基于PET/CT中心的辐射监测及放射防护评价

PET/CT中心使用¹⁸F-FDG作为正电子放射性诊断药物,为此研究该中心的辐射水平,为临床辐射防护提供参考依据。利用X、γ辐射剂量率仪测量各工作区的辐射剂量率,利用热释光剂量仪估算工作人员的年有效剂量,并进一步研究了作为放射源的受检者离开前,周围人员与其保持不同距离时的辐射剂量率。结果表明:PET/CT中心各工作区及工作人员的辐射剂量符合国家标准。当周围人员与受检者保持3 m以上距离时,所测辐射剂量率近似环境本底值。     

基于蒙特卡罗数学模型评价不同螺距冠状动脉CCTA受检者辐射剂量的特点与验证

收集61例采用双源CT Flash大螺距冠状动脉CCTA (Coronary Computed Tomography Angiography,CCTA)受检者资料,按WHO亚洲人体质量指数(BMI )标准将研究对象分为三组:正常组(12例)、超重组(41例)和肥胖组(8例),应用蒙特卡罗(Monte Carlo)数学模型软件计算三组受检者大螺距与常规螺距行CCTA的器官剂量,比较两种螺距CCTA时受检者的器官剂量分布特点及两种螺距CCTA的有效剂量变化幅度,并与大螺距模式下CT设备直接读取法所得有效剂量值进行比较。结果表明,用蒙特卡罗软件计算的双源CT大螺距CCTA受检者的器官剂量比常规螺距技术的剂量降低约70%,其中心脏、胸腺的器官剂量下降最为明显,降幅最大约80%;三组CCTA受检者大螺距较常规螺距的有效剂量(E)均降低明显(p<0.05),正常组使用大螺距技术后有效剂量E降幅最为明显;大螺距模式下数学模型软件模拟有效剂量E与CT设备所测有效剂量E间的偏差度小于50%。说明Monte Carlo数学模型软件可用于检查前预估或回顾性分析CCTA扫描时受检者的器官剂量与有效剂量的分布情况,并预判CCTA大螺距模式对受检者的胸部器官剂量和有效剂量,从而达到了降低辐射剂量的目的,尤其对BMI较小的受检者(如儿童)控制辐射风险更具意义。对开展低剂量CT技术具有一定实际意义。     

医院级CT辐射剂量及诊断剂量水平研究

探讨医院级各部位CT扫描辐射剂量及成人CT检查诊断剂量水平。采集2018年2月—2019年1月本院在GE Light Speed 16 CT设备上进行诊断性CT检查的全部成年人共15 440例的CT检查数据,按照检查部位进行分类,统计各部位的容积剂量指数(CTDI_vol)、剂量长度乘积(DLP)。使用SPSS 19统计软件分析CTDI_vol、DLP的四分位数并计算有效剂量(ED)。结果表明,各部位CTDI_vol的诊断剂量参考水平(DRL)值为:颅脑87.75 mGy、肺部8.09 mGy、上下腹15.82 mGy、上下腹盆腔15.79 mGy;各部位DLP的诊断剂量参考水平(DRL)值为:颅脑1 053.03 mGy·cm、肺部245.19 mGy·cm、上下腹269.96 mGy·cm、上下腹盆腔835.20 mGy·cm。研究中发现肺部CTDI_vol、DLP的DRL值(分别为8.09 mGy、245.19 mGy·cm)低于我国其他地区和其他国家的DRL值;60岁以下患者肺部CT检查CTDI_vol、DLP的DRL值低于8.09 mGy、245.19 mGy·cm,60岁以上患者肺部CT检查CTDI_vol、DLP的DRL值高于8.09 mGy、245.19 mGy·cm。通过研究可以确定医院级各部位CT检查辐射剂量及成人CT检查诊断剂量水平,能为优化CT检查扫描技术和监测辐射剂量提供基础。     

