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-Spi...     

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.     

蒙特卡罗N粒子运输法计算与实际测量的60Co治疗机剂量分布比较

Objective To discuss the feasibility of Monte Carlo N-particle transport code(MCNP)simulated calculation.Methods The calculation in water phantom was contrasted with the practical measurements and the reported values using the percent depth dose(PDD)curve and normal peak scatter factor.Results There Was no significant difference between calculated and measured results in the 10 cm×10 cm field(t＝-0.41,P>0.05),however,there were significant differences in the 5 cm×5 cm field(t=7.2,P<0.05)and in the 12 cm×12 cm field(t=-4.6,P<0.05).There was no significant difierence between the calculated results and the reported values(t=-1.91,P>0.05).In the same radiation field,the PDD decreased as the depth increased,but increased as the size of the radiation field increased at the same depth.PDD and normal peak scatter factor were both important parameters for calculation of prescribed dose.Conclusions It is possible to establish a set of accurate and comprehensive percent depth doses and normal peak scatter factor parameters so as to provide the basis of clinical use, quality assurance and quality control for radiotherapy.     

蒙特卡罗N粒子运输法计算与实际测量的60 Co治疗机剂量分布比较

目的 探讨蒙特卡罗N粒子运输法(MCNP)模拟计算的可行性.方法 用百分深度剂量(PDD)分布及标准峰值散射因子(NPSP),比较水模体计算值和实际测量及报告值之间的差异.结果 在10 cm×10 cm射野时,测量值和计算值之间差异无统计学意义(t=-0.41,P>0.05),而在5 cm×5 cm及12 cm×12 cm时,测量值与计算值之间差异有统计学意义(t=7.2、-4.6,P<0.05).计算值和报告值之间符合良好,差异无统计学意义(t=-1.906,P>0.05).同一射野最大剂量点下百分深度剂量随深度增大而减少,同一深度处百分深度剂量随射野增大而增大;同一深度处射野中心轴上的剂量最高,向射野边缘剂量逐渐减少.结论 利用蒙特卡罗MCNP可以建立一组准确和全面的百分深度剂量及标准峰值散射因子参数,为放疗质量保证和质量控制提供依据.

Abstract：

Objective To discuss the feasibility of Monte Carlo N-particle transport code(MCNP)simulated calculation.Methods The calculation in water phantom was contrasted with the practical measurements and the reported values using the percent depth dose(PDD)curve and normal peak scatter factor.Results There Was no significant difference between calculated and measured results in the 10 cm×10 cm field(t＝-0.41,P>0.05),however,there were significant differences in the 5 cm×5 cm field(t=7.2,P<0.05)and in the 12 cm×12 cm field(t=-4.6,P<0.05).There was no significant difierence between the calculated results and the reported values(t=-1.91,P>0.05).In the same radiation field,the PDD decreased as the depth increased,but increased as the size of the radiation field increased at the same depth.PDD and normal peak scatter factor were both important parameters for calculation of prescribed dose.Conclusions It is possible to establish a set of accurate and comprehensive percent depth doses and normal peak scatter factor parameters so as to provide the basis of clinical use, quality assurance and quality control for radiotherapy.     

人体体表面积计算方法的比较研究

人体体表面积是体质评价中的重要指标之一。目前 ,对人体体表面积的计算模型有 4种。对运用 4种模型所计算出的 1 8～2 4岁大学男生的体表面积 (m2 )值进行F方差分析 ,各数值之间存在显著性差异 (P <0 0 5)。从中选择相对更合适的计算模型 ,以减少计算的误差 ,为体育训练和科研实践提供相对科学合理的计算方法。     

剂量计算中解析组织非均匀性修正方法的比较研究

目的研究和比较目前放射治疗计划系统中常用的几种组织非均匀性修正方法。方法通过真实病人算例对不同修正方法的计算精度和计算速度进行对比测试。结果等效组织空气比修正（ETAR）方法虽然较Batho等修正方法考虑的影响因素多，但ETAR方法在大大增加计算时间的基础上，计算精度并未得到明显的提高。结论可使用新近开发的混合Batho修正方法替代目前计划系统中常用的ETAR方法。     

