CAJ | 학술논문

研究了医用直线加速器的主要部件对X射线能谱的影响。利用蒙特卡罗软件包EGSnrc/BEAMnrc针对Varian600C 医用直线加速器，模拟完整及分别去除初级准直器、均整器和次级准直器条件下的相空间文件，通过相空间文件分析程序Beamdp对相空间文件进行分析，分别得到相应条件下的X射线能谱。均整器对能谱的影响非常大，对比于无均整器的情况，有均整器时，平均能量上升了48.9%；但初级准直器、次级准直器对能谱的影响小，平均能量的变化小于1%。在射野内，对比于无均整器的情况，有均整器时，能量注量降低了52.4%，但其空间分布变均匀，非平坦度从15.09%变为1.82%；对比于无初级准直器的情况，有初级准直器时，能量注量上升了1.58%；而对比于无次级准直器的情况，有次级准直器时，能量注量下降了2.00%。均整器对X射线的能谱的影响起主要作用，它能够使X射线的平均能量上升和射野内能量注量的分布变均匀。初级准直器对X射线能谱影响小但对X射线的散射不可忽略，而次级准直器对X射线能谱的影响小而且对X射线的散射作用可以忽略，这些结果对加速器X射线束流模型的建立有一定的参考意义。
연구료의용직선가속기적주요부건대X사선능보적영향。이용몽특잡라연건포EGSnrc/BEAMnrc침대Varian600C 의용직선가속기，모의완정급분별거제초급준직기、균정기화차급준직기조건하적상공간문건，통과상공간문건분석정서Beamdp대상공간문건진행분석，분별득도상응조건하적X사선능보。균정기대능보적영향비상대，대비우무균정기적정황，유균정기시，평균능량상승료48.9%；단초급준직기、차급준직기대능보적영향소，평균능량적변화소우1%。재사야내，대비우무균정기적정황，유균정기시，능량주량강저료52.4%，단기공간분포변균균，비평탄도종15.09%변위1.82%；대비우무초급준직기적정황，유초급준직기시，능량주량상승료1.58%；이대비우무차급준직기적정황，유차급준직기시，능량주량하강료2.00%。균정기대X사선적능보적영향기주요작용，타능구사X사선적평균능량상승화사야내능량주량적분포변균균。초급준직기대X사선능보영향소단대X사선적산사불가홀략，이차급준직기대X사선능보적영향소이차대X사선적산사작용가이홀략，저사결과대가속기X사선속류모형적건립유일정적삼고의의。
Background: It is well known that the main components of clinical linac such as the primary collimator, flattening filter and secondary collimator affect the X-ray energy spectra. How does it appear is the foundation of dose calculation, and it is helpful for building up a beam model.Purpose:This paper aims to make a detailed study on the effects of these main components on the X-ray energy spectra of a clinical linac beam.Methods:Monte Carlo program EGSnrc/BEAMnrc is employed to build up the beam model of Varian 600C linac, as well as the other three different beam models: without primary collimator, without flattening filter, without secondary collimator at the same time. After respective simulations, we use Beamdp program to analyze the phase space files, so as to obtain energy spectra for different models.Results:Flattening filter has heavy influence on X-ray beam’s energy spectra, the mean energy increases by 48.9% compared with its absence. But the primary collimator and secondary collimator have little influence on energy spectra, the change of mean energy is within 1% compared their absence. In the center field size of 10 cm×10 cm, flattening filter could let the energy fluence decrease by 52.4%, but the distribution becomes more flat and the unflatness changes from 15.09% to 1.82%; primary collimator could increase energy fluence by 1.58%; but secondary collimator could decrease the energy fluence by 2.00%.Conclusion:Flattening filter has mainly influence on the energy spectra of X-ray beam, it could let the mean energy increase and the energy fluence distribution become more flat; the scatter of primary collimator for X-ray beam must be taken into account whilst the scatter of secondary collimator for X-ray beam can be neglected. The results are meaningful to build a X-ray beam model for clinical linac.