Almond P R, Attix F H, Humphries L J, Kubo H, Nath R, Goetsch S, Rogers D W
Department of Radiation Oncology, University of Louisville, Kentucky 40202.
Med Phys. 1994 Aug;21(8):1251-60. doi: 10.1118/1.597359.
This report is an extension of the 1983 AAPM protocol, popularly known as the TG-21 Protocol. It deals with the calibration of plane-parallel ionization chambers and their use in calibrating therapy electron beams. A hierarchy of methods is presented. The first is to calibrate the plane-parallel chamber in a high energy electron beam against a cylindrical chamber which has an Ncylgas value that has been obtained from a NIST traceable 60Co beam calibration. The second method, which is recommended for implementation by the ADCLs is an in-air calibration against a NIST-traceable calibrated cylindrical chamber in a Cobalt-60 beam to obtain a plane-parallel-chamber calibration factor in terms of exposure or air kerma. The third method places the two chambers in a phantom in a Cobalt-60 beam, and leads to an Nppgas value for the plane-parallel chamber. This report also gives Nppgas/NxAion)pp and Nppgas/(NkAion)pp values for five commonly used commercially available plane-parallel chambers: the Capintec PS-033, the Exradin P-11, the Holt, the NACP and the PTW-Markus. The calculation of these Ngas ratios introduces a Kcomp factor which is also calculated for the five parallel plate chambers. The use of the plane-parallel chambers follows the 1983 AAPM protocol for absorbed dose calibrations of electrons, except that new energy-dependent Prepl values are given for the Capintec PS-033 and PTW-Markus chambers consistent with the consensus of reports in the literature. For all the chambers, however, Prepl is unity for 20 MeV electrons. This report does not address the issue of the use of plane-parallel chambers in calibrating photon beams.
本报告是1983年美国医学物理学会（AAPM）协议（即广为人知的TG - 21协议）的扩展。它涉及平行板电离室的校准及其在校准治疗电子束中的应用。文中介绍了一系列方法。第一种方法是在高能电子束中，将平行板电离室与圆柱形电离室进行比对校准，该圆柱形电离室的Ncylgas值是通过可溯源至美国国家标准与技术研究院（NIST）的60Co束流校准获得的。第二种方法（ADCLs建议采用）是在60Co束流中，相对于可溯源至NIST校准的圆柱形电离室进行空气校准，以获得基于照射量或空气比释动能的平行板电离室校准因子。第三种方法是将两个电离室置于60Co束流的模体中，从而得到平行板电离室的Nppgas值。本报告还给出了五种常用商用平行板电离室（Capintec PS - 033、Exradin P - 11、Holt、NACP和PTW - Markus）的Nppgas / (NxAion)pp和Nppgas / (NkAion)pp值。这些Ngas比值的计算引入了一个Kcomp因子，该因子也针对这五个平行板电离室进行了计算。平行板电离室的使用遵循1983年AAPM关于电子吸收剂量校准的协议，不过对于Capintec PS - 033和PTW - Markus电离室给出了与文献报道共识一致的新的能量相关Prepl值。然而，对于所有电离室，20 MeV电子的Prepl均为1。本报告未涉及平行板电离室在光子束校准中的应用问题。