成年女性体表面积计算方法比较研究

目的:比较5种成年女性人体体表面积计算模型的差异,从中选择相对最适宜的计算模型。方法:依据浙江省丽水市2005年国民体质监测数据库中成年女性的身高、体重等指标,运用5种计算模型计算其体表面积,并进行F方差分析检验。结果:5种模型计算的体表面积(m2)值,经F方差分析检验,模型1与模型2、模型1与模型3、模型1与模型4、模型2与模型3、模型2与模型4、模型2与模型5、模型3与模型5之间,差异性显著(P<0.05);模型1与模型5、模型3与模型4之间无显著性差异(P>0.05)。依据5种人体体表面积计算模型所计算出的∑rij值的大小排序,依次是模型4、模型5、模型2、模型3、模型1。结论:模型4相对较为符合当代成年女性体表面积的计算。     

MRI与正电子发射计算机体层、单光子发射计算机体层显像检测活性心肌的对比研究

目的评估各种影像学方法检测心肌活性的价值。方法建立慢性心肌缺血模型猪10只，按照美国心脏病协会推荐的方法将左心室分为16节段，分别于制作模型前和后1～2个月进行MR多技术联合应用扫描及正电子发射计算机体层显像(PET)、^201铊单光子发射计算机体层显像(^201Tl SPECT)检查，判断心肌缺血区和坏死区的大小，并与病理结果对照，了解各种方法的敏感性、特异性。结果7只动物顺利完成所有检查，共计112个节段。静息时MR电影扫描共有10个(8.93％)节段运动丧失，4个(3．57％)节段运动轻度减弱，2个(1.78％)节段运动明显减弱；负荷后MR电影扫描共有10个(8.93％)节段运动丧失；心肌灌注扫描见34个(30．36％)节段缺血，心肌活性扫描见12个(10.71％)节段坏死；PET检查见17个(15．18％)节段为梗死心肌；SPECT检查见9个(8.04％)节段为梗死心肌；氯化三苯基四氮唑(TTC)染色见14个(12．50％)节段为无红染的苍白色梗死区。PET检出的坏死节段多于MR心肌活性扫描(X^2=5，P=0．0253，Kappa=0．8028)和电影扫描(X^2=7，P=0．0082，Kappa=0.7079)，并有统计学意义；亦多于TTC染色显示的坏死节段，但无统计学意义(X^2=3，P=0．0833，Kappa=0．8879)；SPECT检出的坏死节段较TTC染色显示的节段少，并有统计学意义(X^2=5，P=0.0253，Kappa=0．7590)；MR电影检出的坏死节段较TTC染色显示的节段稍少，并有统计学意义(X^2=4，P=0．0455，Kappa=0、8100)；MR心肌活性扫描检出的坏死节段和TTC染色显示的坏死节段相比无统计学意义(X^2=2，P=0、1573，Kappa=0．9130)。以TTC染色结果为金标准，MR电影、MR心肌活性扫描、PET和SPECT检出无活性心肌的敏感性、特异性分别为71．43％、100．00％；85.71％、100．00％；100．00％、96．94％；64.29％、100．00％。结论MR心脏检查可结合形态、功能及灌注多种方法检测活性心肌，清晰显示心肌梗死的位置、程度，并可对左室室壁运动进行直观显示，且价格相对PET便宜；PET检查高估心肌坏死范围，且不能判断心肌梗死是透壁梗死还是心内膜下梗死；MRI和PET、病理结果均有较高一致性。     

Effects of heterogeneities in dose distributions under nonreference conditions: Monte Carlo simulation vs dose calculation algorithms

The purpose of this study is to evaluate the performance of dose calculation algorithms used in radiotherapy treatment planning systems (TPSs) in comparison with Monte Carlo (MC) simulations in nonelectronic equilibrium conditions. MC simulations with PENELOPE package were performed for comparison of doses calculated by pencil beam convolution (PBC), analytical anisotropy algorithm (AAA), and Acuros XB TPS algorithms. Relative depth dose curves were calculated in heterogeneous water phantoms with layers of bone (1.8?g/cm³) and lung (0.3?g/cm³) equivalent materials for radiation fields between 1?×?1?cm² and 10?×?10?cm². Analysis of relative depth dose curves at the water-bone interface shows that PBC and AAA algorithms present the largest differences to MC calculations (u_MC?=?0.5%), with maximum differences of up to 4.3% of maximum dose. For the lung-equivalent material and 1?×?1?cm² field, differences can be up to 24.3% for PBC, 11.5% for AAA, and 7.5% for Acuros. Results show that Acurus presents the best agreement with MC simulation data with equivalent accuracy for modeling radiotherapy dose deposition especially in regions where electronic equilibrium does not hold. For typical (nonsmall) fields used in radiotherapy, AAA and PBC can exhibit reasonable agreement with MC results even in regions of heterogeneities.     