多排(层)螺旋CT的辐射剂量表达及其影响因素探讨

多排(层)螺旋CT反映了放射学影像设备与技术的最新进展.它的迅速推广应用有益于临床医学诊断,但同时也增加了受检者医疗照射,随之可能增加一定的电离辐射风险.然而相应的放射防护监测及评价的前提是准确表达并测量其辐射剂量.因此本文侧重辐射剂量学角度,从总结归纳多排(层)螺旋CT的主要特点入手;系统评述X射线CT所致辐射剂量的表征量及其测量或估算方法;进而分析探讨影响多排(层)螺旋CT扫描所致辐射剂量的主要因素.显然,正确掌握这些X射线CT所致辐射剂量的表达及其测量与评价方法,进而统筹兼顾优化提高影像质量与合理降低受检者剂量,已经成为放射防护学界、医学物理学界、临床医学放射学界以及医疗器械研发部门等共同关注的重点和热点.     

新一代多模型迭代算法在70 kVp成人副鼻窦CT扫描中的应用

探讨成人在70 kVp副鼻窦CT检查中降低有效辐射剂量的同时,获取最佳图像质量的新一代多模型迭代算法(Adaptive Statistical Iterative Reconstruction-V,Asir-V)的权重。本研究对20例成人患者进行副鼻窦Revolution CT检查,采用70 kVp、230 mA条件下进行螺旋CT扫描,扫描完成后对每例患者的原始数据采用不同权重(0,20%,40%,60%,80%,100%)的后置新一代多模型迭代算法(Adaptive Statistical Iterative Reconstruction-V,Asir-V)重建的方法,共获得120幅图像,并对每例6组图像进行客观评价及主观评分。客观评价包括噪声(standard deviations, SD)和对比噪声比(contrast noise ratio,CNR),主观评价由2名评价医生对图像质量评分并对两者的主观一致性进行评价。每例患者扫描完成后,记录其剂量长度乘积(dose-length product,DLP)和CT容积剂量指数(CT dose index volume,CTDI_vol),并计算其平均有效辐射剂量(effective dose,ED)。客观评价结果表明不同权重的Asir-V图像噪声随着Asir-V权重的提升而降低,CNR值随着Asir-V权重的提升而升高,且有效辐射剂量ED较常规头颈部CT检查的平均辐射剂量明显减少;主观评价结果表明不同权重的Asir-V图像评分不同,在Asir-V 60% 时评分最高,且2名医生主观评价一致性好。结合主客观评价结果,认为在70 kVp、230 mA成人副鼻窦Revolution CT检查中,Asir-V 60％的图像既可满足临床诊断的需要,也可明显降低有效辐射剂量。     

双着丝粒染色体分析在核与辐射事故应急生物剂量估算中的应用与进展

双着丝粒染色体作为生物剂量估算的“金标准”,用于核与辐射事故受照者生物剂量的估算已有近60年的发展史,积累了较为丰富的资料。本文介绍了双着丝粒染色体人工和自动分析检测方法,以及该指标在核与辐射事故生物剂量估算的应用现状与进展,为国内同行开展基于双着丝粒染色体指标估算生物剂量研究提供参考。     

CT-W_4(日立)躯干扫描时患者的剂量分布

本文介绍在 CT—W_4(日立)全身扫描机分别对胸部、腹部和盆腔部器官扫描时利用人体模型测量并估计了扫描受检者的最大体表照射量、器官剂量和加权剂量当量;特别是下腹部及盆腔器官扫描时测量了性腺剂量,并导出了男女性腺剂量的估算公式。     

北京市消化道造影检查所致受检者的剂量

本文介绍北京市消化道造影检查所致受检者剂量的实验研究结果。文中主要叙述了体模实验的典型照射条件、实验测量结果和剂量估算方法;给出了各种消化道造影的器官剂量转换因子;并采用 Drexler 等人给出的权重因子,估算了食道、上消化道、下消化道和全消化道造影的加权剂量当量,其值对男性受检者分别为2.00、14.70、12.00、和13.70mSv,对女性受检者分别为4.10、14.50、10.80和15.20mSv。     

