一种直线加速器电离室保护装置的研制

目的:为了减少因电离室工作温度、湿度变化引起的直线加速器故障,延长直线加速器电离室使用寿命,设计一种电离室保护装置。方法:通过使用温度23℃、湿度15%、流量10L/min的干燥空气吹拂电离室的方法,改变电离室的工作环境,减少外部应用环境的变化对电离室产生的不良影响。结果:将装置安装在2台直线加速器上使用,同比上年同期的故障次数,故障率减少80%以上。结论:通过实际运行及参数检测,该电离室保护装置运行稳定,在一定程度上改善了电离室的工作环境,可以减少外部应用环境的变化对电离室产生的不良影响,减少电离室故障,延长使用寿命。     

18 MeV医用直线加速器防护门的防护效果评价

在中、高能加速器的运行中 ,存在Ｘ、γ射线和中子的混合辐射场。防护门的设计制作既要考虑Ｘ、γ射线 ,又要考虑中子辐射。近年来 ,加速器的配置越来越多且能量越来越高。但是 ,防护门设计和选材较混乱 ,大多仍沿用低能加速器的防护设计[1] ,因此 ,防护门不符合防护要求的现象时有发生[2 ] 。为提供高能加速器防护门的制作经验 ,保障放射工作人员和公众的健康与安全 ,现将某 18ＭｅＶ医用直线加速器防护门的设计及防护效果评价报告如下。1　仪器与方法1 1　测量仪器　ＦＪ 3 42Ｇ1型中子测试仪、美国产 45 0Ｐ电离室测试仪1 2　测试对象及…     

医用回旋加速器生产正电子核素的质量控制

提出了要想做好医用回旋加速器的质量控制，保证回旋加速器良好稳定的运行，提供足额且符合要求的正电子核素，就要做好回旋加速器的维护保养工作，同时，要注重技术人员的操作培训和质控意识养成，并将维修和备件的供应列入回旋加速器的质控项目。     

Varian 600C直线加速器YLD联锁的分析与故障排除

美国Varian 600C直线加速器是一种用于肿瘤放射治疗的低能医用直线加速器，它只能产生单一6MV能量的X射线。600C加速器采用了磁控管作为微波功率源，在设备的控制电路中设计了一个YLD联锁电路，用以检测和调整输出射线能量的稳定性，一旦能量发生变动时，YLD联锁电路动作，使加速器不能用于肿瘤患者的治疗。     

医科达加速器电离室故障判断

电离室是直线加速器上用来检测机器输出射线（X射线和电子线）剂量大小的关键器件，其工作性能的好坏，直接影响到加速器剂量特性和对病人的精确治疗，严重时会出现放射性医疗事故，而电离室价格昂贵，对其好坏的鉴别和对其平时维护，对降低维修成本和运行成本至关重要。电离室是一种高精度放射线计量检测器件，它的外层是石墨，中心是铝质的探针，石墨与探针之间充满空气，     

CL-1800型直线加速器X线靶移动装置的结构、工作原理及其故障处理

在直线加速器中，从加速管出来的高能电子束经过照射头束流系统、偏转磁铁偏转270°，滤去部分高低能电子，打在X线靶上产生X射线。再经散射膜、匀整器、电离室、上下光栏等，以便提供所需要的各种类型的照射，使照射野内射线照射均匀，能量得以控制。X线靶是金属钨靶，不同能量的电子束穿过不同厚度的钨靶材料，产生不同能量的X射线。根据不同的治疗要求，X射线靶在照射头中平稳准确地移动。变换靶的位置（厚度）以得到不同能量的X射线和电子线。二、CL—1800型直线加速器X线靶移动装置的结构及工作原理CL—1800型直线加速器，其X线靶…     

医用直线加速器电离室高压的检修

医用直线加速器电离室功能是,按设计剂量率对输出剂量进行检测,传送给控制台进行剂量控制。电离室出现故障时,电离室无法检测到输出剂量,使控制台出现低剂量报警及电离室故障报警,使机器终止出束,以保证设备及治疗安全。下面以西门子M-77医用直线加速器的电离室为例分析。西门子M-77医用直线加速器的电离室为内置,一般采用多极多层射线穿透型平行板电离室,以空气为介质,有多个相对独立的平行板构成,平行板包括一个收集极、一个高压极和接地极。当有射线穿过电离室时,极板间的空气被电离形成正、负离子,在电离室高电场作用下,向高压极和收集…     

医用回旋加速器质量控制与安全策略探讨

医用回旋加速器为临床PET/CT检查提供正电子放射性核素,做好回旋加速器的质量控制和安全防护就是要保证回旋加速器良好稳定的运行,保证安全生产,从而提供足额且符合要求的正电子核素,这就要求做好回旋加速器的维护保养工作,同时要注重技术人员的操作培训和质量控制意识的养成,维修和备件的供应也列入回旋加速器的质控项目。本文总结了医用回旋加速器各结构维护和保养的方法,阐述了对技术人员进行操作培训,培养质量控制意识的重要性。     

