A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems

Purpose

To investigate the variability of the global gamma index (γ) analysis in various commercial IMRT/VMAT QA systems and to assess the impact of measurement with low resolution detector arrays on γ.

Materials

Five commercial QA systems (PTW 2D-Array, Scandidos Delta4, SunNuclear ArcCHECK, Varian EPID, and Gafchromic EBT2 film) were investigated. The response of γ analysis to deliberately introduced errors in pelvis and head & neck IMRT and RapidArc™ plans was evaluated in each system. A theoretical γ was calculated in each commercial QA system software (PTW Verisoft, Delta4 software, SNC Patient, Varian Portal Dosimetry and IBA OmniPro, respectively), using treatment planning system resolution virtual measurements and compared to an independent calculation. Error-induced plans were measured on a linear accelerator and were evaluated against the error-free dose distribution calculated using Varian Eclipse™ in the relevant phantom CT scan. In all cases, global γ was used with a 20% threshold relative to a point selected in a high dose and low gradient region. The γ based on measurement was compared against the theoretical to evaluate the response of each system.

Results

There was statistically good agreement between the predicted γ based on the virtual measurements from each software (concordance correlation coefficient, ρ_c > 0.92) relative to the independent prediction in all cases. For the actual measured data, the agreement with the predicted γ reduces with tightening passing criteria and the variability between the different systems increases. This indicates that the detector array configuration and resolution have greater impact on the experimental calculation of γ due to under-sampling of the dose distribution, blurring effects, noise, or a combination.

Conclusions

It is important to understand the response and limitations of the gamma index analysis combined with the equipment in use. For the same pass-rate criteria, different devices and software combinations exhibit varying levels of agreement with the predicted γ analysis.     

移动DR乳腺摄影研究

目的:研究普通DR进行数字乳腺摄影可行性。方法:用佳能可移动DR板和国产乳腺钼靶X线机进行试验拍片对比。结果:制作的数字乳腺片质量较高。结论:普通DR板可用于高质量的数字乳腺片制作。     

Rapid resolution liquid chromatography (RRLC) analysis and studies on the stability of Shuang-Huang-Lian preparations

Shuang-Huang-Lian (SHL) is a traditional Chinese formula which comprises of three medicinal herbs: Flos Lonicerae, Radix Scutellariae and Fructus Forsythiae, and is commonly used to treat acute upper respiratory tract infection, acute bronchitis and light pneumonia. A simple, reliable and reproducible rapid resolution liquid chromatography (RRLC) method was developed for the quality control of SHL preparations, which baseline separates the major bioactive compounds within 6 min. The method uses a C18-HST column (2.5 μm, 100 mm × 3.0 mm) kept at 40 °C. The mobile phases consist of 0.1% phosphoric acid aqueous solution and acetonitrile. Flow rate is 1.0 ml/min and UV detection is performed at 327 nm from 0 to 4 min and 229 nm from 4 to 7 min. This method was further validated according to the ICH guidelines. Eight batches of commercial SHL preparations obtained from different pharmaceutical manufacturers as well as individual herbs were examined and their chromatographic profiles were compared. The stability test revealed that chlorogenic acid is stable only at acidic pH, and hence it is necessary to further evaluate and optimize the preparatory procedures and storage conditions for commercial SHL preparations.     

Detection accuracy of in vitro approximal caries by cone beam computed tomography images

Aims

To evaluate the diagnostic accuracy of approximal carious lesions among five CBCT systems and to assess the effect of detector types employed by different CBCT systems on the accuracy of approximal caries diagnosis.

Materials and methods

Thirty-nine extracted non-cavitated human permanent teeth were employed in the study. Seven observers evaluated 78 approximal surfaces of the teeth with respect to caries by the images from the following five CBCT systems: (1) NewTom 9000; (2) Accuitomo 3DX; (3) Kodak 9000 3D; (4) ProMax 3D; and (5) DCT PRO, respectively. The lesions were validated by histological examination. The area under receiver operating characteristic (ROC) curve (A_z) was used to evaluate the diagnostic accuracy.

Results

Microscopy of approximal surfaces found 47.4% sound, 39.8% enamel and 12.8% dentin lesions. The differences of A_z values among the five CBCT systems were not statistically significant (p = 0.348). No significant difference was found between the two detector types of CBCT systems (p = 0.47).

