BJ-6B加速器脉冲调制器故障分析

脉冲调制器是向微波源提供脉冲功率的电源，其任务是输出一系列振荡器所需的具有足够大功率的、一定重复频率和一定宽度、波形合适的脉冲电压。调制器的负载是磁控管和电子枪。只有调制器的内阻与负载阻抗匹配时才能工作在最佳状态。一般采用脉冲变压器解决匹配问题。由于磁控管在调制器输出脉冲的平顶部分相当于几百欧姆（静态阻抗），所以一般只考虑磁控管与调制器的相互影响。下面以BJ-6B加速器为例，分析调制器应用中出现的问题并给出相应的解决方案。     

瓦里安Clinac IX直线加速器BMAG联锁的故障检修

通过对瓦里安ClinacIX直线加速器BMAG联锁故障的3次维修分析发现,偏转磁体电源全波整流二极管击穿、偏转磁铁联锁设置不当、调制器CB3空气开关故障均可引起BMAG联锁。通过更换配件、调整参数等,使故障得到解决。     

加速器脉冲形成网络故障维修体会

笔者在日常维修加速器工作时遇到脉冲形成网络故障,经检修得以修复,经验供大家参考. 一、材料与方法 机器故障实例:瓦里安6100加速器,只要加高压出束,就立刻报高压电源故障(HVPS).因时间不到1 s,无法通过示波器观测脉冲形成网络电压波形.由于这是高压电路,不可随意短接报警连锁电路进行波形观测,否则可能造成更大破坏和更严重故障.     

电压波动对BJ-6B加速器剂量传递的影响分析

目的 研究市内电压变化对BJ-6B加速器剂量率、剂量传递准确性的影响.方法 在变压器332V时校准加速器.模拟市内电压变化在321～338V范围改变变压器输出电压,监测剂量率变化.在机器出束为100 MU,照射野为10 cm×10 cm,源皮距离为100 cm,水模体射野中心轴为1.5、5.0、10.0 cm深度处时测量吸收剂量5次求平均值.分析变压器输出电压对剂量率、剂量传递准确性影响.结果 市内电压变化对剂量率有影响.在一定变化范同内变压器输出电压增加加速器输出剂虽率增加,水模中射野中心轴线上不同深度处吸收剂量增加.结论 为BJ-6B加速器配备高精度的稳压器非常重要,用户在使用时务必把稳压器稳压精度调整到最高.     

加速器调制器电源故障排除一例

本院西门子Ｍ－７４４５型加速器在正常使用时，突然停机，故障表现为：一开机即停，经检查，调制器高压电源变压器开关ＣＢ３（ＭＯＤＵＬＡＴＯＲＰＯＷＥＲＳＵＰＰＬＹＴＲＡＮＳＦＯＲＭＥＲ）跳闸。用示波器观察：没有ＰＵＬＳＥＩ（磁控管脉冲电流）波形，说明调制器没有工作。一般情况下，ＣＢ３跳闸故障原因多为闸流管性能下降或损坏，造成闸流管过流而引起，也有可能是副闸流管或ｃｈｏｋｅ（高压扼流圈）损坏造成，但较为少见。打开调制器检查：主、副闸流管状态正常，ｃｈｏｋｅ亦无损坏。在进一步检查中，移去调制器触发信号，…     

加速器磁控管的使用与寿命浅析

我科在1975年安装了菲利浦SL75-10直线加速器使用至今,低压小时为16600,高压小时为3840,从这18年工作情况来看,平均故障率不超过3％,现将近期一次维修体会绍介如下。 一次在进行每周常规剂量监测时,发现10MeV电子线剂量下降到只有正常值的1/4左右,剂量率也不稳,而其他能量如:G,8MeV电线和8MeV X线与正常值相同,只是X线剂量率略低一些。马停止8MeV电子线的使用,而后又进行了多次测量(不同日期),其结果与发现故障时完全相同。然后开始寻找原因,因当时我们手里没有备用磁控管(EEV、     

