Difference in the relative response of the alanine dosimeter to megavoltage x-ray and electron beams
Difference in the relative response of the alanine dosimeter to megavoltage x-ray and electron beams
复制标题
丙氨酸剂量计对兆伏 X 射线和电子束的相对响应的差异
DOI：
10.1088/0031-9155/58/10/3259
复制
发表时间：
2013
影响因子：
3.5
通讯作者：
M. McEwen
中科院分区：
文献类型：
--
作者：
Mathias Anton;R. Kapsch;A. Krauss;P. V. Voigts;K. Zink;M. McEwen
为了提高丙氨酸剂量计在使用MV x射线的放射治疗中作为质量保证测量工具的有效性，需要准确地知道相对于水的剂量的响应。这个量是相对于来自两个临床加速器的4、6、8、10、15和25 mV X射线的~(60)Co实验确定的。在校准中，使用了电离室的KQ因子，不确定度为0.31%，通过量热测量获得。这些结果虽然与所有MV X射线质量的响应与60Co相比的恒定差异并不一致，但表明从低能(4-6 mV)时的约0.996下降到最高能量(25 MV)时的0.989。相对响应的相对不确定度在0.35%至0.41%之间。NRC的修正实验数据以及使用结晶丙氨酸密度校正的蒙特卡罗模拟证实了这一结果。通过与模拟和测量数据的比较，对于MeV电子，弱的能量依赖关系可以用丙氨酸剂量计从光子探测器到电子探测器的转变(随着mV值的增加)来解释。有兴趣的读者可在附录中对计算结果和相应的不确定度分量进行深入说明。与以前的出版物相比，由于新的证据以及PTB使用的丙氨酸/血沉测量和分析方法的变化，不确定性预算不得不修改。
In order to increase the usefulness of the alanine dosimeter as a tool for quality assurance measurements in radiotherapy using MV x-rays, the response with respect to the dose to water needs to be known accurately. This quantity is determined experimentally relative to 60Co for 4, 6, 8, 10, 15 and 25 MV x-rays from two clinical accelerators. For the calibration, kQ factors for ionization chambers with an uncertainty of 0.31% obtained from calorimetric measurements were used. The results, although not inconsistent with a constant difference in response for all MV x-ray qualities compared to 60Co, suggest a slow decrease from approximately 0.996 at low energies (4–6 MV) to 0.989 at the highest energy, 25 MV. The relative uncertainty achieved for the relative response varies between 0.35% and 0.41%. The results are confirmed by revised experimental data from the NRC as well as by Monte Carlo simulations using a density correction for crystalline alanine. By comparison with simulated and measured data, also for MeV electrons, it is demonstrated that the weak energy dependence can be explained by a transition of the alanine dosimeter (with increasing MV values) from a photon detector to an electron detector. An in-depth description of the calculation of the results and the corresponding uncertainty components is presented in an appendix for the interested reader. With respect to previous publications, the uncertainty budget had to be modified due to new evidence and to changes of the measurement and analysis method used at PTB for alanine/ESR.