基于闪烁凝胶的放疗二维剂量验证系统研制及可行性研究

为实现放疗二维剂量验证结果的实时、高分辨获取,基于灌装好的组织等效闪烁凝胶材料和相机等光学元器件搭建了剂量测量系统,并对该系统在IMRT质控剂量验证中的可行性进行实验验证。采用TPS剂量值对放疗均匀射束闪烁凝胶发光图像的像素灰度值进行标定。构建便于分区域对比分析的放疗计划,利用标定系数将凝胶闪烁光分布转换为剂量的二维分布。利用平板电离室对放疗计划进行测量,将凝胶系统与平板电离室的测量结果进行对比。结果显示,凝胶系统的测量分辨率远高于平板电离室;在有效成像区域内,凝胶系统的测量结果与平板电离室测量结果相对误差小于5%。这充分说明基于闪烁凝胶的放疗二维剂量验证系统在IMRT质控剂量验证中具有较高的可行性,尤其是对高剂量梯度放疗计划的实时、高分辨验证,后续深入开发可用于临床剂量验证。     

凝胶剂量计调强放射治疗三维剂量验证初探

调强放射治疗(IMRT)是最先进的放射治疗技术之一,因其复杂性和三维治疗计划系统的逆向计算的优化算法在某些方面还不够成熟,所以治疗前必须进行剂量验证以确保治疗剂量的准确性.本文使用聚合物凝胶剂量计对调强放射治疗三维剂量的验证进行初步探索.用丙烯酰胺、明胶、交联剂、除氧剂在常氧条件下制备凝胶剂量计,使用调强放射治疗计划对...     

Fricke凝胶剂量计在毛细管中的扩散限制及校正

在放射治疗中,吸收剂量空间分布的准确测定是决定放疗效果的关键。通常Fricke凝胶剂量计用于空间剂量分布的测量,但Fricke凝胶剂量计存在Fe~(3+)扩散问题,限制了剂量计测定的准确性,导致剂量验证产生误差。提出毛细管型Fricke凝胶剂量计,通过物理限制与化学限制的方法,限制Fe~(3+)在二维方向上扩散问题,反演推导实现Fe~(3+)在一维方向上的扩散校正。在一维方向上构建毛细管型Fricke凝胶剂量计结合二分之一合并法的图像处理方法,实现对Fricke凝胶剂量计的准确校正。为临床吸收剂量空间分布的准确测定提供良好的前景。     

γ图像重构放射源三维分布的物理模型设计

快速测定放射性物质污染的位置、分布、剂量对核安全有重要意义。γ相机成像是快速测定核污染位置二维图像的主要手段,用二维图像重构核污染位置三维分布是一种实现快速测定核污染位置、分布的主要技术。通过对γ相机成像过程进行研究,建立了放射源三维分布重构对应的物理模型,并在ML-EM重建算法下得到基本正确的结果。     

辐射法制备Fricke凝胶剂量计

辐射剂量验证技术是肿瘤放射治疗过程中的关键技术,Fricke凝胶剂量计因其制备简单、组织等效性好正逐步成为研究的热点。本研究采用辐射交联"一步法"制备Fricke凝胶剂量计,利用傅里叶红外光谱仪(Fourier transform infrared spectrometer,FTIR)、X线衍射仪(X-ray diffractometer,XRD)与热重分析仪(Thermo-gravimetric analyser,TGA)等仪器对凝胶样品的化学结构和成分进行了分析,利用分子动力学模拟研究了亚铁离子在凝胶剂量计中的扩散行为,并在医用加速器下对凝胶进行辐照,利用多功能酶标仪测定凝胶的辐射剂量响应。结果表明,辐射法制备的Fricke凝胶剂量计中,聚丙烯酸链可以抑制亚铁离子在凝胶样品中的扩散行为,添加二甲酚橙(Xylenol orange,XO)可以改善Fricke凝胶剂量计的剂量敏感性。     

