Department of Radiation Oncology, University Medical Centre Mannheim, University of Heidelberg, Mannheim, Germany.
J Appl Clin Med Phys. 2023 Sep;24(9):e14105. doi: 10.1002/acm2.14105. Epub 2023 Jul 26.
In the Monte Carlo-based treatment planning system (TPS) Monaco, transmission probability filters (TPF) are utilized to describe the transmission through the multi leaf collimator (MLC). By having knowledge of the TPF parameters for various photon beam energies, adjusting the MLC transmission parameters becomes easier, enhancing the accuracy of the Monte Carlo algorithm in achieving a dose distribution that closely aligns with the irradiated dose at the Versa HD linear accelerator (linac). The objective of this study was to determine the TPF parameters for 6MV, 10MV, 6MV flattening filter free (FFF) and 10MV FFF for a Versa HD linac equipped with Agility MLC. The TPF parameters were adjusted using point dose measurements and vendor-provided fields specifically designed to fine-tune the MLC. After adjusting the TPF parameters, a gamma passing rate (GPR) analysis was conducted on 25 treatment plans to ensure that the Monte Carlo model, with the updated TPF parameters, accurately matched the actual linac delivery. The TPF values ranged from 0.0018 to 0.0032 for leaf transmission and 1.15 to 1.25 for Leaf Tip leakage across the different energies. The average GPR ranged from 97.8% for 10MV FFF to 98.5% for 6MV photon energies. Additionally, the TPF parameters for 6MV obtained in this study were consistent with previously published TPF values for 6MV photon energy. Hence, it was concluded that optimizing the TPF does not need to be performed for every individual Versa HD linac with Agility MLC. Instead, the published parameters can be applied to other Versa HD linacs to enhance clinical accuracy. In conclusion, this study determined the TPF parameters for 6MV and previously unpublished photon energies 10MV, 6MV FFF and 10MV FFF. These parameters can be easily transferred to other facilities, resulting in improved agreement between the dose distribution from the TPS and the linac.
在基于蒙特卡罗的治疗计划系统（TPS）Monaco 中，使用传输概率滤波器（TPF）来描述多叶准直器（MLC）的透射。通过了解各种光子束能量的 TPF 参数，可以更轻松地调整 MLC 传输参数，从而提高蒙特卡罗算法在实现与 Versa HD 直线加速器（linac）实际照射剂量紧密匹配的剂量分布的准确性。本研究的目的是确定配备有 Agility MLC 的 Versa HD linac 的 6MV、10MV、6MV 无均整滤波器（FFF）和 10MV FFF 的 TPF 参数。通过点剂量测量和供应商提供的专门用于微调 MLC 的场来调整 TPF 参数。调整 TPF 参数后，对 25 个治疗计划进行伽马通过率（GPR）分析，以确保使用更新的 TPF 参数的蒙特卡罗模型准确匹配实际的直线加速器输送。TPF 值在不同能量下的叶透射范围为 0.0018 至 0.0032，叶尖泄漏范围为 1.15 至 1.25。平均 GPR 范围从 10MV FFF 的 97.8%到 6MV 光子能量的 98.5%。此外，本研究中获得的 6MV 的 TPF 参数与先前发表的 6MV 光子能量的 TPF 值一致。因此，结论是优化 TPF 不需要为每台配备有 Agility MLC 的特定 Versa HD linac 执行。相反，可以将已发布的参数应用于其他 Versa HD linacs 以提高临床准确性。总之，本研究确定了 6MV 以及以前未发表的光子能量 10MV、6MV FFF 和 10MV FFF 的 TPF 参数。这些参数可以轻松转移到其他设施，从而提高 TPS 和直线加速器之间的剂量分布的一致性。
