑。Passive Scattering Proton Therapy (PSPT) is one of the main technologies for proton radiation therapy. The dose distribution in the patient deviates from the ideal state due to the edge scattering effect when the beam passes through the aperture. In this paper, TOPAS, a Monte Carlo software, was used to simulate the passive scattering treatment head. The influence of the edge scattering effect of the two aperture sets on the dose distribution was compared. The proton beam at 70, 110, 160, 200, 230 and 250 MeV was tested respectively. We found that the scattering effect of the conventional aperture is most obvious at 70 MeV, and the flatness and hetergeneity of the lateral dose curve at the inlet of 0.5 cm of the tank reach 4.63%, 108.05%, respectively. The dose shift caused by the edge scattering effect decreases with increasing water depth and disappears at the Bragg peak. After using the divergent aperture, the flatness and uniformity at 70 MeV are reduced to 1.28% and 101.31%, respectively, and the 100, 160, and 200 MeV proton beams are improved in different extents. For a proton beam with an energy close to 250 MeV, there is no advantage in the lateral dose curve of the divergent aperture. For all energy protons, the secondary neutrons are reduced with divergent aperture. The results show that the divergent aperture is effective for PSPT and this study provides data support for further application in clinical practice.     

100 MeV质子束流品质诊断及剂量测量准确性评估方法研究

质子辐射生物学效应是太空放射生物学和质子束放疗研究的重要基础,可为空间环境下人员的危险性评估以及质子治疗优化设计提供科学依据。依托加速器建立相应的生物样本辐照技术是开展此类研究的前提条件。中国原子能科学研究院最近建立的100 MeV强流质子回旋加速器提供的中能质子束流为目前国内能量最高,特别适合用于太空放射生物学和质子治疗相关研究。本研究中,利用在束和离线等多种手段建立了中能质子束流诊断和剂量测量方法,对加速器引出的100 MeV质子照射野大小、均匀性等束流品质以及剂量测量系统准确性进行了分析和评估。结果表明,对光子剂量响应好的LiF(Mg, Ti)热释光探测器,对90 MeV质子同样具有良好的剂量响应关系,可作为中能质子剂量准确性评估的手段之一。在5.0 cm×5.0 cm照射野范围内,加速器引出的100 MeV质子束流的均匀性好于90%,在线剂量测量系统准确性好于93%,束流品质和剂量测量条件基本满足辐射生物学的要求,可为质子辐射生物学效应研究的开展提供可靠保障。     

Symmetric Swallowtail Beams in the Rectangle Frame

A new type of symmetric swallowtail beam (SSB) in the rectangle frame is introduced here. These kinds of beams are highly tunable with multiple manipulation parameters. The focal length and the focus intensity can be controlled precisely. The SSBs can guide the off-axis vortex to their center. And the experimental results agree well with the numerical simulations. Besides, stable trapping of particles by utilizing the SSBs' auto-focusing property and rectangle symmetry is also observed.     

Controlling Beam Halo-Chaos by Adaptive Control Exterior Magnetic Field

In this paper, the parametric adaptive method for controlling the beam halo-chaos in the periodic focusing channels of high-current proton linacs is presented. The study of proton beam halo-chaos based on controlled beam envelope equation and the results of particles-in-ceU simulations for macro-particle beam show that the proton beam chaotic envelope as well as the beam rsm radius can be controlled to the beam matched radius using this method. For the Kapchinskij-Vladimirskij (K-V) distribution of initial proton beam, all statistical physical, quantities of the beam halo-chaos are largely reduced. This control method has an advantage of the control halo-chaos since the exterior magnetic field as controlled parameter can be rather easily adjusted in the periodical magnetic focusing channels for the experiment.     

Controlling Beam Halo-Chaos by Adaptive Control Exterior Magnetic Field

In this paper, the parametric adaptive method for controlling the beam halo-chaos in the periodic focusing channels of high-current proton linacs is presented. The study of proton beam halo-chaos based on controlled beam envelope equation and the results of particles-in-cell simulations for macro-particle beam show that the proton beam chaotic envelope as well as the beam rsm radius can be controlled to the beam matched radius using this method.For the Kapchinskij-Vladimirskij (K- V) distribution of initial proton beam, all statistical physical, quantities of the beam halo-chaos are largely reduced. This control method has an advantage of the control halo-chaos since the exterior magnetic field as controlled parameter can be rather easily adjusted in the periodical magnetic focusing channels for the experiment.     

Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris)

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8 degrees and 10 degrees, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0 degrees-50 degrees. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field.     

