医用直线加速器质量控制中星形片分析的初步研究

A Preliminary Study for Starshot Analysis During Quality Control of Medical Linacs

目的研究医用直线加速器质量控制中星形片分析的影响因素。材料和方法在西门子医用直线加速器质量控制过程中,使用FilmQA软件和KODAK慢感光胶片对准直器的旋转中心进行星形片分析。分别研究辐照时不同准直器宽度、加速器机架角的偏移、准直器偏心、照射能量以及扫描分辨率对星形片分析结果的影响。结果本研究中,准直器偏心对分析结果有影响,偏心距离与分析结果呈线性关系。能量和扫描分辨率对分析结果影响较小,最大的影响小于0.2mm。4o机架角对分析结果的影响稍大,而2o机架角对分析结果影响小于0.1mm。准直器宽度对射野的影响比较大,而且两次测试的影响方向相反。结论临床工作中,当星形片分析结果超标时,需要仔细分析诸多因素,再做出最后的判断。

Objective This study was to discuss the influencing factors of Starshot analysis during the quality control of medical linacs. Methods During the quality control of a Siemens medical linac, Starshot analysis were carried out using FilmQA software and KODAK low sensitive films. The influence of setting to the results of Starshot analysis were explored, including Jaw width, shit of gantry angles, center shifts of Jaws, Beam energy and scan resolution. Result The offset of Jaws＇s center had effect on the analysis result and the center offset was linearly related to the result. The influence of Beam energy and scan resolution was much smaller, and the maximum deviation was less than 0.2mm. The deviation for gantry angle at 4 degree was a little larger than 2 degree which deviation was less than 0.1mm.The Jaw width had greater effort on the analysis result, and two trends were found in 2 tests. Conclusion In clinic, if the result of Starshot analysis was out of tolerance, a careful check to multi factors should be made before the last determination.