Geant4中不同物理列表对硼中子俘获治疗剂量分布的影响

Geant4是基于C++编写的开源蒙特卡洛模拟软件,提供多种包含中子与物质相互作用的物理列表。本研究采用Geant4提供的几种物理列表,对沿中子束方向的总吸收剂量、硼剂量和非硼剂量深度分布进行计算,并与FLUKA进行比较,模拟中子能量从0.025 3 eV到10 MeV。对于整个模拟中子能段,结果显示添加S（α, β）热模型的高精度中子物理列表（Geant4_HP_T）在总吸收剂量、硼剂量和非硼剂量深度分布上均与FLUKA符合很好,初步验证了Genat4能应用于硼中子俘获治疗（BNCT）相关研究。对于低能中子（<1 MeV）,S（α, β）热模型对BNCT剂量深度分布的影响较大,QBBC和QGSP_BERT不适用于BNCT剂量分布计算。     

胃癌单克隆抗体的硼化及其硼中子俘获治疗效应

胃癌单克隆抗体MGb2与硼化物Cs_2~(10)B_(12)H_(11)SH通过马来酰亚胺苯甲酸-N-羟基琥珀酰亚胺酯反应交联,每个单抗分子连接220个~(10)B原子。硼化抗体与人胃癌细胞SGC-7901孵育2h,可结合2.6×10~9 ~(10)B/细胞,是正常人胚肺细胞SL7的5.2倍,达到BNCT所需浓度。用~(125)Ⅰ标记MGb2-~(10)B,腹腔注射荷人胃癌裸鼠(SWISS DF nu/nu,370 KBq/只),第5天肿瘤摄取为10.14％1D/g,显著高于正常鼠IgG-~(10)B(1.19％ID/g),(P<0.01)。SPECT放射免疫显像可见~(125)Ⅰ-MGb2-~(10)B在肿瘤部位明显的放射性浓集,而胸腹腔放射性少。MGB2-~(10)B处理的胃癌细胞经49-2型核反应堆热中子照射(3.12×10~(11)n/cm~2,γ-射线0.84Gy),存活率30％,显著低于未照射组和非特异硼化物组(P<0.001),显示出导向硼中子俘获治疗效应。     

射野区域的剂量验证研究

目的:实现射野区域剂量分布Gamma（[γ]）通过率的计算,对治疗传输的准确性进行评估。方法:从Oncentra Masterplan治疗计划系统中随机提取6位完全匿名患者的调强放射治疗验证计划,导出DICOM格式的验证计划并利用Matlab软件重建多叶准直器区域和剂量。然后将验证计划移植到MatriXX模体并测量剂量分布。用Matlab代码对验证计划剂量分布和模体测量的绝对剂量分布进行分析。结果:传统方法[γ]通过率受计算区域选择影响较大,而以射野区域作为计算区域则避免了这个问题,两种方法计算得到的[γ]通过率有统计学差异（[P]<0.05）。结论:射野区域的剂量验证避免了[Dn]值对[γ]通过率的影响,而且对射野区域利用剂量面积直方图分析其剂量特性,有利于评估治疗计划系统临床治疗的准确性和指导临床工作。     

金标伪影对射波刀剂量计算及分布的影响

目的:分析金标伪影对射波刀剂量计算及分布的影响。方法:采用能谱CT的GSI扫描技术和MARS重建技术获取Lucy模体的原始CT图像和去除金标伪影后的CT图像,利用射波刀Multiplan?划系统对两组CT图像进行等中心计划设计计算,分析金标伪影对剂量计算及分布的影响。结果:金标伪影使CT图像伪影区域的CT值发生改变,最大可达63.22%,金标伪影低估了金标周围（伪影区域）正常重要组织的最大剂量值,高估了金标周围（伪影区域）正常重要组织的最小剂量值,高估了PTV的剂量覆盖率。结论:使用能谱CT可降低金标伪影对射波刀剂量计算及分布的影响。 【关键词】射波刀;金标伪影;剂量计算;剂量分布     

基于血管匹配的三维超声与CT图像的配准方法

提出一种基于血管匹配的三维超声与CT图像配准的新方法.首先,基于水平集方法自动分割出CT图像中的血管；其次,由于超声图像中的声影与血管均属于低回声区域,我们结合声影形成的物理原理及图像纹理特性,自动检测出声影区域,以提高配准的鲁棒性；最后,采用进化算法,将CT图像中分割出的血管与超声图像中低回声区域进行匹配.在肝脏体模和临床脾脏数据上进行了实验验证,自动配准的成功率在95％以上,平均目标配准误差在2 mm以内,实验结果验证了本方法的可行性.     