23EX直线加速器 7年故障统计分析经验

目的 研究故障统计分析在23EX加速器日常维护中的应用。方法 收集2008-2015年间23EX加速器的故障数据。分析23EX加速器故障率与时间关系,利用帕累托图统计分析影响23EX加速器稳定性的主要子系统和主要零部件。结果 23EX加速器运行 7年共发生故障318次,更换零部件358个。加速器投入使用后1.5年内故障率逐渐增加,最高时达38次/半年,之后有所下降并保持相对稳定,1年中第3季度是加速器故障率最高时间段。影响23EX加速器稳定性的主要子系统是MLC和机械系统,分别占总故障数66.4%和11.9%;影响23EX加速器稳定性的主要零部件是MLC叶片螺母和叶片马达,分别占总更换零部件的38.8%和28.5%。结论 加速器故障统计分析有助于维护人员发现故障的分布规律,找出影响加速器稳定性的主要因素,为制定日常维护计划、改善维护策略提供依据。     

螺旋断层治疗设备多叶准直器故障分析

目的 通过对螺旋断层治疗设备二进制气动多叶准直器故障现象及处理方法的分析,总结相关维修经验,达到准确判断故障部件,缩短停机时间,提高开机率的目的。方法 对螺旋断层治疗设备48个月的多叶准直器维修情况进行统计和分析,总结出多叶准直器常见的故障部件、故障原因及处理方法。结果 在48个月内,设备共出现多叶准直器故障20次,空气压缩机11次,位置验证板4次,叶片驱动器2次,叶片缓冲阀2次,叶片位置验证杆滑脱1次。多叶准直器故障与高压气体湿度有很大关系,设备出束时间对多叶准直器部分部件使用寿命也有很大影响。结论 螺旋断层治疗设备多叶准直器结构复杂,高强度工作增加了其故障率,高压气体湿度影响设备多叶准直器的正常运行,通过总结多叶准直器维修经验可初步判断故障原因,确定故障部件,达到缩短停机时间、提高开机率的目的。     

西门子K型和M型加速器真空过流连锁维修一例

由于采用不同的微波发生器 (速调管或磁控管 ) ,西门子加速器可分为Ｋ型和Ｍ型 ,但用于监测波导管系统真空度的连锁电路大致相同。通过对此例故障的分析与维修 ,以期对从事放射治疗设备技术工作的人员提供参考。一、材料与方法1.故障现象 :控制台显示器显示 2 5 #ＶａｃｕｕｍＯｖｅｒＣｕｒ ｒｅｎｔＩｎｔｅｒｌｏｃｋ(真空过流连锁 ) ,Ｓ4 0Ｂ面板上的 10只电流指示发光二极管Ｕ3全亮 (每亮 1只二极管表示有 2 μＡ电流增量 ) ,加速器不能正常工作。2 .故障分析 :波导管系统需保持很高的真空度 ,一般情况下气压 <1.33× 10 -3 Ｐａ ,所以…     

瓦里安2100C/D加速器枪驱动系统热端电路故障分析及检测

瓦里安2100C/D加速器枪驱动系统,由冷端和热端两部分组成.系统采用数字栅控电子枪,实现数字化自动控制,提供精确稳定的灯丝电压、栅极脉冲电压和阴极高压. 系统具有完备的监控功能，对所提供的电压、电流实时监控，并自动监测系统电路工作状态，检测系统故障。当系统所提供的电压发生改变或监测系统发现异常时将产生GFIL联锁，终止枪驱动系统运行。枪驱动系统故障多数发生在热端枪灯丝电源板、枪驱动脉冲板、低压电源板和背板。笔者根据这部分电路原理结合实际工作中的具体情况，依据故障后出现的故障报告和A／D状态监测信息，绘制出故障检测流程图，为瓦里安加速器的维修提供参考。     

CT-Sim技术在乳腺癌放射治疗中的应用

用大恒STAR 2 0 0 0三维放射治疗系统、GE双螺旋CT、国产北医BJ 6B型加速器对乳腺癌患者实施精确定位、虚拟计划设计、射野间无缝连接照射 ,可提高患者重复摆位的精度 ,定位时间短 ,射野间衔接好 ,患者皮肤反应轻 ,放射性肺炎发生率明显下降。     

