一种医用直线加速器机械参数测量分析系统

目的:设计并实现一种医用直线加速器的机械参数测量系统,可对医用直线加速器等中心等各项机械参数进行测量并定量分析。方法:系统硬件采用双目光学测量套件,在加速器各部件上贴上定位小球,双目相机以20 Hz频率输出定位小球的空间坐标。软件上位机根据定位小球坐标实时更新加速器三维模型和各部件运动参数的拟合,实现对医用直线加速器的运动跟踪功能。完成测量后,软件可以输出测量分析报告,报告内容包括加速器各部件机械运动参数和反映性能的特征量,测量精度达0.5 mm。结果:实现本系统后,在两家医院对两台不同使用时长医用直线加速器分别进行多次测量和分析,得到等中心误差、机架机械运动参数和统计量、治疗床机械运动参数和统计量、机架和治疗床重复运动误差等。结论:本系统可帮助技术人员和物理师进行加速器维护工作,为医用直线加速器的日常检测和质量控制提供指导。     

锥形束CT的验收与QA探讨

目的:探讨锥形束CT的验收与质量保证;方法 :CBCT的验收主要包括系统与机械的安全验收。利用承球模体验收CBCT的中心与加速器的治疗中心的一致性。使用Catphan模体验收CBCT的图像质量,包括刻度的精度,灰度值均匀性,最低可见对比度,最高空间分辨率等。结果:CBCT的系统与机械相关联锁工作正常。CBCT中心与加速器中心的偏差在左右,前后与垂直方向分别为0.25 mm、0.16 mm,和0.19 mm。灰度值均匀度为1.35%。刻度精确度在垂直,水平与长轴方向上的误差分别为0.2 mm,0.5 mm和0.4 mm。最高空间分辨为11 lp/cm,最低可见对比度为1.07%。结论:CBCT的验收与质量保证对其在图像引导的放射治疗中的正确使用,发挥其最大的临床优势至关重要。本文所探讨的对KV级CBCT的验收与质量保证方法步骤,将为CBCT在临床的安全应用提供指导。     

放射治疗用锥形束CT图像引导设备技术审评要求探讨

主要分析放射治疗kV级锥形束CT（CBCT）图像引导系统和诊断用扇形束CT的技术原理及临床应用的差异,包 括数据获取方式、图像处理方式、空间分辨率、成像剂量、图像噪声、密度分辨率等方面的差异,从而进一步分析CBCT和 扇形束CT技术审评要求中电气安全、性能指标等要求的差异,以及CBCT说明书、注册单元划分的要求,预期为制造商准 备CBCT图像引导系统的注册申报资料提供参考。     

影像引导放疗中常用CT设备影像质量的比较分析

目的:分析影像引导放疗中常用的模拟定位螺旋CT(MSCT)、加速器机载锥形束CT(CBCT)和螺旋断层治疗机MV螺旋CT(MVCT)的影像质量。方法:CatPhan600模体测量三种成像设备的CT值均匀性和线性、空间分辨率、低对比度分辨率、3D影像的几何准确性和金属伪影大小。结果:MSCT、CBCT和MVCT的CT值与物质密度均呈线性关系;均匀模体中的CT均匀性分别为1.07%,1.40%,39.81%;空间分辨率分别为8 lp/cm,7 lp/cm,4 lp/cm;MSCT可显示低对比度为1%的3 mm圆孔,CBCT只能略微分辨圆孔,而MVCT则无法显示圆孔,几何准确性均良好;MVCT的金属伪影较小。结论:CBCT和MVCT的成像质量均不如MSCT,但能满足患者治疗体位验证和监测的需要。     

