OBI影像引导放射治疗系统的质量保证（QA）及维护保养

目的：利用瓦里安厂家提供的质量保证工具。对瓦里安直线加速器的机载影像引导系统进行常规测量,保证放射治疗中患者位置验证的准确性和安全性。通过对设备日常维护保养的介绍,使操作人员熟悉OBI设备的维护保养,为治疗工作的顺利进行,创造良好的设备环境。方法：根据影像引导系统OBI（OnBoardImager）的验收报告和测量方法,对OBI影像引导系统的安全性、功能性、几何准确性和图像质量进行检测,完成质量保证项目的检测及维护保养。结果：影像引导系统的安全性和功能性均正常,几何准确性方面和图像质量均在允许范围内。未出现因保养不及时而发生的故障。结论：定期的质量保证检测和维护保养表明,OBI系统性能稳定可靠,各项参数指标在允许范围内。定期的维护保养可以有效的减少故障率的发生,提高设备的安全性和可靠性。     

医用直线加速器质控数据分析与管理系统-QAManager的功能设计与临床应用

目的:基于Python Django框架的加速器质控自动化分析网页系统（QAManager）的开发和测试。方法:利用Python Django和MySQL数据库开发系统QAManager,实现加速器质控数据的统计分析和OBI系统影像自动分析功能。使用QAManager对TrueBeam加速器为期半年的质控结果统计分析并进行功能性测试,包括:[①]利用QAManager分析各项质控数据分布和变化趋势,对该段时间内TrueBeam的状态进行综合评估;[②]选取一年内TrueBeam OBI系统扫描Catphan504所得影像,分别使用人工、QAManager分析,并比较两者结果,分析QAManager图像自动识别算法的准确性和精确性;[③]将模体分别向前、后、左、右4个方向移动1 cm,采用QAManager自动检测,分析算法的鲁棒性。结果:QAManager界面简洁紧凑,用户能够使用QAManager自由选择需要展示的质控项目绘制曲线图,清晰显示各项目整体的分布趋势以及出现偏差最大的时间;QAManager能够准确识别到Catphan504 CBCT影像检测中各模块,除层厚（P=0.05）外,人工分析和自动分析结果比较差异没有统计学意义（P>0.05）。结论:QAManager系统准确可靠,算法能够准确地检测出加速器OBI影像系统参数,具有很强的应用性,对科室实现网络化管理具有重要意义。     

隐匿性HBV感染血清学特征及发生机制的研究进展

隐匿性乙型肝炎病毒感染(occult HBV infection,OBI)是一种难以诊断的肝病,具有发展成肝细胞癌的风险,给病毒性肝炎的研究带来了巨大挑战.OBI是宿主免疫控制和病毒基因组变异综合作用的结果,使乙型肝炎病毒的共价闭合环状DNA(cccDNA)处于低复制状态并影响病毒颗粒的分泌,进而导致患者血清HBsAg无法检出.在过去的几十年里,高度敏感的分子生物学技术的广泛应用阐明了OBI的病毒学机制和可能的临床意义,提高了临床上检测OBI的敏感性.本文综述了OBI的概念、血清学特征、发生机制以及临床意义的最新观点.     

Varian多叶准直器(MLC)常规测量方法及质量保证

目的:通过建立一套多叶准直器(MLC)常规测量方法,探讨用MLC进行三维适形放射治疗(3-Dimension confor-mal radiation therapy,3D CRT)质量保证(QA)的内容.方法:物理师采用胶片法对Varian 23EX加速器,120叶MLC、Cadplan治疗计划系统进行治疗前、每日、每月、三个月的质量保证项目检测.结果:MLC形成的照射野与灯光野的重合性、叶片位移的精确度、数字化仪的精度、叶片运动的倾斜度、下垂度、照射野中心均在允许范围内,符合临床要求.结论:Varian 120叶MLC性能稳定、可靠.     

