Physics Department, Hakim Sabzevari University, Shohada-e Hastei Blvd, P.O. 9617976487, Sabzevar, Iran.
Department of Medical Physics and Radiological Sciences, Sabzevar University of Medical Sciences, Shohada-e Hastei Blvd, Sabzevar University of Medical Sciences Campus, P.O. 9617913112, Sabzevar, Iran; Vasei Radiotherapy & Oncology Center, Vasei Hospital, P.O. 9617913113, Sabzevar, Iran.
Phys Med. 2019 Feb;58:81-89. doi: 10.1016/j.ejmp.2019.01.019. Epub 2019 Feb 5.
Employing routine dosimetry protocols for intraoperative electron beam needs further refinements to obtain reliable results. In this regard, the performance of some cylindrical and parallel plate ion chambers for both relative and absolute dosimetry of intraoperative electron beam has been evaluated.
Four different ion chambers including Semiflex and PinPoint cylindrical chambers as well as Advanced Markus and Roos parallel plate ones were employed for PDD measurement and dose rate determination in reference condition of the electron beam produced by LIAC intraoperative accelerator. The results of PDD measurements were compared with those of Gafchromic EBT2 film. Specific recommendations were followed to determine the chamber correction factors including k and [Formula: see text] for absolute dosimetry in intraoperative reference condition.
There was good agreement between PDDs measured by employed chambers and EBT2 film at all nominal energies. Nevertheless, Advanced Markus chamber had the best performance based on the gamma analysis results. Obtained [Formula: see text] and k for studied ion chambers largely differed from expected values by TRS-398 protocol. The difference of measured dose rates at 12 MeV energy by investigated chambers was less than 1.1% and Advanced Markus had the best accordance with pre-set dose rate by manufacture.
Results showed that ignoring the specific recommended procedures in determining the chamber correction factors causes the overestimation of the measured dose. Therefore, dedicated dosimetry protocol should be developed for high dose per pulse intraoperative electron dosimetry including all of the updated correction factors and deviations from routine ionometric electron dosimetry formalisms.
为了获得可靠的结果，术中电子束的常规剂量学方案需要进一步改进。在这方面，评估了一些圆柱形和平行板离子室对于术中电子束的相对和绝对剂量测量的性能。
使用了包括 Semiflex 和 PinPoint 圆柱形室以及 Advanced Markus 和 Roos 平行板室在内的四种不同的离子室，用于测量 PDD 和在 LIAC 术中加速器产生的电子束的参考条件下的剂量率。PDD 测量的结果与 Gafchromic EBT2 胶片的结果进行了比较。遵循了特定的建议来确定腔室校正因子，包括 k 和[Formula: see text]，用于术中参考条件下的绝对剂量测量。
在所有标称能量下，所使用的腔室和 EBT2 胶片测量的 PDD 之间存在良好的一致性。然而，根据伽马分析结果，Advanced Markus 腔室的性能最佳。研究的离子室的[Formula: see text]和 k 与 TRS-398 协议中预期的值有很大的差异。在所研究的腔室中，在 12 MeV 能量下测量的剂量率差异小于 1.1%，并且 Advanced Markus 与制造商设定的预设剂量率最一致。
结果表明，忽略确定腔室校正因子的特定推荐程序会导致测量剂量的高估。因此，应该为包括所有更新的校正因子和偏离常规离子计电子剂量学公式的高脉冲剂量术中电子剂量测量开发专门的剂量学方案。
