6MeV医用电子直线加速器中束斑尺寸的计算与测量

Beam spot size calculation and measurement of 6-MeV medical linear accelerator

区别于大型加速器上对于束斑的定义与计算,医用电子直线加速器的束斑会影响剂量的X辐射分布(Profile)的半影区,从而影响放疗设备的治疗精度,对它的研究侧重点也不同于其它类型的加速器。基于这个原因,针对目前医用电子直线加速器尤其是国内医用电子直线加速器对电子束束斑计算与测量数据不够的问题,从束斑的理论计算出发,归纳了两种方法,并进行了对比研究。在理论研究的基础上,对上海联影医疗有限公司的6 Me V医用电子直线加速器的束斑进行了实验测量,采用两种高斯分布叠加拟合实验数据以得到较好的精度,对实验中的系统误差进行了分析,与理论计算较为吻合。

Background The spot size is of interest to the beam quality for the accelerator facility. As comparedwith the large accelerator scientific facility, the method to calculate the spot size is found to be different in themedical linear accelerator. The spot size in medical linear accelerator determines the penumbra field of the dose,which is important for the effective operation of medical linear accelerator. Purpose： This paper aims to summarizethe calculation methods of spot size, hence the discrepancy between both methods is investigated here to give a betterunderstanding of the beam spot size. Methods： The experiment setup based on the optical detection technique waspresented here to given rise to the spot size results of medical linear accelerator in Shanghai United ImagingHealthcare Co., Ltd. （UIH）, and a combined non-Gaussian method was proposed here to give a suitable fitting for theexperiment results. Results： The spot full width at half maximum （FWHM） of the 6-MeV medical linear acceleratorwas about 1.81 mm and 1.84 nun in x and y direction respectively, which is close to the results of calculation.Conclusion： The definition of the spot size proposed here is useful for the optimizing of accelerator design, as well asthe penumbra field of dose.