Ibbott G S, Attix F H, Slowey T W, Fontenla D P, Rozenfeld M
University of Kentucky, Lexington 40536, USA.
Med Phys. 1997 Aug;24(8):1249-54. doi: 10.1118/1.598146.
The American Association of Physicists in Medicine, through a subcommittee (formerly Task Group 3) of the Radiation Therapy Committee, has accredited five laboratories to perform calibrations of instruments used to calibrate therapeutic radiation beams. The role of the accredited dosimetry calibration laboratories (ADCLs) is to transfer a calibration factor from an instrument calibrated by the National Institute of Standards and Technology (NIST) to a customer's instrument. It is of importance to the subcommittee, to physicists using the services of the ADCLs, and to the ADCLs themselves, to know the uncertainty of instrument calibrations. The calibration uncertainty has been analyzed by asking the laboratories to provide information about their calibration procedures. Estimates of uncertainty by two procedures were requested: Type A are uncertainties derived as the standard deviations of repeated measurements, while type B are estimates of uncertainties obtained by other methods, again expressed as standard deviations. Data have been received describing the uncertainty of each parameter involved in calibrations, including those associated with measurements of charge, exposure time, and air density, among others. These figures were combined with the uncertainty of NIST calibrations, to arrive at an overall uncertainty which is expressed at the two-standard deviation level. For cable-connected instruments in gamma-ray and x-ray beams of HVL > 1 mm Al, the figure has an upper bound of approximately 1.2%.
美国医学物理学会通过放射治疗委员会的一个小组委员会（前身为任务组3），认可了五个实验室对用于校准治疗性辐射束的仪器进行校准。认可剂量测定校准实验室（ADCL）的作用是将校准因子从由美国国家标准与技术研究院（NIST）校准的仪器传递到客户的仪器。对于该小组委员会、使用ADCL服务的物理学家以及ADCL自身而言，了解仪器校准的不确定度至关重要。通过要求各实验室提供其校准程序的相关信息，对校准不确定度进行了分析。要求通过两种程序估算不确定度：A类是作为重复测量的标准偏差得出的不确定度，而B类是通过其他方法获得的不确定度估算值，同样表示为标准偏差。已收到描述校准中涉及的每个参数不确定度的数据，包括与电荷测量、曝光时间和空气密度等相关的参数。这些数值与NIST校准的不确定度相结合，得出以两倍标准偏差水平表示的总体不确定度。对于HVL＞1mm Al的γ射线和X射线束中的电缆连接仪器，该数值的上限约为1.2%。
