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利用BEAMnrc和DOSXYZnrc蒙特卡罗程序研究西门子直线加速器6 MV能量均整和未均整光子束的剂量学特点。比较两种射束的深度剂量分布、离轴比剂量分布、中心轴剂量率和总散射因子。结果表明,未均整射束各射野的百分深度剂量均比均整射束的低;中心轴剂量率比均整射束大,且两种射束中心轴剂量率比值随射野和深度的增加逐渐下降;除此之外,未均整射束的半影宽度及总散射因子随深度的变化趋势均比均整射束小。未均整射束的剂量学优势可用于临床应用。
The dosimetry characteristics of 6 MV homogeneous and non-uniform photon beams of Siemens linear accelerator were studied by using BEAMnrc and DOSXYZnrc Monte-Carlo programs. Depth dose distribution, off-axis dose distribution, central axis dose rate, and total scatter factor were compared for both beams. The results show that the percent depth dose of each field in the non-uniform beam is lower than the average beam; the dose rate of the central axis is larger than the average beam, and the ratio of the central axis dose rate increases with the field and depth In addition, the half-shadow width and total scattering factor of the non-uniform beam are smaller than the average beam length with the change of depth. The dosimetric advantage of a non-homogenous beam can be used clinically.