一种用于多叶准直器适形放疗的剂量算法研究

描述了一种用于多叶准直器适形放疗的剂量计算方法。 在不同大小的方野和非规则野照射情况下, 将此方法得到的剂量分布与微分卷积法计算得到的剂量分布进行了精度验证。 结果表明, 这种算法具有较高的剂量精度和较快的计算速度, 因此可在适形放疗中用作MLC适形野的自动生成。 A dose calculation algorithm for MLC based conformal radiotherapy is described in this paper. The algorithm is formulated by the coordinate of MLC leaves. Verification on the algorithm is made by comparing the dose distributions generated by this algorithm with that generated by a Differential Convolution Superposition algorithm for various regular and irregular fields. The results demonstrate that the present algorithm has suitable accuracy and high computational efficiency, thus it could be useful for the treatment planning process in MLC based conformal radiotherapy, where the workload for interactively or automatically designing the shapes of MLC is heavy.     

绝对检验参考镜误差分析与热变形模型建立

绝对检验是提高菲佐(Fizeau)型干涉仪参考面面形精度的重要方法.研究了过程中温度、重力和夹持力对绝对检验精度的影响.采用Gram-Schmidt拟合方法对参考面面形的变形量进行了拟合,分析了K9、融石英和微晶材料的参考镜均匀温度变化下的热变形及由于热变形导致的相应泽尼克(Zernike)系数的变化.最后,分析了变形...     

基于中国参考人体素模型环境外照射剂量转换系数的计算

基于中国参考人体素模型计算地面污染和空气浸没情况下环境外照射剂量转换系数,主要用于核事故情况下公众及工作人员有效剂量的快速估算.首先,采用二次源项方法,基于Geant4模拟进入人体周围圆柱面入射光子的高度、角度和能量分布;其次,利用中国参考人体素模型和二次源项结果作为MCNPX模拟的输入项,计算15 keV至10 MeV能量范围内20组单能光子外照射剂量转换系数,和文献数据吻合;最后,利用ICRP第107报告核素衰变程序并对单能光子外照射剂量转换系数进行插值,计算了核事故情况下68种常见核素外照射剂量转换系数.与本文结果对比,国标中用于快速估算人员受照剂量转换系数值在地表沉积情况下偏保守,而空气浸没下中高Z放射性核素则偏低.     

混合笔束模型在电子剂量算法中的应用

将双群模型计算的宽束电子的能量沉积与FermiEyges理论的侧向解相结合来构造电子笔束模型,即混合笔束模型.由于混合笔束模型的计算精度和效率较好,并且适用范围较大,因此,混合笔束模型展示了在放射治疗临床应用上的可能性.在混合笔束模型的基础上,改进了混合笔束模型对电子侧向分布的参数计算.计算结果表明,改进的混合笔束模型的精度符合临床应用的要求,同时,其计算速度非常快.因而显示出较好的临床应用价值 关键词： 笔束模型 双群模型 混合笔束模型     

基于扩展卡尔曼滤波算法的船载绝对重力测量数据处理

基于冷原子干涉仪的高精度绝对重力动态测量为海洋重力测量提供新的手段,因而备受关注.利用自己搭建的船载冷原子干涉式绝对重力测量系统,在中国南海某海域开展了一系列测量实验.在动态条件下,测量噪声的抑制对测量性能的提升至关重要.本文根据船载绝对重力动态测量系统的物理模型,提出了一种基于扩展卡尔曼滤波算法的动态绝对重力数据处理方法,对观测的原子干涉条纹数据进行了时域滤波处理,获得了绝对重力值的最优估计.基于该处理方法将航速小于2.1 km/h条件下的绝对重力测量灵敏度从300.2 mGal/Hz^1/2提升至136.8 mGal/Hz^1/2(T=4 ms).此外,将处理后的数据与利用地球重力模型(XGM2019)计算的数据进行了比对,发现两者符合度较好.这些结果证实了本文提出的数据处理方法的有效性,并为船载冷原子干涉式绝对重力测量系统的测量噪声的抑制提供了一种新的处理方法.     

