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中轴上的百分深度剂量是放射治疗必需的基本数据。一般是把剂量计的电离室置入水模中,测定各个深度的吸收剂量。本文介绍两种由计算得到百分深度剂量的方法:TAR法和参数法。第一种方法通过对组织空气比的计算得出百分深度剂量;另一种方法则通过组织空气比与面积的函数关系推得经验公式,用两个参数在不同深度t的值代入公式算得。前者较精确,后者参数不多,可用袖珍计算器计算,迅速、简便。一、TAR法组织空气比的定义为
The percentage depth dose on the central axis is essential for radiotherapy. In general, the ionization chamber of the dosimeter is placed in a water mold and the absorbed dose at each depth is measured. This article describes two methods for calculating the percent depth dose: the TAR method and the parametric method. The first method calculates the percentage depth dose by calculating the tissue air ratio. The other method derives the empirical formula from the tissue air ratio as a function of area, and formulates the values of the two parameters at different depths t . The former is more accurate, the latter few parameters, available pocket calculator calculation, quickly and easily. First, TAR law air ratio is defined as