直线加速器电离室的工作原理和故障检修

电离室是直线加速器的重要部件,在放射治疗中电离室将直线加速器出束的射线能量转换成电信号的装置,其利用气体分子在高能射线作用下电离的原理,收集放大正离子和电子形成电流信号,由计算机收集并对加速器的射线系统进行反馈和控制。结合电离室的工作原理对其故障进行分析排查和检修,从而排除设备的故障,保证设备的正常使用。     

Varian 600C加速器枪高压打火故障检修

美国Varian 600C直线加速器是Varian公司生产的低能医用电子直线加速器，它提供单一的6MV能量的x射线，用于治疗。它具有结构简单，工作稳定耐用等很多优点，所以被很多医院大量的采用。     

Study of the radiation field characteristics of a 137Cs irradiator by Monte Carlo simulation

In this work a study of the energy fluence of the photon beam produced by a commercial irradiator that uses a single collimated 137Cs source is performed by employing the Monte Carlo code PENELOPE. A set of lead attenuators is placed at the exit window of the irradiator to vary the air kerma rate that is required to cover the instrument scales at a particular calibration distance. A possible variation in response due to this beam modification isalso investigated for LiF (TLD-100) dosimeters and for a secondary standard radiation protection level ionization chamber. The results show an important enhancement of beam mean energy from 633 to 642 keV as the lead attenuators increase in thicknesses. For this energy range, a maximum response change of 45% was found for LiF and 4.4% for the ionization chamber. These results reinforce the idea that a single source may very well be a practical solution for calibration laboratories without compromising the overall uncertainties acceptable for this application.     

针尖电离室水中吸收剂量校准方法研究

目的 ⁶⁰Co γ射线下,建立针尖电离室水中吸收剂量校准方法。方法 参考剂量仪（DOSE 1静电计+FC65-G型电离室）经过中国计量科学研究院校准,得到水中吸收剂量校准因子。采用⁶⁰Co γ射线,IAEA TRS-398测量程序,用参考剂量仪测量水下10 cm吸收剂量。替代法,用针尖电离室剂量仪进行水吸收剂量测量并对其进行水吸收剂量因子校准。更换⁶⁰Co γ射线辐射场,用参考剂量仪、针尖电离室剂量仪进行剂量验证测量。结果 参考剂量仪在水下10 cm处,参考条件下测得水吸收剂量结果为0.249 9 Gy。两台针尖电离室剂量仪测量结果分别为0.248 0 Gy和0.250 0 Gy;两台针尖电离室剂量仪测量结果与参考剂量仪测量结果相对偏差均在±0.8%内,针尖电离室剂量仪测量水吸收剂量不确定度为2.8%（k=2）。结论 针尖电离室可用于小野水中吸收剂量的测量。     

Quantification of the temperature equilibrium time of the cavity in parallel-plate-type ionization chambers by thermal analysis

Temperature corrections are necessary to account for the varying mass of air in the cavity volume of a vented ionization chamber. The temporal response resulting from temperature changes in a cylindrical and/or Farmer-type ionization chamber, which is the standard dosimeter, has been thoroughly discussed by some researchers. The purpose of this study was to characterise and analyse the dependence of the cavity air temperature of the parallel-plate-type ionization chamber on changes in the ambient temperature. Ionization chambers NACP-02 (IBA Dosimetry, GmbH) and Advanced Markus TN34045 (PTW, Freiburg) were modelled using thermal analysis software to present the temperature equilibrium time and the entire ionization chamber temperature distribution. The temporal response of each ionization chamber was measured for comparing the calculation results of the thermal analysis. The ionization chamber cavities of NACP-02 and TN34045 reached complete equilibrium in 670 and 750 s, respectively. Heat transfer occurred faster at the centre of the front wall of TN34045 than at the outside of the centre except for the edges. Further, the non-uniformity of temperature in the cavity was in the range of 24.2–24.8°C for NACP-02 and 23.7–24.4°C for TN34045 at 200 s after the ionization chamber was installed in the water phantom. The previous proposal to wait for about 15 mins after submerging the chamber in a water phantom before the measurement is demonstrated to be appropriate for parallel-plate-type ionization chambers.     

Detection system for measuring dose equivalent from fast neutrons in mixed gamma-neutron fields.

A hybrid detector for measuring fast neutrons in mixed gamma-neutron fields is discussed in this paper. The detector consists of an ionization chamber with components made from a plastic scintillator. Its operation is based on the two detection systems thus combined. Its parameters and domain of applicability are explained. This paper proposes a rapid integral method for measuring the neutron-dose equivalent based on this detector, which allows a good separation of the gamma component.     

Standards and calibration facilities of the Australian Radiation Laboratory for ionizing radiation beams

The Australian Radiation Laboratory (ARL) maintains national standards of exposure and working standards of absorbed dose. Some of the exposure standards maintained by ARL have been compared recently with those of the Bureau International des Poids et Mesures (BIPM) for 100 to 250 kV x-rays and 60Co gamma rays. The absorbed dose standard for 60Co gamma rays is compared regularly with other standards through the International Atomic Energy Agency (IAEA) and World Health Organization (WHO). All results show good agreement. A range of calibration qualities is offered at ARL, extending from 10 kV x-rays to 60Co gamma rays. A system of regional facilities has been developed for radiation protection calibrations; each facility is supplied with a set of 137Cs sources and an ionization chamber and electrometer for use with x-rays. The system is now almost complete throughout Australia.     

