蒙特卡罗方法计算外照射所致红骨髓剂量方法的研究

目的 对现有的红骨髓剂量模拟计算方法进行比较和分析.为确定更为合理的计算方法提供依据.方法 借助MCNPX蒙特卡罗模拟软件,模拟了能量20 keV～10 MeV的γ光子源,对Rensselaer理工学院(RPI)体素人体模型进行前后(AP)全身均匀照射,分别采用直接能量沉积法、剂量响应函数法(DRF)、King-Spiers因子法和质能吸收系数法(MEAC),进行红骨髓剂量的模拟计算.结果 在入射γ光子能量低于100 keV时,直接能量沉积法的结果最大,而质能吸收系数法和King-Spiels因子法的结果更为合理;在入射γ光子能量高于150 keV时,King-Spiers因子法给出的结果要略高于其他方法的结果,但其能够反映出红骨髓对γ光子能量更强的吸收能力.结论 综合比较低能区和高能区不同方法给出的结果后,发现King-Spiers因子法是最合理的估算红骨髓剂量的方法.     

炫速CT双能量与常规减影血管成像在诊断颅内血管病变显示的对比研究

目的 对双能量直接去骨减影法(Dual-Energy CTA)与常规减影法(Neuro-DSA)在脑动脉成像的图像质量、患者接受辐射剂量及图像处理效率及检查成功率方面进行比较,探讨两种减影方法的差异.方法 根据投照技师操作习惯不同,将连续120名接受头颅CTA检查的患者随机分为双能量扫描组和常规扫描组,采用SIMENS SOMATOMDefinition Flash CT机分别以双能量模式及常规模式进行扫描.结果 双能量减影法与常规减影法对图像质量无明显影响,辐射剂量明显低于常规减影,降低率为44％,图像处理效率及检查成功率均明显高于对照组,差异具有统计学意义(t=1.66,P＜0.01).结论 双能量直接去骨减影法具有辐射剂量低,图像质量清晰,图像处理快,检查成功率高的优势,具有广阔的应用前景,值得推广应用.     

用牙釉电子自旋共振方法估算慢性辐射损伤人员的受照剂量

目的 用于牙釉电子自旋共振对慢性辐射损伤人员的受照剂量进行估算的方法。方法 用电子自旋共振仪测定慢性辐射损伤人员牙釉电子自旋共振信号强度，用剂量－效应曲线法和附加剂量法来重建辐射损伤人员的受照剂量，探讨牙釉电子自旋共振法估算受照剂量的可行性；并比较了不同能量的射线（1.25MeV的γ射线和6MeV的X射线）对牙釉电子自旋共振信号强度的影响。结果 用两种方法估算的辐射损伤人员受照剂量基本一致；对能量1.25MeV的γ射线和6MeV的X射线进行比较，无论从剂量－效应曲线的直线系数，还是用混合照射后的剂量估算，两者差别不大。结论 慢性辐射损伤人员的受照剂量可以用于牙釉电子自旋共振方法进行估算，射线能量在1.25MeV-6MeV范围内对牙釉电子自旋共振信号强度影响不大。     

立体定向放疗计划中蒙特卡罗与射线追踪算法剂量计算结果的比较

G4射波刀治疗计划系统提供了射线追踪算法和蒙特卡罗算法(MC算法)两种剂量算法.射线追踪算法利用射线追踪函数来计算计划设计中每个射束的靶区体素(最大剂量点)的累积剂量,只对主要路径上不均匀介质的校正[1].MC算法采用的是随机抽样的模拟方法,模拟光子在入射路径上的能量沉积,考虑了非均匀介质的散射剂量的影响.MC算法是与福克斯·蔡斯癌症中心(美国)联合开发,采用了方差缩减方法,利用体素模型将各种材料视为与密度可变的水等效,利用电子迁移算法计算可变密度水的吸收剂量[2].随着低分次、大剂量照射方式的广泛应用,对剂量计算的准确性要求越来越高,MC算法具有很高的计算精度,尤其是在显著的非均匀介质中,如肺等空腔脏器[3].本研究选取相对均匀组织(如头部、肝脏等)和显著非均匀组织(如肺等)进行剂量计算,对两种算法的计算结果进行比较和评价.     

金黄色葡萄球菌肠毒素食物中毒检测方法的比较

我们用ELISA夹心法和反向间接血凝试验(RPHA)对6种模拟污染葡萄球菌C_1型肠毒素(SEC_1)的食品标本和三起食物中毒8份标本进行了检测.通过对两种方法的比较,证明ELISA法比RPHA法更敏感、准确,但RPHA法比ELISA法更简便、快速.     

