Verification of the Dose Distributions With GEANT4 Simulation for Proton Therapy

A GEANT4-based simulation of an irradiation system for proton therapy has been developed for the verification of dose distributions. The simulation represents the treatment room and beam irradiation system at the Hyogo Ion Beam Medical Center (HIBMC). The beam irradiation system consists of a lateral beam-spreading system and a range modulating system, which enable a three-dimensional dose distribution to be achieved. The simulation was carried out for proton beams at the isocentric gantry nozzle for therapeutic energies of 150, 190, and 230 MeV. The simulated distributions were compared to measured dose distributions obtained by using a water phantom at the isocenter. This arrangement simulates the practical aspects of the beam irradiation of a patient. The validation of the simulation was performed in proton range for important materials in the beam line, and in the lateral uniformity of the radiation field at the isocenter. Dose distributions based on GEANT4 were verified with measurements of the Bragg peak and the spread-out Bragg peak. This verification shows that the simulations are in good agreement with measurements.     

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.     

Design and development of the beamline for a proton therapy system

A proton therapy(PT)facility with multiple treatment rooms based on the superconducting cyclotron scheme is under development at Huazhong University of Science and Technology(HUST).This paper attempts to describe the design considerations and implementation of the PT beamline from a systematic viewpoint.Design considerations covering beam optics and the influence of high-order aberrations,beam energy/intensity modulation,and beam orbit correction are described.In addition to the technical implementation of the main beamline compo-nents and subsystems,including the energy degrader,fast kicker,beamline magnets,beam diagnostic system,and beamline control system are introduced.     

Recent Progress Made in the SBS PCM Approach to Self-navigation of Lasers on Direct Drive IFE Targets

Current status of SBS PCM based IFE approach proposed recently as an alternative to the IFE classical approach is presented. This technology is of a particular importance to the direct drive scheme taking care of automatic self-navigation of every individual laser beam on the injected pellets without any need for final optics adjustments. An upgraded scheme was developed with a low energy illumination laser beam (glint) entering the reactor chamber through the same entrance window as used subsequently by the corresponding high energy irradiation laser beam. Experimental verification of this improved design was performed using a complete setup including a pellet—at this stage realized by a static steel ball of 4 mm in diameter. The pellet survival conditions between its low energy illumination and high energy irradiation were studied and the upper limits on the allowed energies absorbed for both DD and DT fuels were determined.     

用于蓝姆移动型极化离子源的低能强流双等源

建立了用于蓝姆移动型极化离子源的双等源和低能引出聚焦系统，实验比较了等离子体出口孔径和聚焦电极之间的距离对引出束的影响，并调整了离子源的运行参数。离子束的质子比可达６０％以上，满足了极化离子源的工作要求。约有４ｍＡ低能氢离子束（５５０ｅＶ）或氘离子束（１１００ｅＶ）进入铯蒸汽电荷交换管道，在极化源上使用低能强流双等源后，可获得２００ｎＡ左右的极化质子（或氘核）束。     

CSNS/RCS中主要阻抗元件的仿真计算研究

中国散裂中子源（CSNS）快循环同步加速器（RCS）是强流质子加速器,对环中真空元件的阻抗研究是判断束流能否稳定运行的重要依据。通过正确估算环中元件阻抗,可及时对元件的阻抗进行有效控制和防止束流不稳定性发生,从而减小束流损失。本文利用CST电磁场仿真软件给出了RCS环中高频腔及准直器的耦合阻抗,并探讨了bus-bar结构对高频腔本身及束流稳定的影响,发现需重新设计bus-bar结构使腔固有频率大于10 MHz才能彻底解决因共振可能引起的丢束。此外,计算表明,主准直器屏蔽有利于减小耦合阻抗及损失功率,在安装代价较小的情况下需对主准直器进行屏蔽。     

Nonlinear processes of probe formation of a beam with inhomogeneous phase density at nuclear microprobe

The work describes nonlinear processes of probe formation on the target with allowance for an inhomogeneous density of ion distribution in phase space in the object collimator plane taken from experimental data. The chromatic aberrations, intrinsic aberrations of the 3rd order and parasitic aberrations caused by sextupole and octupole components of the magnetic quadrupole lens field have been taken into account in the object-target phase coordinate transformation. The criterion of obtaining the optimal resolution was defined as the minimum spot size (FWHM) for a fixed ratio I_FWHM/I₀ of beam current in this spot to the total beam current. The conditions for which the initial density of ion distribution in phase space is matched with the ion-optical characteristics of the probe-forming system were considered. The influence of axial brightness and parasitic sextupole and octupole field components on the beam current distribution at the target has been determined.     