基于双目红外相机定位的自由式三维超声图像重建系统

目的:设计并实现自由式三维超声图像重建系统,该系统能对自由式采集的二维超声图像阵列进行三维重建与显示交互。方法:系统使用双目红外相机及其配套测量器件,在超声探头上固定定位小球,双目红外相机可以实时追踪探头的空间位置,从而获取超声图像阵列的相对关系。软件部分根据实时探头位置并计算转换矩阵,获取超声图像阵列的数据并填充三维体数据网格,使用光线投射法绘制图像。结果:该系统可以实现超声图像阵列的采集与存储、超声图像感兴趣区域勾画、三维重建与可视化功能。结论:该研究提出的基于双目红外相机定位的自由式三维超声图像重建系统对未来的临床使用以及科学研究奠定了良好基础。     

放疗计划系统DeepPlan光子放疗剂量计算的临床可行性验证

目的:评估DeepPlan放疗计划系统患者计划剂量计算的准确性和临床应用的可行性。方法:剂量算法准确性评估主要是针对YY 0775号和YY/T 0889号报告中的例题内容进行测量验证。临床病例验证是基于Pinnacle计划系统设计的前列腺肿瘤患者9例、胸部肿瘤患者13例和头颈部肿瘤患者5例，试验将各病例原计划优化的子野等信息直接导入DeepPlan进行重新剂量计算，比较不同计划系统得到的靶区和危及器官剂量分布，并用PTW VeriSoft软件对两组计算结果进行全空间剂量γ分析。结果:DeepPlan光子剂量算法通过了剂量计算准确性验证，YY 0775号报告中所有测试例题误差均在2%以内。YY/T 0889号报告中所有患者计划的γ通过率均在96.8%以上，复合野的γ通过率平均值为98.1%。在病例验证中，前列腺肿瘤病例的等中心层面2D γ通过率平均值为97.6%，3D γ通过率平均值为96.9%。胸部肿瘤病例的等中心层面2D γ通过率平均值为98.7%，3D γ通过率平均值为98.3%。头颈部肿瘤病例的中间层面2D γ通过率为98.6%，3D γ通过率平均值为98.8%。结论:通过模体实际测量和临床病例测试，验证了DeepPlan光子放疗剂量计算的准确性和临床应用的可行性。     

独立三维剂量验证在鼻咽癌容积调强放射治疗计划中的应用

目的:探讨独立三维剂量验证在鼻咽癌容积调强放射治疗（VMAT）计划中应用的可行性。方法:选取31例鼻咽癌患者的VMAT计划,采用Bland-Altman统计方法对基于独立三维剂量分布和实测重建三维剂量分布的一致性进行分析,从而论证独立三维剂量验证应用于鼻咽癌VMAT计划中的可行性。根据独立三维剂量验证的DVH图和γ通过率分类绘制出受试者工作特征（ROC）曲线,得到鼻咽癌VMAT计划中独立三维剂量验证的最佳γ通过率阈值。结果:鼻咽癌患者的VMAT计划中,两种验证方法有95.34%的测试点落在一致性界限内,因此两种验证方法之间具有较好的一致性。根据ROC曲线和AUC值,选取结构PTV2参数用于γ通过率评价时效果最好,其最佳阈值为95.41%。结论:独立三维剂量验证可以检验计划系统计算的准确性,快速地对计划进行治疗前的验证。最佳阈值有助于对放疗计划进行筛查,为放疗计划的准确实施提供安全、有效的技术保障。     

基于视频跟踪的前交叉韧带重建导航及仿真评估系统研究

植入点位置的确定以及重建后是否满足等距性,对于前交叉韧带(ACL)的重建是至关重要的.针对ACL重建入点定位困难以及缺少术后评估等问题,借助于视频跟踪相机,实现了一种基于膝关节侧位X光片的股骨四分格和胫骨46%方法的ACL重建导航及仿真评估系统,并分别介绍了视频跟踪、空间映射及C臂标定、图像融合、图像校正、曲面重建算法等关键技术的实现.利用该系统进行了8例模型骨的实验,并对采集到的特征点进行了精度验证,入点定位误差最大为2.59 mm,平均为1.59 mm.实验结果表明,该系统利用两幅X光图像可以完成ACL重建手术规划,入点定位误差可以基本满足临床应用要求,初步验证了该方法的可行性.     