双能量CT低剂量成像结合迭代重建技术在超重者冠状动脉成像中的研究

目的 探讨低剂量双能量CT结合迭代重建技术在超重者冠状动脉血管成像中的价值.方法 对60例受检者行双能量CT低剂量成像,因重建方法分为A组(FBP法),B组(SAFIRE法),同时将单能谱keV分为6个水平(65、70、75、80、85、90 keV).采用随机区组设计的方差分析比较不同单能谱keV水平各指标,选择最佳keY;比较最佳keV水平的A、B组间CT值、噪声(SD)、信噪比(SNR)、对比噪声比(CNR)及图像评分等.结果 60例受检者不同keV水平主动脉(左冠状动脉开口处)CT值、SD、SNR、CNR的差异均有统计学意义(P＜0.05);B组SNR值及CNR值显著高于A组,SD值显著低于A组,差异有统计学意(P＜0.05);B组中节段评分为优的血管节段比例高,差异有统计学意义(P＜0.05).辐射剂量指标剂量长度乘积(DLP)为(238.7±30.82) mGy· cm,有效剂量(ED)为(3.3±0.43) mSv.结论 在低剂量冠状动脉CT血管成像(CTA)的双能量扫描中,使用迭代重建算法结合最佳单能量谱成像能够提高图像质量,其中75 keV为最佳纯化单能谱图像.     

双源CT肺动脉成像不同扫描模式图像质量及辐射剂量的对比研究

目的 探讨双源CT肺动脉成像双能量扫描与普通扫描(单能量扫描)对图像质量及辐射剂量的影响.方法 临床怀疑肺栓塞并行炫速双源CT肺动脉成像单、双能量扫描患者各61例,按扫描方式不同分为A、B2组,A组为双能量扫描(80/Sn140 kV),B组为普通扫描(Care kV选择输出管电压).对2组图像进行图像质量评分及测量2组肺动脉CT值、空气标准差(背景噪声)并计算信噪比(SNR),同时对2组图像的辐射剂量进行对比分析,以P＜0.05为具有统计学意义.结果 2组图像质量主观评分2名观察者间一致性较好,Kappa分别为0.705、0.827,2组图像质量评分差异无统计学意义(P＞0.05);A组右下肺动脉CT值高于B组,差异有统计学意义(P＜0.05),其余肺动脉的CT值差异均无统计学意义(P＞0.05);A组图像噪声稍高于B组,SNR稍低于B组,差异无统计学意义(P＞0.05);A、B2组CT剂量指数(CTDIvol)、剂量长度乘积(DLP)有效剂量(ED)分别为(6.13± 1.09)mGy和(12.41±3.42) mGy、(172.49士41.35)mGy· cm和(332.16±115.65) mGy.cm、(2.41±0.58) mSv和(4.65±1.62) mSv,差异具有统计学意义(P=0.000),A组CTDIvol、DLP、ED较B组分别减少50.60％、48.07％、48.17％.结论 双源CT肺动脉成像双能量扫描(80/Sn140 kV)的图像质量与单能量扫描相近,X线辐射剂量较单能量扫描明显降低.     

评估胎儿辐射剂量的不同方法的比较

正摘要目的利用病人特异性蒙特卡罗(Monte Carlo,MC)模拟和商业软件包(CSP)对文献中用于评估胎儿辐射剂量(D_(胎儿))的不同方法进行比较。方法孕妇腹盆部CT检查的     

心血管病介入诊疗程序中第一术者有效剂量估算方法的比较研究

目的 通过模拟实验测量,比较国际辐射防护委员会（ICRP）139号报告推荐的4种单双剂量计算法对估算心血管介入诊疗程序中第一术者有效剂量之间的差异,以探讨这4种算法对介入诊疗场景的适用性。方法 模拟第一术者的男性躯干模体穿戴铅衣和铅围脖,在其体内布放热释光探测器,在其铅衣内外布放热释光个人剂量计,模拟心血管病介入诊疗场景,通过模拟测量得到的器官剂量计算第一术者的有效剂量,与通过个人剂量计及4种单双剂量计算法得到的结果进行比较。结果 在本实验条件下,由模拟测量计算得到的有效剂量为0.581 mSv;而用Swiss ordinance法、McEwan法、Von Boetticher法与Martin-Magee法估算得到的有效剂量分别为0.667、0.484、0.485和0.726 mSv,与模拟测量得到的有效剂量的相对偏差分别为14.8%、-16.7%、-16.5%和24.9%。结论 4种计算方法得到第一术者有效剂量与模拟测量结果均有较大的差异;从辐射防护观点出发,推荐使用Swiss ordinance法开展心血管病介入诊疗程序中第一术者的个人剂量监测。     

