医用直线加速器无均整器下6MV X线能谱特性的蒙特卡罗研究  

Monte Carlo research on 6 MV X-ray spectrum characteristic of linear accelerator without flattening filter

作　　者：周鹏[1] 胡南[1] 刘岩海[1] 游士虎 徐婷婷[1] 余娴[1] 杨镇洲[1] 王阁[1] 

机构地区：[1]第三军医大学大坪医院野战外科研究所肿瘤中心,重庆400042

出　　处：《中国医学物理学杂志》2016年第8期761-765,共5页Chinese Journal of Medical Physics

基　　金：吴阶平医学基金(#320.6750.12177)

摘　　要：目的:利用蒙特卡罗方法研究医用直线加速器产生的6 MV-X射线在有均整器和无均整器状态下,光子能谱和空间分布的差异。方法:使用Geant4蒙特卡罗模拟程序计算医用加速器射野大小分别为5 cm×5 cm、10 cm×10 cm、15 cm×15 cm和20 cm×20 cm的6 MV-X射线在具备均整器和移除均整器条件下,初始光子的能谱和空间分布。结果:均整器移除后光子能谱光子注量变大,且随着射野的增大,射野内光子通量比值都明显减小,而且平均能量明显降低。此外,均整器的移除改变光子的相对分布,射野外光子数在整个相空间平面内光子中所占份额明显减少,而且与射野大小有关,5cm×5 cm时减少6.00%,10 cm×10 cm时减少4.42%,15 cm×15 cm时减少3.48%,20 cm×20 cm时减少2.28%,这表明移除均整器对于尺寸较小的射野意义重大。结论:均整器的移除可以优化射野的能谱分布,特别是对于调强放射治疗无均整器模式成为更有益模式。但是,由于均整器移除后导致的高剂量率在提高治疗增益的同时也带来了治疗风险,因此需要更进一步的研究和论证。Objective To analyze the differences of 6 MV X-ray spectrum and spatial distribution of linear accelerator with and without flattening filter by using Monte Carlo method. Methods With the field sizes of （5×5） cm2,（10×10） cm2,（15×15）cm2 and（20×20） cm2, the initial photon spectrums and spatial distributions of 6 MV X-ray with and without flattening filter were calculated and analyzed by using Geant4 Monte Carlo simulation program. Results The photon fluence increased when the flattening filter was removed. With the increase of field size, the photon flux ratio in the field reduced, and the average energy decreased significantly. When the flattening filter was removed, the relative photon distribution was changed, and the ratio of photon fluence of the out-filed to the whole phase plane was reduced significantly and related to field sizes. The reduction percentages of field sizes changing from（5×5） cm2 to（20×20） cm2 were respectively reduced by 6.00%, 4.42%, 3.48% and 2.28%, which showed flattening filter free had significant influences on the smaller field sizes.Conclusion The photon spectrum and distribution were optimized by removing the flattening filter. Flattening filter free is more benefit for intensity- modulated radiotherapy. However, the high dose rate of flattening filter free would cause the treatment risk, so the further research and discussion are necessary.

关 键 词：蒙特卡罗 直线加速器 均整器 光子能谱 

分 类 号：R815.6[医药卫生—放射医学] R811.1[医药卫生—临床医学]