肝脏肿瘤三维可视化方法研究

肝脏肿瘤三维可视化是肝癌微波热疗规划系统设计中的关键技术,其重建效果的好坏将直接影响到手术计划的可靠性和有效性。本研究提出一种基于自动分割的肝脏肿瘤三维可视化新方法。首先使用基于图论的方法自动分割出肝肿瘤,然后借助新的移动立方体算法重建出肿瘤表面,最后调用OpenGL库进行肿瘤模型绘制与显示。对6例肝癌患者CT图像进行肿瘤三维重建,实验结果表明;分割过程不需要人为干预,三维重建时程也较短,肿瘤模型的显示效果令人满意。     

Optimizing a three-stage Compton camera for measuring prompt gamma rays emitted during proton radiotherapy

In this work, we investigate the use of a three-stage Compton camera to measure secondary prompt gamma rays emitted from patients treated with proton beam radiotherapy. The purpose of this study was (1) to develop an optimal three-stage Compton camera specifically designed to measure prompt gamma rays emitted from tissue and (2) to determine the feasibility of using this optimized Compton camera design to measure and image prompt gamma rays emitted during proton beam irradiation. The three-stage Compton camera was modeled in Geant4 as three high-purity germanium detector stages arranged in parallel-plane geometry. Initially, an isotropic gamma source ranging from 0 to 15 MeV was used to determine lateral width and thickness of the detector stages that provided the optimal detection efficiency. Then, the gamma source was replaced by a proton beam irradiating a tissue phantom to calculate the overall efficiency of the optimized camera for detecting emitted prompt gammas. The overall calculated efficiencies varied from ～ 10(-6) to 10(-3) prompt gammas detected per proton incident on the tissue phantom for several variations of the optimal camera design studied. Based on the overall efficiency results, we believe it feasible that a three-stage Compton camera could detect a sufficient number of prompt gammas to allow measurement and imaging of prompt gamma emission during proton radiotherapy.     

Evaluation of a stochastic reconstruction algorithm for use in Compton camera imaging and beam range verification from secondary gamma emission during proton therapy

In this paper, we study the feasibility of using the stochastic origin ensemble (SOE) algorithm for reconstructing images of secondary gammas emitted during proton radiotherapy from data measured with a three-stage Compton camera. The purpose of this study was to evaluate the quality of the images of the gamma rays emitted during proton irradiation produced using the SOE algorithm and to measure how well the images reproduce the distal falloff of the beam. For our evaluation, we performed a Monte Carlo simulation of an ideal three-stage Compton camera positioned above and orthogonal to a proton pencil beam irradiating a tissue phantom. Scattering of beam protons with nuclei in the phantom produces secondary gamma rays, which are detected by the Compton camera and used as input to the SOE algorithm. We studied the SOE reconstructed images as a function of the number of iterations, the voxel probability parameter, and the number of detected gammas used by the SOE algorithm. We quantitatively evaluated the capabilities of the SOE algorithm by calculating and comparing the normalized mean square error (NMSE) of SOE reconstructed images. We also studied the ability of the SOE reconstructed images to predict the distal falloff of the secondary gamma production in the irradiated tissue. Our results show that the images produced with the SOE algorithm converge in ~10,000 iterations, with little improvement to the image NMSE for iterations above this number. We found that the statistical noise of the images is inversely proportional to the ratio of the number of gammas detected to the SOE voxel probability parameter value. In our study, the SOE predicted distal falloff of the reconstructed images agrees with the Monte Carlo calculated distal falloff of the gamma emission profile in the phantom to within ±0.6 mm for the positions of maximum emission (100%) and 90%, 50% and 20% distal falloff of the gamma emission profile. We conclude that the SOE algorithm is an effective method for reconstructing images of a proton pencil beam from the data collected by an ideal Compton camera and that these images accurately model the distal falloff of secondary gamma emission during proton irradiation.     

Validation of the scanning -gamma-ray telescope for in vivo dosimetry and boron measurements during BNCT.