对细胞施加力学作用的实验方法

对细胞施加力学作用的实验方法有很多种,但大多是对体内、体外环境中某一力学因素的模拟.按照所模拟力的来源不同,分为模拟体内力学环境的实验方法和模拟体外力学环境的实验方法两类.模拟体内力学环境的实验方法主要有:流动剪切力法、静水压法、圆周应力法、基底拉伸法;模拟体外力学环境的实验方法主要有:微重力细胞培养法、离心力场法、气体加压法、声波刺激法、微光束辐照法.另外,还有一类用于研究单细胞力学特性的实验方法,主要有微管吸吮法、原子力显微镜悬臂刺激法、磁珠扭转法和光钳法.本文针对这些主要的实验方法进行综述.     

Monte Carlo simulations used to calculate the energy deposited in the coronary artery lumen as a function of iodine concentration and photon energy

Purpose: To better understand the risks of cumulative medical X-ray investigations and the possible causal role of contrast agent on the coronary artery wall, the correlation between iodinated contrast media and the increase of energy deposited in the coronary artery lumen as a function of iodine concentration and photon energy is investigated.

Materials and methods: The calculations of energy deposition have been performed using Monte Carlo (MC) simulation codes, namely PENetration and Energy LOss of Positrons and Electrons (PENELOPE) and Monte Carlo N-Particle eXtended (MCNPX). Exposure of a cylinder phantom, artery and a metal stent (AISI 316L) to several X-ray photon beams were simulated.

Results and discussion: For the energies used in cardiac imaging the energy deposited in the coronary artery lumen increases with the quantity of iodine. Monte Carlo calculations indicate a strong dependence of the energy enhancement factor (EEF) on photon energy and iodine concentration. The maximum value of EEF is equal to 25; this factor is showed for 83?keV and for 400?mg Iodine/mL. No significant impact of the stent is observed on the absorbed dose in the artery for incident X-ray beams with mean energies of 44, 48, 52 and 55?keV.

Conclusion: A strong correlation was shown between the increase in the concentration of iodine and the energy deposited in the coronary artery lumen for the energies used in cardiac imaging and over the energy range between 44 and 55?keV. The data provided by this study could be useful for creating new medical imaging protocols to obtain better diagnostic information with a lower level of radiation exposure.     

低剂量照射对小鼠骨髓移植造血功能的影响

目的探讨低剂量照射促进小鼠骨髓移植后受体造血功能的重建。方法通过对小鼠体外骨髓细胞进行不同剂量的照射，用^3H-TdR掺入法确定产生最佳刺激增殖效应的照射剂量。在骨髓移植前，对供体小鼠骨髓细胞给予最佳刺激剂量的照射，然后将被照射的骨髓细胞输入受体小鼠内，最后动态监测受体小鼠的外周血细胞和骨髓单个核细胞数量。结果在离体情况下，经6和8cGy低剂量照射的小鼠骨髓细胞增殖能力明显增强。用低剂量照射的骨髓细胞进行骨髓移植后，受体小鼠骨髓单个核细胞数和外周血细胞计数普遍高于相应的对照组。结论低剂量照射可能促进小鼠骨髓移植后受体造血功能的重建。     

A comparison of X-ray and proton beam low energy secondary electron track structures using the low energy models of Geant4

Abstract

Purpose: Lethal cell damage by ionising radiation is generally initiated by the formation of complex strand breaks, resulting from ionisation clusters in the DNA molecule. A better understanding of the effect of the distribution of ionisation clusters within the cell and particularly in regard to DNA segments could be beneficial to radiation therapy treatment planning. Low energy X-rays generate an abundance of low energy electrons similar to that associated with MeV protons. The study and comparison of the track structure of photon and proton beams could permit the substitution of photon microbeams for single cell ion irradiations at proton facilities used to predict the relative biological effectiveness (RBE) of charged particle fields. Materials and methods: The track structure of X-ray photons is compared with proton pencil beams in voxels of approximate DNA strand size (2 × 2 × 5 nm). The Very Low Energy extension models of the Monte Carlo simulation toolkit GEometry ANd Tracking 4 (Geant4) is used. Simulations were performed in a water phantom for an X-ray and proton beam of energies 100 keV and 20 MeV, respectively. Results: The track structure of the photon and proton beams are evaluated using the ionisation cluster size distribution as well as the radial dose deposition of the beam. Conclusions: A comparative analysis of the ionisation cluster distribution and radial dose deposition obtained is presented, which suggest that low energy X-rays could produce similar ionisation cluster distributions to MeV protons on the DNA scale of size at depths greater than ～10 μm and at distances greater than ～1 μm from the beam centre. Here the ionisation cluster size for each beam is less than ～100. The radial dose deposition is also approximately equal at large depths and at distances greater than 10 μm from the beam centre.     

