Guan Fada, Chen Huixiao, Draeger Emily, Li Yuting, Aydin Resat, Tien Christopher J, Chen Zhe
Department of Therapeutic Radiology Yale University School of Medicine New Haven Connecticut USA.
Department of Radiation Physics The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard Houston Texas USA.
Precis Radiat Oncol. 2023 Jun 25;7(2):84-91. doi: 10.1002/pro6.1204. eCollection 2023 Jun.
A newly developed Gafchromic EBT4 film model was released recently. According to the vendor-stated specifications, this new model maintains major features of its more recent predecessor, EBT3, but has a great improvement in the signal-to-noise ratio (SNR). The purpose of this study was to fully characterize the EBT4 model by testing its dose response dependence on beam energy using clinical photon and electron beams and validating its improvement in SNR.
In the beam energy dependence experiments, 6 MV and 15 MV photon beams, 6 MeV, 12 MeV and 20 MeV electron beams, 120 kVp and two 250 kVp x-ray beams (with different half-layer values) were selected, representing different clinical beam energies and radiation types. In the noise and SNR analyses, only the 6 MV photon beam was selected as the representative to compare between EBT4 and EBT3 models.
The energy dependence test results showed that there was a slight difference (<2% at most dose levels) in the dose response among the clinical MV photons and MeV electrons. However, a large deviation (>10%) in the dose response was found for the 120 kVp x-ray beam. For the two 250 kVp x-ray beams, the difference in the dose response was moderate (<5%), but not negligible. The noise and SNR results showed a reduced noise and strengthened SNR in EBT4.
We conclude that the EBT4 film has a minimal energy dependence for MV photon and MeV electron beams but has a notable energy dependence for kilovoltage x-ray beams, and the vendor-stated features of the reduced noise and improved SNR in EBT4 are validated.
一种新开发的Gafchromic EBT4薄膜模型最近发布。根据供应商声明的规格，这种新模型保留了其最新前身EBT3的主要特征，但在信噪比（SNR）方面有了很大改进。本研究的目的是通过使用临床光子束和电子束测试其剂量响应与束能量的依赖性，并验证其在信噪比方面的改进，来全面表征EBT4模型。
在束能量依赖性实验中，选择了6 MV和15 MV光子束、6 MeV、12 MeV和20 MeV电子束、120 kVp和两个250 kVp X射线束（具有不同的半价层值），代表不同的临床束能量和辐射类型。在噪声和信噪比分析中，仅选择6 MV光子束作为代表，以比较EBT4和EBT3模型。
能量依赖性测试结果表明，临床MV光子和MeV电子之间的剂量响应存在轻微差异（在大多数剂量水平下最多<2%）。然而，发现120 kVp X射线束的剂量响应存在较大偏差（>10%）。对于两个250 kVp X射线束，剂量响应的差异适中（<5%），但不可忽略。噪声和信噪比结果表明，EBT4中的噪声降低，信噪比增强。
我们得出结论，EBT4薄膜对MV光子束和MeV电子束的能量依赖性最小，但对千伏X射线束有明显的能量依赖性，并且EBT4中供应商声明的降低噪声和提高信噪比的特征得到了验证。
