^(60)钴治疗机鼻咽癌颈部分割野剂量计算的实验研究

Study on dose calculation of the split fields to the neck on radiotherapy of nasophayngeal carcinoma with cobalt machine

目的：颈部分割野是鼻咽癌放疗设计常用的照射野。目前常规的剂量计算方法计算结果误差很大，特别是大野照射时，误差可达１０％以上，本文是为了寻求一种能减少误差的计算方法。方法：通过实验导出一种处方剂量计算的近似方法。结果：经实验推导出的公式为：Ｄｆ＝Ｄｏａ·ｆＤａ·（ｆｏ／（ｆｏ＋ｄ））２·Ｓｃ·ＴＡＲｆ。其中，Ｄｆ为颈模参考点的剂量，ＤＯａ为空气中１０ｃｍ×１０ｃｍ野的输出剂量，（ｆｏ／（ｆｏ＋ｄ））２为距离平方反比因子，ｆＤａ为分割野的空气中输出剂量修正因子，Ｓｃ为空野的准直器散射校正因子，ＴＡＲｆ为分割野的组织空气比。结论：采用此公式，可减少颈部分割野的剂量计算误差，除ｆＤａ外，不用再额外测量其它数据。

Purpose: The anterior and posterior split fields to the neck are frequently used in the radio-therapy of nasopharyngeal carcinoma.While being calculated by traditional method,a significant error in the calculation of prescribed dose cannot be neglected,especially in large field,in which the error is more than 10%.Our purpose is to search for a calculation method to reduce error.Methods: Based on experiments,a formula for the approximate calculation of the dose is established.Result: The formula is: D f=D Oa·f Da·(fo/(fo+d))2÷Sc·TARf, where,Df is the dose of reference point in phantom neck,Doa is the output dose of 10 cm×10cm field in free air,(fo/(fo+d))2 is inverse-square-law factor,fDa is output dose correction factor of split field in free air,Sc is collimator-scatter correction factor of the open field,TARf is tissue air ratio of split field.Conclusion: The formula can reduce error of calculating dose for the split field,and extra data,except fDa,is unnecessary to be measured.