基于EPID的IGRT剂量学质量控制研究

发布时间：2018-05-12 12:22

本文选题：电子射野影像系统 + 加速器日志文件　；参考：《中国疾病预防控制中心》2017年硕士论文

【摘要】：电子射野影像系统(EPID)最初主要用于位置验证,但是它实际上是一组辐射探测器,经过适当的刻度和校准可以用于放射治疗剂量学测量。许多研究表明,EPID在治疗前和在体剂量测量中都具有明显的优势。在体剂量测量是通过在计划实施过程中实时获取透射影像来重建体内剂量,从而实现患者体内计算和照射剂量分布的比较。加速器日志文件(Dynalog files)记录了计划执行过程中设备的运行参数,通过调用“Dynalogfiles”信息在CT图像上重建剂量分布,可以辅助实验测量方法进行剂量学质量控制。本文针对基于EPID的剂量学质量控制进行了深入的研究。首先,研究了基于EPID的治疗前剂量验证系统EPIbeam和基于治疗计划系统(TPS)计划治疗参数的Mobius 3D系统的建模、算法及剂量计算过程;其次,结合这两套治疗前剂量验证系统对28例盆腔病例容积调强放射治疗(VMAT)计划进行了剂量验证研究;然后,深入地研究了基于EPID重建体内剂量的验证系统EPIgray和基于“Dynalogfiles”的MobiusFX系统的建模、算法及剂量计算;最后,选取30例VMAT(15例盆腔病例和15例头颈部病例)计划进行了体内剂量学验证,分别利用电离室测量等中心处剂量值、基于EPID影像结合EPIgray重建等中心点剂量值和“Dynalog files”结合MobiusFX重建等中心点的剂量,将两组重建值与电离室测量值进行比较分析。EPIbeam系统是将实际上的EPID影像和TPS计算的射野影像同时经过相应剂量模型转换成水下5 cm处的平面剂量分布,进而将两者进行对比;Mobius 3D系统是将TPS的原始计划治疗参数经过倒锥卷积/叠加算法(CCC/S)重新计算剂量分布;治疗前剂量验证中,基于EPID结合软件EPIbeam的方法得到的是二维平面剂量分布的结果,其γ通过率均大于95%,Mobius 3D计算的是三维体素内的剂量分布,有两例γ通过率低于95%,但是均高于90%,大部分计划γ通过率高于95%,均符合临床剂量学要求;EPIgray借助于“fTMR”算法利用治疗过程中EPID获取的射野影像重建出模体内感兴趣点的剂量;Mobius FX是在“Dynalog files”反馈的计划执行时设备的运行参数的基础上利用CCC/S算法重建剂量;在体剂量验证中,盆腔计划和头颈部计划电离室测量值以及基于EPID和“Dynalog files”的重建平均值分别为(2.34±0.28)Gy、(2.31±0.26)Gy、(2.35±0.29)Gy和(1.58±0.12)Gy、(1.56±0.12)Gy 和(1.59±0.10)Gy。两个部位基于 EPID的重建值与电离室测量值相对偏差以及“Dynalog files”的重建值与电离室测量值相对偏差的平均值分别为(-1.11±2.42)%、(0.82±1.73)%和(-1.27±2.48)%、(0.56±1.91)%,符合临床剂量学要求。两组重建值与电离室测量值分别进行配对t检验,结果显示两组重建值与电离室测量值之间相比较差异均无统计学意义(t=1.91、-1.83,P0.05;t=2.01、-0.88,P0.05)。综上所述,正确合理的利用EPID对先进放疗技术进行剂量学质量控制的方法不影响治疗、便于推广,不仅可以提高治疗前剂量验证的效率,而且在实时监测患者接受放疗剂量方面具有很大的优势,有利于开展对患者剂量核查工作。基于完整的、准确的“Dynalog files”重建剂量的方法操作简单,可以同测量方法相辅相成,为形成一种快速、简单的先进放疗技术剂量监测方法提供参考。
[Abstract]:Electronic field imaging system (EPID) is primarily used for location verification, but it is actually a set of radiation detectors. After appropriate calibration and calibration, it can be used for radiation therapy dosimetry. Many studies have shown that EPID has obvious advantages in both before and in volume measurement. In the process of application, the transmission image is obtained in real time to reconstruct the dose of the body, thus the comparison of the dose distribution in the patient's body is realized. The accelerator log file (Dynalog files) records the operating parameters of the equipment during the execution of the plan. The dose distribution can be reconstructed by calling the "Dynalogfiles" information on the CT image, which can assist the experimental test. Quantitative method is used to control dosimetry quality control. In this paper, the quality control of dosimetry based on EPID is studied deeply. First, the modeling, algorithm and dose calculation process of the pre treatment dose verification system based on EPID EPIbeam and the Mobius 3D system based on the treatment planning system (TPS) plan treatment parameters are studied. Secondly, the two sets are combined. The pre treatment dose verification system conducted a dose verification study on 28 cases of pelvic case volume intensity modulated radiation therapy (VMAT). Then, we studied the modeling, calculation and dose calculation of the system EPIgray and the MobiusFX system based on "Dynalogfiles" based on the EPID reconstruction. Finally, 30 cases of pelvic disease (15 cases of pelvic disease) were selected. In the case of 15 cases and 15 cases of head and neck, the dose value of the center