An empirical relationship for determining photon beam quality in TG-21 from a ratio of percent depth doses
An empirical relationship for determining photon beam quality in TG-21 from a ratio of percent depth doses
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DOI：
10.1118/1.598396
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发表时间：
1998-07-01
期刊：
影响因子：
3.8
通讯作者：
Hanson, WF
中科院分区：
文献类型：
--
作者：
Followill, DS;Tailor, RC;Hanson, WF
放射物理中心（RPC）现场剂量测定审查访问的一个关键组成部分是光子束校准，其中确定x射线的能量是一个关键因素。在任务组21方案中，将恒定SCD的20 cm和10 cm深度处10 cm x 10 cm场的电离比TPR 20/TPR 10用作射束质量的定量测量。RPC测量了大多数加速器型号和型号的TPR 20/TPR 10和在恒定SSD下685光子束（4-25 MV）的相应深度剂量百分比比（D-20/D-10）。TPR 20/TPR 10和D-20/D-10之间存在很强的相关性，这使得可以根据深度剂量百分比的测量来确定TPR比。对TG-21系数（（L）/bar/p、P-壁、P-repl）中引入的不确定性进行分析，这些不确定性是由测量数据中的分布引起的，并转化为TPR比的测定结果，误差不显著（< 0.3%）。这种经验关系提供了一种替代技术，用于量化TG-21协议中定义的光束质量，而不会在输出校准中损失任何精度。在固定SSD上校准的人可能会发现这种技术是一种更容易和更快的方法。(C)1998年美国医学物理学家协会。
A key component of the Radiological Physics Center's (RPC) on-site dosimetry review visits are photon beam calibrations for which determination of the energy of the x rays is a key element. The ratio of ionizations, TPR20/TPR10, for a 10 cm x 10 cm field at depths of 20 and 10 cm for a constant SCD is used as a quantitative measure of beam quality in the Task Group 21 protocol. The RPC has measured both TPR20/TPR10 and the corresponding ratio of percent depth dose (D-20/D-10) at a constant SSD for 685 photon beams (4-25 MV) for most makes and models of accelerators. A strong correlation between TPR20/TPR10 and D-20/D-10 is presented which allows the determination of the TPR ratio from the measurement of the ratio of percent depth doses. An analysis of the uncertainty introduced in the TG-21 factors ((L) over bar/p, P-wall, P-repl) caused by the spread in the measured data and translated into the determination of the TPR ratio results in an insignificant error (< 0.3%). This empirical relationship provides an alternate technique for quantifying the beam quality defined in the TG-21 protocol without surrendering any loss of precision in output calibration. This technique may be found by those who calibrate at a fixed SSD to be an easier and quicker method. (C) 1998 American Association of Physicists in Medicine.