医用X射线CT主要检查类型所致成年受检者剂量研究

研究与掌握广泛普及的医用X射线CT(X-CT)所致受检者的剂量水平,是加强医疗照射防护的一个关键课题.在上海市“十一五”期间医疗照射水平调查研究中,根据全市拥有X-CT机各种品牌及其在各级医院实际应用比例情况,抽取全市约占30％的X-CT机计45台进行现场调研.累计针对8种常见主要检查类型的500例成年受检者,调查他们进行X-CT检查时所用的扫描参数及其相关剂量学信息,借助剂量转换系数等估算其所致典型有效剂量.研究结果表明,头颅、胸部和腹部的X-CT扫描中,各自加权CT剂量指数(CTDIw)的均值分别为55.4 mGy、12.5 mGy和18.4 mGy,而相应的剂量长度乘积(DLP)的均值分别为603 mGy·cm、294 mGy·cm和415mGy·cm.由此估算出头颅、胸部和腹部X-CT扫描所致成年受检者有效剂量的典型值分别为1.4 mSv、5.3 mSv和7.5 mSv.头颅扫描检查的CTDIw值通常高于耳道、眼部或鼻窦的诊断检查.显然,必须进一步加强X-CT扫描检查的影像质量及其所致剂量的优化匹配研究,尤其必须注意恰当选取各类X-CT检查所用的扫描参数,并不断完善相应的X-CT检查医疗照射指导(参考)水平,推动X-CT检查的医疗照射防护最优化.     

核电厂正常运行放射性流出物对婴儿的食入剂量研究

由于有时核电厂址附近自然村婴儿膳食谱的缺乏,使评价核电厂放射性流出物对婴儿的辐射环境影响缺乏完整性。本文参考国际原子能机构(IAEA) 19号报告和国际放射防护委员会(ICRP) 95号报告计算婴儿食入母乳所受的辐射剂量,给出一套婴儿辅食合理的通用膳食谱。研究表明,参考IAEA 19号报告的方法将使评价结果偏小,失去保守性,参考ICRP 95号报告方法更为合理可行。     

利用蒙特卡罗建模及估算儿童X-CT检查受照剂量

在儿科X射线-CT检查迅速增加的当下,尤其对电离辐射敏感的儿童,其所致医疗照射剂量的评估是十分重要和迫切的课题。本文结合已建立的1岁儿童体素体模,利用蒙特卡罗技术建立扫描模型,进行CT检查所致儿童受检者的医疗照射剂量估算。建立了CT单层轴向扫描时对1岁儿童36个器官或组织所产生医疗照射剂量的数据库,利用该数据库,可快速估算1岁儿童受检者接受CT扫描时的医疗照射剂量。并与同样扫描条件下的实验测量值进行了比较,结果显示二者相对偏差在25%以内。     

Managing patient dose in multi-detector computed tomography(MDCT). ICRP Publication 102

Computed tomography (CT) technology has changed considerably in recent years with the introduction of increasing numbers of multiple detector arrays. There are several parameters specific to multi-detector computed tomography (MDCT) scanners that increase or decrease patient dose systematically compared to older single detector computed tomography (SDCT) scanners. This document briefly reviews the MDCT technology, radiation dose in MDCT, including differences from SDCT and factors that affect dose, radiation risks, and the responsibilities for patient dose management. The document recommends that users need to understand the relationship between patient dose and image quality and be aware that image quality in CT is often higher than that necessary for diagnostic confidence. Automatic exposure control (AEC) does not totally free the operator from selection of scan parameters, and awareness of individual systems is important. Scanning protocols cannot simply be transferred between scanners from different manufacturers and should be determined for each MDCT. If the image quality is appropriately specified by the user, and suited to the clinical task, there will be a reduction in patient dose for most patients. Understanding of some parameters is not intuitive and the selection of image quality parameter values in AEC systems is not straightforward. Examples of some clinical situation shave been included to demonstrate dose management, e.g. CT examinations of the chest, the heart for coronary calcium quantification and non-invasive coronary angiography, colonography, the urinary tract, children, pregnant patients, trauma cases, and CT guided interventions. CT is increasingly being used to replace conventional x-ray studies and it is important that patient dose is given careful consideration, particularly with repeated or multiple examinations.     

