目标:尽管它们的可用性和使用简单,电子门户成像设备(EPID)尚未取代3D中患者特定QA的检测器阵列。这项研究的目的是针对3D中的绝对剂量测量,对运输和非运输EPID剂量测定进行大规模剂量学评估。
方法:在评估EPID和两个检测器阵列(Octavius1500和Octavius1000SRS)的基本剂量特性之后,68个VMAT弧的3D剂量分布,使用过境EPID剂量测定法在相同的体模几何结构内重建了10个IMRT计划,非过境EPID剂量测定,还有Octavius4D系统.通过γ分析直接比较重建的3D剂量分布(2L2=2%局部/2毫米,3G2=3%全局/2毫米,50%等剂量)和中值剂量与高剂量体积的百分比差异(%ΔHDVD50)。
结果:关于剂量率依赖性,剂量线性度,和字段大小的依赖性,发现EPID剂量测定与两个检测器阵列之间的一致性在1.0%以内。在2L2γ与Octavius4D剂量分布的比较中,过境和非过境EPID剂量测定的平均γ通过率值分别为92.2±5.2%(1SD)和94.1±4.3%(1SD),分别。150/156例中,3G2γ通过率高于95%。134/156例HDVD50值在2%以内,155/156例HDVD50值在3%以内。关于警报的临床分类,通过EPID剂量测定法和Octavius4D将97.5%的治疗分类相同。
结论:传输和非传输EPID剂量学在剂量学方面与用于患者特定QA的常规检测器阵列等效。非过境3DEPID剂量测定可以很容易地用于IMRT和VMAT的治疗前患者特定的QA,消除幻影定位的需要。
OBJECTIVE: Despite their availability and simplicity of use, Electronic Portal Imaging Devices (EPIDs) have not yet replaced detector arrays for patient specific QA in 3D. The purpose of this study is to perform a large scale dosimetric evaluation of transit and non-transit EPID dosimetry against absolute dose measurements in 3D.
METHODS: After evaluating basic dosimetric characteristics of the EPID and two detector arrays (Octavius 1500 and Octavius 1000SRS ), 3D dose distributions for 68 VMAT arcs, and 10 IMRT plans were reconstructed within the same phantom geometry using transit EPID dosimetry, non-transit EPID dosimetry, and the Octavius 4D system. The reconstructed 3D dose distributions were directly compared by γ-analysis (2L2 = 2% local/2 mm and 3G2 = 3% global/2 mm, 50% isodose) and by the percentage difference in median dose to the high dose volume (%∆HDVD 50 ).
RESULTS: Regarding dose rate dependency, dose linearity, and field size dependence, the agreement between EPID dosimetry and the two detector arrays was found to be within 1.0%. In the 2L2 γ-comparison with Octavius 4D dose distributions, the average γ-pass rate value was 92.2 ± 5.2%(1SD) and 94.1 ± 4.3%(1SD) for transit and non-transit EPID dosimetry, respectively. 3G2 γ-pass rate values were higher than 95% in 150/156 cases. %∆HDVD 50 values were within 2% in 134/156 cases and within 3% in 155/156 cases. With regard to the clinical classification of alerts, 97.5% of the treatments were equally classified by EPID dosimetry and Octavius 4D.
CONCLUSIONS: Transit and non-transit EPID dosimetry are equivalent in dosimetric terms to conventional detector arrays for patient specific QA. Non-transit 3D EPID dosimetry can be readily used for pre-treatment patient specific QA of IMRT and VMAT, eliminating the need of phantom positioning.