放疗用高能电子束光栏不固定限束方式下照射野大小对输出量的影响

The influence of field on output factor when the jaws are unfixed

目的 研究高能电子束光栏不固定限束方式下照射野大小对输出量的影响。方法 采用GESaturne 41型直线加速器 ,以 12MeV和 9MeV高能电子束为辐射源 ,用Farmer 2 5 70剂量仪测量各种不同照射野的输出剂量率 ,以 10cm× 10cm照射野为基准 ,进行归一 ,计算输出因子。结果 在该种限束方式下 ,当保持Y方向 (准直器上铅门 )为实际照射野的长边时 ,采用公式S =2ab/(a +b)计算等效方野 ,然后计算等效输出因子 ,它与实际测量值之间的误差小于 2 %。结论 对这种电子束限束方式 ,只要保持Y方向为实际照射野的长边 ,可以采用面积周长比公式S =2ab/(a +b)计算等效方野 ,然后计算等效输出因子。

Objective To study the influence of field on output factor when the jaws are unfixed.Methods High energy electron with 12?MeV and 9?MeV were used as the radiation,the doserates for different fields were measured by Farmer 2570,and the output factors for different fields were calculated.Results If the formula S=2ab/ (a+b) was used to calculate the equivalent field for rectangular field and to get the equivalent output factor when the Y jaw was fixed as the longer side of the actual field,the difference between the equivalent output factor and the real output factor was less than 2%.Conclusion The formula S=2ab/(a+b) can be used to calculate the equivalent field and to get the equivalent output factor when the Y jaw is fixed as the longer side of the actual field.