医用高能电子在介质中轫致辐射研究

The study on bremsstrahlung of high energy electron in material

目的研究医用高能电子在介质中轫致辐射带来的影响。方法利用蒙特卡罗程序EGS4软件包中的新版本EGSnrc详细地研究了高能电子束在类人体介质中所产生的轫致辐射光子的剂量和通量分布。模拟的高能电子束能量是放射治疗中常用的电子束能量(4—22MeV)。结果 1)在类人体介质中同一深度处,随着入射电子能量的增加,轫致辐射产生的剂量值也增加。2)对于相同入射能量的电子,在水中和肌肉组织中的同一深度,轫致辐射产生的剂量值非常相近,但是在骨中的剂量值明显增大。3)电子在人体介质(肌肉组织、骨)中轫致辐射的剂量约为总剂量的5%～10%,并且轫致辐射光子的影响范围远超过电子的射程。4)随着入射电子能量的增加,轫致辐射光子通量的最大值在增加,并且最大值点也在向介质深处移动。5)在水与肌肉组织中,轫致辐射光子通量在轴线上随深度的变化很相似,但是在骨中,通量的峰值点都较接近表面。结论在精确电子束放射治疗中,电子的轫致辐射对剂量的影响和对电子射程外的人体器官的辐射损伤是必须考虑的因素。特别是在胸部和头部的电子束放射治疗中,尤其需要考虑轫致辐射影响在骨中和其它组织中的差别。

Objective This paper illustrates the influence of bremsstrahlung produced by highenergy electron in body-like material. Methods Dose and flux distributions in body-like material of bremsstrahlung photons, produced by electrons with energy ranging from 4 MeV to 22 MeV, have been studied by using EGSnrc, a new set of Monte Carlo code EGS4. Results It is shown that, 1) the dose of bremsstrahlung photon increases when the energy of incident electron becomes higher. 2) the depth dose is similar in the water and tissue material, but the dose is higher in bone than that in water or tissue. 3)the bremsstrahlung photons contribute 5—10% of the total dose of electron. 4) the depth of maximum flux becomes deeper when incident electron energy beacomes higher. 5) the maximum flux point is near surface in bone than that in water or tissue. Conclusions The hremsstrahlung of high electrons makes great effect on the dose and would bring radiation damage to organos, the influence of bremsstrahlung must be taken into account in the electron radiotherapy. Especially, the differences of effects of the bremsstrahlung on bone and other tissues need be considered carefully in the electron radiotherapy of head and chest.