A reticle retrofit and dosimetric consideration for a linear accelerator

PURPOSE: An imperfect reticle system in an accelerator causes uncertainties in source-skin distance (SSD), off-axis distance (OAD), isocenter, and so forth. A reticle was designed and fabricated, and its implications on x-ray and electron beam dosimetry were investigated. METHODS AND MATERIALS: A new reticle frame was dimensioned to fit snugly in the accelerator. The frame was fabricated to carry a pair of adjustable cross wires and to allow the machine operation in the photon and electron modes. The impact of the cross wires on 6 MV photon and 5-10 MeV electron beam parameters such as dose rate (Gy/monitor unit), beam uniformity, surface dose, and so forth, were studied using suitable ion chambers and phantoms. RESULTS: The retrofitted system offered long-term mechanical stability leading to precise SSD, OAD, and isocenter measurements. Changes introduced by the cross wires on the 6 MV photon and 5-10 MeV electron beams are presented. CONCLUSION: Long-term stability of a reticle in an accelerator is important for an accurate patient setup and for making reliable dosimetric measurements. Beam characteristrics have to be studied whenever modifications on a reticle system are made.     

A radiographic and tomographic imaging system integrated into a medical linear accelerator for localization of bone and soft-tissue targets.

PURPOSE: Dose escalation in conformal radiation therapy requires accurate field placement. Electronic portal imaging devices are used to verify field placement but are limited by the low subject contrast of bony anatomy at megavoltage (MV) energies, the large imaging dose, and the small size of the radiation fields. In this article, we describe the in-house modification of a medical linear accelerator to provide radiographic and tomographic localization of bone and soft-tissue targets in the reference frame of the accelerator. This system separates the verification of beam delivery (machine settings, field shaping) from patient and target localization. MATERIALS AND METHODS: A kilovoltage (kV) x-ray source is mounted on the drum assembly of an Elekta SL-20 medical linear accelerator, maintaining the same isocenter as the treatment beam with the central axis at 90 degrees to the treatment beam axis. The x-ray tube is powered by a high-frequency generator and can be retracted to the drum-face. Two CCD-based fluoroscopic imaging systems are mounted on the accelerator to collect MV and kV radiographic images. The system is also capable of cone-beam tomographic imaging at both MV and kV energies. The gain stages of the two imaging systems have been modeled to assess imaging performance. The contrast-resolution of the kV and MV systems was measured using a contrast-detail (C-D) phantom. The dosimetric advantage of using the kV imaging system over the MV system for the detection of bone-like objects is quantified for a specific imaging geometry using a C-D phantom. Accurate guidance of the treatment beam requires registration of the imaging and treatment coordinate systems. The mechanical characteristics of the treatment and imaging gantries are examined to determine a localizing precision assuming an unambiguous object. MV and kV radiographs of patients receiving radiation therapy are acquired to demonstrate the radiographic performance of the system. The tomographic performance is demonstrated on phantoms using both the MV and the kV imaging system, and the visibility of soft-tissue targets is assessed. RESULTS AND DISCUSSION: Characterization of the gains in the two systems demonstrates that the MV system is x-ray quantum noise-limited at very low spatial frequencies; this is not the case for the kV system. The estimates of gain used in the model are validated by measurements of the total gain in each system. Contrast-detail measurements demonstrate that the MV system is capable of detecting subject contrasts of less than 0.1% (at 6 and 18 MV). A comparison of the kV and MV contrast-detail performance indicates that equivalent bony object detection can be achieved with the kV system at significantly lower doses (factors of 40 and 90 lower than for 6 and 18 MV, respectively). The tomographic performance of the system is promising; soft-tissue visibility is demonstrated at relatively low imaging doses (3 cGy) using four laboratory rats. CONCLUSIONS: We have integrated a kV radiographic and tomographic imaging system with a medical linear accelerator to allow localization of bone and soft-tissue structures in the reference frame of the accelerator. Modeling and experiments have demonstrated the feasibility of acquiring high-quality radiographic and tomographic images at acceptable imaging doses. Full integration of the kV and MV imaging systems with the treatment machine will allow on-line radiographic and tomographic guidance of field placement.     