基于光学表面监测系统进行头部肿瘤放疗实时定位准确性的初步研究

目的:评估瓦里安直线加速器EDGE上搭载的光学表面监测系统(OSMS)对偏差探测的准确性(或纠错能力)。方法:使用一个颅脑体模,评估OSMS治疗前摆位准确性、治疗中监测偏移精确度、特定条件下(非零床角和仅双摄像头工作)能否正常使用。结果:OSMS实现治疗前摆位,其等中心与锥形束CT(CBCT)摆位的偏差范围为(0.6±0.5)mm,角度最大偏差为0.3°;治疗中监测偏移精确度,探测平移偏差范围(0.1±0.2)mm,探测角度偏差范围0.10°±0.07°;不同的床角下OSMS的精确度接近,挡住其中一个摄像头产生约0.5 mm的不确定度。结论:OSMS配合CBCT能够为头部肿瘤放疗的治疗前摆位及治疗中实时监测提供保证。     

图像引导鼻咽癌调强放疗摆位误差及剂量学验证研究

目的:探讨锥形束CT(CBCT)影像引导鼻咽癌调强放疗的摆位误差及建立个体化调强计划剂量验证方法。方法:利用X线千伏锥形束CT对32例鼻咽癌调强放疗患者进行426次治疗前扫描,通过图像融合软件将计划CT与CBCT影像匹配,得到靶区中心的摆位误差,在线修正后,重新扫描得到116次CBCT影像,再匹配后得到修正后靶区偏差;在治疗完成后,重新扫描36次,得到治疗后靶区偏差中心。通过修正固体水模测试和矩阵电离室的参数,可验证高剂量区、低剂量区、中心点、均匀区和高梯度区域的绝对剂量;利用Gama分析得到单野和个体计划的通过评价率。结果:对32例鼻咽癌426次CBCT扫描中,三个方向偏差,X(左右)、Y(上下),Z(前后)分别为(0.44±2.03)mm、(0.51±2.75)mm、(-0.37±2.14)mm;当三个方向大于2 mm时进行位置修正,修正后重新进行CBCT扫描和匹配得到新的三个方向的偏差,X为(0.07±0.59)mm、Y为(0.07±0.80)mm、Z为(-0.02±0.75)mm;治疗完成后再扫描36次,匹配得到的偏差三个方向X、Y、Z分别为(0.19±0.59)mm、(0.15±0.73)mm、(-0.08±0.72)mm;用矩阵电离室验证调强计划相对剂量,对于单野,Gamma值为88.2%～99.2%,对于整个计划Gamma值为90.2%～99.7%。绝对剂量验证主要是对等中心点、剂量均匀区、高剂量区、较低剂量区、高梯度区选择5个点进行检测共完成160个点,百分偏差范围为-3.9%～4.2%。结论:通过在线的摆位修正和调强计划的个体化验证,可保证鼻咽癌调强放疗的位置和剂量的准确;利用摆位误差计算得到的CTV-PTV外扩边界,可能对增加疗效和减小正常器官副反应有重要意义。     

锥形束CT引导机器人辅助反肩关节肩盂基座螺钉导针置入精准度研究

目的 评估锥形束CT(cone beam CT,CBCT)引导下机器人辅助置入反肩关节肩盂基座螺钉导针的精准度,为机器人辅助反肩关节置换手术的开展提供理论支持.方法 使用CBCT对12例SYNBONE肩胛骨模型置入反肩关节肩盂基座螺钉导针前后行断层扫描.采用TiRobot软件术前规划螺钉导针入针点、尾端止点及导针置入路径的位置坐标.计算机根据规划位置控制机械臂定位并辅助置入肩盂基座螺钉导针,术后比较规划入止点、路径与实际入止点、路径的差异.结果 所有肩胛骨模型均一次完成导针置入.规划与实际入针点位置偏差为(1.155±0.517)mm,规划与实际尾端止点位置偏差为(1.047±0.288)mm,计划路径与实际路径夹角偏差为(1.564±0.888)°.结论 CBCT引导下机器人辅助反肩关节肩盂基座螺钉导针置入精确度高,为临床中反肩关节置换精准治疗手术重要步骤提供可行性选择.     

