Both Joseph A, Pawlicki Todd
Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Int J Med Sci. 2004;1(2):63-75. doi: 10.7150/ijms.1.63. Epub 2004 Jun 1.
This work is a report on the commissioning of low energy electron beams of a medical linear accelerator for Monte Carlo dose calculation using NXEGS software (NXEGS version 1.0.10.0, NX Medical Software, LLC). A unique feature of NXEGS is automated commissioning, a process whereby a combination of analytic and Monte Carlo methods generates beam models from dosimetric data collected in a water phantom. This study uses NXEGS to commission 6, 9, and 12 MeV electron beams of a Varian Clinac 2100C using three applicators with standard inserts. Central axis depth-dose, primary axis and diagonal beam profiles, and output factors are the measurements necessary for commissioning of the code. We present a comparison of measured dose distributions with the distributions generated by NXEGS, using confidence limits on seven measures of error. We find that confidence limits are typically less than 3% or 3 mm, but increase with increasing source to surface distance (SSD) and depth at or beyond R(50). We also investigate the dependence of NXEGS' performance on the size and composition of data used to commission the program, finding a weak dependence on number of dose profiles in the data set, but finding also that commissioning data need be measured at only two SSDs.
本研究报告了使用NXEGS软件（NXEGS版本1.0.10.0，NX医疗软件有限责任公司）对医用直线加速器的低能电子束进行调试以用于蒙特卡罗剂量计算的情况。NXEGS的一个独特功能是自动调试，即通过解析法和蒙特卡罗法相结合的过程，根据在水模体中收集的剂量数据生成射束模型。本研究使用NXEGS对瓦里安Clinac 2100C的6、9和12 MeV电子束进行调试，使用三种带有标准插入件的施源器。中心轴深度剂量、主轴线和对角线射束剖面以及输出因子是调试该代码所需的测量值。我们使用七个误差测量的置信限，对测量的剂量分布与NXEGS生成的分布进行了比较。我们发现，置信限通常小于3%或3毫米，但随着源皮距（SSD）的增加以及在R(50)及以上深度处而增大。我们还研究了NXEGS性能对用于调试该程序的数据大小和组成的依赖性，发现对数据集中剂量剖面数量的依赖性较弱，但也发现调试数据只需在两个SSD处进行测量。
