Shepard Andrew J, Frigo Sean P
Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA.
J Appl Clin Med Phys. 2021 Mar;22(3):216-223. doi: 10.1002/acm2.13206. Epub 2021 Mar 5.
To assess the implementation, accuracy, and validity of the dosimetric leaf gap correction (DLGC) in Mobius3D VMAT plan calculations.
The optimal Mobius3D DLGC was determined for both a TrueBeam with a Millennium multi-leaf collimator and a TrueBeamSTx with a high-definition multi-leaf collimator. By analyzing a broad series of seven VMAT plans and comparing the calculated to the measured dose delivered to a cylindrical phantom, optimal DLGC values were determined by minimizing the dose difference for both the collection of all plans, as well as for each plan individually. The effects of plan removal from the optimization of the collective DLGC value, as well as plan-specific DLGC values, were explored to determine the impact of plan suite design on the final DLGC determination.
Optimal collective DLGC values across all energies were between -0.71 and 0.89 mm for the TrueBeam, and between 0.35 and 1.85 mm for the TrueBeamSTx. The dose differences ranged between -6.1% and 2.6% across all plans when the optimal collective DLGC values were used. On a per-plan basis, the plan-specific optimal DLGC values ranged from -4.36 to 2.35 mm for the TrueBeam, and between -1.83 and 2.62 mm for the TrueBeamSTx. Comparing the plan-specific optimal DLGC to the average absolute leaf position from the central axis for each plan, a negative correlation was observed.
The optimal DLGC determination depends on the plans investigated, making it essential for users to utilize a suite of test plans that encompasses the full range of expected clinical plans when determining the optimal DLGC value. Validation of the secondary dose calculation should always be based on measurements, and not a comparison with the primary TPS. Varying disagreement with measurements across plans for a single DLGC value indicates potential limitations in the Mobius3D MLC model.
评估在Mobius3D容积调强弧形治疗（VMAT）计划计算中剂量学叶片间隙校正（DLGC）的实施情况、准确性和有效性。
针对配备Millennium多叶准直器的TrueBeam和配备高清多叶准直器的TrueBeamSTx，分别确定最佳的Mobius3D DLGC。通过分析一系列广泛的七个VMAT计划，并将计算得到的剂量与输送到圆柱形模体的测量剂量进行比较，通过最小化所有计划集合以及每个计划单独的剂量差异来确定最佳DLGC值。研究从集体DLGC值优化中去除计划以及特定计划的DLGC值的影响，以确定计划组设计对最终DLGC确定的影响。
对于TrueBeam，所有能量下的最佳集体DLGC值在-0.71至0.89毫米之间，对于TrueBeamSTx，在0.35至1.85毫米之间。使用最佳集体DLGC值时，所有计划的剂量差异在-6.1%至2.6%之间。就每个计划而言，TrueBeam的特定计划最佳DLGC值范围为-4.36至2.35毫米，TrueBeamSTx的范围为-1.83至2.62毫米。将特定计划的最佳DLGC与每个计划从中心轴起的平均绝对叶片位置进行比较，观察到负相关。
最佳DLGC的确定取决于所研究的计划，这使得用户在确定最佳DLGC值时必须使用一套涵盖所有预期临床计划范围的测试计划。二次剂量计算的验证应始终基于测量，而不是与原始治疗计划系统（TPS）进行比较。对于单个DLGC值，不同计划与测量值之间存在差异，这表明Mobius3D多叶准直器（MLC）模型存在潜在局限性。