一种自动确定放疗原始等中心的新方法

目的:提出一种通过勾画标记点结构自动确定放疗原始等中心的方法（以下简称新方法）,通过与常规方法作比较分析测试新方法的应用价值。方法:选取40例接受放射治疗的腹部肿瘤患者的定位CT图像,其中标记点出现在1层、2层CT层面各20例。使用常规方法（通过Eclipse计划系统的十字定位工具手动确定原始等中心）,然后使用新方法（通过自动勾画标记点结构并进行位置计算自动确定放疗原始等中心）,分析两种方法确定的原始等中心之间坐标的差异。此外,还手动勾画了标记点结构。结果:与手动勾画标记点结构相比,自动勾画20例2层CT图像中标记点的Dice相似性指数（DSC）值为（0.79±0.06）,40例左右方向（x轴）偏差绝对值、腹背方向（y轴）偏差绝对值的均值分别为0.04、0.05 cm。标记点出现在2层CT图像的20例中,头脚方向（z轴）偏差绝对值的平均值、标准差、最大值、最小值分别为0.22、0.03、0.26、0.16 cm。结论:本文提出的新方法可以快速、精确地计算出放疗原始等中心坐标,特别是当标记点出现在2层CT图像时,可以有效弥补常规方法的缺陷。     

基于双目红外相机定位的自由式三维超声图像重建系统

目的:设计并实现自由式三维超声图像重建系统,该系统能对自由式采集的二维超声图像阵列进行三维重建与显示交互。方法:系统使用双目红外相机及其配套测量器件,在超声探头上固定定位小球,双目红外相机可以实时追踪探头的空间位置,从而获取超声图像阵列的相对关系。软件部分根据实时探头位置并计算转换矩阵,获取超声图像阵列的数据并填充三维体数据网格,使用光线投射法绘制图像。结果:该系统可以实现超声图像阵列的采集与存储、超声图像感兴趣区域勾画、三维重建与可视化功能。结论:该研究提出的基于双目红外相机定位的自由式三维超声图像重建系统对未来的临床使用以及科学研究奠定了良好基础。     

口腔锥形束CT影像的存储传输与临床应用

背景:口腔锥形束CT具有图像精度高、扫描时间短、辐射剂量小、空间分辨率高等优势,它应用于口腔临床至今约10余年,但发展迅速,现已广泛应用于口腔医学临床。目的:介绍锥形束CT的数据处理特点、工作站配置、数据存储传输,及其在口腔临床医疗科研中的应用价值。方法:查阅有关CT影像存储与传输的文献资料,结合口腔锥形束CT数据的特点,举例说明锥形束CT工作站的设计与配置、影像存储架构的设计、诊断工作站软件和硬件的配置。采用锥形束CT对口腔临床患者进行CT扫描,分析锥形束CT在口腔临床的应用效果。结果与结论:口腔锥形束CT影像的数据量较大,宜采用存储区域网存储架构进行影像资料的存储:诊断工作站电脑的配置应高于CT设备厂家的推荐参数,同时应配备激光干式打印机等设备以便图像输出。口腔锥形束CT可以提供口腔颌面部硬组织结构的三维影像及任意层面的断层影像,有利于口腔颌面部疾病的影像诊断。提示口腔锥形束CT影像对于口腔临床医疗工作具有重要价值。     

基于红外定位系统放疗实时摆位预警系统的摆位数据误差统计

目的:利用红外定位系统（OPS）放疗实时摆位预警系统,对放疗摆位累积产生的海量数据,进行与设备性能及体态体姿相关的误差统计与监测,进而实时对摆位进行指导。方法:首先选取264例腹部癌症摆位数据、195例头颈部癌症摆位数据以及186例头部癌症摆位数据;然后搭建归一转换系统,量化标注不同摆位方法产生的不同摆位结果及差异,将现有的摆位结果数据统一转换到一个坐标系下;最后基于放疗摆位累积产生的海量数据,开发模型预警系统,实时监控等中心注册、相机移动、激光线偏移、体膜变形以及锥形束CT本身机械问题5种摆位误差。结果:OPS放疗实时摆位预警系统能够实时监控摆位数据,在腹部264例摆位数据中,5种误差分别为5、1、11、4、7例;在头颈部195例摆位数据中,5种误差分别为13、4、40、0、27例;在头部186例摆位数据中,5种误差分别为10、3、25、0、19例。结论:OPS放疗实时摆位预警系统能较为准确实时预警摆位质量和摆位精度,当摆位出现较大误差时,该系统能够迅速报警,及时指出摆位存在的问题,第一时间提醒、纠正存在的问题。     

