一种计算不规则野的散射剂量的方法研究

目的寻找一种可用于计算放射治疗不规则野的散射剂量的可靠方法。方法通过对原用于计算规则野等效方野的Day氏函数法进行改进,使之扩大应用到不规则野,从而既能计算不规则野的等效方野,也可以计算不规则野中任意点的散射剂量。结果改进后的Day氏函数随照射深度的变化进行修正,大大提高了计算精度,不规则野的散射剂量的计算误差在1.5%以内。结论用改进的Day氏函数法可以计算不同照射能量和照射深度的任意形状射野的散射剂量,并取得满意的精度。     

X射线1/4照射野的输出剂量计算及剂量测量验证

新型的直线加速器中均配有独立准直器 ,在某些临床治疗中 ,需要用到非对称射野来削弱线束扩展的影响 ,以减少对正常组织的照射剂量。有时为了相邻野的衔接 ,避免组织中剂量冷热点的出现 ,也要用到独立准直器功能。对于常规不对称射野处方剂量的计算许多文献均有论述[1 3 ] ,某些病例如乳腺癌病人等需用到的双不对称射野 ,Ｘ轴切线照射避免正常肺受量 ,Ｙ轴切线照射能使得与锁骨上野有良好衔接。笔者分析了这一类双不对称射野 (简称 1 4照射野 )的剂量计算 ,并对结果进行实测验证 ,现报道如下。一、材料和方法1 使用的仪器设备 :西门子Ｍｅ…     

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。     

医用高能X射线剂量测量SSDL-TLD国际比对

医用高能Ｘ射线剂量测量ＳＳＤＬ－ＴＬＤ国际比对程金生姜庆寰李开宝张绍刚国际原子能机构（ＩＡＥＡ）和世界卫生组织（ＷＨＯ）为了提高世界范围内放射治疗剂量的一致性和准确度，在发展中国家建立了二级标准剂量学实验室网（ＳＳＤＬｓ），ＩＡＥＡ为了检查各ＳＳＤＬ...     

利用MC方法计算小鼠体内辐射剂量的体素模型的建立

目的建立一个与蒙特卡罗方法结合进行辐射剂量计算的小鼠体素模型。方法采用一只28g雄性裸鼠的序列切片图像,对此序列图片进行配准、组织识别、分割、颜色赋值后,最后在蒙特卡罗程序MCNP中赋予一定的物理属性。结果建立了一个可以满足剂量分布计算所需精度,并且模拟计算时间适中的小鼠体素模型,此模型器官数量为14个,体素大小为0.2mm×0.2mm×0.2mm。结论该研究所建立的小鼠体素模型可用来进行电离辐射剂量学的模拟计算,以开展放射医学、核医学及空间辐射医学等相关领域的研究。     

组织不均匀条件对调强计划系统计算模型精度的影响

目的 探讨在组织不均匀条件下,治疗计划系统(MONACO)中的有限笔形束算法(FSPB)与快速X射线体积元蒙特卡罗算法(XVMC)的调强放射治疗计划计算精度差别,以及对临床治疗的影响和各自的应用范围。方法 在非均匀仿真人体模型中,对两种算法模型计算的规则照射野及调强照射野的剂量精度,利用经过刻度的放射性铬胶片(EBT2胶片),进行剂量测量以及二维平面剂量的分析比对。结果 在非均匀仿真人体模型中,不同能量的X射线规则照射野,XVMC算法在不同介质中的剂量计算与胶片测量的结果偏差均在±2.00%范围内,而FSPB计算的结果与测量结果的偏差除了15 MV射野为10 cm×2 cm情况下肺中的剂量偏差高达6.51%以外,其他条件下的结果偏差都在±3%范围内。调强放疗计划(IMRT)的胶片验证测量结果中,3%/3 mm γ通过率XVMC算法组>90%;FSPB算法组为80%~90%,且4%/4 mm γ通过率>90%。结论 当临床治疗病例的组织密度不均匀性较大、子野数较多时,XVMC算法的剂量计算精度优于FSPB算法,采用XVMC治疗设计胸腹部IMRT治疗计划可以将算法所引起的误差控制在±3%以内,而且可以避免由于算法原因所致的计划靶区剂量缺失。     

基于中国儿童参考体模的X射线摄影剂量评估

目的:建立中国儿童面元参考体模,并将其应用于儿童X射线摄影的剂量评估中。方法:基于不同年龄儿童的CT原始数据,经过器官勾画、器官调整优化等过程建立起5和10岁的中国儿童面元参考体模。基于上述体模,利用蒙特卡罗方法,对X射线摄影进行建模,计算不同照射条件下儿童受检者器官剂量转换系数及有效剂量转换系数。结果:建立的5和10...     

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.     

