Development of a one-stop beam verification system using electronic portal imaging devices for routine quality assurance

In this study, a computer-based system for routine quality assurance (QA) of a linear accelerator (linac) was developed by using the dosimetric properties of an amorphous silicon electronic portal imaging device (EPID). An acrylic template phantom was designed such that it could be placed on the EPID and be aligned with the light field of the collimator. After irradiation, portal images obtained from the EPID were transferred in DICOM format to a computer and analyzed using a program we developed. The symmetry, flatness, field size, and congruence of the light and radiation fields of the photon beams from the linac were verified simultaneously. To validate the QA system, the ion chamber and film (X-Omat V2; Kodak, New York, NY) measurements were compared with the EPID measurements obtained in this study. The EPID measurements agreed with the film measurements. Parameters for beams with energies of 6 MV and 15 MV were obtained daily for 1 month using this system. It was found that our QA tool using EPID could substitute for the film test, which is a time-consuming method for routine QA assessment.     

Improving image quality in portal venography with spectral CT imaging

Objective

To investigate the effect of energy spectral CT on the image quality of CT portal venography in cirrhosis patients.

Materials and methods

30 portal hypertension patients underwent spectral CT examination using a single-tube, fast dual tube voltage switching technique. 101 sets of monochromatic images were generated from 40 keV to 140 keV. Image noise and contrast-to-noise ratio (CNR) for portal veins from the monochromatic images were measured. An optimal monochromatic image set was selected for obtaining the best CNR for portal veins. The image noise and CNR of the intra-hepatic portal vein and extra-hepatic main stem at the selected monochromatic level were compared with those from the conventional polychromatic images. Image quality was also assessed and compared.

Results

The monochromatic images at 51 keV were found to provide the best CNR for both the intra-hepatic and extra-hepatic portal veins. At this energy level, the monochromatic images had about 100% higher CNR than the polychromatic images with a moderate 30% noise increase. The qualitative image quality assessment was also statistically higher with monochromatic images at 51 keV.

Conclusion

Monochromatic images at 51 keV for CT portal venography could improve CNR for displaying hepatic portal veins and improve the overall image quality.     

A comparative evaluation of two head and neck immobilization devices using electronic portal imaging

A study was performed to compare the positioning reproducibility and the cost efficiency for two head and neck immobilization devices: the Uvex (Uvex Safety, Smithfield, USA) plastic mask system and the Finesse Frame with Ultraplast System (PLANET Medical, Svendborg, Denmark). 20 patients treated with 3D conformal radiation therapy for head and neck cancers were randomly selected (10 for each of the two different immobilization systems) and electronic portal images acquired during their course of treatment were saved and used in this study. The anatomical landmark coordinates and their shifts in the anteroposterior (AP) and craniocaudal (CC) directions with respect to the digitized simulator films for lateral fields were analysed using an in-house developed portal image registration system. Statistically, no evidence was found to indicate that the systematic components of the displacement for the Uvex system and the Finesse Frame with Ultraplast System were different from each other or from zero. The random component of displacement was slightly smaller in the AP direction for the Uvex than the Ultraplast system (sigma = 1.9 mm and 2.9 mm, respectively, p = 0.007), but larger in the CC direction (sigma = 3.8 mm and 2.2 mm, respectively, p<10(-9)). Production time and required materials for a radiation therapy department were also quantified to assess costs for each system. The overall costs per patient were estimated at 141.50 dollars (CAD) and 82.10 dollars for the Uvex and Ultraplast systems, respectively. The Finesse Frame with Ultraplast System of immobilization for head and neck cancer treatment provides a field placement reproducibility that is equal to, or greater than, that of the Uvex plastic mask immobilization system and, while it requires more expensive materials, the workload and consequently overall cost is greatly reduced.     

Evaluation of AutoCAL for electronic portal imaging device-based multi-leaf collimator quality assurance

Modern radiotherapy treatment techniques commonly include multi-leaf collimators (MLCs) to shape the treatment fields and to conform the radiation dose to the target volume. MLCs require accurate and frequent quality assurance (QA) to ensure spatial and temporal accuracy of the leaves in order to allow optimal dose delivery to the patient. In this study, the accuracy and efficacy of AutoCAL, a commercial software for MLC QA, were evaluated. The software was found to be reproducible to within 0.2 mm and to correspond with conventional QA methods (within 1.2 and 0.9 mm of film and water tank measurements, respectively.) Thus, AutoCAL was found to be an accurate and efficient tool for routine MLC QA and calibration.     