大面积照射及其相应的一次全身等效剂量的研究

本文主要应用红骨髓干细胞法来估算大面积、非均匀条件的照射剂量归一于全身均匀照射剂量,这样就可以利用日常的一些特殊照射来建立不同程度的造血型放射病模型。通过对各种不同的归一等效剂量的方法进行比较,认为干细胞法的估算与临床实际最为符合,是一种值得重视的估算等效剂量的方法。     

Samarium — 153 EDTMP therapy of disseminated skeletal metastasis

¹⁵³Sm-EDTMP (ethylenediaminetetramethylene phosphonate), prepared from a kit, was administered to 28 patients in a clinical trial of therapy for painful skeletal metastases unresponsive to all conventional treatment. The 103 keV gamma emission of ¹⁵³Sm was utilized for prospective individual estimation of beta radiation absorbed dose to red marrow to minimize myelotoxicity and provide optimum internal radiotherapy to skeletal metastases in each patient. Pain relief occurred within 14 days of administration of ¹⁵³Sm-EDTMP in 15 of 19 patients (79%) who could be evaluated at 6 weeks, when clinical response was maximal. Duration of response ranged from 4 to 35 weeks. Recurrence of pain responded to retreatment with ¹⁵³Sm-EDTMP in five of eight cases. No dose-response relationship was apparent for pain relief but reversible myelotoxicity was frequently observed at radiation absorbed doses to bone marrow 270 cGy. Dosimetry calculation was based on pharmacokinetic studies of a tracer administration of ¹⁵³Sm-EDTMP in each patient. Assumptions inherent in this prospective method of predicting dose to bone marrow were validated experimentally. Biodistribution studies in rats demonstrated rapid skeletal uptake and long term retention of ¹⁵³Sm-EDTMP in bone over 5 days. Urinary clearance accounted for 40% of injected dose, and less than 1.0% of administered activity was retained in non osseous tissue. Microdensitometry of autoradiographs of sheep vertebra and femur confirmed surface uptake of ¹⁵³Sm-EDTMP in cortical bone and demonstrated relatively high trabecular bone activity which is the major component of radiation absorbed dose to bone marrow. Haematological studies in rabbits showed ¹⁵³Sm-EDTMP-induced myclotoxicity to be transient and no histopathological abnormalities were demonstrable with doses ten times greater than those administered to patients.     

Considerations of marrow cellularity in 3-dimensional dosimetric models of the trabecular skeleton.

Dose assessment to active bone marrow is a critical feature of radionuclide therapy treatment planning. Skeletal dosimetry models currently used to assign radionuclide S values for clinical marrow dose assessment are based on bone and marrow cavity chord-length distributions. Accordingly, these models cannot explicitly consider energy loss to inactive marrow (adipose tissue) during particle transport across the trabecular marrow space (TMS). One method to account for this energy loss is to uniformly scale the resulting TMS absorbed fractions by reference values of site-specific marrow cellularity. In doing so, however, the resulting absorbed fractions for self-irradiation of the trabecular active marrow (TAM) do not converge to unity at low electron source energies. This study attempts to address this issue by using nuclear magnetic resonance microscopy images of trabecular bone to define 3-dimensional (3D) dosimetric models in which explicit spatial distributions of adipose tissue are introduced. METHODS: Cadaveric sources of trabecular bone were taken from both the femoral heads and humeral epiphyses of a 51-y-old male subject. The bone sites were sectioned and subsequently imaged at a proton resonance frequency of 200 MHz (4.7 T) using a 3D spin-echo pulse sequence. After image segmentation, voxel clusters of adipocytes were inserted interior to the marrow cavities of the binary images, which were then coupled to the EGS4 radiation transport code for simulation of active marrow electron sources. RESULTS: Absorbed fractions for self-irradiation of the TAM were tabulated for both skeletal sites. Substantial variations in the absorbed fraction to active marrow are seen with changes in marrow cellularity, particularly in the energy range of 100-500 keV. These variations are seen to be more dramatic in the humeral epiphysis (larger marrow volume fraction) than in the femoral head. CONCLUSION: Results from electron transport in 3D models of the trabecular skeleton indicate that current methods to account for marrow cellularity in chord-based models are incomplete. At 10 keV, for example, the Eckerman and Stabin model underestimates the self-absorbed fraction to active marrow by 75%. At 1 MeV, the model of Bouchet et al. overestimates this same value by 40%. In the energy range of 20-200 keV, neither model accurately predicts energy loss to the active bone marrow. Thus, it is proposed that future extensions of skeletal dosimetry models use 3D transport techniques in which explicit delineation of active and inactive marrow is feasible.     