平行板电离室两种校准方法研究

目的 研究用γ光子线束(⁶⁰Co模体法)和高能电子线束(电子束法)校准平行板电离室吸收剂量因子方法。方法 电子束法:0.65cc指形电离室放在水中有效点深度2.88 cm (考虑电离室半径),平行板电离室(NACP02)放在水中有效点深度2.70 cm,都距监督指形电离室3 cm处,电子线束能量18 MeV,照射野15 cm×15 cm,SSD=100 cm,照射:300MU,测量;不加监督电离室,并按上述条件照射并测量;根据国际原子能机构(IAEA)381号报告,分别计算平行板电离室空气吸收剂量校准因子。⁶⁰Co模体法:水模体30 cm×30 cm×30 cm,0.65cc指形电离室放在水中深度5cm,照射野10 cm×10 cm,SSD=80 cm,照射时间60s;水模体25 cm×25 cm×25 cm,平行板电离室放在水中有效点深度5cm,其他条件相同,计算平行板电离室空气吸收剂量校准因子。最后将两种方法校准结果进行比较。结果 电子束方法校准平行板电离室结果为52.30 Gy/C·kg ^-1(不加监督电离室的值为52.27Gy/C·kg ^-1)。⁶⁰Co模体法校准平行板电离室结果为52.33 Gy/C·kg ^-1。结论 电子束法与⁶⁰Co模体法校准平行板电离室空气吸收剂量因子偏差仅为0.05%。因此,测量电子线束输出剂量,对平行板电离室的校准既可选择高能电子线束也可选择⁶⁰ Co光子γ线束。     

Development of GATE Monte Carlo simulation for a CsI pixelated gamma camera dedicated to high resolution animal SPECT

GATE is currently considered in scintigraphic imaging as a powerful tool to develop, design and optimize nuclear medicine modalities. This paper describes the GATE simulation of a pixelated gamma camera which is dedicated to high resolution of small animals imaging. It consists of a CsI(Na) crystal array coupled to position sensitive photomultiplier tube. The simulation model includes photon tracking through low energy high resolution hexagonal parallel holes collimator, CsI(Na) pixelated crystal, back-compartment, and camera shielding. Simulations were compared with experimental results by some criteria such as energy spectrum, energy resolution, spatial resolution, sensitivity and count profiles obtained from line and point sources imaging. The acquired energy resolution show good agreement with measured spectra. Difference between calculated and experimental values is about 0.3% for absolute sensitivity measurement. The result of the image uniformity is more consistent after implementation of non-uniformity correction. These values were about 1.3 and 1.2% for experimental and simulation study in the central field of view, respectively. Measurements showed that the spatial resolutions differences at the head surface along the long dimensions of gamma camera for simulation and experimental differed by no more than 4%.Differences along the short axis were about 6%. The FWHMs of images of point and line sources show good consistency between experimental images and corresponding simulated ones. The difference between experimental and simulated system parameters was within 11%. Our results demonstrate the ability and flexibility of the Monte Carlo simulation for modeling pixelated gamma camera with position sensitive detector by selecting the appropriate parameters for digitizer chain and collimator position on the detector surface.     

Evaluation of effective energy for QA and QC: Measurement of half-value layer using radiochromic film density

The effective energy of diagnostic X-rays is important for quality assurance (QA) and quality control (QC). However, the half-value layer (HVL), which is necessary to evaluate the effective energy, is not ubiquitously monitored because ionization-chamber dosimetry is time-consuming and complicated. To verify the applicability of GAFCHROMIC XR type R (GAF-R) film for HVL measurement as an alternative to monitoring with an ionization chamber, a single-strip method for measuring the HVL has been evaluated. Calibration curves of absorbed dose versus film density were generated using this single-strip method with GAF-R film, and the coefficient of determination (r ²) of the straight-line approximation was evaluated. The HVLs (effective energies) estimated using the GAF-R film and an ionization chamber were compared. The coefficient of determination (r ²) of the straight-line approximation obtained with the GAF-R film was more than 0.99. The effective energies (HVLs) evaluated using the GAF-R film and the ionization chamber were 43.25 keV (5.10 mm) and 39.86 keV (4.45 mm), respectively. The difference in the effective energies determined by the two methods was thus 8.5%. These results suggest that GAF-R might be used to evaluate the effective energy from the film-density growth without the need for ionization-chamber measurements.     

基于溴化镧探测器的γ射线空气吸收剂量率的测量方法

目的 针对溴化镧闪烁体探测器,开展了G(E)函数的计算方法研究,最终实现了空气吸收剂量率的测量.方法 首先,基于蒙特卡罗模拟计算方法,模拟计算出溴化镧探测器的γ能谱,给出不同能量的响应函数;然后,利用最小二乘法计算得到了G(E)函数;最后,利用标准点源实验,将溴化镧探测器利用G(E)函数转换测量得到的空气吸收剂量率与理...