CSNS/RCS粒子散射束流损失研究

在中国散裂中子源快循环同步加速器（CSNS/RCS）中,质子束流在加速过程中会与一些器件（如剥离膜、准直器、散射引出膜等）相互作用,产生粒子散射并导致束流损失。本工作首先利用ORBIT模拟RCS束流注入过程,并用FLUKA模拟注入束流穿过剥离膜的粒子散射过程,计算剥离膜散射所造成的束流损失。其次,模拟质子束流与准直器相互作用的粒子散射,计算质子束流与不同尺寸的次级准直器相互作用的吸收效率,作为对次级准直器优化的依据。最后,研究CSNS/RCS膜散射引出方案,利用FLUKA对不同引出方案进行模拟并比较,得到最佳的可行性方案。     

100 MeV回旋加速器的高功率质子束流线研制

为调试100 MeV回旋加速器高功率束流及放射性同位素研制,设计了一条高功率质子束流线及可插拔式高功率束流调试靶。研究了100 MeV回旋加速器引出区色散效应及剥离膜的散射效应,从而优化了光学模拟的初始参数,使得模拟结果更加精确。高功率束流调试靶设计为可插拔式以代替常用固定式调试靶,该靶插入束流管道中时可进行高功率质子束流调试,在拔出时,质子束流可直接轰击束流线终端的靶站以生产放射性同位素。优化了高功率束流调试靶的水冷结构,确保调试靶可承受500 μA以上的质子束流。经调试,该束流线可传输最高流强520 μA的质子束流。     

Measurement of Resonance Activation Integral of 55Mn

The resonance activation integral of ⁵⁵Mn was measured relatively to that of ¹⁹⁷Au by absolute counting on ⁵⁶Mn and ¹⁹⁸Au: ⁵⁶Mn was measured with a Ge(Li) counter whose detecting efficiency for γ-rays had been previously determined by a set of IAEA calibrated γ-sources, while ¹⁹⁸Au was measured with a 4πβ-γ coincidence counter. The neutron spectrum was determined by p ₁ calculation and was verified by time-of-flight method.

The ratio I _1/v/I _res was obtained experimentally making use of boron filters of three different thicknesses.

The results were I _total= 14.1±0.6 barn and I _1/v/I _res =0.57±0.06, for a cutoff energy of 0. 63 eV.     

Cooling as a means of obtaining a bright and achromatic proton microbeam

An electron cooling ring for a 50 MeV proton beam is proposed for the University of Manitoba Accelerator Centre, With suitable extraction this system would produce 0.25 nA of monochromatic dc beam with a pulse length of 0.1 s deliverable within 1 μm².     

Peak load-impulse characterization of critical pulse loads in structural dynamics

The P-I characterization scheme greatly facilitates specification of critical loads for structures subjected to air blast loading and is generally useful for structures subjected to pulse loads. A general feature of the P-I characterization scheme is that critical load curves are represented reasonably well by a rectangular hyperbola

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, where P is the peak load, P₀ the step load required to produce the critical displacement, I the impulse, area under the load-time curve, I₀ the ideal (zero duration) impulse required to produce the critical displacement. This representation is useful for common structural elements such as beams, plates and shells. Some increase in accuracy is obtained by replacing the right-hand side with a constant C, determined by fitting to experimental results or to a theoretical critical load curve. A key feature of the P-I characterization scheme is that the critical load curves are not sensitive to pulse shape. The P-I characterization scheme contains the same information as the dynamic load factor (DLF). Although they contain the same information, these two characterizations emphasize different aspects. The DLF characterization displays the relation of dynamic loads to an equivalent static load. The P-I characterization displays equivalent dynamic loads in terms of peak load and impulse, the load parameters that are important at the long-duration and short-duration extremes.     

Beam stability improvement of the HIMAC synchrotron using a feed-forward system for magnet power supplies

In order to realize a precise dose distribution in heavy-ion cancer therapy, high beam stability is required for the accelerator complex. Owing to load fluctuation caused by the upper ring, which is one of the two rings in HIMAC, current dips of ≈5-10 Hz were observed in the power supply for the bending/quadrupole magnet of the other lower ring. The parameters of the beam stability, such as the spill variation, the beam position, and the size, were adversely affected by the current dips. In order to suppress these current dips, we developed a new feed-forward system in the magnet power supply. We verified the performance of the feed-forward system by measuring the suppression of the current dips. We also performed beam experiments to measure the variation of the horizontal tune and the structure of the beam spill, which is slowly extracted by the resonance method. The experimental result showed that the current dips were successfully reduced by the system to ΔI/I ∼ 10⁻⁶. It was also confirmed that the horizontal tune and the spill structure could be stabilized by the current dip suppression.     

Taper angle dependence of the focusing effect of high energy heavy ion beams by glass capillaries

The 6.4 MeV ¹⁵N²⁺ ion beams are focused using glass capillary optics. The transmitted beam includes ions which have suffered slight energy loss. The areal density of the transmitted beam is enhanced by approximately 10 times, and the enhancement factor does not depend on the incident beam current. The NRA spectrum intensity decreases with the increase of the capillary taper angle. These results all together suggest that the nuclear forward scattering is more significant in the focusing mechanism than the low energy ions case.     