DR成像系统非优质图像的原因分析及图像质量控制

目的探讨数字化X线摄影(DR)成像系统各环节产生非优质图像的成像因素及质量控制。方法回顾性分析DR片的质量优劣及各成像环节造成乙级片和废片的具体因素并加以控制。结果各成像环节过程中人为因素或设备故障是造成高乙片率和废片率的主要原因。合理控制这些因素是得到优质图像的保证,熟练掌握各设备的功能、特点及充分发挥计算机后处理的优势是解决问题的关键。结论做到设备操作程序的规范化、投照技能熟悉化及计算机后处理功能熟练运用,完全可以使数字图像及照片完全符合临床诊断要求。     

Clinical practice and evaluation of electronic portal imaging device for VMAT quality assurance

Volumetric-modulated arc therapy (VMAT) is a novel extension of the intensity-modulated radiation therapy (IMRT) technique, which has brought challenges to dose verification. To perform VMAT pretreatment quality assurance, an electronic portal imaging device (EPID) can be applied. This study's aim was to evaluate EPID performance for VMAT dose verification. First, dosimetric characteristics of EPID were investigated. Then 10 selected VMAT dose plans were measured by EPID with the rotational method. The overall variation of EPID dosimetric characteristics was within 1.4% for VMAT. The film system serving as a conventional tool for verification showed good agreement both with EPID measurements ([94.1 ± 1.5]% with 3 mm/3% criteria) and treatment planning system (TPS) calculations ([97.4 ± 2.8]% with 3 mm/3% criteria). In addition, EPID measurements for VMAT presented good agreement with TPS calculations ([99.1 ± 0.6]% with 3 mm/3% criteria). The EPID system performed the robustness of potential error findings in TPS calculations and the delivery system. This study demonstrated that an EPID system can be used as a reliable and efficient quality assurance tool for VMAT dose verification.     

HDCT能谱技术提高肝硬化门静脉血管成像图像质量的价值研究

目的探讨能谱技术在提高肝硬化患者CT门静脉血管成像质量方面的价值。方法 45例肝硬化患者,采用的能谱扫描模式行动脉期门脉期扫描后,运用能谱分析软件获得门静脉期最佳对比信噪比(CNR)单能图像和传统混合能量图像(QC图像),并对门静脉及侧枝血管进行容积再现(volume rendering,VR)、最大密度投影(maximum inten-sity projection,MIP)重建。采用双盲法对重建质量进行评估。对二组图像的评分数据行两独立样本T检验分析。结果最佳CNR单能图像的VR、MIP重建图像对门静脉与侧枝血管及肝内分支的显示级别均优于混合能量图像,差异有显著统计学意义(P<0.01)。结论最佳CNR单能图像能明显提高肝硬化CTPV门静脉与侧枝血管及肝内分支显示的图像质量。     

Soft-copy quality control of digital spot images obtained by using X-ray image intensifiers

PURPOSE: To evaluate 12 x-ray image intensifier (XRII) digital spot systems. MATERIALS AND METHODS: Four objective tests were performed to assess XRII digital spots: entrance exposure, patient exposure, soft-copy gray scale, and pixel noise. Two additional tests were performed to assess high-contrast limiting resolution and threshold contrast detection. RESULTS: Digital spot XRII entrance exposures averaged 1 x 10(-7) C/kg (0.38 mR) for units with large fields of view (FOVs); mean entrance exposure in a medium-sized patient was 1. 25 x 10(-5) C/kg (48 mR). Luminance measurements of the table-side monitors provided a mean of 473 just-noticeable differences in gray scale with the room lights off. Mean resolution with a bar test pattern was measured as 1.5 line pairs per millimeter for systems with a 40-cm FOV. Measured pixel noise (in relative units) was 6-25. Mean threshold contrast with the lights off was 0.85%. CONCLUSION: Once input exposure is normalized for FOV and image matrix size, soft-copy assessment of limiting resolution with either low-contrast detection or, preferably, an off-line noise metric (pixel SD) provides objective measurements of digital spot image quality. With the lights on, 10 systems with room-light sensors had an 11% loss of gray scale. For systems without sensors, the loss was 33%.     

