基于SRIM分析碳离子治疗中Bragg峰的分布特征

目的 基于SRIM软件对碳离子束在材料中布拉格（Bragg）峰的分布特征进行分析,并探索利用CT值计算碳离子束入射能量。方法 通过SRIM软件,研究能量范围在100～300 MeV/u的碳离子束入射到不同等效材料中的输运情况,分析碳离子入射能量、等效材料及厚度等对其Bragg峰深度的影响。采用Origin 2017进行数据拟合,分析CT值与Bragg峰深度水等效比间的函数关系。结果 随着入射碳离子束能量增加,发现碳离子束在等效材料中的Bragg峰深度与水中Bragg峰深度的比值近乎为常数。通过CT值与Bragg峰深度水等效比D_i间的函数关系,能够将特定能量碳离子束在等效材料中的Bragg峰深度换算为水中等效Bragg峰深度。结论 利用人体组织不同体积单元的Bragg峰深度水等效比D_i和CT值,能够精确算出Bragg峰落在肿瘤部位所需的水中等效Bragg峰深度,据此可反推出碳离子束所需的入射能量。     

基于Geant 4程序模拟质子打薄靶能量和角度歧离

目的 讨论能量歧离和角度歧离与入射质子能量、靶材料及厚度的关系。方法 利用Monte Carlo模拟软件Geant4,模拟100 keV~10 MeV质子垂直入射铍(Be)、碳(C)、水(H₂O)、铝(Al)、铜(Cu)薄膜后的能量歧离值和角度歧离值。结果 得到能量歧离和角度歧离与薄膜厚度、薄膜材料及入射质子能量的关系。结论 能量歧离主要发生在入射质子100 keV~200 keV能量范围内,当薄膜厚度越大且薄膜材料原子序数越高时,能量歧离和角度歧离越大;当入射质子能量越大时,能量歧离和角度歧离越小。     

应用Geant4模拟EBT3胶片的能量响应和质子射程测量

目的 计算EBT3胶片吸收剂量的能量依赖性，展示EBT3胶片测量质子吸收剂量时的误差。方法 在临床光子和质子能量照射范围内逐步增加射线束能量，应用Geant4计算EBT3胶片吸收剂量与同体积水吸收剂量的差异，并与理论结果进行比对。结果 对于光子和质子来说，EBT3胶片吸收剂量能量依赖性与理论结果一致的分界线分别为100 keV和11 MeV；光子和质子能量高于相应值时EBT3胶片能量依赖性与理论结果保持一致，低于相应值时EBT3胶片能量依赖性与理论结果无关；计算EBT3胶片测量质子布拉格峰和50%剂量点与实际位置的差异，最大误差小于1%。结论 对较高能量区间内的质子和光子来说，EBT3胶片吸收剂量能量依赖性可忽略；对低能量区间的质子和光子，EBT3胶片吸收剂量能量依赖性差异较大，应给予重点关注。EBT3胶片测量的质子布拉格峰和50%剂量点与实际位置基本一致。     

窄束X-γ射线打靶反散射剂量分布

目的 利用窄束X-γ射线打靶模型分析现场探伤时反散射射线剂量分布。方法 通过康普顿散射模型和蒙特卡罗程序MCNP 4C模拟多种打靶条件下反散射剂量分布。结果 反散射射线致剂量在接近±90°时数值最小,最大值出现在接近0°的某处,并随着射线能量的增加而趋于0°。结论 在实际现场探伤中人员应在垂直射线入射方向上寻找最优化撤离隐蔽方案。     

放疗质子束水中分布特性及检测项研究

目的 通过研究质子束流水中分布特性,提出质子束流质量控制的检测项目。方法 参考医用电子加速器性能检测有关内容来提取质子束流检测项目。结果 获得了放疗质子束流的检测项目和指标。结论 质子束质量控制检测项目可以全面的检验质子束流性能。     

应用PEAKFINDER测量质子束深度剂量分布

目的 测量点扫描质子束流水中深度剂量分布,检测最大剂量点与穿透深度的重复性。方法 利用PEAKFINDER测量低能、中能和高能质子束流的水中深度剂量分布,给出深度分布曲线。结果 最大剂量点与穿透深度值重复性的最大标准差分别为0.05、0.03 mm,远低于允许值1 mm。结论 PEAKFINDER测的最大剂量点与穿透深度精确度和重复性满足检测要求。     

质子加速器治疗系统感生放射性辐射场分布

目的 通过测量描述质子加速器治疗系统感生放射性辐射场分布及其变化,提醒放射工作人员注意对感生放射性的防护。方法 使用451P型X、γ电离室巡测仪对质子加速器治疗系统感生放射性辐射场进行测量。结果 描述了该系统不同出束能量后感生放射性剂量分布,通过连续测量分析感生放射性剂量随时间推移的变化。结论 治疗机头部位感生放射水平较高,患者档铅模型对感生剂量场分布影响较大。     

