医科达APEX外置微型多叶准直器射野相对输出因子的测量与蒙特卡罗计算  

Measurement and Monte Carlo calculations of relative output factors of APEX external micro multi-leaf collimator of Elekta

作　　者：张富利[1] 王雅棣[1] 许卫东[1] 蒋华勇[1] 高军茂[1] 刘清智[1] 王平[1] 陈建平[1] 赵一虹[1] 何合良[1] 

机构地区：[1]北京军区总医院放疗科,北京100700

出　　处：《中国医学物理学杂志》2015年第3期306-309,共4页Chinese Journal of Medical Physics

基　　金：全军医学计量专项课题(2011-JL2-005)

摘　　要：目的:应用三种探测器测量外置微型多叶准直器的射野相对输出因子(Relative Output Factor,ROF),并与蒙特卡罗(Monte Carlo,MC)方法的计算结果进行比较,对结果予以分析评估。方法:在6 MV、15 MV X线条件下,采用cc01、cc13、SFD三种探测器在IBA第二代蓝水箱中测量医科达APEX外置微型多叶准直器0.49 cm×0.49 cm^11.3 cm×11.3 cm照射野的ROF值;采用商业化的蒙特卡罗XVMC(X-Ray Voxel Monte Carlo,XVMC)源程序计算上述几何条件下的ROF,并与测量值进行比较。结果:对于cc01探测器,0.49 cm×0.49 cm照射野条件下,ROF测量值与MC计算值相对偏差较大,射线能量6 MV时为21.11%,射线能量15 MV时为11.34%。对于cc13探测器,照射野面积为0.49 cm×0.49cm、0.98 cm×0.98 cm时,测量值与MC计算值偏差很大,射线能量6 MV时分别达到53.17%和15.03%,射线能量15 MV时分别达到49.66%和15.85%。对于SFD探测器,由于其内径仅为0.6 mm,各个射野面积条件下测量结果基本不受空腔尺寸的影响,各个射野面积条件下其测量值与MC计算值吻合均较好。结论:测量外置微型多叶准直器小照射野ROF值时,由于缺侧向电子平衡和边缘剂量梯度多大,需要谨慎选择探测器。本研究证实,不同的探测器对ROF值的准确性存在较大的影响。选择灵敏区体积极小的半导体探测器并注意测量的几何条件,可以准确地测量小照射野的ROF值。Objective To compare the relative output factors （ROF） of external micro multi-leaf collimator measured by three kinds of detectors with those calculated by Monte Carlo （MC）. Methods Three types of detectors （cc01, cc13, SFD） were applied to measure the ROF values under 6/15 MV X-rays in the 2nd blue water tank of IBA, and the beam sizes ranged from 0.49 cm×0.49 cm to 11.3 cm×11.3 cm. Commercially available X-ray Voxel Monte Carlo （XVMC） was used to calculated ROF values at the same beam size, compared with those measured values. Results When cc01 detector was applied, for the field size of 0.49 cm×0.49 cm, the relative errors between measured and calculated ROF values were fairly large, 21.11% for 6 MV X-ray and 11.34% for 15 MV X-ray. When cc13 detector was applied, for the field size of 0.49 cm×0.49 cm and 0.98 cm×0.98 cm, the relative errors were also very large, 53.17% and 15.03% for 6 MV X-ray respectively, while 49.66% and 15.85% for 15 MV X-ray respectively. When SFD detector was applied, the measurement results had good consistence with those calculated by MC simulation for any field size, and the measured results were not affected by the cavity size for its inner diameter was only 0.6 mm. Conclusion Due to the absence of lateral electron equilibrium and high dose gradients at the beam edge for the smaller fields, a suitable detector is very important for measuring ROF values of external micro multi-leaf collimator. Different detectors have significantly different influences on the measurement accuracy of ROF values. When the geometrical conditions are considered, silicon diode with tiny sensitive volume is the best choice for the measurement of ROF values in x-ray stereotactic radiotherapy.

关 键 词：微型多叶准直器 相对输出因子 剂量学 蒙特卡罗方法 

分 类 号：R851[医药卫生—航空、航天与航海医学]