Dosimetric properties of the Theraview fluoroscopic electronic portal imaging device

Electronic portal imaging devices (EPIDs) can be used for non-imaging applications in radiotherapy such as patient dosimetry. Of the systems available, the fluoroscopic camera-based EPID Theraview (InfiMed Inc.) has not been studied to date, and a review of the dosimetric properties of the system is presented here. In the "single set-up" mode of image acquisition, pixel intensity increases sublinearly with applied dose. The response was dependent on the system's video signal gain and showed a threshold dose to the detector in the range 0.05-0.35 cGy, and pixel saturation at detector doses in the range 1.2-1.6 cGy. Repeated exposures of the EPID were observed to be extremely reproducible (standard deviation 0.5%). The sensitivity of the system showed a linear decline of 0.04% day-1 over a 68-day period, during which time the relative off-axis response within 10 x 10 cm2 field was constant to within a standard deviation of 0.56%. The system shows spatial non-uniformity, which requires correction for application to dose measurements in two-dimensions. Warm-up of the camera control unit required a period of at least 40 min and was associated with an enhancement in pixel intensity of up to 12%. A radiation dose history effect was observed at doses as low as 0.2 Gy. Camera dark current was shown to be negligible at normal accelerator operation. No discernible image distortion was found. Mechanical stability on gantry rotation was also assessed and image displacement of up to 5 mm at the isocentre was observed. It was concluded that the device could be used for dosimetry provided necessary precautions were observed and corrections made.     

基于电子射野影像系统建立医用直线加速器晨检工具的临床测试

目的 利用电子射野影像系统（EPID）建立加速器快速晨检工具,并进行评估。方法 用Synergy加速器EPID测得10 cm×10 cm开野及楔形野图像,由Matlab提取并分析图像参数,实现快速晨检。对EPID剂量-机械重复性、灰度值与MU值线性、输出量及射野大小测量准确性测试,用电离室、EPID分别测量Synergy输出量随MU变化情况,用DailyQA3及研究中所开发的工具对Synergy进行2个月的监测。结果 EPID剂量重复性测试稳定,射野大小和中心测试精度分别为0.5和1.0 mm,平坦度和对称性测试精度均为0.17%;机械精度测试结果与剂量重复性测试一致。EPID对加速器输出剂量响应线性相关（R²>0.999）。EPID对输出剂量和射野大小的探测灵敏度较高。EPID与DailyQA3所有临床测试结果均在允许限值内,且两种结果一致。结论 EPID剂量-机械稳定性及响应线性均良好,输出量及射野大小监测结果均准确,研究中建立的晨检工具准确可靠。     

电子射野影像系统在放疗中的应用进展

电子射野影像系统已成为放疗质量控制和质量保证的重要设备之一,可用于摆位误差验证分析、加速器本身日常质量控制、剂量验证、实时剂量验证等放疗质控指标的采集分析,以保障放疗实施的准确性。笔者就电子射野影像系统在放疗中的应用研究进行简要综述。     

快速千伏开关的虚拟单色光谱成像:对比常规120kV CT的影像质量的改善

目的在给定的辐射剂量下,比较虚拟单色光谱(VMS)和120kVCT对模型的成像质量。材料与方法 3支注射器充满稀释的对比剂(分别为5、10、15mgI/mL),第4支     

Physiology and pathology of TASER® electronic control devices

TASER^® ECDs (electronic control device) are small, battery powered, handheld devices. They deliver short duration, low energy pulses to stimulate motor neurons, causing transient paralysis. While the experience is painful, proper use of the device is rarely associated with significant side effects in spite of 1070 human worldwide exposures daily. In fact, there have been more than 780,000 training exposures and 630,000 field uses (total of over 1.4 million human uses) without any credible evidence of a resulting cardiac arrhythmia. In this article we describe the mechanisms by which the device operates, and review possible morbidities.     

电子射野影像系统用于调强放疗剂量验证

目的 探讨电子射野影像系统(aS1000)用于调强放疗剂量验证的可行性和效率.方法 分别使用美国Varian公司生产的Trilogy直线加速器的aS1000电子射野影像系统和瑞典IBA公司的二维空气电离室矩阵MatriXX及其配套的Multicube模体对10例接受调强放疗的患者进行剂量验证,记录和比较两种方法验证的γ通过率和时间.结果 采用3％和3 mm的标准,aS1000和MatriXX验证的γ通过率分别为95.82％和99.08％,平均时间为12.7和47.8 min.结论 aS1000电子射野影像系统可以作为患者调强放疗的剂量验证工具,比MatriXX更方便快捷.     