核反应堆中石墨潜能计算方法研究

目的 计算中国原子能科学研究院重水研究堆（101堆）石墨反射层内潜能,为101堆退役工作的开展提供技术支持。方法 利用MCNP的PTRAC卡记录反应堆模型内中子与初级碰撞原子（PKA）碰撞后的中子位置、方向余弦和能量信息,计算得到PKA的能量分布。利用MATLAB将数据制成输入文件导入SRIM软件,模拟PKA对石墨的级联损伤过程,考虑温度对辐照效应的影响后,计算得出石墨反射层内潜能累积量分布。结果 重水研究堆的石墨反射层潜能主要分布在靠近堆芯的内层,且位于轴向上部区域,最大值为1 215.4 J/g。结论 与国外实验数据的对比结果表明,利用MCNP和SRIM软件模拟石墨辐照损伤过程计算石墨潜能积累是可行的。     

某同步辐射光源辐射场特性研究

目的 通过对同步辐射光源电子直线加速器输运段以及储存环所在工作大厅周围辐射场特性分布的研究,掌握类似装置辐射屏蔽应关注的问题。方法 采用经验公式以及FLUKA程序对直线加速器屏蔽体外的剂量率进行计算和模拟,并对结果进行比较分析。结果 取得了较好的一致性。结论 在进行直线加速器的刮束器类部件检修时,应做好防护工作,使有关人员避免受到不必要的照射。直线加速器的运行对外环境和工作人员的影响很小,可以忽略。利用经验公式和利用Monte Carlo进行屏蔽计算两种方法各有其特点,在实际使用时可灵活选择合适的方法。     

基于蒙特卡罗方法的质子治疗室屏蔽防护探讨

目的 探讨质子治疗室屏蔽防护材料和屏蔽厚度的选择,积累质子治疗室屏蔽防护经验,为质子治疗室的建设提供科学依据。方法 采用基于蒙特卡罗方法的FLUKA程序建立质子治疗室的屏蔽计算模型,模拟质子治疗室的辐射场分布,对质子治疗室的屏蔽进行优化。结果 厚度为250 cm混凝土控制室墙外30 cm处周围剂量当量最大为3.12 μSv/h,改变屏蔽方案为5 cm钢板（机房侧）+237 cm混凝土+8 cm聚乙烯（控制室侧）后,周围剂量当量最大值为1.43 μSv/h,调整材料位置后,治疗室控制室墙外30 cm周围剂量当量率最大为3.95 μSv/h。结论 质子治疗室辐射场中,主要是中子和γ射线,中子对剂量当量的贡献占绝大部分比重。且质子治疗室辐射场中主要以高能中子和快中子为主。因此其屏蔽防护主要考虑中子防护,在屏蔽材料的选择上应充分考虑辐射场的中子能量。     

六种不同混凝土在质子治疗机房屏蔽性能研究

目的 研究6种不同混凝土为主墙时,230 MeV质子治疗室主屏蔽体外的剂量水平,获取6种不同混凝土的屏蔽性能.方法 采用FLUKA程序构建计算模型,将不同混凝土组成引入FLUKA程序,模拟230 MeV质子束流照射情况下关注点周围剂量当量率随混凝土厚度的变化,拟合6种混凝土透射曲线,得到6种不同混凝土的屏蔽性能参数.结...     

A fast numerical method for calculating the 3D proton dose profile in a single-ring wobbling spreading system

Based on the determination of protons fluence at the phantom’s surface, a 3D dose distribution is calculated inside a water phantom using a fast method. The dose contribution of secondary particles, originating from inelastic nuclear interactions, is also taken into account. This is achieved by assuming that 60% of the energy transferred to secondary particles is locally absorbed. Secondary radiation delivers approximately 16.8% of the total dose in the plateau region of the Bragg curve for monoenergetic protons of energy 190 MeV. The physical dose beyond the Bragg peak is obtained for a proton beam of 190 MeV using a Geant4 simulation. It is found that the dose beyond the Bragg peak is <0.02% of the maximum dose and is mainly delivered by protons produced via reactions of the secondary neutrons. The relative dose profile is also calculated by simulation of the proposed beam line in Geant4 code. The dose profile produced by our method agrees, within 2%, with the results predicted by the Fermi Eyges distribution function and the results of the Geant4 simulation. It is expected that the fast numerical approach proposed herein may be utilised in 3D deterministic treatment planning programs, to model proton propagation in order to analyse the effect of modifying the beam line.     