point at the ionization chamber measurement, based on the dose values of the central point of the EPID image combined with EPIgray reconstruction and the dose of "Dynalog files" combined with the MobiusFX reconstruction, are used to compare the values of the two rebuilt values to the ionization chamber measurements to compare and analyze.EPIbeam The system is to convert the actual EPID images and TPS images into the plane dose distribution at 5 cm under the corresponding dose model at the same time, and then compare them. The Mobius 3D system is to re calculate the dose distribution through the inverted convolution convolution / superposition algorithm (CCC /S) of the TPS's original planned treatment parameters, and to verify the dose before treatment. In this method, the method based on EPID combined with software EPIbeam is the result of two-dimensional plane dose distribution, its gamma passing rate is greater than 95%, Mobius 3D is calculated in the dose distribution of three-dimensional voxel, two cases of gamma passing rate are lower than 95%, but all are higher than 90%, most of the planned gamma pass rate is higher than 95%, all in line with the clinical dosimetric requirements; EPIgray with the aid of The "fTMR" algorithm uses the field images obtained by the EPID in the treatment process to reconstruct the dose of the point of interest in the body; Mobius FX is based on the operating parameters of the "Dynalog files" feedback device, using the CCC/S algorithm to reconstruct the dose. In the body dose verification, the pelvic cavity plan and the head and neck ionization chamber are measured and the measured values are also measured. The reconstruction averages based on EPID and "Dynalog files" are (2.34 + 0.28) Gy, (2.31 + 0.26) Gy, (2.35 + 0.29) Gy and (1.58 + 0.12) Gy, (1.56 + 0.12) Gy and (1.59 + 0.10) Gy. two parts based on the relative deviation of the reconstructed values of EPID from the measured values of the ionization chamber and the relative deviation between the reconstructed values of the "Dynalog files" and the measured values of the ionization chamber. The mean values were (-1.11 + 2.42)%, (0.82 + 1.73)% and (-1.27 + 2.48)% and (0.56 + 1.91)%, which conformed to the clinical dosimetry requirements. The two sets of reconstruction values were paired with the measured values of the ionization chamber respectively. The results showed that the two groups were not statistically different from the ionization chamber measured values (t=1.91, -1.83, P0.05; t=2.01, -0.88, P0.05). As mentioned above, the correct and reasonable method of using EPID to control the quality of dosimetry for advanced radiotherapy technology does not affect treatment and is easy to spread. It not only improves the efficiency of dose verification before treatment, but also has a great advantage in real-time monitoring the patient's dose of radiotherapy. It is helpful to carry out patient dose verification. The accurate method of "Dynalog files" reconstruction dose is simple and can be supplemented with the measurement method, providing a reference for the formation of a fast and simple advanced radiotherapy technology dose monitoring method.

【学位授予单位】：中国疾病预防控制中心
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R730.55

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