Finite element analysis of crack propagation in three-dimensional solids under cyclic loading

This paper is concerned with an efficient computational procedure for analyzing crack propagation in solids. The method is general; however, its application to semi-elliptical surface cracks in thick plates is discussed in particular. The strain energy release rate G for a crack in mode I is a function of the crack geometry, the direction of crack propagation and the state of loading. When G is known, the stress intensity factor K_I can easily be obtained. In this paper the strain energy of the plate is computed numerically for a wide range of crack geometries using the finite element method. A 20-node isoparametric solid element is employed in modelling the structure. Certain special techniques for increasing the computational efficiency of the method, such as multilevel subdivision of the structure (substructuring) and condensation of degrees of freedom that are not needed in the crack propagation analysis, are emphasized. In fact, analysis of a large number of crack geometries requires only insignificantly more computational efforts than treating a single crack. Certain other aspects of the finite element modelling are also discussed.Two methods for replacing the computed discrete values of strain energy by continuous functions are presented. These functions are expressed in terms of the two half-axes defining the geometry of the elliptical crack and they are determined using a least square technique. G and K_I are easily deduced from these functions. As an example, a semi-elliptical, part-through, surface crack in a thick nickel steel plate is analyzed. The crack is subjected to a combination of axial and bending loading, applied cyclically. From the finite element calculations of the strain energy and the stress intensity factors which are computed accordingly, crack propagation along the two half-axes of the ellipse is calculated by utilization of a formula suggested by Paris. The results are checked against laboratory fatigue tests. The method has proved to be very efficient and accurate, and due to its generality it can also be applied to complicated geometries and complex states of loading.     

Physical Startup of the TWAC Storage Ring

C⁶⁺ ions with energy 200 MeV/nucleon have been accumulated in the chamber of the ring magnet of the U-10 proton synchrotron used as a storage ring in the TWAC setup. A C⁴⁺ ion beam from the laser source was first accelerated in the I-3 injector up to 1.3 MeV/nucleon and in the UK booster synchrotron up to final energy with periodicity 3.5 sec. Ions have been accumulated in U-10 using the multiple charge-exchange injection scheme C⁴⁺ C⁶⁺. An increase in the ion intensity in the accumulator has been observed during several injection cycles. Experimental data on the attained parameters of the accumulated beam are presented, and the status of the optimization of the accumulation regime is discussed.     

The use of a Perovskite crystal as a detector for proton beamcurrent

Using a Perovskite crystal, a thermal detector has been designed for measurements of proton beam currents. For a given energy, the detector has a linear response with current intensity and an inverse response with chopping frequency. Measurements up to 50 nA (4.5 MeV H ⁺) were carried out using a cyclotron, and a calibration curve is presented. The detector may be used over a wide range of energies, has a low cost, and is simple to construct. In addition, it can be used inside or outside vacuum, and it does not require an external bias field     

Rearranging a nanoprobe: Line foci,grid shadow patterns and performance tests

After a major modification of the target chamber at the Leipzig high energy ion nanoprobe the probe forming lens system, consisting of two separated quadrupole doublets, had been carefully realigned. This was done by adjusting the line foci position of each individual quadrupole on the centre position defined by the unfocused beam. Using a high magnification microscope the alignment process is very effective and precise. The lens system could be precisely realigned except an intrinsic rotational misalignment which is essentially reduced by a correction lens.Grid shadow patterns have been taken and analysed in order to assess the characteristics of the system. The dominant aberrations are spherical with an additional parasitic octupole.The grid shadow method is also very useful to determine the best position of the aperture diaphragms which minimizes the influence of the aberrations onto the beam spot size.The rearrangement allowed larger aperture diaphragms for higher beam currents at a moderate increase in beam spot sizes. Performance tests yielded proton microbeam currents and half-widths of 4.5 nA at 1.5 μm, 8.3 nA at 1.5 μm and 17.2 nA at 2 μm. For high resolution work the expected beam spots around 0.3 μm at 100 pA were not achieved. The reason is very likely interference on the beam scanner, correlated in x- and y-direction, which results from the insufficiently rectified power supply voltage of the transconductance amplifier.     

Computed tomography reconstruction from two transmission measurements for iodine-marked cancer detection

The authors invented the transXend detector, which measures X-rays as electric currents, and then gives the energy distribution of the X-rays after an unfolding process. In a previous paper, it was shown that the material thickness distributions can be estimated with the transXend detector by using reference points plotted from the electric current ratios, such as the I ₂/I ₁ ? I ₃/I ₁ graph, where I_i denotes the electric current measured by the i-th segment of the transXend detector. In this paper, the tomographic images of iodine, aluminum, and the acrylic those surround the other two materials are reconstructed from their material thickness distributions, which are estimated from two X-ray incidence directions. The X-ray event ratios are also used to estimate the material thickness distributions.