Spenkelink Guus B, Huijskens Sophie C, Zindler Jaap D, de Goede Marc, van der Star Wilhelmus J, van Egmond Jaap, Petoukhova Anna L
Haaglanden Medical Center, Department of Medical Physics, Leidschendam, The Netherlands.
Haaglanden Medical Center, Department of Radiation Oncology, Leidschendam, The Netherlands.
J Appl Clin Med Phys. 2024 Dec;25(12):e14522. doi: 10.1002/acm2.14522. Epub 2024 Sep 17.
Many studies have demonstrated superior performance of Monte Carlo (MC) over type B algorithms in heterogeneous structures. However, even in homogeneous media, MC dose simulations should outperform type B algorithms in situations of electronic disequilibrium, such as small and highly modulated fields. Our study compares MC and Collapsed Cone (CC) dose algorithms in RayStation 12A. Under consideration are 6 MV and 6 MV flattening filter-free (FFF) photon beams, relevant for VMAT plans such as head-and-neck and stereotactic lung treatments with heterogeneities, as well as plans for multiple brain metastases in one isocenter, involving highly modulated small fields. We aim to investigate collimator angle dependence of small fields and performance differences between different combinations of ArcCHECK configuration and dose algorithm.
Several verification tests were performed, ranging from simple rectangular fields to highly modulated clinical plans. To evaluate and compare the performance of the models, the agreements between calculation and measurement are compared between MC and CC. Measurements include water tank measurements for test fields, ArcCHECK measurements for test fields and VMAT plans, and film dosimetry for small fields.
In very small or narrow fields, our measurements reveal a strong dependency of dose output to collimator angle for VersaHD with Agility MLC, reproduced by both dose algorithms. ArcCHECK results highlight a suboptimal agreement between measurements and MC calculations for simple rectangular fields when using inhomogeneous ArcCHECK images. Therefore, we advocate for the use of homogeneous phantom images, particularly for static fields, in ArcCHECK verification with MC. MC might offer performance benefits for more modulated treatment fields. In ArcCHECK results for clinical plans, MC performed comparable to CC for 6 MV. For 6 MV FFF and the preferred homogeneous phantom image, MC resulted in consistently better results (13%-64% lower mean gamma index) compared to CC.
许多研究表明，在非均匀结构中，蒙特卡罗（MC）算法比B型算法具有更优的性能。然而，即使在均匀介质中，在电子不平衡的情况下，如小而高度调制的射野，MC剂量模拟也应优于B型算法。我们的研究比较了RayStation 12A中的MC和坍缩圆锥（CC）剂量算法。考虑了6 MV和6 MV无 flattening 滤波器（FFF）光子束，这些与VMAT计划相关，如头颈部和立体定向肺部治疗中的非均匀性射野，以及一个等中心内多个脑转移瘤的计划，涉及高度调制的小射野。我们旨在研究小射野的准直器角度依赖性以及ArcCHECK配置和剂量算法不同组合之间的性能差异。
进行了多项验证测试，从简单的矩形射野到高度调制的临床计划。为了评估和比较模型的性能，比较了MC和CC之间计算值与测量值的一致性。测量包括测试射野的水箱测量、测试射野和VMAT计划的ArcCHECK测量以及小射野的胶片剂量测定。
在非常小或窄的射野中，我们的测量结果显示，对于配备Agility MLC的VersaHD，剂量输出对准直器角度有很强的依赖性，两种剂量算法都能重现这种依赖性。ArcCHECK结果突出表明，在使用非均匀ArcCHECK图像时，对于简单矩形射野，测量值与MC计算值之间的一致性不理想。因此，我们主张在使用MC进行ArcCHECK验证时，特别是对于静态射野，使用均匀体模图像。对于更多调制的治疗射野，MC可能具有性能优势。在临床计划的ArcCHECK结果中，对于6 MV，MC的表现与CC相当。对于6 MV FFF和首选的均匀体模图像，与CC相比，MC的结果始终更好（平均伽马指数低13%-64%）。