Conclusions

The five CBCT systems employed in the study showed no significant difference in the in vitro approximal caries detection. Neither the detector nor the FOV employed by the CBCT systems has an impact on the detection accuracy of approximal caries.     

浅谈螺旋CT机维护与保养

本文从环境、电源、球管、部件等方面，以日常、定期维护双角度出发，阐述了螺旋CT机维护与保养的方法措施和注意事项，以提高机器的运转率和社会经济效益。     

数字X线摄影技术

本文介绍几种数字X线摄影检测技术.     

HPGe探测效率和符合相加修正系数的蒙特卡罗计算

目的 介绍用蒙特卡罗(MC)方法编写的计算HPGe探测器探测效率和符合相加修正系数的程序(Cool 2000-HpGe),及实验值与计算值的比较研究。方法 用MC计算得到的探测效率和符合相加修正系数与实验得到的值进行比较。结果 对空气、水和土壤三种模拟基质体标准源由实验(ORTEC ADCOM100+GEM50195 HPGe γ谱仪系统)得到的符合相加修正系数值与模拟计算值之间的相对偏差绝对值分别为5.14%、12.1%和10.4%,在点源距探测器端窗5、10和25 cm处的由实验得到的探测效率值与模拟计算值之间的相对偏差绝对值分别为10.6%、5.6%和3.0%。结论 笔者报道的MC计算软件Cool 2000可以在环境放射性监测中用于计算HPGe探测器探测效率和符合相加修正系数。     

小野剂量学临床实践指南

小野剂量学是立体定向放射治疗、立体定向放射外科手术以及调强放疗等精确放疗技术中小照射野物理剂量精确性的理论基础。相比于常规射野,小野的应用增加了临床剂量的不确定度,而且剂量误差较常规射束大。为了确保小野剂量学和探测器标准化使用,在国家癌症中心/国家肿瘤质控中心的组织领导下,多家医疗单位共同参与,结合国内临床需求以及加速...     

东北地区土壤中放射性核素含量的抽样测量与分析

目的 测量东北地区土壤中放射性核素含量,从当地气候、成土母岩分布、植被分布、受放射性污染的程度等角度研究不同区域土壤中放射性核素含量存在差异的原因,并评估其对地表γ辐射量的贡献。方法 应用北京核仪器厂生产的BH 1936型低本底多道γ谱仪对由中国计量科学研究院提供的混合体标准源进行测量,得到探测器对²³²Th、²²⁶Ra、²³⁸U和⁴⁰K四种核素所发出的最大γ分支比的全能峰探测效率。测量土壤样品的γ能谱,分析计算得到土壤样品中的放射性核素的含量。结果 通过对东北地区不同区域26份常见土壤样品中天然放射性核素的放射性活度进行抽样测量与数据处理,得出土壤中²³²Th、²²⁶Ra、²³⁸U和⁴⁰K的含量均值分别为:52.9 Bq/kg,44.8 Bq/kg,50.3 Bq/kg,820.3 Bq/kg,较以往年所得数值略有增加。结论 结果表明,²³²Th含量在残积母质类土壤中最高,在沉积母质类土壤中最低;²²⁶Ra和²³⁸U含量在冲积母质类土壤中最高,在残积母质类土壤中最低;⁴⁰K含量在沉积母质类土壤中最高,在冲积母质类土壤中最低。²³²Th和⁴⁰K含量在山地中最高,在平原中最低,而²²⁶Ra和²³⁸U含量则是在平原中最高,在山地中最低。根据土壤中放射性核素含量估算东北地区的年有效环境剂量(0.54 mSv),其值符合正常标准。     

60Co治疗机辐射场分布的研究

目的 研究⁶⁰Co治疗机房内辐射场分布,为辐射屏蔽防护设计和放疗设备的性能质量控制提供基础数据,建立估算方法。方法 采用热释光TLD对⁶⁰Co治疗机工作状态下,场所内的辐射剂量空间分布进行研究。结果 在同一高度平面,2 π范围内,距中心轴等距处的剂量分布呈一致趋势,最大偏差3.9%。在同一高度平面,各角度上的剂量随与中心轴距离增大而呈幂指数衰减。不同高度平面上,地面的剂量最高,机房顶层3 m以上空间剂量分布趋于均匀。结论 采用的TLD剂量计测定⁶⁰Co治疗室内辐射场分布是有效可行的,通过实验数据得到的辐射场剂量分布曲线可用于辐射防护屏蔽设计。