献血者隐匿性乙肝病毒感染的研究进展

隐匿性乙肝病毒感染(occult hepatitis B virus infection, OBI)是乙肝病毒(HBV)感染的特殊类型, 即乙肝表面抗原(HBsAg)检测阴性, 但HBV核酸检测为阳性。本文主要综述了OBI在献血者中的流行情况、传播可能性和检测建议。世界部分国家和国内具有代表性地区献血者OBI的流行率各不相同, 分析表明非洲地区献血者OBI流行率远远高于世界其他地区, 我国南方地区献血者OBI流行率高于北方地区。献血者OBI存在传播乙肝病毒的可能性, 核酸检测和乙肝核心抗体对献血者OBI筛查具有重要意义, 应根据当地HBV流行状况和经济情况选择合适的检测方式, 以期最大限度降低OBI对输血安全的影响。     

献血人群隐匿性乙型肝炎病毒感染的流行病学和血清学研究

目的了解广州地区献血人群隐匿性乙型肝炎病毒感染（OBI）的流行病学和血清学情况。方法对广州地区199631例无偿献血者标本同时用ELISA法检测HBsAg、紫外-乳酸脱氢酶法检测ALT、核酸扩增技术（NAT）联合检测HBV/HCV/HIV及HBV单项鉴别试验,对HBsAg阴性HBV DNA阳性者进行随访,用荧光定量PCR检测病毒载量,用ELISA法检测乙肝两对半。结果 199631例标本中共检出104例HBsAg阴性HBV DNA阳性者,经随访有54例为OBI,OBI检出率为0.027%,年龄以46～55岁组检出率最高（P〈0.01）,外地身份证的献血者检出率高于广州市身份证者（P〈0.01）,OBI检出率与性别和献血次数无关（P〉0.05）。104例HBsAg阴性HBV DNA阳性的标本ALT均正常,病毒载量均〈1000IU/ml,平均值为162IU/ml。随访标本中,除6例ALT异常外其余均正常,54例OBI标本病毒载量均〈1000IU/ml,平均值为122IU/ml,乙肝两对半中抗-HBc阳性率明显高于其他项目（P〈0.01）。结论 HBsAg阴性献血者中存在OBI,有必要在献血者中开展核酸检测。     

做好加速器质量保证的体会

1质量保证的意义 质量保证QA是指为了保证产品或服务满足所要求的质量而必须采取的一系列有计划的或系统的行为措施.在放射治疗中,QA是指为了保证放射治疗设备输出高质量射线使病人的治疗效果最好、副作用最小而采取的有计划和系统的行为措施.在放射治疗领域,质量保证贯穿于对病人实施正确治疗的全过程.     

电子射野影像系统在放疗中的质量保证应用

目的:把电子影像射野系统(EPID)应用到放疗质量保证的多个方面,从而保障病人得到精确放疗。方法:根据不同目的采用EPID不同模式拍片,如单曝光,双曝光,开始-中途-结束,连续拍片等模式,将获得的图像与目的图像进行比较。结果:对于患者的正位和侧位图像能较好的控制摆位误差;能简洁快速地验证光野和射野一致性;能大概地验证治疗计划系统(TPS)中调强射野的注量图;能检验多叶准直器(MLC)的到位精度。结论:充分合理地利用EPID,可在放疗中进行多项质量保证,保证精确放疗。     

电子射野影像装置用于放射治疗的研究进展

用于放射治疗的电子射野影像装置(EPID)探测器主要有荧光屏摄像机系统、扫描矩阵电离室系统和有源矩阵平板探测器系统.基于非晶硅的有源矩阵平板探测器EPID,由于其具有使用方便、分辨率高、采集效率高及性能稳定等特点,已成为近年来用于放射治疗的主流探测器系统.EPID最初主要用于放射治疗的患者靶区位置和射野的验证,后逐步用于放疗设备本身的质量控制.目前的研究方向主要是用于放射治疗的剂量验证.相信通过深入了解EPID特性,开发相应的算法及软件后,其用于放疗设备的常规质量保证、实现在线位置验证和剂量验证等将成为一种常规方法.     

外照射放射治疗计划系统（RTPS）质量控制国际规范综述

目的:研究有关外照射放射治疗计划系统质量控制的国际规范,为我们规范RTPS提供参考.方法:本文简要阐述了关于放射治疗计划系统(RTPS)质量控制(QC)和质量保证(QA)的报告和指导性文件,包括美国医学物理学家协会(AAPM)、国际原子能机构(IAEA)、国际电工技术委员会(IEC)等有关组织发表的RTPS质量控制和质量保证规范,侧重讨论了RTPS进入临床使用之前的质量控制规范.结果:讨论分析了它们关于RTPS进入临床使用之前的质量控制规范.结论:这些规范对于我们开展RTPS的型式试验和验收检验具有指导价值,预期能够形成规范RTPS产品的相关标准.     