A way forward for the development of an exposure computational model to computed tomography dosimetry

A way forward for the development of an exposure computational model to computed tomography dosimetry has been presented. In this way, an exposure computational model (ECM) for computed tomography (CT) dosimetry has been developed and validated through comparison with experimental results. For the development of the ECM, X-ray spectra generator codes have been evaluated and the head bow tie filter has been modelled through a mathematical equation. EGS4 and EGSnrc have been used for simulating the radiation transport by the ECM. Geometrical phantoms, commonly used in CT dosimetry, have been modelled by IDN software. MAX06 has also been used to simulate an adult male patient submitted for CT examinations. The evaluation of the X-ray spectra generator codes in CT dosimetry showed dependence with tube filtration (or HVL value). More generally, with the increment of total filtration (or HVL value) the X-raytbc becomes the best X-ray spectra generator code for CT dosimetry. The EGSnrc/X-raytbc combination has calculated C_100,c in better concordance with C_100,c measured in two different CT scanners. For a Toshiba CT scanner, the average percentage difference between the calculated C_100,c values and measured C_100,c values was 8.2%. Whilst for a GE CT scanner, the average percentage difference was 10.4%. By the measurements of air kerma through a prototype head bow tie filter a third-order exponential decay equation was found. C_100,c and C_100,p values calculated by the ECM are in good agreement with values measured at a specific CT scanner. A maximum percentage difference of 2% has been found in the PMMA CT head phantoms, demonstrating effective modelling of the head bow tie filter by the equation. The absorbed and effective doses calculated by the ECM developed in this work have been compared to those calculated by the ECM of Jones and Shrimpton for an adult male patient. For a head examination the absorbed dose values calculated by the ECM developed by Jones and Shrimpton overestimates up to three times the absorbed dose to brain compared to the ECM developed in this work. The effective dose calculated by the ECM of Jones and Shrimpton was 26% greater than effective dose calculated by the ECM developed in this work.     

X射线计算机断层摄影(CT)受检者剂量检测方法的研究

本文介绍了目前国际上两种通用的ＣＴ受检者剂量的表示方法和检测方法。通常用多层扫描平均剂量（ＭＳＡＤ）或ＣＴ剂量指数（ＣＴＤＩ）来表示ＣＴ受检者的剂量；用ＣＴ标准电离室（笔形电离室）或热释光剂量计（ＴＬＤ）进行检测。通过实验和数学模拟方法，找出了ＭＳＡＤ与ＣＴＤＩ之间和不同方法检测结果之间的关系，为今后推广使用这两种检测方法进行ＣＴ受检者剂量监测和推广使用国际电离辐射防护与辐射源安全基本标准（ＩＢＳＳ）推荐的ＣＴ受检者剂量指导水平打下技术基础。     

Validation of recent Geant4 physics models for application in carbon ion therapy

Cancer treatment with energetic carbon ions has distinct advantages over proton or photon irradiation. In this paper we present a simulation model integrated into the Geant4 Monte Carlo toolkit (version 9.3) which enables the use of ICRU 73 stopping powers for ion transport calculations. For a few materials, revised ICRU 73 stopping power tables recently published by ICRU (P. Sigmund, A. Schinner, H. Paul, Errata and Addenda: ICRU Report 73 (Stopping of Ions Heavier than Helium), International Commission on Radiation Units and Measurements, 2009) were incorporated into Geant4, also covering media like water which are of importance in radiotherapeutical applications. We examine, with particular attention paid to the recent developments, the accuracy of current Geant4 models for simulating Bragg peak profiles of ¹²C ions incident on water and polyethylene targets. Simulated dose distributions are validated against experimental data available in the literature, where the focus is on beam energies relevant to ion therapy applications (90-400 MeV/u). A quantitative analysis is performed which addresses the precision of the Bragg peak position and proportional features of the dose distribution. It is shown that experimental peak positions can be reproduced within 0.2% of the particle range in the case of water, and within 0.9% in the case of polyethylene. The comparisons also demonstrate that the simulations accurately render the full width at half maximum (FWHM) of the measured Bragg peaks in water. For polyethylene slight deviations from experimental peak widths are partly attributed to systematic effects due to a simplified geometry model adopted in the simulation setup.     

