Verification of dosimetric accuracy on the TrueBeam STx: Rounded leaf effect of the high definition MLC
Verification of dosimetric accuracy on the TrueBeam STx: Rounded leaf effect of the high definition MLC
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DOI：
10.1118/1.4752444
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发表时间：
2012-10-01
期刊：
影响因子：
3.8
通讯作者：
Luxton, Gary
中科院分区：
文献类型：
--
作者：
Kielar, Kayla N.;Mok, Ed;Luxton, Gary
目的：Varian Eclipse治疗计划系统中的剂量测定叶隙（DLG）在调试期间确定，并用于模拟多叶准直器（MLC）的圆形叶端的影响。该参数试图模拟辐射和光场之间的物理差异，并解释叶尖之间的固有泄漏。随着需要更大监测单元的单次高剂量治疗的使用增加，泄漏计算的准确性受到了更大的关注，因为它占了患者剂量的很大一部分。本研究旨在验证用于模拟TrueBeam STx圆叶效应的算法的剂量测定准确性，并描述了一种确定最佳实践参数值的方法，考虑到直线加速器的新功能，如无平坦滤波器（FFF）治疗和高清晰度MLC（HDMLC）。方法：在调试期间，验证标称MLC位置，并使用MLC定义的射野大小和移动间隙测试确定DLG参数，这在临床测试中很常见。创建治疗计划，并优化DLG，以实现测量剂量和计算剂量之间的差异小于1%。在TrueBeam STx上可用的所有能量（6 MV、10 MV、15 MV、6 MV FFF、10 MV FFF）和模式（3D常规、IMRT、适形弧、VMAT）的治疗计划上测试发现的DLG值。结果：初始MLC测试期间发现的DLG参数与在临床治疗计划中提供最准确剂量输送的叶隙建模参数不匹配。使用的物理叶间隙的大小作为DLG的HDMLC可以导致5%的差异，测量和计算doses.Conclusions：单独优化的DLG参数使用端到端的测试必须进行，以确保剂量测定的准确性，在建模的圆叶结束Eclipse治疗计划系统。在HDMLC和Millennium MLC的Eclipse最新版本中，叶隙建模与物理叶隙尺寸的差异更为明显。一旦使用基于治疗计划验证的方法正确调试和测试，Eclipse就能够使用TrueBeam STx准确建模SBRT治疗所输送的辐射剂量。(c)2012年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4752444]
Purpose: The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC).Methods: During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx.Results: The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses.Conclusions: Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical leaf gap dimensions is more pronounced in the more recent versions of Eclipse for both the HDMLC and the Millennium MLC. Once properly commissioned and tested using a methodology based on treatment plan verification, Eclipse is able to accurately model radiation dose delivered for SBRT treatments using the TrueBeam STx. (c) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4752444]