基于康普顿成像系统的碳离子治疗剂量监测研究

为实现碳离子治疗的精准放疗,精确监测患者体内的三维剂量分布,本文设计一种双层康普顿成像系统和简单反投影算法,利用Geant4仿真软件优化探测系统的结构,评估探测系统的探测效率、成像性能,分析200 MeV/μ的碳离子束轰击有机玻璃（PMMA）靶的三维剂量分布。此外,还使用四对像素1.5 mm×1.5 mm×10.0 mm、12×12阵列型的硅酸钇镥（LYSO）晶体对直径约为3 mm的²²Na点源进行康普顿成像实验,并对影响三维剂量监测精度因素进行分析。结果表明,对于0.847 MeV的γ点源,重建图像在横截面上半高宽（FWHM）增加至2.38 mm、冠状面上扩展至7.02 mm。康普顿成像系统通过探测碳离子束轰击PMMA靶产生的4.439 MeV瞬发γ射线,重建的三维剂量分布与真实三维剂量分布偏差为9.3%。利用LYSO康普顿成像系统样机的²²Na点源成像实验,得到半高宽为4.05 mm的重建图像,验证了康普顿成像方法的实用性。     

基于Geant4的碳离子治疗三维电离室阵列仿真设计

为快速准确地实现碳离子治疗计划的三维剂量验证，采用有机玻璃PMMA(聚甲基丙烯酸甲酯)为电离室室壁和水等效模体，设计了一种三维电离室阵列，并通过Geant4软件对三维电离室阵列的结构设计进行了深入研究与验证。首先通过模拟不同能量碳离子束在水和PMMA模体中沉积的剂量分布，计算了PMMA模体的水等效厚度系数；然后研究了三维电离室阵列中电离腔室间的距离及信号导线对其剂量测量准确度的影响；最后模拟并验证了碳离子束在三维电离室阵列中沉积的剂量分布。结果表明：PMMA模体的水等效厚度系数为1.151;相邻电离腔室间的信号串扰主要来源于前侧的电离腔室，且串扰程度与电离腔室间距呈反比，间距为1 mm时串扰程度占电离腔室内剂量的3%,间距为30 mm时串扰影响可完全消除；信号导线对后侧电离腔室内剂量的干扰影响约为1%。将碳离子束在三维电离室阵列中沉积的剂量分布与PMMA模体中的剂量分布进行对比，碳离子束的射程具有良好的一致性，偏差为0.5 mm。     

粒子通量场的建立与研究

为了开展反应堆压力容器中子辐照损伤、射线辐照生物效应等方面的研究,研究了蒙特卡罗通量计算技巧,建立了形成大范围粒子的精细通量分布的快速方法,并可以根据介质的不同转换为剂量场分布。 利用上述手段,进行了大探伤加速器实时成像技术中的研究和体部伽玛刀准直器辅助设计中的应用。 基于人体内剂量场计算的粒子源组织间三维立体定向肿瘤治疗计划系统也正在研制中,很快将投放市场。     

基于锥形束CT图像的肿瘤放疗计划剂量计算可行性分析

随机选取40例(头颈部组、胸部组、腹部组、盆腔组各10例)不同部位的Rapid Arc病例,首先导出所有病例首次治疗时位置验证产生的锥形束电子计算机断层扫描(Cone-beam computed tomography,CBCT)原始投影文件,用自行开发的锥形束CT图像处理工具(Cone-beam CT imaging toolkit,CITK)对CBCT投影进行散射校准并三维重建为0.5 cm层厚的断层CBCT图像;然后用Eclipse软件将计划CT图像与该病例对应的CBCT图像进行配准并将计划CT上勾画的靶区等结构映射到CBCT图像上保存;接着用相同的处方剂量和优化条件设计放疗计划,采用各自的HU-ED标定曲线进行剂量计算后生成剂量体积直方图(Dose volume histogram,DVH)并导出;最后计算所有DVH的剂量分布指数(Dose distribution index,DDI)值,用配对t检验分析两种方法的结果是否存在差异。结果显示,4组病例中只有胸部组病例有统计学差异(t=2.284,p0.05),其余组病例均无统计学差异(p0.05)。实验结果提示,在对CBCT图像进行有效的散射校准并标定对应的HU-ED曲线后,其可用于肿瘤放疗计划的剂量计算。     