Gamma-ray telescope scans of a box phantom with inhomogeneous boron concentrations have proven the feasibility of in vivo measurements of different boron distributions in the head of a patient during boron neutron capture therapy (BNCT). Small structures with enhanced boron concentration can be reconstructed in a head phantom, even if the brain compartment of the phantom is surrounded by a skin layer with a ten times higher boron concentration. The motor-controlled telescope can scan the head/phantom, detecting boron and hydrogen prompt y-rays emitted at neutron capture reactions with a two-dimensional spatial resolution of 14 mm full width at half maximum. For reconstruction of the boron concentrations from the measured y-ray detection rates, a mathematical reconstruction algorithm is derived and discussed. Proper reconstruction requires position-dependent y-ray measurements combined with treatment planning programme calculations of the thermal neutron distribution. In a head phantom, in which the brain and the skull (bulk) were represented using a homogeneous boron distribution of 5.2 +/- 0.5 ppm 10B, surrounded by a skin layer with a ten times higher boron concentration, the bulk concentration was reconstructed to 4.7 +/- 0.3 ppm 10B. Telescope scans along and perpendicular to the beam axis showed the influence of inhomogeneities with a high boron concentration such as skin and a simulated blood vessel, respectively with a low boron concentration such as white matter. The profiles of the boron and hydrogen y-ray detection rates indicate how future patient measurements can be interpreted. In clinical trials, the telescope can then be used to investigate the averaged boron concentration in the bulk of a patient and local enhanced boron concentrations (e.g. in tumour tissue) in order to relate the measured boron dose distributions to the clinical effects of BNCT. Simultaneously, it can serve as quality control of the dosimetry during the irradiation.     

Image reconstruction from limited angle Compton camera data

The Compton camera is used for imaging the distributions of gamma ray direction in a gamma ray telescope for astrophysics and for imaging radioisotope distributions in nuclear medicine without the need for collimators. The integration of gamma rays on a cone is measured with the camera, so that some sort of inversion method is needed. Parra found an analytical inversion algorithm based on spherical harmonics expansion of projection data. His algorithm is applicable to the full set of projection data. In this paper, six possible reconstruction algorithms that allow image reconstruction from projections with a finite range of scattering angles are investigated. Four algorithms have instability problems and two others are practical. However, the variance of the reconstructed image diverges in these two cases, so that window functions are introduced with which the variance becomes finite at a cost of spatial resolution. These two algorithms are compared in terms of variance. The algorithm based on the inversion of the summed back-projection is superior to the algorithm based on the inversion of the summed projection.     

An electronically collimated gamma camera for single photon emission computed tomography. Part II: Image reconstruction and preliminary experimental measurements

Iterative algorithms have been investigated for reconstructing images from data acquired with a new type of gamma camera based upon an electronic method of collimating gamma radiation. The camera is composed of two detection systems which record a sequential interaction of the emitted gamma radiation. Coincident counting in accordance with Compton scattering kinematics leads to a localization of activity upon a multitude of conical surfaces throughout the object. A two-stage reconstruction procedure in which conical line projection images as seen by each position sensing element of the first detector are reconstructed in the first stage, and tomographic images are reconstructed in the second stage, has been developed. Computer simulation studies of both stages and first-stage reconstruction studies with preliminary experimental data are reported. Experimental data were obtained with one detection element of a prototype germanium detector. A microcomputer based circuit was developed to record coincident counts between the germanium detector and an uncollimated conventional scintillation camera. Point sources of Tc-99m and Cs-137 were used to perform preliminary measurements of sensitivity and point spread function characteristics of electronic collimation.     

Material efficiency studies for a Compton camera designed to measure characteristic prompt gamma rays emitted during proton beam radiotherapy

Prompt gamma rays emitted from biological tissues during proton irradiation carry dosimetric and spectroscopic information that can assist with treatment verification and provide an indication of the biological response of the irradiated tissues. Compton cameras are capable of determining the origin and energy of gamma rays. However, prompt gamma monitoring during proton therapy requires new Compton camera designs that perform well at the high gamma energies produced when tissues are bombarded with therapeutic protons. In this study we optimize the materials and geometry of a three-stage Compton camera for prompt gamma detection and calculate the theoretical efficiency of such a detector. The materials evaluated in this study include germanium, bismuth germanate (BGO), NaI, xenon, silicon and lanthanum bromide (LaBr(3)). For each material, the dimensions of each detector stage were optimized to produce the maximum number of relevant interactions. These results were used to predict the efficiency of various multi-material cameras. The theoretical detection efficiencies of the most promising multi-material cameras were then calculated for the photons emitted from a tissue-equivalent phantom irradiated by therapeutic proton beams ranging from 50 to 250 MeV. The optimized detector stages had a lateral extent of 10 × 10 cm(2) with the thickness of the initial two stages dependent on the detector material. The thickness of the third stage was fixed at 10 cm regardless of material. The most efficient single-material cameras were composed of germanium (3 cm) and BGO (2.5 cm). These cameras exhibited efficiencies of 1.15 × 10(-4) and 9.58 × 10(-5) per incident proton, respectively. The most efficient multi-material camera design consisted of two initial stages of germanium (3 cm) and a final stage of BGO, resulting in a theoretical efficiency of 1.26 × 10(-4) per incident proton.     

