[Research Photon Energy Spectrum of Medical Linear Accelerator by Monte Carlo Method].

The distribution of the photon energy spectrum in isocenter plane of the medical linear accelerator and the influence of secondary collimator on the photon energy spectrum are studied. By analyzing the photon energy spectrum of a medical linear accelerator with a nominal energy of 6 MV, it is found that the secondary collimator has little effect on the photon energy spectrum; different fields have different photon energy spectrum distributions; the photon energy spectrum in different central regions of the same field have the same normalized distribution. In the dose calculation of radiation therapy, the influence of photon energy spectrum should be carefully considered. 研究医用直线加速器在等中心平面的光子能谱分布和次级准直器对光子能谱的影响。. 使用BEAMnrc程序模拟5 cm×5 cm、10 cm×10 cm、15 cm×15 cm和20 cm×20 cm射野下，能量为6 MeV电子和光子在加速器治疗头中的输运行为，在等中心平面处设置相空间记录文件，以记录经过此平面的粒子信息。然后利用BEAMdp程序对相空间文件进行分析，从而获得在等中心平面的光子能谱分布及次级准直器对光子能谱的影响。. 通过分析标称能量为6 MV的医用直线加速器的光子能谱，发现次级准直器对光子能谱影响很小；不同射野具有不同的光子能谱分布；同一射野不同中心区域的光子能谱具有相同的归一化分布。. 在放射治疗的剂量计算中，应仔细考虑光子能谱的影响。.