Kalach N I, Rogers D W O
National Research Council of Canada, Ottawa K1A OR6, Canada.
Med Phys. 2003 Jul;30(7):1546-55. doi: 10.1118/1.1573205.
Previous work has demonstrated that, for photon beam dosimetry, TPR10(20) is not an ideal beam quality specifier for all bremsstrahlung beams, especially for lightly filtered beams in some standards laboratories. This paper addresses the following questions: Is TPR10(20) an adequate beam quality specifier for all modern clinical therapy accelerators? When can nonclinical beams in standards laboratories be used to calibrate ion chambers or measure kQ factors as a function of TPR10(20)? Based on detailed Monte Carlo simulations of Varian, Siemens, Elekta, and GE (Saturn) accelerators one can conclude that TPR10(20) is an adequate beam quality specifier for all these machines in the sense that for a given value of TPR10(20), the value of stopping-power ratios is the same. It is shown that, for the heavily filtered beams used in standards laboratories, TPR10(20) is an adequate beam quality specifier. It is also demonstrated that, for a larger range of bremsstrahlung beams than previously, %dd(10)x is a good beam quality specifier for all clinical beams as well as the lightly and heavily filtered beams in some standards laboratories. A criterion, based on the measured values of TPR10(20) and %dd(10)x for the beam, is proposed for determining whether a nonclinical beam is well specified by TPR10(20). Agreement between calculations for specific accelerators and measured beam quality specifiers is shown to be good, but agreement with published data for a variety of clinical accelerators is not as good. Possible reasons for the discrepancy are discussed.
先前的工作已经表明，对于光子束剂量测定，对于所有轫致辐射束，尤其是一些标准实验室中的低过滤束，TPR10(20)并非理想的束流质量指定参数。本文探讨以下问题：TPR10(20)对于所有现代临床治疗加速器而言是否是一个合适的束流质量指定参数？标准实验室中的非临床束何时可用于校准电离室或测量作为TPR10(20)函数的kQ因子？基于对瓦里安、西门子、医科达和通用电气（土星）加速器的详细蒙特卡罗模拟，可以得出结论，从对于给定的TPR10(20)值，阻止本领比的值相同这一意义上来说，TPR10(20)对于所有这些机器是一个合适的束流质量指定参数。结果表明，对于标准实验室中使用的高过滤束，TPR10(20)是一个合适的束流质量指定参数。还证明，对于比以前更大范围的轫致辐射束，%dd(10)x对于所有临床束以及一些标准实验室中的低过滤束和高过滤束都是一个良好的束流质量指定参数。提出了一个基于束流的TPR10(20)和%dd(10)x测量值的标准，用于确定非临床束是否由TPR10(20)很好地指定。特定加速器的计算结果与测量的束流质量指定参数之间的一致性显示良好，但与各种临床加速器的已发表数据的一致性则没那么好。讨论了差异的可能原因。
