Varian Trilogy直线加速器6MV X线无均整器条件下剂量特性的蒙特卡罗研究

发布时间：2018-03-07 23:22

本文选题：均整器　切入点：蒙特卡罗方法　出处：《南华大学》2012年硕士论文　论文类型：学位论文

【摘要】：在传统的医用直线加速器中，均整器是一重要的组成部分。X线经过均整器后将原本不均匀的剂量分布修正成均匀的剂量分布，以满足常规放疗和三维适形放疗的需求。调强放疗中，优化产生的注量分布一般是不均匀的，通过多叶准直器(MLC)的运动可获得治疗所需要的注量。实际上，在这个过程中，MLC把加速器输出的注量分布从均匀调制为不均匀。当然，MLC也可以把加速器输出的注量从固有的不均匀分布调制为调强所需的不均匀分布。为了让加速器产生固有的不均匀分布，可以将均整器去除，但这可能对输出射线的特性产生很大的影响，为此，，本论文对Varian Trilogy加速器6MV X线在有均整器(Flattening Filter,FF)和无均整器(Flattening Filter Free,FFF)条件下的剂量特性进行了蒙特卡罗模拟，探讨均整器对剂量特性的影响。本研究先用BEAMnrc和DOSXYZnrc分别模拟计算Varian Trilogy加速器6MV射线在具备均整器和去除均整器条件下，体积为50cm×50cm×50cm的均匀水体模中，方野边长分别为1cm、2cm、3cm、4cm、6cm、8cm、10cm、12cm、15cm、20cm、30cm和40cm时的深度剂量（DD）和离轴比（OAR，最大剂量、5cm、10cm和20cm深度处）、总散射因子Sc,p和中心轴剂量比值，用BEAMDP分析光子能谱，然后对两种条件下以上各物理量进行分析和比较。研究结果表明无均整器条件下光子谱左移，射线质变软，光子通量增加；建成区深度剂量增加，建成区后深度剂量有一定幅度的降低；射野平坦度变差，射野越大越明显；加速器输出剂量率明显增大；射野边缘剂量减小；总散射因子Sc,p与射野的依赖关系相对变小。总之，去除均整器后，加速器的输出特性发生了明显改变，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。
[Abstract]:In the traditional medical linear accelerator, the integrator is an important component. After the X-ray is passed through the uniform device, the original uneven dose distribution is corrected into a uniform dose distribution. In order to meet the needs of conventional radiotherapy and three-dimensional conformal radiotherapy. In intensity modulated radiotherapy, the optimal dose distribution is generally uneven, and the dose required for treatment can be obtained through the motion of the MLC (multileaf collimator). In fact, In this process, MLC modulates the flux distribution of accelerator from uniform modulation to non-uniformity. MLC can also modulate the flux output from the inherent non-uniform distribution to the non-uniform distribution needed to adjust the intensity of the accelerator. The speeder produces an inherently uneven distribution, The integrator can be removed, but this may have a great influence on the characteristics of the output ray. In this paper, the dose characteristics of the Varian Trilogy accelerator 6MV X-ray under the condition of the FFF with the uniform device Flattening filter and the non-uniform Filter FFFF are simulated by Monte Carlo method. To investigate the effect of the integrator on the dose characteristics. In this study, BEAMnrc and DOSXYZnrc were used to simulate and calculate the 6 MV ray of Varian Trilogy accelerator in a uniform water model with 50 cm 脳 50 cm 脳 50 cm in volume under the condition of uniform device and removal of integral device, respectively. The side length of the square field is 1 cm, 2 cm, 3 cm, 3 cm, 6 cm, 6 cm, 8 cm, 10 cm, 12 cm, 15 cm, 20 cm, 20 cm, 30 cm and 40 cm depth. The depth dose (DDD) and off-axis ratio (Oar), maximum dose of 5 cm / 10 cm and 20cm depth, the ratio of total scattering factor scp to central axis dose, are analyzed by BEAMDP, and the energy spectra of photons are analyzed by BEAMDP. Then the above physical quantities under the two conditions are analyzed and compared. The results show that the photon spectrum shifts to the left, the ray quality becomes soft, the photon flux increases, the depth dose increases, the depth dose decreases to a certain extent, the field flattening becomes worse, the larger the field is, the more obvious the field is. The output dose rate of the accelerator is obviously increased, the edge dose of the projectile field decreases, and the dependence of the total scattering factor SCP on the ejection field is relatively small. In a word, the output characteristics of the accelerator have changed obviously after the whole device is removed, which may bring about some benefit or unknown situation in clinic, and need further research support.
【学位授予单位】：南华大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH774

【参考文献】