Evaluation of the incident directional dependence of radiochromic film by use of Monte Carlo simulation and measurement
Evaluation of the incident directional dependence of radiochromic film by use of Monte Carlo simulation and measurement
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利用蒙特卡罗模拟和测量评估放射变色膜的入射方向依赖性
DOI：
10.1007/s12194-016-0353-6
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发表时间：
2016
影响因子：
1.6
通讯作者：
Shibuya K
中科院分区：
文献类型：
--
作者：
Yuasa Y;Kawamura S;Shiinoki T;Uehara T;Koike M;Kanzaki R;Hanazawa H;Takahashi S;Shibuya K
在高精度放射治疗中，针对患者特异性调强放射治疗（IMRT）质量保证（QA）评估绝对和相对剂量。在我们的机构中，我们使用GAFCHROMIC EBT3（EBT3）进行IMRT QA中的相对剂量评估。我们通常使用两个方向的胶片配置，即轴向和矢状面。我们机构的QA显示轴向和矢状方向的伽马通过率存在一些差异。本研究的目的是通过使用百分比深度剂量（PDD）和EBT3膜之间的偏心比（OCR）垂直于射束轴和沿着射束轴定位的入射方向依赖性的EBT3评估。此外，我们比较了在EBT3膜的PDD定位垂直于束轴和PDD通过使用电离室。此外，通过Monte Carlo模拟，计算了在有和没有EBT3膜的水模型中的PDD。结果表明，垂直于电子束轴放置的EBT3薄膜中的PDD随着离体模表面的深度的增加而增加。Monte Carlo模拟显示了与薄膜测量相同的趋势。在低于20%的剂量水平下，OCR结果略有不同。沿着光束轴放置的EBT 3胶片的OCR高于垂直于光束轴的OCR。因此，我们得出结论，EBT3膜具有入射方向依赖性。在调强放射治疗质量保证中，EBT3胶片的入射方向依赖性可能会影响γ分析结果。
In high-precision radiotherapy, absolute and relative doses are evaluated for patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA). In our institution, we use GAFCHROMIC EBT3 (EBT3) for relative dose evaluation in IMRT QA. We usually use two directional film configurations, which are in the axial and sagittal planes. The QA in our institution shows some differences between the gamma pass rates in the axial and sagittal directions. The purpose of this study was to evaluate the incident directional dependence of EBT3 by using the percent depth dose (PDD) and the off-center ratio (OCR) between EBT3 films positioned perpendicular to the beam axis and along the beam axis. Furthermore, we compared the PDD in EBT3 films positioned perpendicular to the beam axis and the PDD by using an ionization chamber. In addition, PDDs in water phantoms with and without EBT3 films were calculated by Monte Carlo simulation. The results showed that the PDD in EBT3 films positioned perpendicular to the beam axis increased with the depth from the phantom surface. Monte Carlo simulation showed the same trend as did the film measurements. The OCR results were slightly different at dose levels below 20 %. The OCR in EBT3 films positioned along the beam axis was higher than that perpendicular to the beam axis. Thus, we conclude that EBT3 film has incident directional dependence. In IMRT QA, the gamma analysis results may be affected by the incident directional dependence of EBT3 film.