放疗加速器束流剂量实时成像系统

介绍了一种放疗加速器束流剂量实时成像系统，采用数字化脉冲X射线成像技术获取放疗加速器的束流强度分布图像，并利用数字图像处理技术生成实时3D剂量图。利用该系统可以实时、直观地获得加速器束流强度的相对分布曲面，给出任意剖面的束流强度分布曲线和FWHM、半影、峰值、对称度、均整度等参数。利用本系统的实时性，在国内首次实现了放疗加速器动态楔形剂量分布和束流过渡过程的测量。给出了系统配置和实测的放疗加速器束流强度分布图像。     

Optical analysis of gel dosimeters: Comparison of Fricke and normoxic polymer gels

The dosimetry method based on optical analysis of gel layers has been experienced utilising both Fricke and polymer (normoxic) gels. The aim of the work was that of investigating the potentiality of a normoxic polymer gel and of performing a further verification of the reliability of Fricke gel dosimeters. Optical absorbance was measured, both with a spectrophotometer and by imaging light transmittance detected with a CCD camera. The results of the study of sensitivity, linearity of the response and reproducibility of the polymer gel dosimeter have shown acceptable performances, except for doses below 2 Gy. The linearity range extends up to 20 Gy. On the other side, dose images and profiles have shown noticeable differences when compared to those calculated or measured with ionisation chambers or Fricke gel dosimeters. Such Fricke dosimeters have given further confirmation of their reliability.     

反应堆堆外中子剂量测量技术试验验证

堆外中子剂量测量技术在反应堆压力容器辐照监督中有广泛的应用。本文介绍了在国内某试验堆上进行的堆外中子剂量测量技术验证试验及其结果。比较了堆外中子剂量测量所用探测片活度的理论计算值、实测值及解谱计算结果,同时分析对比了试验中各辐照位置处中子能谱的理论计算值及解谱结果。结果表明,基于测量值的解谱结果与理论计算结果符合良好。堆外中子剂量测量技术可以有效完成中子能谱测量。     

A Comparative Study of the Effect of Calibration Conditions on the Water Equivalence of a Range of Gel Dosimeters

Gel dosimeters are of increasing interest in the field of radiation oncology as the only truly three-dimensional integrating radiation dosimeter. There are a range of ferrous-sulphate and polymer gel dosimeters. To be of use, they must be water-equivalent. On their own, this relates to their radiological properties as determined by their composition. In the context of calibration of gel dosimeters, there is the added complexity of the calibration geometry; the presence of containment vessels may influence the dose absorbed. Five such methods of calibration are modelled here using the Monte Carlo method. It is found that the Fricke gel best matches water for most of the calibration methods, and that the best calibration method involves the use of a large tub into which multiple fields of different dose are directed. The least accurate calibration method involves the use of a long test tube along which a depth dose curve yields multiple calibration points.     

主动式电离辐射剂量仪的脉冲X射线响应特性研究

国际上对于辐射防护剂量学的研究主要针对连续辐射,然而脉冲式电离辐射在工业探伤、X射线诊断、闪光X射线照相技术、安检和科研等领域中得到了广泛应用。主动式电离辐射剂量仪采用稳态辐射场进行刻度,难以准确测量短脉冲、高剂量率的脉冲式电离辐射。为了解主动式电离辐射剂量仪的脉冲响应特性,基于毫秒级脉冲X射线机搭建脉冲X射线参考辐射场,针对常用4款主动式剂量仪开展脉冲X射线响应特性测试。测试结果表明,目前常用4款主动式剂量仪均不适用于短脉冲、高剂量率辐射场的剂量测量和预警。     

Investigation of optimal scanning protocol for X-ray computed tomography polymer gel dosimetry