非圆截面环流器硬X射线辐射强度的绝对测量

本文给出了逃逸电子在孔拦上轰击出的硬X射线能谱及其辐射强度,描述了硬X射线闪烁谱还原成能谱的分析处理法,并对NaI(T1)探测器的绝对光峰效率进行了测量。     

绝对方位问题封闭形式最优估计的快速算法

提出一种快速的绝对方位问题算法,通过最小二乘法构造目标函数,对目标函数中的旋转矩阵和平移向量进行分离,利用矩阵的Fobenius范数、行列式以及伴随矩阵等构造旋转矩阵和平移向量封闭形式的最优估计。这种算法具有较高的计算精度和抗噪声性能,并且避免了目前常用算法中的奇异值分解运算,从而提高了计算速度。数学实验结果表明,在计算精度与抗噪声能力上与目前性能最优的Umeyama算法相当,同时计算速度较之有大幅提升,尤其适用于对实时性要求较高的领域。     

低能重离子剂量-存活率效应及其拟合模型探讨

低能重离子注入生物体是20世纪80年代中期发展起来的一种诱变手段, 在诱变育种和放射医学等领域有巨大的应用前景。 物理辐照的剂量与存活率之间的关系是辐射生物学效应的最重要的关系之一, 低能离子与生物体相互作用的剂量 存活率曲线表现为特殊的马鞍型。 介绍了低能重离子的马鞍型剂量 存活率效应及其数学模型, 并探讨了模型拟合中存在的一些问题。 Low energy heavy ion implantation is an organism mutation method developed in middle of 1980s, which has a potential application in breeding and radiation therapy. The dose survival curve is a characteristic effect in radiobiology. Implanted with low energy heavy ions, organisms could manifest a Saddle like dose survival curve. In this article, the Saddle like dose survival effect and its modeling has been described, and several topics in model simulation are discussed.     

基于奇偶函数分解算法的绝对检验对比研究

奇偶函数法与N次旋转法是平面绝对检验方法中常用的两种方法,这两方法在恢复面形的过程中都使用了奇偶函数分解算法,但是在求解奇奇项方面使用的方法不同,对比了这两种绝对检验方法。在奇偶函数法与N次旋转法的算法仿真过程中加入待测平晶重力形变的有限元分析,并对100mm口径平晶进行奇偶函数法与N次旋转法实验,将面形恢复结果与液面法测量结果对比,结果显示奇偶函数法恢复面形的PV值差值为4.864nm,N次旋转法恢复面形的PV值差值为1.853nm。结果表明存在重力影响时,N次旋转法恢复面形精度优于奇偶函数法。仿真分析旋转角度误差对于奇偶函数法与N次旋转法的影响,结果显示N次旋转法抗旋转角度误差能力强于奇偶函数法。     

剂量引导精确放射治疗中三维评价算法设计及实现

针对临床剂量学验证中二维评价方法只能反映每张平片上剂量分布情况, 并根据剂量引导精确放疗系统中三维剂量验证需求设计算法实现对三维剂量分布的比较。 根据公式, 在Visual C++控制台下实现剂量偏差、 位置偏差及γ分析三维评价算法。 设计两个计划进行算法验证: 计划1为方野照射等效水, 用于验证算法的正确性; 计划2为适形野照射仿真头模, 用于验证算法的实用性。 结果表明, 计划1中, 对剂量偏差,容许值范围内通过率为100%; 对位置偏差和γ分析, 容许范围内通过率为100%,容许边界值处为100±7.7%。 计划2中, 3种算法通过率分别为88.35%、100%和95.07%。 这说明该算法可用于剂量引导精确放疗系统中实现三维剂量分布的评价。     

康普顿探测器优化设计

康普顿探测器可以获得脉冲X射线照射量随时间变化的波形,探测器特性主要由收集体、介质和金属外壳的材料、尺寸决定。针对神龙一号加速器产生的X射线的能谱结构,应用蒙特卡罗模拟方法,进行探测器结构尺寸设计,获得最佳的有机玻璃介质厚度为30 mm。探测器灵敏度系数随X光能量变化的曲线表明其能量响应较差,分析与计算结果表明在收集体前加低Z金属可有效改善能量响应特性并提高灵敏度系数。计算得到用于测量神龙一号加速器的X射线照射量的康普顿探测器的灵敏度系数为6.86×1011(C/kg)-1。     