Simulations of X-ray spectra,half value layer,and mean energy from mammography using EGSnrc Monte Carlo and SpekPy

IntroductionThis study presents the simulation results of X-ray spectra, half value layers (HVLs), and mean energies (E_mean) of two mammography units using EGSnrc Monte Carlo (MC) and SpekPy computer codes.MethodsThe spectra caused by different combinations of targets/filters at various tube voltages (kVps) of two mammography units were simulated using two different computer codes. The EGSnrc MC simulated data of spectra and E_mean were compared with those obtained from SpekPy. The simulated values of two units’ HVLs obtained from two computer codes were compared with those from physical measurements from mammography machines used in clinical practice.ResultsThe maximum discrepancies in E_mean simulated from two codes were less than 4.1% and 1.5% for the target/filter combination of W/Rh and Mo/Mo, respectively. The HVLs of the SpekPy were well matched to the physical measurements. The percentage differences were within 3.3% and 6.8% for two units, respectively. The EGSnrc MC simulated values of HVLs show the percentage differences within 8.9% and 7.0% with those from physical measurements for two units, respectively. All methods of HVLs determination comply with the requirements of IAEA Human Health Series No.17.ConclusionsThe HVLs, E_mean, spectra varied depending on the target/filter combinations and composition of the mammography tubes. The simulation results verify that the HVLs evaluation using the EGSnrc MC and SpekPy can be validated for mammography standard beam qualities and provide prediction almost immediately compared with physical experiments.Implications for practiceEGSnrc MC and SpekPy have been considered powerful toolkits to simulate typical X-ray tubes used in mammography due to the good agreement between the calculation of E_mean, physical measurements and simulated HVLs.     

Organ and effective dose conversion coefficients for radiographic examinations of the pediatric skull estimated by Monte Carlo methods

The objective of the present work was to provide precise effective and organ dose data for radiographic examinations of the skull performed on pediatric patients. To accomplish this, the MCNP4C2 transport code was utilized and 18 mathematical anthropomorphic phantoms, representing ages from a newborn child to a 17-year-old adolescent, were developed. Three common projections, anterior–posterior, posterior–anterior and lateral, were considered. The results consist of effective and organ radiation doses normalized to the entrance surface dose. Normalized data are presented for a wide range of peak kilovoltages and beam filtration values so that doses for any X-ray unit can be calculated. Both organ and effective dose values showed an inverse correlation with age. Good agreement was observed between the normalized effective doses produced in this study and values derived from calculations based on the National Radiological Protection Board coefficients for specific mathematical phantoms representing 1-, 5-, 10- and 15-year-old children. In the present work, dose data for nine mathematical phantoms representing 0-, 1-, 2-, 3-, 4-, 5-, 6-, 9- and 14-year-old pediatric patients were provided for estimation of organ and effective doses delivered to pediatric patients from radiographic examinations of the skull.     

Monte Carlo dose calculations for a 6-MV photon beam in a thorax phantom

Purpose In this study we evaluated the accuracy of the Monte Carlo (MC) and effective path length (EPL) methods for dose calculations in the inhomogeneous thorax phantom. Materials and methods The Philips SL 75/5 linear accelerator head was modeled using the MCNP4C Monte Carlo code. An anatomic inhomogeneous thorax phantom was irradiated with a 6-MV photon beam, and the doses along points of the central axis of the beam were measured by a small ionization chamber. The central axis relative dose was calculated by the MCNP4C code and the EPL method in a conventional treatment planning system. The results of calculations and measurements were compared. Results For all measured points on the thorax phantom the results of the MC method were in agreement with the actual measurement (local difference was less than 2%). For the EPL method, the amount of error was dependent on the field size and the point location in the phantom. The maximum error was +19.5 and +26.8 for field sizes of 10 × 10 and 5 × 5 cm² for lateral irradiation. Conclusion Our study showed large, unacceptable errors for EPL calculations in the lung for both field sizes. The accuracy of the MC method was better than the recommended value of 3%. Thus, application of this method is strongly recommended for lung dose calculations, especially for small field sizes.     

