Kosunen A, Rogers D W
National Research Council Canada, Ottawa.
Med Phys. 1993 Jul-Aug;20(4):1181-8. doi: 10.1118/1.597150.
It is argued that %dd(10), the percentage depth dose at 10 cm in a 10 x 10 cm2 photon beam at a SSD of 100 cm, is a better beam quality specifier for radiotherapy beams than the commonly used values of TPR10(20) or nominal accelerating potential (NAP). For radiation dosimetry purposes, TPR10(20) is not an ideal beam quality specifier because (i) stopping-power ratios for the same value of TPR10(20) can vary by up to 0.7% for thick-target bremsstrahlung beams; (ii) the value of TPR10(20) becomes insensitive to beam quality changes for high-energy beams; and (iii) it has little intuitive meaning. In contrast, %dd(10) in a pure photon beam specifies stopping-power ratios within 0.2% for all thick-target bremsstrahlung beams, maintains its sensitivity for high-energy beams, and has a simple physical and clinical meaning. It is shown that for all thick-target bremsstrahlung beams the spr (water/air) = 1.2676-0.002 224[%dd(10)] with a rms deviation of 0.1%. The effects of electron contamination in typical high-energy clinical beams can be corrected for using previously published experimental results or by reducing electron contamination using lead scattering foils.
有人认为，在源皮距为100 cm的10 cm×10 cm²光子束中，10 cm深度处的百分深度剂量%dd(10)，相较于常用的组织体模比TPR10(20)或标称加速电位（NAP），是放射治疗束更好的射束质量指标。对于辐射剂量测定而言，TPR10(20)并非理想的射束质量指标，原因如下：(i) 对于厚靶轫致辐射束，相同TPR10(20)值下的阻止本领比变化可达0.7%；(ii) 对于高能束，TPR10(20)值对射束质量变化不敏感；(iii) 其直观意义不大。相比之下，纯光子束中的%dd(10)对所有厚靶轫致辐射束的阻止本领比规定在0.2%以内，对高能束保持其敏感性，且具有简单的物理和临床意义。结果表明，对于所有厚靶轫致辐射束，比释动能率（水/空气）= 1.2676 - 0.002224[ %dd(10)]，均方根偏差为0.1%。典型高能临床束中电子污染的影响可利用先前发表的实验结果进行校正，或通过使用铅散射箔减少电子污染来校正。