放疗中呼吸运动对不同形状射野剂量分布的影响

目的 利用剂量胶片分析研究放射治疗中呼吸运动对靶区剂量分布的影响。方法应用可内置胶片的QUASAR多功能呼吸运动体模,在运动和静止状态下分别照射正方形、圆形、椭圆形、哑铃形和凹形5种形状的模拟射野。比较其剂量分布的差别。用平板体模在位移为0、0.5、1.0、1.5和2.0cm时分别照射圆形、椭圆形、正方形射野,比较不同靶区位移大小对剂量分布的影响。应用的比较方法包括等剂量线、γ值和NAT比较法。提出面积变化因子F_s(运动状态下面积/静止状态面积或位移不为0时的面积/位移为0时的面积。以F_S90、F_S50、F_S25分别代表90%、50%、25%剂量曲线包围的面积在不同状态下的比值)。结果 与静态下相比,水平运动状态下的F_S90减小,F_S25增大。位移越大,它们偏离程度越大。垂直运动状态,正方形和哑铃形射野的F_s有变化,其余变化很小。γ值和NAT比较:各射野的水平运动状态和静止状态比较,P_γ＜60%和P_NAT＜75%;正方形、圆形、凹形和哑铃形照射野的垂直运动状态与静态下相比,P_γ＜85%;平板体模验证中,P_γ和P_NAT随着位移的增大而减小。结论 呼吸运动对靶区放射治疗的剂量分布的影响表现为沿运动方向高剂量区域内收,低剂量区扩大,这种影响随着肿瘤位移的增大而增大。     

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.     

Monte carlo dose calculations in the treatment of a pelvis with implant and comparison with pencil-beam calculations

In the present paper, dose distribution calculated with the Monte Carlo code EGS4 and with a pencil-beam algorithm are compared for the treatment of a pelvis with an implant. Overestimations of dose values inside the target volume by the pencil-beam algorithm of up to 10% were found, which are attributed to the underestimation of the absorption of photons by the implant. The differences in dose distributions are also expressed by comparing the tumor control probability (TCP) of the Monte Carlo dose calculations with the TCP of the pencil-beam calculations. A TCP reduction of order of 30% was found.     

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.     

斑马鱼计算模型构建与相关剂量系数的计算

目的:为了评估核电对周围环境的辐射影响,通过模式动物精细化建模,构建剂量评估模型并确定相关剂量系数。方法:针对核电液态流出物辐射危害评估中的重要水生模式生物斑马鱼,建立用以剂量估算的斑马鱼含有内部骨骼和内脏器官的几何模型。使用蒙特卡罗方法,以核电液态流出物及周围环境监测中常见的 3H、 40K、...     

An equivalent square method for irregular photon fields

A quick formula is proposed for calculating equivalent squares of irregularly shaped photon fields. No complex calculations are required. Three different energies (⁶⁰Co; 6 MV and 18 MV x-rays) were investigated. Comparison with results utilizing the Clarkson technique (⁶⁸Co) and with experimental measurements (6 MV and 18 MV x-rays) indicates that the method is accettable in a wide variety of clinical situations. The applied procedure introduces an indetermination lower than 4%, with maximum absolute percentage errors of 3%, 2.7%, and 3.6% for 6 MV, 18 MV, and ⁶⁰Co photon fields respectively.     

调强放射治疗中剂量计算与射野参数优化研究

目的研究调强放射治疗中剂量计算模型的建立与射野参数自动选择的实现方法.方法用快速傅立叶变换建立三维光子卷积剂量计算模型,用基于剂量的目标函数作为遗传算法个体适应度的评价指标,用遗传算法实现射野权重的优化.结果经过遗传算法100次迭代,能够得到适形度较高、剂量分布较均匀的剂量分布.结论基于快速傅立叶变换的三维光子卷积剂量计算模型是一种较精确的模型;遗传算法是一种效率较高的IMRT射野参数优化方法.     

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.     

光子束不规则射野的等效方野计算方法

目的探讨一种快捷、准确求光子束不规则射野等效方野的方法。方法不规则射野按对称射束中心与不对称射束中心分为两类，每类再以不规则野的周长与原开野周长的比值R分为：R〉1，R=1，R〈1三种情况。选择6种不规则射野，实测吸收剂量；分别用A，B,C3种方法计算其等效方野，用等效后方野剂量参数计算处方剂量，与实测剂量比较。结果R〉1，B方法准确；R=1，A和C方法较准确，B方法亦符合精度要求；R〈1，A，B，C方法一致准确。结论笔者推荐临床使用B方法，便于标准化操作，准确性符合要求。     

点扫描碳离子束流模型的蒙特卡罗模拟与验证的初步研究

目的:使用蒙特卡罗程序FLUKA建立点扫描碳离子束流模型并对其进行验证。方法:使用FLUKA建立同步加速器碳离子束流治疗头的几何模型,匹配实验测量数据中的单能标称能量、高斯能谱分布、初始束斑大小以及束流的角分布等各项参数;利用治疗计划系统生成碳离子束流治疗计划,通过γ分析比较FLUKA束流模型与治疗计划系统输出的剂量分布差异,验证该模型的准确性。结果:单能碳离子束流的深度剂量分布差异均在0.1 mm之内,束斑大小最大差异为0.17 mm;对于每个靶区,2 mm/2%标准下的2D-与3D-γ通过率均在95%以上。结论:基于蒙特卡罗程序FLUKA实现了点扫描碳离子束流输运过程的精准模拟。该模型能够用于临床治疗计划的模拟验证,并进一步应用于新型粒子治疗设备在开发阶段的模拟以及生物有效剂量的计算。