2.5 绝对剂量测量
将水面设置在SSD100的位置,测量PDD20,10,通过经验公式换算得出TPR20,10=1.2661 PDD20,10-0.595[4];将指型电离室设置在水下10 cm的射野中心轴处,无须对有效测量点进行修正[5];使用10×10的方野,根据Ndw和Kq等修正因子计算绝对剂量。由于Varian Halcyon 1.0医用直线加速器使用的是非均整的单能射线,为了修正其平均效应,最终结果需乘以修正系数Kn获得。
3 小结
Varian Halcyon 1.0医用直线加速器的机械精度较高,图像引导功能准确可信,且剂量模型与实际测量的结果一致。
参考文献
[1]佚名.中华人民共和国国家质量监督检验检疫总局公告[C]//防水工程与材料《会讯》第2期(总91).出版地不详:出版社不详,2006:4.
[2]Das IJ,Cheng C,Watta RJ,et al.Accelerator beam data commissioning equipment and procedures:report of the tg-106 of the therapy physics committee of the aapm[J].Med Phys,2008,35(9):4186-4215.
[3]Ezzell GA,Burmeister JW,Dogan N,et al.Imrt commissioning:multiple institution planning and dosimetry comparisons,a report from aapm task group 119[J].Med Phys,2009,36(11):5359-5373.
[4]Followill DS,Tailor RC,Tello VM,et al.An empirical relationship for determining photon beam quality in tg-21 from a ratio of percent depth doses[J].Med Phys,1998,25(7 Pt 1):1202-1205.
[5]International Atomic Energy Agency,Dosimetry Of Small Static Fields Used In External Beam Radiotherapy:An International Code Of Practice For Reference And Relative Dose Determination,Technical Reports Series No.483,Vienna,2017.
