The in-phantom calibration method for radiotherapy kilovoltage x-ray beams requires ionization chamber correction factors. The overall ionization chamber correction factor accounts for changes in the chamber response due to the displacement of water by the chamber cavity and wall, the presence of the stem and the change in incident photon energy and angular distribution in the phantom to that in air. A waterproof sheath, if required, is accounted for in a sheath correction factor. The aim of this study is to determine chamber correction factors through Monte Carlo (MC) simulations and water calorimetry measurements. Correction factors are determined for the PTW TM30013, NE2571, IBA FC65-G, IBA FC65-P and Exradin A12 ionization chambers. They are compared to experimental values obtained at the German national metrology institute Physikalisch-Technische Bundesanstalt (PTB) with their water calorimetry-based absorbed dose to water primary standard and at other national metrological institutes. An uncertainty analysis considers the contributions to the uncertainty on the chamber correction factors from the field size, photon cross sections, photon fluence spectra and chamber wall and central electrode dimensions. The MC calculated chamber correction factors are within 2.2% of unity with a standard uncertainty of 0.3%. For the 50 kV and 100 - 140 kV radiation beam qualities, the calculated correction factors deviate from the measured correction factors (with a standard uncertainty of 1%) by up to 2.6%. The calculated chamber correction factors for the PTW TM30013 and Exradin A12 are consistent with those derived from the BIPM kilovoltage primary standard. The inconsistencies between the calculated and experimental chamber correction factors indicate the need to further investigate the accuracy of kilovoltage absorbed dose to water primary standards and the use of MC simulations to determine kilovoltage beam chamber correction factors.

中文翻译：

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蒙特卡洛和水量热法测定千伏束放射疗法电离室的校正因子。

用于放射治疗千伏x射线束的幻像校准方法需要电离室校正因子。总的电离室校正因子说明了由于腔室腔和壁的水位移，茎杆的存在以及幻像中入射光子能量和角度分布与空气中的角度分布的变化而引起的腔室响应的变化。防水护套（如果需要）是护套校正因子。这项研究的目的是通过蒙特卡洛（MC）模拟和量热法测量来确定腔室校正因子。确定了PTW TM30013，NE2571，IBA FC65-G，IBA FC65-P和Exradin A12电离室的校正系数。将它们与在德国国家计量院Physikalisch-Technische Bundesanstalt（PTB）上获得的实验值进行比较，并得出基于水量热法的基本水吸收剂量标准以及在其他国家计量院获得的实验值。不确定性分析考虑了场大小，光子横截面，光子注量光谱以及腔室壁和中心电极尺寸对腔室校正因子的不确定性的影响。MC计算得出的腔室校正因子在团结的2.2％以内，标准不确定度为0.3％。对于50 kV和100-140 kV辐射束质量，计算出的校正因子与测得的校正因子（标准不确定度为1％）相差最多2.6％。PTW TM30013和Exradin A12的计算室校正系数与从BIPM千伏基本标准得出的校正系数一致。计算得出的腔室校正因子与实验腔室校正因子之间的不一致表明，有必要进一步研究千伏电压对水主要标准物的吸收精度，并需要使用MC模拟来确定千伏束梁腔校正因子。