应用提高分辨率的MatriXX检测等中心偏移的方法简介

目的:以检测等中心在X方向的偏移示例,介绍使用提高分辨率之后的MatriXX检测等中心偏移的方法。方法:在确保MLC的leaf bank关于collimator中心轴旋转对称,且MatriXX中心与等中心的偏差已知的基础上,将gantry和collimator的角度都设为0°,治疗床向X正方向每移动1 mm测量1次5 cm×5 cm照射野100 MU的剂量分布曲线,共7次移动治疗床,测量8组数据,然后将这8组数据叠加为一组复合数据,得到gantry和collimator角度为0°、5 cm×5 cm照射野100 MU时MatriXX在X方向分辨率为1 mm的剂量分布曲线。同样的方法测量得到将gantry角度设为180°时相对应的剂量分布曲线,然后使用OmniPro I’mRT软件对比分析这两个profile,得出等中心在X方向的偏移值。结果:等中心的偏移值为1.8 mm。结论:提高分辨率之后的MatriXX能够检测出等中心的偏移值;等中心的偏移会导致病人接受剂量出现偏差,而这种偏差可以通过调整Elekta Synergy MLC的leaf bank关于gantry旋转中心轴对称和计划设计中设置collimator与couch角度为0°来克服;等中心的偏差使得gantry角度在90°和270°附近照射野的平面剂量偏差非常大。因此,不建议计划设计中设置gantry角度在90°和270°附近的照射野,也不建议选用MatriXX或者其他平面探测器做照射野gantry角度集中在90°和270°附近的病人计划验证。     

Accuracy of a photogrammetry-based patient positioning and monitoring system for radiation therapy.

A photogrammetry system designed to reduce simulator-to-treatment and treatment-to-treatment patient positioning errors has been developed. Two complete systems have been installed in our department: one in the simulator room and one in a treatment room. Each system consists of three charge-coupled device (CCD) cameras; a ring of infrared LEDs around the lens of each camera; and several small, circular, retroreflective markers that are applied to the patient. The markers reflect infrared light directly back to the cameras, producing a binary image of oval hot spots when the image is thresholded. The three-dimensional position of each marker is calculated by conventional photogrammetry methods. At simulation, marker positions are measured, then transferred to the treatment room system. The system may be used to actively position patients, and to passively monitor a patient's position and motion during treatment. Studies have focused on measuring the system's temporal stability, precision, and accuracy; on optimal positioning of markers and cameras; and on assessing the system's capability to reduce the positioning error. The repeatability of measuring a marker's position is <0.1 mm in each orthogonal direction. The accuracy is approximately 0.5 mm over a 40 X 40 X 40 cm3 field of view. The system drift over four hours is approximately +/-0.2 mm. The photogrammetry system has been used to actively position a lead BB, embedded within a head phantom, at the isocenter; repeatability was +/-0.3 mm, as determined radiographically. The system has also been used to passively monitor the positioning of several head and neck patients that were set up by a therapist; setup errors of up to 10 mm in each orthogonal direction were measured, as well as the motion of the patient during treatment.     

机械旋转误差对多发脑转移瘤VMAT计划剂量分布的影响

目的:探讨直线加速器的机械旋转误差对单中心多发转移瘤VMAT计划剂量分布的影响。方法:随机选取21例多发脑转移瘤患者,假定患者均采用非共面VMAT放疗计划,分别将治疗床、准直器的角度旋转偏移[±]0.5°、[±]1.0°、[±]1.5°、[±]2.0°,并通过Eclipse 13.6治疗计划系统模拟机械旋转偏移误差在多发脑转移瘤VMAT计划中对剂量分布的影响。记录并分析不同治疗床、准直器角度旋转偏移下靶区的适形度指数（CI）、剂量梯度跌落指数（GI）、剂量均匀性指数（HI）以及危及器官的最大剂量。结果:当治疗床及准直器角度旋转偏移大于0.5°时,靶区的CI、GI（治疗床除外）及HI指数差异具有统计学意义（P<0.05）;危及器官的最大剂量差异无统计学意义（P>0.05）。结论:在设计多发脑转移VMAT计划时应考虑等中心与靶区之间的距离,六维床旋转误差校正阈值为0.5°更为合理。     