混沌系统模型误差平均绝对误差增长过程研究

混沌系统的平均绝对误差增长最初是用来刻画初始值误差增长的,本文依照平均绝对误差增长的定义来研究模型误差的增长过程,获得了一些很有意义的结论．研究发现,在初期模型误差的平均绝对误差增长呈指数级增长,增长指数同模型的扰动相关,与真实系统最大Lyapunov指数没有直接关系．其后模型误差进入非线性增长过程,误差增长放缓,最终达到饱和．误差饱和值恒定,当真实系统和模型系统吸引子差别较小时,模型误差饱和值基本上同真实系统的初始值误差饱和值相等．利用上述研究结论可以求出模型的可预报期限,这在数值天气预报中具有重要的意义．进而利用模型的可预报期限可以对同一真实系统的不同模型进行评价,相对真实系统越精确的模型拥有更高的可预报期限．这对新模型的开发具有很强的指导作用．     

A dose comparison of proton radiotherapy and photon radiotherapy for pediatric brain tumor

The purpose of this study was to investigate the effectiveness of photon radiotherapy and to compare the dose of treatment planning between proton radiotherapy and 3D conformal radiation therapy (3D-CRT) for pediatric brain tumor patients. This study was conducted in five pediatric brain tumor patients who underwent craniospinal irradiation treatment from October 2013 to April 2014 in the hospital. The study compared organs at risk (OARs) by assessing the dose distribution of normal tissue from the proton plan and 3D-CRT. Furthermore, this study assessed the treatment plans by looking at the homogeneity index (HI) and conformity index (CI). As a result, the study revealed OARs due to the small volume proton radiotherapy dose distribution in the normal tissue. Also, by comparing HI and CI between the 3D-CRT and proton radiotherapy plan, the study found that the dose of proton radiotherapy plan was homogenized. When conducting 3D-CRT and proton radiotherapy in a dose–volume histogram comparison, the dose of distribution turned out to be low. Consequently, proton radiotherapy is used for protecting the normal tissue, and is used in tumor tissue as a homogenized dose for effective treatment.     

基于P范数的核最小对数绝对差自适应滤波算法

为了进一步提高在a稳定分布噪声背景下非线性自适应滤波算法的收敛速度,本文提出了一种新的基于p范数的核最小对数绝对差自适应滤波算法(kernel least logarithm absolute difference algorithm based on p-norm, P-KLLAD).该算法结合核最小对数绝对差算法和p范数,一方面利用最小对数绝对差准则保证了算法在a稳定分布噪声环境下良好的鲁棒性,另一方面在误差的绝对值上添加p范数,通过p范数和一个正常数a来控制算法的陡峭程度,从而提高该算法的收敛速度.在非线性系统辨识和Mackey-Glass混沌时间序列预测的仿真结果表明,本文算法在保证鲁棒性能的同时提高了收敛速度,并且在收敛速度和鲁棒性方面优于核最小均方误差算法、核分式低次幂算法、核最小对数绝对差算法和核最小平均p范数算法.     

Experimental verification of therapeutic doses for the superficially-placed tumor radiotherapy with heavy ions at HIRFL

Up to now, clinical trials of heavy-ion radiotherapy for superficially placed tumors have been carried out for six times and over 60 selected patients have been treated with 80--100 MeV/u carbon ions supplied by the Heavy Ion Research Facility in Lanzhou (HIRFL) at the Institute of Modern Physics, Chinese Academy of Sciences since November, 2006. A passive irradiation system and a dose optimization method for radiotherapy with carbon-ion beams have been developed. Experimental verification of longitudinally therapeutic dose distributions was conducted under the condition of simulating patient treatment in the therapy terminal at HIRFL. The measured depth-dose distributions basically coincide with the expected ones. These results indicate that the irradiation system and the dose optimization method are effective in the ongoing carbon-ion radiotherapy for shallow-seated tumors at HIRFL.     

