Elekta和Varian医用直线加速器束流特性的比较研究

Comparison of the beam characteristics between Elekta and Varian medical linear accelerator

目的：分析和评估Varian和Elekta两台医用直线加速器束流特性的差异,为临床准确地实施其质量保证（QA）和剂量学应用提供依据。方法：采用三维水箱测量,比较分析Varian Clinac i X和Elekta Precise直线加速器6 MV X射线辐射源的开野/60°楔形野条件下百分深度曲线（PDD）、输出因子以及束流离轴曲线等束流剂量学特性,并对电子束相同能量的PDD曲线及输出因子等数据进行分析处理。结果：Varian Clinac i X较Elekta Precise医用加速器在开野/楔形野条件下X射线辐射质均略低,其射野半影值（20%~80%）也较小。电子线平均能量Precise较Clinac i X加速器在4 Me V、6 Me V能量档上明显偏高;而12 Me V和15 Me V时较Clinac i X偏低。两台加速器X射线射野及电子线限光筒束流输出因子均一定程度上存在差异。结论：尽管两台医用加速器标称能量相同,但是因自身机头设计结构、参数条件或采用不同的校准标准,两台医用加速器X射线和电子线束流特性均存在一定的差异。在临床应用中需充分予以考虑其相对应的剂量学特点。

Objective： To analyze and evaluate the differences of beam characteristic for two types of Varian and Elekta medical linear accelerator （Linac） in order to provide the reference of quality assurance （QA） and clinical dosimetric application. Methods：The beam characteristics of the open and 60° wedged fields, such as the percent depth curves （PDDs）, the off-axis ratio curves and output factors, were compared for 6 MV X-ray between Varian Clinac iX and Elekta Precise Linac. And the parameters of electron beam energy were analyzed. Results：The radiation quality of X-ray in Varian Clinac iX under the same conditions of open and wedge field was slightly lower than those in Elekta Precise Linac. And the penumbra values （20%~80%） were also smaller. The mean energy of electron beam for 4 or 6 MV in Precise machine was higher than those in Clinac iX, but the mean energy for 12 or 15 MV was lower. The output factors of X-ray and electron beam for the two Linac were a little different. Conclusion：Although the nominal energy in Elekta and Varian Linac are same, the beam characteristics of their X-ray and electron have a little difference due to the collimator structure, parameters or beam calibration standard. Therefore, the dosimetric characteristics of beams during the clinic application should be carefully considered.