Three-dimensional dose-distribution measurement of therapeutic carbon-ion beams using a ZnS scintillator sheet

The accurate measurement of the 3D dose distribution of carbon-ion beams is essential for safe carbon-ion therapy. Although ionization chambers scanned in a water tank or air are conventionally used for this purpose, these measurement methods are time-consuming. We thus developed a rapid 3D dose-measurement tool that employs a silver-activated zinc sulfide (ZnS) scintillator with lower linear energy transfer (LET) dependence than gadolinium-based (Gd) scintillators; this tool enables the measurement of carbon-ion beams with small corrections. A ZnS scintillator sheet was placed vertical to the beam axis and installed in a shaded box. Scintillation images produced by incident carbon-ions were reflected with a mirror and captured with a charge-coupled device (CCD) camera. A 290 MeV/nucleon mono-energetic beam and spread-out Bragg peak (SOBP) carbon-ion passive beams were delivered at the Gunma University Heavy Ion Medical Center. A water tank was installed above the scintillator with the water level remotely adjusted to the measurement depth. Images were recorded at various water depths and stacked in the depth direction to create 3D scintillation images. Depth and lateral profiles were analyzed from the images. The ZnS-scintillator-measured depth profile agreed with the depth dose measured using an ionization chamber, outperforming the conventional Gd-based scintillator. Measurements were realized with smaller corrections for a carbon-ion beam with a higher LET than a proton. Lateral profiles at the entrance and the Bragg peak depths could be measured with this tool. The proposed method would make it possible to rapidly perform 3D dose-distribution measurements of carbon-ion beams with smaller quenching corrections.     

Early skin reaction following superficial proton irradiation.

Balb/c mice were irradiated on the leg in the area of the spread out Bragg peak (SOBP) of a 30 MeV proton beam. The proton beam was modulated to different ranges in order to determine the early skin reaction versus beam quality at different portions of the SOBP. The respective 50% moist desquamation doses of 1, 3, and 8.5 mm penetration were 25.9, 30.0, and 30.4 Gy. Irradiation of the superficial layer with the distal portion of the SOBP produced a significantly more severe reaction than did whole layer irradiation.     

Microdosimetric evaluation of secondary particles in a phantom produced by carbon 290 MeV/nucleon ions at HIMAC

Microdosimetric single event spectra as a function of depth in a phantom for the 290 MeV/nucleon therapeutic carbon beam at HIMAC were measured by using a tissue equivalent proportional counter (TEPC). Two types of geometries were used: one is a fragment particle identification measurement (PID-mode) with time of flight (TOF) method without a backward phantom, and the other is an in-phantom measurement (IPM-mode) with a backward phantom. On the PID-mode geometry, fragments produced by carbon beam in a phantom are identified by the DeltaE-TOF distribution between two scintillation counters positioned up- and down-stream relative to the tissue equivalent proportional counter (TEPC). Lineal energy distributions for carbon and five ion fragments (proton, helium, lithium, beryllium and boron) were obtained in the lineal-energy range of 0.1-1000 keV/microm at eight depths (7.9-147.9 mm) in an acrylic phantom. In the IPM-mode geometry, the total lineal energy distributions measured at eight depths (61.9-322.9 mm) were compared with the distributions in the PID-mode. Both spectra are consistent with each other. This shows that the PID-mode measurement can be discussed as the equivalent of the phantom measurement. The dose distribution of the carbon beam and fragments were obtained separately. In the depth dose curve, the Bragg peak was observed. Relative biological effectiveness (RBE) for the carbon beam in the acrylic phantom was obtained based on a biological response function as a lineal-energy. The RBE of carbon beam had a maximum of 4.5 at the Bragg peak. Downstream of the Bragg peak, the RBE rapidly decreases. The RBE of fragments is dominated by Boron particles around the Bragg peak region.     

Computer simulations of nuclear reactions by protons with incident energies of 250, 300 and 500 MeV in a human body

Computer simulations of nuclear reactions by protons in a human body were carried out at the incident energies of 250, 300 and 500 MeV. About 20% of the incident protons are absorbed by the body with nuclear interactions and the rest of the protons pass through the body at these energies. Radiation of gamma rays from the body and radioactivity of the body were estimated as a function of the time after irradiation with the proton beam.     

8MeV辐照电子加速器辐射特性研究

目的 分析8 MeV辐照电子加速器的辐射特性。方法 建立8 MeV电子轰击铅靶、铁靶、铝靶产生X射线的几何模型,使用MCNP5程序模拟计算得到了0°~180°方向上产生的X射线能谱和0°、90°、180°方向上的剂量率发射常数。结果 剂量率发射常数与NCRP-51报告中的数据基本相符。结论 剂量率发射常数具有明显的方向性,0°方向轰击铅靶最高,随着靶材原子序数的降低或角度的增大而减小;0°方向的X射线能谱最硬,随着靶材原子序数的降低或角度的增大而逐渐变软。