直线加速器和钴60治疗机放射治疗成本调查

[目的]研究直线加速器和钴60治疗机放射治疗的成本状况。[方法]调查分析了6所医院放射治疗的固定资产投入，及其年总成本和单位成本。[结果]使用直线加速器放射治疗的4所医院，固定资产投入均超过800万元，且每野次成本差异较大(最小44元，最大127．30元)。而使用钴60治疗机的2所医院固定资产投入均为55万元左右，每野次成本均约30元。[结论]各单位应根据自身特点合理配置设备，并加强成本管理。     

瓦里安CLINAC-Ⅸ型直线加速器联锁UDRS原理及不常见故障处理

UDRS联锁是瓦里安高能直线加速器的常见剂量联锁,由于系统的复杂性,该故障的出现几乎一直困扰很多工程师,需要找出解决的方法。本文详细分析了瓦里安CLinac-Ⅸ型直线加速器电路构成和UDRS联锁发生的原理,总结出UDRS联锁故障的检修方法。通过对少见故障处理方法的分享,为解决类似机型出现UDRS故障时提供方法参考。     

Shielding considerations for an operating room based intraoperative electron radiotherapy unit

The leakage radiation characteristics of a dedicated intraoperative radiotherapy linear accelerator have been measured on a machine designed to minimize the shielding required to allow it to be placed in an operating room suite. The scattering foil design was optimized to produce a flat beam for the field sizes employed while generating minimal bremsstrahlung contamination over the available energy range. More lead shielding was used in the treatment head than is used in conventional accelerators. A small amount of borated polyethylene shielding was also employed since neutron production was present at measurable levels. The room shielding installed in the operating room was demonstrated to be adequate to treat at least 20 patients each month to an average dose of 20 Gy. The worst case exposure was found to be 73% maximum permissible exposure. Administrative control was required for adjoining areas when calibrations and maintenance were performed.     

Reduced neutron production through use of a flattening-filter-free accelerator

PURPOSE: To measure and compare neutron fluence around an accelerator operating at 18 MV, both with the flattening filter present (FF mode) and absent (flattening-filter-free [FFF] mode). METHODS AND MATERIALS: The neutron fluence was measured at several locations in the patient plane using gold foil activation in neutron moderators. Differences in neutron fluence between the FF and FFF mode were assessed in three frameworks: (1) measured per monitor unit of machine-on time, (2) determined per dose on the central axis, and (3) determined for a complete course of prostate intensity-modulated radiotherapy. RESULTS: Neutron fluence per monitor unit was approximately 20% lower when the accelerator was operated in the FFF mode than when it was in FF mode. The total amount of neutron fluence that would be obtained during the entire course of prostate intensity-modulate radiotherapy was 69% lower when the accelerator was operated in the FFF mode than when it was in the FF mode. This reduction in neutron fluence would correspond to a drastic reduction in the neutron dose equivalent received by the patient as a byproduct of high-energy radiotherapy. It would also correspond to a reduction in activation within the treatment vault and subsequent exposure to radiation therapists. CONCLUSION: When feasible, operating the accelerator without a FF will benefit both patients and radiation therapists by reducing the number of unwanted neutrons and resultant exposure. This reduces the risk of negative effects from such exposure (e.g., second cancers).     

Recommendations for implementation of high dose rate 192Ir brachytherapy in developing countries by the Advisory Group of International Atomic Energy Agency.

PURPOSE: To provide recommendations for the implementation of high dose rate (HDR) 192Ir brachytherapy technology in developing countries.METHODS: An Advisory Group Meeting of the International Atomic Energy Agency (IAEA) met to address the implementation of HDR 192Ir brachytherapy technology in developing countries. These recommendations reflect only the personal opinions of the authors and do not necessarily represent the opinion of the IAEA.RESULTS: An HDR treatment system should be purchased as a complete unit that includes the 192Ir radioactive source, source loading unit, applicators, treatment planning system, and control console. Infrastructure support may require additional or improved buildings and procurement of or access to new imaging facilities. A supportive budget is needed for quarterly source replacement and the annual maintenance necessary to keep the system operational. The radiation oncologist, medical physicist, and technologist should be specially trained before HDR can be introduced. Training for the oncologist and medical physicist is an ongoing process as new techniques or sites of treatment are introduced. Procedures for quality assurance (QA) of patient treatment, and the planning system must be introduced. Emergency procedures with adequate training of all associated personnel must be in place.CONCLUSIONS: The decision to select HDR in preference to alternate methods of brachytherapy is influenced by the ability of the machine to treat a wide variety of clinical sites. In departments with personnel and budgetary resources to support this equipment appropriately, economic advantage becomes evident only if large numbers of patients are treated. Intangible benefits of source safety, personnel safety, and easy adaptation to fluctuating demand for treatments also require consideration when evaluating the need to introduce this treatment system.