The current study aims to characterize and compare the correction factors of some widely employed cylindrical ion chambers for Megavoltage (MV) photon dosimetry following the recommendations of the IAEA TRS-398 dosimetry protocol. Four different types of cylindrical ion chambers including Farmer (TM30013), Semiflex 0.125 cm (TM31010), Semiflex 0.3 cm (TM31013), and PinPoint (TM31016) were employed, and correction factors of polarity (k), ion recombination (k), and quality conversion factor () were determined at 6 and 15 MV photon energy produced by a Varian Trilogy clinical LINAC. Measurements were performed inside an automatic MP3-M water phantom at the reference condition of 100 cm SSD (source to surface distance), 10 cm measurement depth, and 10 × 10 cm field size at the phantom surface. The maximum k values belonged to the TM31010 chamber, while the minimum values were observed for TM30013 one. The maximum and minimum k values were also related to the TM31016 and TM30013 chambers, respectively. The obtained k values following the TRS-398 dosimetry protocol were in accordance with those measured by Jaffe-plot analysis. The type of employed ion chamber had a minimal impact on value, so that the maximum difference between the measured quality conversion factors with different ion chambers was about 0.3% and 0.05% 6 and 15 MV photon energy, respectively. Based on the obtained results, it can be concluded that the Farmer chamber shows the best performance characteristics for absolute dosimetry purposes. Nevertheless, all considered chambers fulfilled the requested criteria for absolute dosimetry in high energy photon fields.

中文翻译：

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根据 TRS-398 剂量测定协议，一些圆柱形离子室剂量计在兆伏 (MV) 光子束中的性能特征


当前的研究旨在按照 IAEA TRS-398 剂量测定协议的建议，描述和比较一些广泛使用的用于兆伏 (MV) 光子剂量测定的圆柱形离子室的校正因子。采用四种不同类型的圆柱形离子室，包括 Farmer (TM30013)、Semiflex 0.125 cm (TM31010)、Semiflex 0.3 cm (TM31013) 和 PinPoint (TM31016)，并采用极性 (k)、离子复合 (k)、和质量转换因子 () 在瓦里安 Trilogy 临床 LINAC 产生的 6 和 15 MV 光子能量下确定。测量在自动 MP3-M 水体模内进行，参考条件为 100 cm SSD（源到表面距离）、10 cm 测量深度以及体模表面的 10 × 10 cm 场尺寸。 TM31010 室的 k 值最大，而 TM30013 室的 k 值最小。最大和最小 k 值也分别与 TM31016 和 TM30013 室相关。根据 TRS-398 剂量测定方案获得的 k 值与 Jaffe-plot 分析测量的值一致。所采用的离子室类型对值的影响最小，因此不同离子室测量的质量转换因子之间的最大差异分别约为 6 和 15 MV 光子能量的 0.3% 和 0.05%。根据获得的结果，可以得出结论，农夫室显示出绝对剂量测定目的的最佳性能特征。尽管如此，所有考虑的腔室都满足高能光子场中绝对剂量测定的要求标准。