A noninvasive dose estimation system for clinical BNCT based on PG-SPECT--conceptual study and fundamental experiments using HPGe and CdTe semiconductor detectors

A noninvasive method for measuring the absorbed dose distribution during the administration of clinical boron neutron capture therapy (BNCT) using an online three-dimensional (3D) imaging system is presented. This system is designed to provide more accurate information for treatment planning and dosimetry. The single-photon emission computed tomography (SPECT) technique is combined with prompt gamma-ray analysis (PGA) to provide an ideal dose estimation system for BNCT. This system is termed PG-SPECT. The fundamental feasibility of the PG-SPECT system for BNCT is confirmed under the following conditions: (1) a voxel size of 1 x 1 x 1 cm3, comparable to the spatial resolution of our standard dosimetric technique using gold wire activation, where data are available for every 5-10 mm of wire length; (2) a reaction rate of 10B(n,alpha)7Li within the measurement volume is greater than 1.1 x l0(6) interactions/cm3/s, corresponding to a thermal neutron flux of 5 x 10(8) n/cm2/s and a 10B concentration of greater than 10 ppm for the deepest part of the tumor volume under typical BNCT clinical conditions; (3) statistical uncertainty of the count rate for 10B(n,alpha)7Li prompt gamma rays is 10% or less. The desirable characteristics of a detector for the PG-SPECT system were determined by basic experiments using both HPGe and CdTe semiconductor detectors. The CdTe semiconductor detector has the greatest potential for this system because of its compactness and simplicity of maintenance.     

CdZnTe strip detector SPECT imaging with a slit collimator

In this paper, we propose a CdZnTe rotating and spinning gamma camera attached with a slit collimator. This imaging system acquires convergent planar integrals of a radioactive distribution. Two analytical image reconstruction algorithms are proposed. Preliminary phantom studies show that our small CdZnTe camera with a slit collimator outperforms a larger NaI(Tl) camera with a pinhole collimator in terms of spatial resolution in the reconstructed images. The main application of this system is small animal SPECT imaging.     

Toward clinical application of prompt gamma spectroscopy for in vivo monitoring of boron uptake in boron neutron capture therapy

In boron neutron capture therapy (BNCT) the absorbed dose to the tumor cells and healthy tissues depends critically on the boron uptake. Pronounced individual variations in the uptake patterns have been observed for two boron compounds currently used in clinical trials. This implies a high uncertainty in the determination of the boron dose component. In the present work a technique known as prompt gamma spectroscopy (PGS) is studied that potentially can be used for in vivo and noninvasive boron concentration determination at the time of the treatment. The technique is based upon measurement of gamma rays promptly emitted in the 10B(n,alpha)7Li and 1H(n,gamma)2D reactions. The aim of this work is to prepare the present setup for clinical application as a monitor of boron uptake in BNCT patients. Therefore, a full calibration and a set of phantom experiments were performed in a clinical setting. Specifically, a nonuniform boron distribution was studied; a skin/ dura, a larger blood vessel, and tumor within a head phantom was simulated. The results show that it is possible to determine a homogeneous boron concentration of 5 microg/g within +/-3% (1 standard deviation). In the nonuniform case, this work shows that the boron concentration can be determined through a multistep measurement procedure, however, with a somewhat higher uncertainty (approximately 10%). The present work forms the basis for a subsequent clinical application of the PGS setup aimed at in vivo monitoring of boron uptake.     

Automatic boundary identification of a region in gamma camera image

A new automatic method for the identification of the boundary of an image obtained with a gamma camera is proposed. The advantages of this method are a short calculation time and its applicability to images with a low signal-to-noise ratio. The limitations of the method are discussed.