Sawapabmongkon Thitipong, Changkaew Pimolpun, Puttanawarut Chanon, Tangboonduangjit Puangpen, Khachonkham Suphalak
Division of Radiation Oncology, Department of Diagnostic and Therapeutic Radiology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
Chakri Naruebodindra Medical Institute, Mahidol University, Samut Prakan, Thailand.
J Med Phys. 2024 Apr-Jun;49(2):261-269. doi: 10.4103/jmp.jmp_11_24. Epub 2024 Jun 25.
The dosimetric leaf gap (DLG) is a parameter for correcting radiation transmission through the round leaf end of multileaf collimators. The purpose of this study was to determine and investigate the optimal DLG correction factor for 6 MV volumetric-modulated arc radiotherapy (VMAT) plan dose calculations in Mobius3D.
Seventeen VMAT plans were selected for the DLG correction factor optimization process. The optimal DLG correction factor was defined as the minimum difference between the measured dose and the Mobius3D-calculated dose on the Mobius Verification Phantom™ with different DLG correction factors. Subsequently, the optimal DLG correction factor was applied for Mobius3D dose calculation, and accuracy was assessed by comparing the measured and calculated doses. For verification and validation, the 17 previous plans and 10 newly selected plans underwent Mobius3D calculations with the optimal DLG correction factor, and gamma analysis was performed to compare them to the treatment planning system (TPS). Gamma analysis was also performed between the electronic portal imaging device (EPID) and the TPS for cross-comparison between systems.
The DLG correction factor was optimized to -1.252, which reduced the average percentage differences between measured and Mobius3D-calculated doses from 2.23% ±1.21% to 0.03% ±1.82%. The cross-comparison between Mobius3D/TPS and EPID/TPS revealed a similar trend in gamma passing rate (>95%) in both the verification and validation plans.
The DLG correction factor strongly influences the accuracy of Mobius3D-calculated doses. Applying the optimal DLG correction factor can increase dose agreement and gamma passing rate between calculation and delivered doses of VMAT plans, which emphasizes the importance of optimizing this factor during the commissioning process.
剂量学叶片间隙（DLG）是用于校正通过多叶准直器圆形叶片末端的辐射传输的参数。本研究的目的是确定并研究用于在Mobius3D中进行6MV容积调强弧形放疗（VMAT）计划剂量计算的最佳DLG校正因子。
选择17个VMAT计划用于DLG校正因子优化过程。最佳DLG校正因子定义为在具有不同DLG校正因子的Mobius验证体模上测量剂量与Mobius3D计算剂量之间的最小差异。随后，将最佳DLG校正因子应用于Mobius3D剂量计算，并通过比较测量剂量和计算剂量来评估准确性。为了进行验证和确认，对之前的17个计划和新选择的10个计划使用最佳DLG校正因子进行Mobius3D计算，并进行伽马分析以将它们与治疗计划系统（TPS）进行比较。还在电子门静脉成像设备（EPID）和TPS之间进行伽马分析以进行系统间的交叉比较。
DLG校正因子优化为 -1.252，这将测量剂量与Mobius3D计算剂量之间的平均百分比差异从2.23%±1.21%降低到0.03%±1.82%。Mobius3D/TPS与EPID/TPS之间的交叉比较显示，在验证计划和确认计划中伽马通过率（>95%）具有相似趋势。
DLG校正因子对Mobius3D计算剂量的准确性有很大影响。应用最佳DLG校正因子可以提高VMAT计划计算剂量与交付剂量之间的剂量一致性和伽马通过率，这强调了在调试过程中优化该因子的重要性。