A quality assurance program for the on-board imagers

To develop a quality assurance (QA) program for the On-Board Imager (OBI) system and to summarize the results of these QA tests over extended periods from multiple institutions. Both the radiographic and cone-beam computed tomography (CBCT) mode of operation have been evaluated. The QA programs from four institutions have been combined to generate a series of tests for evaluating the performance of the On-Board Imager. The combined QA program consists of three parts: (1) safety and functionality, (2) geometry, and (3) image quality. Safety and functionality tests evaluate the functionality of safety features and the clinical operation of the entire system during the tube warm-up. Geometry QA verifies the geometric accuracy and stability of the OBI/CBCT hardware/software. Image quality QA monitors spatial resolution and contrast sensitivity of the radiographic images. Image quality QA for CBCT includes tests for Hounsfield Unit (HU) linearity, HU uniformity, spatial linearity, and scan slice geometry, in addition. All safety and functionality tests passed on a daily basis. The average accuracy of the OBI isocenter was better than 1.5 mm with a range of variation of less than 1 mm over 8 months. The average accuracy of arm positions in the mechanical geometry QA was better than 1 mm, with a range of variation of less than 1 mm over 8 months. Measurements of other geometry QA tests showed stable results within tolerance throughout the test periods. Radiographic contrast sensitivity ranged between 2.2% and 3.2% and spatial resolution ranged between 1.25 and 1.6 lp/mm. Over four months the CBCT images showed stable spatial linearity, scan slice geometry, contrast resolution (1%; <7 mm disk) and spatial resolution (>6 lp/cm). The HU linearity was within +/-40 HU for all measurements. By combining test methods from multiple institutions, we have developed a comprehensive, yet practical, set of QA tests for the OBI system. Use of the tests over extended periods show that the OBI system has reliable mechanical accuracy and stable image quality. Nevertheless, the tests have been useful in detecting performance deficits in the OBI system that needed recalibration. It is important that all tests are performed on a regular basis.     

术中光子立体定向放射治疗的质量保证和质量控制

【摘要】目的:从术中光子立体定向放疗设备物理剂量学方面,总结和分析术中放疗质量保证的内容和方法以及术中放疗实际应用中的注意事项,保证术中放疗物理剂量准确性,旨在建立该系统的日常质量保证程序。方法:利用蔡司公司提供的水箱、剂量仪、电离室等,测量术中立体定向放射外科系统的临床运用数据。监测内容主要包括剂量线性、稳定性、均匀性、射线几何聚焦的位置、绝对剂量标定以及在水模体的衰减等。结果:术中光子立体定向放疗仪产生50 kV低能射线。剂量线性、均匀性良好,短期稳定性也在临床接受的误差范围以内,36 h内剂量误差小于1%。对比24个月的剂量测量值,其误差达到-4.5%。结论:该设备稳定性良好,各检测指标均在临床要求精度范围以内。通过测量了解了卡尔蔡司公司的INTRABEAM术中放射治疗设备临床应用特性,获得了临床使用数据,为临床提供了质量保证方法。     

放疗定位装置的质控内容与质控管理

质控标准和内容，并进行周期性检测，建立科室放射治疗定位装置台账，专人管理，明确标识，规范使用。结果:经过实践，规范了放射治疗定位装置的使用，完善精确放射治疗质控体系。结论:放疗定位装置的质控减少了放射治疗流程中的摆位误差，提高了放射治疗精度。     

GafChromic RTQA film for routine quality assurance of high-energy photon beams

Self-developing film offers many advantages over conventional radiographic verification film for routine radiotherapy quality assurance (QA). This paper presents results from an initial evaluation of a beam measurement system using GafChromic RTQA film and a flatbed scanner. Variability and energy dependence of the film calibration and accuracy of scanner readout are investigated in the context of QA measurements. For exposures of film between 2 and 4 Gy, the system is adequate for measurement of beam dimensions, as in multi-leaf collimator (MLC) offsets and secondary jaw calibrations, where agreement with conventional film measurements is within 0.5 mm. However, the measurement of absolute dose is subject to errors of about 25 cGy.     