光阴极直流高压电子枪束流偏轴发射研究

离子反轰会造成直流高压电子枪内光阴极的量子效率衰减,降低阴极的工作寿命和稳定性,是限制光阴极直流高压电子枪性能的重要因素之一。基于中国工程物理研究院太赫兹自由电子激光(THzFEL)的直流高压电子枪,通过束流动力学模拟和阴极量子效率测量,研究了束流偏轴发射对离子反轰的抑制作用及其应用限制。模拟结果表明:束流偏轴发射时,离子主要轰击阴极的电中心附近,光电发射区域的离子通量较轴上发射时降低约95%;但束流发射度增大约4πmm·mrad,横向运动幅度增加约1倍。通过电子枪运行前后阴极量子效率测量,发现束流偏轴发射时离子反轰引起电中心附近量子效率大面积的衰减,而光电发射区域量子效率损失较小,验证了束流偏轴发射抑制离子反轰的可行性。     

投影光刻离轴照明用衍射光学元件的矢量分析

使用衍射光学元件(DOE)作为投影光刻照明系统实现离轴照明(OAI)的光束整形匀光器件,能够在保持较高照明效率的基础上精确控制OAI光束的形状及光强分布.在矢量角谱传输方法的基础上,建立了投影光刻用DOE的矢量分析模型,并对标量方法设计的DOE在偏振照明情况下的匀光与整形性能进行了分析.分析结果表明DOE在大角度衍射、...     

Mode Competition in the Gyro-Peniotron Oscillator

The gyro-peniotron oscillator holds great promise for generating microwave radiation with efficiencies far greater than those obtainable through the electron cyclotron-maser interaction. Theoretical modeling has shown that extremely high efficiencies (>90 percent) may be possible for the gyro-peniotron. Stable operation of the gyro-peniotron oscillator requires, however, that mode competition from the electron cyclotron-maser interaction be avoided. This mode competition can be quite serious since the cyclotron-maser start-oscillation currents are generally much smaller than those from the peniotron interaction. We examine here the start-oscillation conditions for the peniotron and the electron cyclotron-maser interactions from linear theory. Both large-orbit axis-encircling and small-orbit off-axis electron beams are investigated. Conditions under which a gyro-peniotron oscillator may be operable are presented, including the important limitations on the spread of the beam guiding center. The results of this study indicate that mode competition for the gyro-peniotron can be easily avoided for TE211 and other low-order azimuthal modes when a large-orbit axis-encircling beam is used. Serious mode competition and gyro-peniotron suppression is found for small-orbit off-axis beams.     

矩形口径离轴非球面镜的加工与检测

介绍了240mm×180mm矩形口径离轴双曲面反射镜的加工与检测。提出了一种通过配块把矩形镜拼接成母镜来实现离轴镜加工的方法。完成了最佳比较球面和最大非球面度等工艺参数的计算。抛光阶段的非球面检测采用零位补偿法,其中零位补偿器是补偿检验中的关键元件。该离轴双曲面镜的最终面形RMS达到了0.02λ,满足了设计要求。     

fs激光在靶背表面产生的质子束成丝

 介绍了利用3TW/60fs钛宝石超短超强激光与20μm铜薄膜靶相互作用的实验。实验观测到质子束的角分布随激光功率密度有所变化。在较高的功率密度（～1×10¹⁸ W/cm²）时，观测到环状的质子束分布，发散角较大。在较低的激光功率密度（～2×10¹⁷ W/cm²）时，质子束发散角减小，质子束出现成丝现象。质子束的角分布实际上反映了从靶前输运到靶背的超热电子电流横向分布。在输运过程中，由于Weibel不稳定性会使超热电子电流出现空心化并最后破裂成丝。     

基于液晶空间光调制器的激光束整形

采用相位混合算法(PMA)与平滑修正法相结合的混合算法,对激光发出的高斯光束进行整形,得到了均方误差和顶部不均匀度均明显降低的等光强分布。利用液晶空间光调制器(LCSLM)的相位调制特性,实现了对高斯光束的光束整形,获得了光强均匀分布的圆光束和矩形光束输出。得到的输出光束顶部不均匀度和均方误差都低于5%,能量集中度在90%以上。表明此方法是一种实时、可控和高效的激光束整形方法。     

Development of dosimetry tools for proton therapy research

Dosimetry tools for proton therapy research have been developed to measure the properties of a therapeutic proton beam. A CCD camera–scintillation screen system, which can verify the 2D dose distribution of a scanning beam and can be used for proton radiography, was developed. Also developed were a large area parallel-plate ionization chamber and a multi-layer Faraday cup to monitor the beam current and to measure the beam energy, respectively. To investigate the feasibility of locating the distal dose falloff in real time during patient treatment, a prompt gamma measuring system composed of multi-layer shielding structures was then devised. The system worked well for a pristine proton beam. However, correlation between the distal dose falloff and the prompt gamma distribution was blurred by neutron background for a therapy beam formed by scattering method. We have also worked on the design of a Compton camera to image the 2D distribution of prompt gamma rays.     

