蒙特卡罗方法研究均整器对6MVX线能谱的影响

Monte Carlo Study of The Effect of Flattening Filter For 6 MV X Ray Spectrum

目的:用蒙特卡罗方法计算Varian Trilogy加速器无均整器条件下6 MV X射线能谱,分析均整器对能谱的影响。方法:先用BEAMnrc分别模拟计算Varian Trilogy加速器6 MV射线在具备均整器和无均整器条件下,方野边长分别为4cm、6 cm、8 cm、10 cm、20 cm和40 cm时的相空间文件,以相空间文件为输入用BEAMDP分析光子能谱。结果:无均整器条件下光子注量增大,在光子能谱峰值附近最明显,射野边长为4 cm时去掉均整器后光子注量增加的最多为6.284倍,随着射野增大增加倍数减小,射野边长为40 cm时最小为2.398倍,无均整器条件下光子谱峰值能量降低,光子谱整体左移,平均能量明显减小。结论:去除均整器后,加速器的输出光子能谱发生较大变化,随之剂量特性发生改变,临床上可能产生一定的获益或未知情况,尚需要进一步的研究支持。

Objective：Used the Monte Carlo method to calculate 6 MV X-ray spectrum of Varian Trilogy accelerator without flattening filter, and analysis the effect of flattening filter for 6 MV X ray spectrum. Methods：First, simulated the 6-MV X ray phase space file ofa Varian Trilogy linear accelerator with and without flattening filter by the Monte Carlo code BEAMnrc. The field sizes used in this study were 4 cm,6 cm,8 cm, 10 cm,20 cm and 40 cm. Made the phase space file as input file to analyze the photon energy spectrum by the BEAMDP. Results：For the accelerator without flattening filter, the photon fluence was in- creased, it was obvious near the spectrum peak, it was increased 6.284 times when the field size was 4 cm, the increasing trend was decreased with the field size increased,when the field size was 40 cm the increased time was least was 2.398.In the condi- tion of without flattening filter the photon energy spectrum peak energy is reduced, the photon energy spectrum moved to the left and the average energy was significantly reduced. Conclusions： After removing flattening filter, the photon energy spectrum changed greatly, the dose characteristics changed subsequently and it may has some benefits or some unknown situations in clin ical treatment. As well as needed to further research to support.