Performance analysis of a film dosimetric quality assurance procedure for IMRT with regard to the employment of quantitative evaluation methods

A system for dosimetric verification of intensity-modulated radiotherapy (IMRT) treatment plans using absolute calibrated radiographic films is presented. At our institution this verification procedure is performed for all IMRT treatment plans prior to patient irradiation. Therefore clinical treatment plans are transferred to a phantom and recalculated. Composite treatment plans are irradiated to a single film. Film density to absolute dose conversion is performed automatically based on a single calibration film. A software application encompassing film calibration, 2D registration of measurement and calculated distributions, image fusion, and a number of visual and quantitative evaluation utilities was developed. The main topic of this paper is a performance analysis for this quality assurance procedure, with regard to the specification of tolerance levels for quantitative evaluations. Spatial and dosimetric precision and accuracy were determined for the entire procedure, comprising all possible sources of error. The overall dosimetric and spatial measurement uncertainties obtained thereby were 1.9% and 0.8 mm respectively. Based on these results, we specified 5% dose difference and 3 mm distance-to-agreement as our tolerance levels for patient-specific quality assurance for IMRT treatments.     

On-Board Imager-based MammoSite treatment verification

Contemporary radiation oncology departments are often lacking a conventional simulator due to common use of virtual simulation and recent implementation of image guided radiation therapy. A protocol based on MammoSite method was developed using CT based planning, a Source Position Simulator (SPS) with a Simulator Wire and a linear accelerator based On-Board Imager (OBI) for daily verification. After MammoSite balloon implantation, the patient undergoes a CT study. The images are evaluated for tissue conformance, balloon symmetry, and balloon surface to skin distance according to the departmental procedure. Prior to the CT study the SPS is attached to the transfer tube that in turn is attached to the balloon catheter. The length from the indexer to the first dwell position is measured using the simulator wire with X-ray markers. After the CT study is performed, the data set is sent to the Varian Eclipse treatment planning system (TPS) and to the Nucletron PLATO brachytherapy planning system. The reference digitally reconstructed radiographs (DRRs) of anterior and lateral setup fields are created using Eclipse TPS and are immediately available on the OBI console via the Varian Vision integrated system. The source dwell position coinciding with the balloon center is identified in the CT dataset, followed by the offset calculation, catheter reconstruction, dose points placement and dwell time calculation. OBI fluoroscopy images are acquired and marked as initial. Prior to each treatment fraction balloon diameter and symmetry are evaluated using OBI fluoroscopy and tools available on the OBI console. Acquired images are compared with reference DRRs and/or initial OBI images. The whole process from initial evaluation to daily verification is filmless and does not undermine the precision of the procedure. This verification time does not exceed 10 min. The balloon diameter correlates well (within 1 mm) between initial CT and OBI verification images. The balloon symmetry is defined with 1 mm accuracy using existing OBI console tools. It is feasible to use OBI based simulation for the MammoSite balloon placement evaluation, balloon integrity daily verification, and treatment dwell position coincidence with balloon center. This verification is a rapid process and is an alternative to the conventional simulator based technique. The simulator wire with X-ray markers for the SPS is the recommended tool for the CT based MammoSite procedure.     

Comprehensive quality assurance for stereotactic radiosurgery treatments

We have used a commercially available high precision Lucy phantom to perform comprehensive quality assurance for stereotactic radiosurgery treatments. The quantitative evaluation of system uncertainties included imaging, planning and treatment delivery systems. The quality assurance tests showed that the well-defined targets were identified to within +/-1 mm in all the imaging modalities. The pre-known target volumes were reproduced within 2 cm3 in both MR and CT. The planned target was delivered within 2% of the prescribed dose and to within 2 mm accuracy. The inaccuracy in the isocentre position at the Linac was less than 1.2 mm. The maximum error observed in the depth helmet was 0.5 mm and the overall uncertainty was within 0.23 mm. We have also established a quality assurance program based on the study and proposed the tolerance and the frequency of the tests required to be carried out. The tests were carried out using a Radionics planning system and delivered on a Varian Clinac 2100 linear accelerator machine. These tests also established a base line for future comparisons.