一种提高热释光探测器低能光子响应的新方法

ICRU 39号报告提出的四个剂量当量新量值及光子能量响应转换系数,使得一些有效原子序数较低的热释光探测器的低能光子响应变得明显地欠响应。针对这一问题,本文探索了一条加入少量高原子序数添加剂作为“光电子炮弹库”的新途径,既能不起掺杂剂的作用而对原有的优良性能无任何影响,又能有效地抬高低能光子响应并在较大的范围内任意调节低能光子响应的抬高幅度,从而可优选出基本满足Hp(10)和H(10)要求的两种配方。     

Neutron and photon doses in high energy radiotherapy facilities and evaluation of shielding performance by Monte Carlo method

Medical accelerators operating above 10 MV are a source of undesirable neutron radiations which contaminate the therapeutic photon beam. These photoneutrons can also generate secondary gamma rays which increases undesirable dose to the patient body and to personnel and general public. In this study, the Monte Carlo N-Particle MCNP5 code has been used to model the radiotherapy room of a medical linear accelerator operating at 18 MV and to calculate the neutron and the secondary gamma ray energy spectra and the dose equivalents at various points inside the treatment room and along the maze. To validate our Monte Carlo simulation we compared our results with those evaluated by the recommended analytical methods of IAEA Report No. 47, and with experimental and simulated values published in the literature. After validation, the Monte Carlo simulation has been used to evaluate the shielding performance of the radiotherapy room. The obtained results showed that the use of paraffin wax containing boron carbide, in the lining of the radiotherapy room walls, presents enough effectiveness to reduce both neutron and gamma ray doses inside the treatment room and at the maze entrance. Such evaluation cannot be performed by the analytical methods since room material and wall surface lining are not taken into consideration.     

Neutronic analysis of iter cryopump system

The ITER Vacuum Vessel has upper, equatorial and lower port structures. The bottom ports are dedicated to the divertor replacement (five ports) and to vacuum pumping by means of cryopumps (four ports). The latest cryopump port design is more complex as it has a pump with a direct view of the vessel (upper cryopump) and a second pump at the end of a branch port (lower cryopump).3D neutronic analyses have been performed in order to study the radiation conditions in and around the port system. In detail, nuclear heating on the cryopump has been calculated updating previous analysis performed in 2003 [L. Petrizzi, ITER CTA Detailed Neutronic Analyses, Final Report on contract EFDA/01-633 ENEA ref NE-VV-R-001 April 2003. Also included in Nuclear Analyis Report NAR ITER ref document G 73 DDD 2W 0.2 (v2.0) March 2006]. Calculations have been performed by means of MCNP 5 Monte Carlo code supplied with FENDL 2.1 library. In this work a new 40° model of ITER has been used in which full details of the cryopump system and remote handling ports have been included as well as the updated divertor components.The paper will present the neutronics results. They consist of nuclear heating on cryopump components; a map of dpa and helium production is provided as well.Gamma doses after shutdown have been calculated around the port flange to have an idea of the possible dose to which the eventual operator will be subject and to plan adequately manual operations.The cryopump is located at a distance of almost 5 m from the mouth of the divertor port and it is 3 m long. Calculations of such deep penetration problem are very challenging require special variance reduction techniques with Monte Carlo codes in order to use in an efficient way the computer resources. These will be described.     

内照射个人剂量数据管理和评价程序

本文介绍一种用于内照射个人剂量数据管理和评价的实用程序（ＩＮＤＯＢＡＳＥ），包括程序的主要功能、数据库结构、内照射剂量估算方法和数据评价方法等。该程序经在２８６以上几种档次微机上运行测试，结果表明，其各项功能达到了设计要求，现已应用于中国原子能科学研究院内照射个人剂量管理工作