红外定位系统在精确放疗中的应用

目的:介绍红外定位系统(OPS)在精确放疗的摆位和验证中的应用。方法:在患者面膜或体膜上粘贴红外自动跟踪装置专用标记球4个,通过红外线探头探测标记球的位置,在x、y、z方向上移动治疗床,将病灶中心精确定位于加速器的等中心上。比较模拟定位时荧光球与实际治疗时荧光球的位置差异,测量x、y、z方向上的摆位误差。结果:用红外定位系统测量的摆位误差结果为:摆位误差在x、y、z方向上,头颈部肿瘤误差最小,盆腔、腹部肿瘤误差为1 mm~4 mm,主要发生在x、z方向,胸部肿瘤误差为2 mm~5 mm,主要发生在y、z方向。结论:红外定位系统能准确完成摆位与验证,与EPID相比使用更加方便、效率更高、更加适应临床需要。     

A phantom study on the positioning accuracy of the Novalis Body system

A phantom study was conducted to investigate inherent positioning accuracy of an image-guided patient positioning system-the Novalis Body system for three-dimensional (3-D) conformal radiotherapy. This positioning system consists of two infrared (IR) cameras and one video camera and two kV x-ray imaging devices. The initial patient setup was guided by the IR camera system and the target localization was accomplished using the kV x-ray imaging system. In this study, the IR marker shift and phantom rotation were simulated and their effects on the positioning accuracy were examined by a Rando phantom. The effects of CT slice thickness and treatment sites on the positioning accuracy were tested. In addition, the internal target shift was simulated and its effect on the positioning accuracy was examined by a water tank. With the application of the Novalis Body system, the positioning error of the planned isocenter was significantly reduced. The experimental results with the simulated IR marker shifts indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.5 +/- 0.2, and 0.7 +/- 0.2 mm along the lateral, longitudinal, and vertical axes, respectively. The experimental results with the simulated phantom rotations indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.7 +/- 0.2, and 0.5 +/- 0.2 mm along the three axes, respectively. The experimental results with the simulated target shifts indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.7 +/- 0.2, and 0.5 +/- 0.2 mm along the three axes, respectively. On average, the positioning accuracy of 1 mm for the planned isocenter was achieved using the Novalis Body system.     

A phantom evaluation of a stereo-vision surface imaging system for radiotherapy patient setup