A technology for the calculation and manufacture of devices for shaping a proton beam in radiotherapy

A therapeutic proton beam for an actual irradiation procedure is shaped using customized collimator leaves made out of Cerrobend, while to make the proton-beam depth-dose distribution conformal to the target volume, so-called boluses (compensators) with sophisticated shapes are calculated and then fabricated to compensate for the heterogeneities of a patient??s tissues and organs in the beam path. This article describes the main stages of testing a technology for manufacturing bolus from industrial wax which was developed at the Medico-Technical Complex (MTC) at the Dzelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research (DLNP JINR), by comparing the spatial dose distributions obtained under a computer simulation of proton irradiation and the actually measured ones under the experiment.     

Gafchromic® EBT films for ion dosimetry

For dose delivery to patients, scanning ion beams are going to be increasingly used in the upcoming ion beam therapy facilities. Especially carbon ion beams are able to produce steep dose gradients. However, the currently used method for patient dose verification, employing ionization chamber arrays, provides a spatial resolution of 1 cm only. As continuous media, EBT films, widely used in photon therapy, are interesting candidates to be used for this purpose. The EBT film is the ancestor of the currently available EBT2 film. In our contribution two dimensional dosimetry and film response quenching in ion beams were investigated. For a real ¹²C patient plan a good qualitative agreement with the planned dose distribution including a high signal-to-noise ratio and a good resolution in the measured photon-equivalent dose was found. The depth-dose response of EBT films for a ¹²C ion beam shows response quenching, which rises towards the Bragg peak. It was quantified by the relative efficiency determined at different depths. Furthermore, the relative efficiency was measured in monoenergetic proton and carbon ion beams. All the measured efficiencies show no significant dependency on the dose up to the highest measured doses of 6 Gy. However, differences between proton and carbon ions as well as between carbon ion beams of different energies were observed. The measurements reveal, that the use of EBT films for absolute dose verification measurements requires to take the relative efficiency into account, dependent on the ion type and energy.     

In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co⁶⁰ gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co⁶⁰ neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy^?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.     

Investigation of chromosome damage in human cells irradiated by beam for proton therapy produced by phasotron at the joint institute for nuclear research

The physical characteristics of the proton beam produced by a phasotron at JINR for radiation therapy are given. Chromosome damage in cells on the model of human blood lymphocytes irradiated by the initial proton beam with an energy of 170 MeV at the entrance to the object and in the Bragg peak region is studied, which corresponds to the irradiation of surrounding tissues along the beam path and tumor tissues. High proton efficiency in the Bragg peak is shown. RBE in the Bragg peak is ～1.25 in the dose range 1–4 Gy, while the proton efficiency of the initial beam is the same as that of standard γ radiation. Since delivering a dose to a tumor is performed by irradiating the patient from several directions (up to 7), the level of cytogenetic damage to cells of the surrounding tissues on the path of the initial beam is reduced by approximately an order of magnitude. Thus, for a dose of 3 Gy in a tumor, up to 80% of its cells are damaged, while the level of damage in the surrounding tissues does not exceed 10%. The results of investigations confirm the high efficiency of proton beams for radiation therapy.     

质子束治疗中非均匀组织的等效水厚度修正研究

非均匀组织等效水厚度修正是研究质子放射治疗的重要组成部分, 利用蒙特卡罗Fluka2011.2程序模拟了不同能量(50–250 MeV)的质子束入射到不同介质中的输运过程, 总结出了在不同介质中质子束初始能量与质子束Bragg峰深度关系, 并拟合出质子束在介质中的等效水厚度修正公式. 结果表明, 对不同能量的质子束入射到非均匀组织中, 通过拟合公式计算出Bragg峰深度值与Fluka模拟的质子束Bragg峰的位置相差在1 mm 之内. 如果建立起介质和水的Bragg峰比与电子密度比关系的数据库, 该公式有可能用于临床上的质子放射治疗的剂量计算中. 关键词： 蒙特卡罗 质子治疗 等效水厚度 Bragg 峰     

Study correlation vortices in the near-field of partially coherent vortex beams diffracted by an aperture

We have derived the analytical expression of the electric cross-spectral density in the near-field of partially coherent vortex beams diffracted by an aperture. Taking the Gaussian Schell-model vortex beam as a typical example of partially coherent vortex beams, the spatial correlation properties and correlation vortices in the near-field of partially coherent vortex beams diffracted by a rectangle aperture are studied. It is shown that the off-axis displacement, spatial degree of coherence parameter, propagation distance, and the opening factor of the aperture affect the spectral degree of coherence and positions of correlation vortices. With the optimization algorithm, we obtain the symmetric distributing coherent vortex.