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Estimating the dose delivered to the patient in X-ray computed tomography (CT) examinations is not a trivial task. Monte Carlo (MC) methods appear to be the method of choice to assess the 3D dose distribution. The purpose of this work was to extend an existing MC-based tool to account for arbitrary scanners and scan protocols such as multi-slice CT (MSCT) scanners and to validate the tool in homogeneous and heterogeneous phantoms. The tool was validated by measurements on MSCT scanners for different scan protocols under known conditions. Quantitative CT Dose Index (CTDI) measurements were performed in cylindrical CTDI phantoms and in anthropomorphic thorax phantoms of various sizes; dose profiles were measured with thermoluminescent dosimeters (TLD) in the CTDI phantoms and compared with the computed dose profiles. The in-plane dose distributions were simulated and compared with TLD measurements in an Alderson-Rando phantom. The calculated dose values were generally within 10% of measurements for all phantoms and all investigated conditions. Three-dimensional dose distributions can be accurately calculated with the MC tool for arbitrary scanners and protocols including tube current modulation schemes. The use of the tool has meanwhile also been extended to further scanners and to flat-detector CT.     

蒙特卡罗模拟方法结合不同体模在剂量估算中的应用

随着核与辐射在人们日常生活中的应用越来越广泛,其所带来的危害也备受关注。剂量估算是辐射技术应用的重要一环,估算出人体所受的剂量对评价辐射造成的确定效应与随机效应起着重要作用。蒙特卡罗（MC）模拟与人体参考模型结合可对核事故、医疗照射和环境的辐射剂量进行估算,是一种快速且对硬件要求较少的剂量估算方法,目前正面临模型开发和计算耗时的瓶颈,笔者对此现状进行综述。     

153Sm-EDTMP吸收剂量的MonteCarlo和MIRD算法比较

目的以153Sm-乙二胺四甲撑膦酸(153Sm-EDTMP)治疗鼻咽癌多发性骨转移为例,分别用蒙特卡罗法(Monte Carlo,MC)和MIRD方法计算153Sm-EDTMP治疗后病灶和骨髓等靶器官的吸收剂量,探讨其临床应用之不同.方法基于病人时序性SPECT/CT扫描和累积尿液的放射性测定,利用优化的MC EGS4程序和MIRD方法分别计算病灶和其他靶器官的吸收剂量.结果MC EGS4法计算结果提示病灶内剂量分布不均匀.患者注射153Sm-EDTMP 33.6×37 MBq,左髂骨转移病灶最高吸收剂量约为5.6 Gy,病灶边缘的吸收剂量为2.0 Gy,以病灶区最高剂量点为参考点,则椎体、皮质、骨髓、脊髓和盆腔组织仅相当于最高剂量的37%、12%、13%、21%和2%;MIRD方法的计算数据仅能粗略提示全身红骨髓吸收剂量,为2.39 Gy.结论MC EGS4方法能准确计算病灶、骨髓和其他靶器官的内照射吸收剂量,故可以真正指导核素临床治疗;而MIRD仅能大致评估153Sm-EDTMP的骨髓毒性.     

蒙特卡罗模拟在放射诊断辐射剂量估算和优化中的应用

放射诊断成像的频次和对公众的累积剂量不断提升, 带来的辐射风险引起广泛关注, 但人体所接受辐射剂量的准确测量很难实现。蒙特卡罗模拟作为以概率统计理论为指导的数值计算方法, 已应用于各种放射诊断成像的剂量评估、成像优化和辐射防护。本文就蒙特卡罗方法的原理、蒙特卡罗模拟的建模过程及其在放射诊断剂量估算的应用进展进行综述。     

蒙特卡罗方法在质子重离子加速器治疗场所屏蔽计算中的应用

目的 利用蒙特卡罗方法建立质子重离子加速器治疗场所的屏蔽计算模型,为治疗场所的屏蔽设计提供可靠的计算方法。方法 采用基于蒙特卡罗方法的FLUKA程序建立质子重离子治疗场所的屏蔽计算模型,模拟质子重离子加速器治疗场所辐射场的分布,通过对质子重离子加速器治疗场所的检测,验证计算模型。结果 FLUKA程序模拟计算结果与现场检测结果具有较好的符合性。结论 FLUKA程序建立的质子重离子加速器治疗场所屏蔽计算模型能够模拟质子重离子产生的辐射场。基于FLUKA程序建立的屏蔽计算模型,质子重离子治疗场所屏蔽设计应根据加速器最高可达的束流强度及能量进行计算。在质子和重离子加速器运行时的治疗室辐射场中,中子对剂量当量的贡献是主要的,因此,屏蔽设计中应重点考虑中子的屏蔽。