X-ray computed tomography is one of the potential tool used to evaluate the polymer gel dosimeters in three dimensions. The purpose of this study is to investigate the factors which affect the image noise for X-ray CT polymer gel dosimetry. A cylindrical water filled phantom was imaged with single slice Siemens Somatom Emotion CT scanner. The imaging parameters like tube voltage, tube current, slice scan time, slice thickness and reconstruction algorithm were varied independently to study the dependence of noise on each other. Reductions of noise with number of images to be averaged and spatial uniformity of the image were also investigated. Normoxic polymer gel PAGAT was manufactured and irradiated using Siemens Primus linear accelerator. The radiation induced change in CT number was evaluated using X-ray CT scanner. From this study it is clear that image noise is reduced with increase in tube voltage, tube current, slice scan time, slice thickness and also reduced with increasing the number of images averaged. However to reduce the tube load and total scan time, it was concluded that tube voltage of 130 kV, tube current of 200 mA, scan time of 1.5 s, slice thickness of 3 mm for high dose gradient and 5 mm for low dose gradient were optimal scanning protocols for this scanner. Optimum number of images to be averaged was concluded to be 25 for X-ray CT polymer gel dosimetry. Choice of reconstruction algorithm was also critical. From the study it is also clear that CT number increase with imaging tube voltage and shows the energy dependency of polymer gel dosimeter. Hence for evaluation of polymer gel dosimeters with X-ray CT scanner needs the optimization of scanning protocols to reduce the image noise.     

高剂量水平吸收剂量测量用辐射变色薄膜剂量计研究

为建立制备高剂量水平吸收剂量测量的辐射变色薄膜剂量计的方法,对相应的配方及制备工艺进行研究,批量制备了以尼龙为基材,副品红氰化物为染料的辐射变色薄膜剂量计。在60 Coγ参考辐射场中对辐射变色薄膜的各剂量学响应性能进行了研究,结果表明,重复性好于1.0%,在5~210kGy剂量范围内具有较好的剂量响应线性,辐射变色薄膜剂量计辐照后置于低温条件下贮存2周内信号较稳定。此外,该辐射变色薄膜剂量计在本实验范围内未发现明显的剂量率依赖性。通过上述剂量学性能研究,在线性剂量范围内,测量吸收剂量的扩展不确定度为4.2%(k=2)。通过在加速器上进一步实验表明,该膜可用于电子束辐照参数测量。     

头部CT扫描时受检者剂量研究

应用热释光剂量和头部CT剂量监测模体,在日立W-1000型机器上测定了模体中心和距体表1cm处,单层和多层扫描时的剂量分布。给出了单层扫描时,散射线所致剂量与扫描中心距离的拟合方程,分析了用不同积分区间计算CT剂量指数（CTDI）时对结果的影响。为今后进行广泛的CT受检者的剂量监测,推广使用国际电离辐射防护和辐射源安全基本标准（IBSS）推荐的CT受检者剂量指导水平提供统一标准。并对CT剂量监测中一些值得关注的问题进行探讨。     

Thermally Stimulated Current Radiation Dosimeter

Thermally stimulated current (TSC) radiation dosimeters were made from the borosilicate sealing glass used to make transistor headers. These dosimeters, consisting of a metal-glass-metal sandwich structure with electrodes (Kovar or Nicoseal) bonded to the glass with glass-to-metal seals, were experimentally studied to determine how they operate, and how they can be used in the design of a practical dosimetry system. Exposure to ionizing radiation (Co60-gamma or 175 kV X-rays) created trapped charge in the glass. Heating the dosimeter from one side, so as to produce a temperature gradient across the glass, released the trapped charge and produced a TSC which was observed as a TSC vs. temperature glow curve. The integrated charge output from a dosimeter was proportional to the radiation dose. This output for a given dose increased with increasing temperature gradient but was relatively independent of the heating rate. Eiectrodes that were pressed against the glass rather than bonded with a glass-to-metal seal were found to yield large current reversals and thus are unsuitable for dosimetry applications. A simple model is proposed to explain the origin of the TSC and the qualitative behavior of this current. The TSC dosimeter is small, rugged, and inexpensive. Because it produces an electrical output, it requires simpler readout equipment than other dosimetry systems currently available, such as the LiF, TLD system. Its main disadvantage is the rapid fading of the stored charge in the glass at room temperature (~50 percent five hours after irradiation).     

丙氨酸／EPR剂量标定及对电子直线加速器辐照场的测量

用标准丙氨酸剂量计对ER-200D型电子顺磁共振仪进行标定,并利用这一标定结果对合肥国家同步辐射实验室的200MeV直线加速器周围的辐射场进行了测量,获得了满意的结果。