Experimental verification of therapeutic doses for the superficially-placed tumor radiotherapy with heavy ions at HIRFL

Up to now, clinical trials of heavy-ion radiotherapy for superficially placed tumors have been carried out for six times and over 60 selected patients have been treated with 80--100 MeV/u carbon ions supplied by the Heavy Ion Research Facility in Lanzhou （HIRFL） at the Institute of Modern Physics, Chinese Academy of Sciences since November, 2006. A passive irradiation system and a dose optimization method for radiotherapy with carbon-ion beams have been developed. Experimental verification of longitudinally therapeutic dose distributions was conducted under the condition of simulating patient treatment in the therapy terminal at HIRFL. The measured depth-dose distributions basically coincide with the expected ones. These results indicate that the irradiation system and the dose optimization method are effective in the ongoing carbon-ion radiotherapy for shallow-seated tumors at HIRFL.     

硅双极器件及电路电离总剂量辐照损伤研究

针对硅双极器件及其构成的双极集成电路有着如低剂量率辐照损伤增强效应等不同于其他类型电路的特殊的辐照响应问题, 分析了空间辐射电离总剂量环境及铝屏蔽作用, 双极晶体管及电路总剂量辐照损伤机理, 低剂量率辐照损伤增强效应、规律和电参数变化。通过选取几种典型的双极晶体管和电路进行地面辐照模拟试验和测试, 证明了双极器件及电路的关键参数受辐照影响较大, 特别是对低剂量率辐照损伤增强效应敏感, 低剂量率辐照损伤增强因子基本都大于1.5, 不同双极器件和电路的低剂量率辐照损伤增强效应有着明显的不同, 与器件类型、加工工艺(如氧化层厚度)等密切相关。     

Total ionizing radiation-induced read bit-errors in toggle magnetoresistive random-access memory devices

The 1-Mb and 4-Mb commercial toggle magnetoresistive random-access memories(MRAMs) with 0.13 μm and 0.18-μm complementary metal–oxide–semiconductor(CMOS) process respectively and different magnetic tunneling junctions(MTJs) are irradiated with a Cobalt-60 gamma source. The electrical functions of devices during the irradiation and the room temperature annealing behavior are measured. Electrical failures are observed until the dose accumulates to 120-krad(Si) in 4-Mb MRAM while the 1-Mb MRAM keeps normal. Thus, the 0.13-μm process circuit exhibits better radiation tolerance than the 0.18-μm process circuit. However, a small quantity of read bit-errors randomly occurs only in 1-Mb MRAM during the irradiation while their electrical function is normal. It indicates that the store states of MTJ may be influenced by gamma radiation, although the electrical transport and magnetic properties are inherently immune to the radiation. We propose that the magnetic Compton scattering in the interaction of gamma ray with magnetic free layer may be the origin of the read bit-errors. Our results are useful for MRAM toward space application.     

Renormalized-free-atom model and Compton profile of hcp cobalt

Compton profile of cobalt has been calculated employing the renormalized-free-atom model for fcc as well as hcp phases choosing several 3d-4s configurations. The results have been compared with recent gamma-ray measurements on polycrystalline Co. Best agreement between theory and experiment is found for 3d ⁷4s ² configuration. Comparison with free electron model has also been made for this case.     

双极线性稳压器电离辐射剂量率效应及其损伤分析

为了对双极线性稳压器在电离辐射环境下损伤变化特征及其剂量率效应进行研究,选择一组器件进行⁶⁰Co γ高低剂量率的辐照和退火试验. 结果表明线性稳压器的输出电压、最大负载电流、线性调整率、压降电压等多个关键参数都有不同程度的蜕变. 且各器件在高低剂量率下的辐照响应略有不同,表现出不同的剂量率效应. 文中通过多种形式的测试结果分析,系统地讨论了各参数变化的原因及其内部各模块对稳压器功能的影响. 结合电离损伤退火特性,探讨了各剂量率效应形成的原因. 这不但对工程应用考核提供了参考,而且为设 关键词： 双极线性稳压器 总剂量效应 剂量率效应 辐射损伤