6 MV医用电子直线加速器的蒙特卡罗模拟

目的 探讨入射电子束的能量和径向强度分布对百分深度剂量曲线和离轴比的影响,并寻找与百分深度剂量曲线和离轴比的测量值最接近的两者参数组合.方法 利用OMEGA/EGSnre系统,模拟Varian 600C医用电子直线加速器,计算水模体百分深度剂量曲线和10 cm深度处离轴比.若测量值和计算值的相对误差经过剂量最大点后在2%之内,则接受入射电子束值.结果 电子束的能量在经过剂量最大点后对深度剂量曲线没有明显影响.离轴比对能量敏感,能量越高,离轴比尖角越小.径向强度分布对深度剂量曲线在误差允许的范围内没有影响,而离轴比曲线对电子束径向强度分布非常敏感.随着径向强度分布半高全宽增大而减小.深度剂量曲线的计算值与测量值一致.在射野范围内,离轴比曲线计算值和测量值一致;但在半影区和射野外,个别测量点的最大误差达到了18.5%.结论 在射野内找到了电子柬能量和径向强度分布的最优参数组合,而在半影区和射野外,未能找到合适的两者参数组合.

Abstract：

Objective To analyze the influence of the mean energy and the full-width of half msximum(FWHM)of incident electron beam intensity distilbution(assumed Gaussian distribution)on depth dose curves and off-axis ratios and to derive a most optimal combination of mean energy and FWHM of incident electron beam intensity distribution.Methods The study simulated 6 MV photon beam produced by Varian 600C medical linear accelerator with OMEGA/EGSnrc by matching the relative error of calculated and measured depth dose curves past depth of maximum dose and off-axis ratios at a depth of 10.0 cm in water within 2%.Results The depth dose curves were relatively insensitive to the mean energy past depth of maximum dose and the FWHM of the incident electron beam intensity distribution.Dose profiles were sensitive tO the mean energy and FWHM.The dose profiles horns decreased as the mean energy and tlle FWHM of the ineident electron beam intensity distilbution increased.The calculated value of the depth dose curves matched well with the measured value.The calculated value of the off-axis ratio was consistent with the measured value within the radiation field.However, the maximum errors of individual measurement points in the penumbra region and OUt of the field reached 18.5%.Conclusions In the field.the most optimal combination of mean energy and FWHM of incident electron beam intensitv distribution Can be derived, however,can not be derived out of the field and in the penumbra region.     

Practical determination of patient-specific marrow dose using radioactivity concentration in blood and body.

Accurate determination of red marrow radiation is important because myelotoxicity is often dose limiting in radioimmunotherapy. The S-value methodology assumes a fixed red marrow mass as defined by the standard Medical Internal Radiation Dose (MIRD) mathematic phantom. Substantial error can be introduced in marrow radiation estimates because red marrow mass varies from patient to patient. In this work we describe a patient-specific marrow dosimetry methodology that does not require an explicit estimate of marrow mass. METHODS: Photon radiation to marrow from all sources can be considered as the total body to marrow. Based on photon radiation from body and electron radiation from blood, a patient-specific marrow dose can be determined by counting blood and total body radioactivity and measuring body weight. RESULTS: The deviation in marrow dose calculation using total body to represent all photon radiation was 3.9% in 66 patients administered 131I-labeled antibodies and was 9.1% in 18 patients administered 67Cu-labeled antibodies. The differences between this patient-specific approach and estimates based on standard anatomy were considerable, ranging from -35% to 88%. The differences were greater when patients' weights differed substantially from the MIRD reference man phantom. CONCLUSION: For radiopharmaceuticals that do not bind marrow, patient-specific marrow dosimetry can be independent of the actual marrow mass of a patient. Patient-specific marrow dosimetry can be determined using radioactivity concentration in blood and body.