External beam irradiation requires precise positioning of the target relative to the treatment planning coordinate system. A three-dimensional (3D) surface imaging system for patient positioning has recently been installed in one of our linear accelerator (linac) rooms. The device utilizes close-range photogrammetry to generate a 3D model of the patient's surface. This geometric model can be made to look like a digital camera image if wrapped with a gray-level image (texture mapping) that shows surface coloration. The system is calibrated to the linac coordinate system and has been designed as a patient setup device. To reproduce patient position in fractionated radiotherapy, the daily patient surface model is registered to a previously recorded reference surface. Using surface registration, the system calculates the rigid-body transformation that minimizes the distance between the treatment and the reference surface models in a region-of-interest (ROI). This transformation is expressed as a set of new couch coordinates at which the patient position best matches with the reference data. If respiratory motion is a concern, the surface can be obtained with a gated acquisition at a specified phase of the respiratory cycle. To analyze the accuracy of the system, we performed several experiments with phantoms to assess stability, alignment accuracy, precision of the gating function, and surface topology. The reproducibility of surface measurements was tested for periods up to 57 h. Each recorded frame was registered to the reference surface to calculate the required couch adjustment. The system stability over this time period was better than 0.5 mm. To measure the accuracy of the system to detect and quantify patient shift relative to a reference image, we compared the shift detected by the surface imaging system with known couch transitions in a phantom study. The maximum standard deviation was 0.75 mm for the three translational degrees of freedom, and less than 0.1 degrees for each rotation. Surface model precision was tested against computed tomography (CT)-derived surface topology. The root-mean-square rms of the distance between the surfaces was 0.65 mm, excluding regions where beam hardening caused artifacts in the CT data. Measurements were made to test the gated acquisition mode. The time-dependent amplitude was measured with the surface imaging system and an established respiratory gating system based on infrared (IR)-marker detection. The measured motion trajectories from both systems were compared to the known trajectory of the stage. The standard deviations of the amplitude differences to the motor trajectory were 0.04 and 0.15 mm for the IR-marker system and the 3D surface imaging system, respectively. A limitation of the surface-imaging device is the frame rate of 6.5 Hz, because rapid changes of the motion trajectory cannot be detected. In conclusion, the system is accurate and sufficiently stable to be used in the clinic. The errors computed when comparing the surface model with CT geometry were submillimeter, and deviations in the alignment and gating-signal tests were of the same magnitude.     

Optimal marker placement in photogrammetry patient positioning system

A photogrammetry-based patient positioning system has been used instead of the conventional laser alignment technique for patient set-up in external beam radiotherapy. It tracks skin affixed reflective markers with multiple infrared cameras. The three-dimensional (3D) positions of the markers provide reference information to determine the treatment plan isocenter location and hence provide the ability to position the lesion at the isocenter of the treatment linear accelerator. However, in current clinical practice for lung or liver lesion treatments, fiducial markers are usually randomly affixed onto the patients' chest and abdomen, so that the actual target registration error (TRE) of the internal lesions inside the body may be large, depending on the fiducial registration error (FRE). There exists an optimal marker configuration that can minimize the TRE. In this paper, we developed methods to design the patient-specific optimal configurations of the surface makers to minimize the TRE, given the patient's surface contour, the lesion position and the FRE. Floating genetic algorithm (GA) optimization was used to optimize the positions of the skin markers. The surface curve of the patient body was determined by an automatic segmentation algorithm from the planning CT. The method was evaluated using a body phantom implanted with a metal ball (a simulated target). By registering two CT scans using the surface markers and measuring the displacement of the target, the TRE was measured. The TRE was also measured by taking two orthogonal portal films after positioning the phantom using the photogrammetry based patient positioning system. A 50% reduction in TRE has been achieved by using the optimal configuration compared to the random configuration. This result demonstrates that the optimization of a fiducial configuration can result in improved tumor targeting ability.     

AlignRT在乳腺癌术后放疗体表引导摆位中感兴趣区优选

目的：光学体表追踪系统Align RT引导乳腺癌术后放疗摆位中,通过对比3种典型感兴趣区（ROI）Align RT与CBCT误差之间摆位一致性差异,确定临床最优ROI勾画范围。方法：回顾性分析33例利用Align RT引导摆位的乳腺癌患者病例数据,摆位结束后记录197次CBCT同分次下全胸、患侧乳腺和胸部刚性3种ROI的AlignRT误差数据,CBCT与定位CT进行基于脊柱6维配准靶区微调后,获得6维CBCT误差,Align RT与CBCT误差差值绝对化后用于量化摆位一致性,比较全胸、患侧乳腺和胸部刚性这3组ROI的Align RT误差及摆位一致性差异。结果：Align RT引导摆位CBCT误差线性方向/旋转方向在±0.50 cm/±2.0°之间的占比为99.92%。全胸、患侧乳腺、胸部刚性3组ROI的Align RT误差在Pitch(P<0.001)、Roll(P=0.002)方向差异有统计学意义。全胸ROI在x、Rtn、Pitch和Roll方向摆位一致性均优于患侧乳腺和胸部刚性ROI,x(P=0.001)、Rtn(P<0.001)、Roll(P=0.001)方向差异有统...