The performance of a fluoroscopic electronic portal imaging device modified for portability

Advances in external beam therapy technology have made routine, efficient conformal therapy a reality. With it comes the increasing need for online treatment verification, which is only achievable at present through the use of electronic portal imaging devices (EPIDs). For a large radiotherapy centre, the provision of one EPID per treatment machine proves extremely expensive. This paper details modifications to the design of a commercial fluoroscopic EPID (the SRI-100) to produce a portable system, capable of providing quick, high quality imaging on more than one treatment machine. We describe the necessary hardware and software changes made to the system, as well as the variety of mechanical and quality control checks performed for testing the stability and quality of the imaging. The modified system has been found to be both electronically and mechanically robust, with associated image quality, scaling, distortion and movement similar to other EPIDs in the department. Although the modification was designed specifically to allow for the acquisition of images from multiple treatment machines, it may also enable the operation of the EPID for other uses such as total body irradiation (TBI) treatment verification and a further range of quality control procedures on the linear accelerator itself.     

Short communication: A printed image quality test phantom for mammography

This communication describes a novel design for a mammographic image quality test phantom, the final design of which was produced as a radiographer weekly quality assurance phantom for breast screening and symptomatic mammography. The phantom is based on low contrast test features which are built up by superimposing sheets of Mylar overhead projector transparency, on which the test features are printed using a standard LaserJet printer. The required radiation contrast at mammographic energies is produced by the approximately 50% by weight component of iron oxide (Fe(3)O(4)) present in the toner. An easily replicated design of mammographic image quality phantom based on LaserJet printed test features is described. Approximately 40 of these phantoms were constructed, and these have been used successfully for 5 years in both breast screening and symptomatic mammography. The phantom design offers a performance similar to much more expensive mammographic contrast-detail phantoms, but suffers from the disadvantage that high contrast resolution bar patterns cannot be produced using the standard printing process.     

Assessment of setup accuracy in patients receiving postmastectomy radiotherapy using electronic portal imaging

Purpose The aim of this study was to investigate the setup accuracy for patients undergoing postmastectomy radiotherapy using electronic portal imaging. Materials and methods Ten patients undergoing radiotherapy via tangent (TG), supraclavicular-axillary (SA), and internal mammary (IM) fields were included. To explore the setup accuracy, distances between chosen landmarks were taken as reference parameters (RPs). The difference between measured RPs on simulation films and electronic portal images (EPIs) was calculated as the setup error. Results A total of 30 simulation films and 120 EPIs were evaluated. In the SA field, calculated RPs were lung length (LL), clavicle-field center perpendicular distance, and clavicle-field center transverse distance. The mean of the standard deviations (SDs) of the random errors (σ) for these parameters were 4.7, 7.3, and 7.6; and the SDs of the systematic errors (Σ) were 6.8, 4.4, and 13.5, respectively. In the TG fields, the calculated RPs were the central lung distance (CLD), maximum lung distance (MLD), and central soft-tissue distance (CSTD). In the medial TG field, the σ values for these parameters were 3.4, 3.6, and 4.1, respectively; and the σ values were 6.6, 2.6, and 3.4, respectively. In the lateral TG field, Σ values for the calculated RPs were 2.4, 3.2, and 3.3l, respectively; and the Σ values were 5.6, 3.6, and 4.8, respectively. Conclusion CLD, MLD, and CSTD in TG fields and LL in SA fields are easily identifiable and are helpful for detecting setup errors using EPIs in patients undergoing postmastectomy radiotherapy.     

Image quality parameters for the production standard Eliav PORTpro portal imaging device

Measurements of the high contrast spatial resolution and contrast-to-noise ratio of the production standard Eliav "PORTpro" portal imaging system have been made using a commercially available quality assurance phantom. The spatial resolution of the images is comparable with published data for other commercial systems, but somewhat lower than that published previously for the prototype of this system. These data may be of use to those involved in the selection, commissioning or quality assurance testing of electronic portal imaging systems.