Christie Medical Physics and Engineering (CMPE), The Christie NHS Foundation Trust, Manchester, UK; Manchester Academic Health Science Centre (MAHSC), Faculty of Medical and Human Sciences, University of Manchester, UK.
Radiother Oncol. 2013 Dec;109(3):377-83. doi: 10.1016/j.radonc.2013.08.046. Epub 2013 Oct 3.
To investigate the use of a software-based pre-treatment QA system for VMAT, which incorporates realistic linac motion during delivery.
A beam model was produced using the GATE platform for GEANT4 Monte Carlo dose calculations. Initially validated against static measurements, the model was then integrated with a VMAT delivery emulator, which reads plan files and generates a set of dynamic delivery instructions analogous to the linac control system. Monte Carlo simulations were compared to measurements on dosimetric phantoms for prostate and head and neck VMAT plans. Comparisons were made between calculations using fixed control points, and simulations of continuous motion utilising the emulator. For routine use, the model was incorporated into an automated pre-treatment QA system.
The model showed better agreement with measurements when incorporating linac motion: mean gamma pass (Γ<1) over 5 prostate plans was 100.0% at 3%/3mm and 97.4% at 2%/2mm when compared to measurement. For the head and neck plans, delivered to the anatomical phantom, gamma passes were 99.4% at 4%/4mm and 94.94% at 3%/3mm. For example simulations within patient CT data, gamma passes were observed which are within our centre's tolerance for pre-treatment QA.
Through comparison to phantom measurements, it was found that the incorporation of a realistic linac motion improves the accuracy of the model compared to the simulation of fixed control points. The ability to accurately calculate dose as a second check of the planning system, and determine realistic delivery characteristics, may allow for the reduction of machine-based pre-treatment plan QA for VMAT.
研究一种基于软件的 VMAT 预治疗 QA 系统，该系统在传输过程中包含真实的直线加速器运动。
使用 GATE 平台为 GEANT4 蒙特卡罗剂量计算生成束流模型。该模型最初经过静态测量验证，然后与 VMAT 传输仿真器集成，该仿真器读取计划文件并生成一组类似于直线加速器控制系统的动态传输指令。对前列腺和头颈部 VMAT 计划的剂量体模进行了蒙特卡罗模拟与测量的比较。比较了使用固定控制点的计算和使用仿真器的连续运动模拟。为了常规使用，将该模型纳入了自动化预治疗 QA 系统。
当包含直线加速器运动时，该模型与测量结果的一致性更好：与测量结果相比，5 个前列腺计划的平均伽玛通过率（Γ<1）在 3%/3mm 时为 100.0%，在 2%/2mm 时为 97.4%。对于交付给解剖体模的头颈部计划，伽玛通过率在 4%/4mm 时为 99.4%，在 3%/3mm 时为 94.94%。例如，在患者 CT 数据内的模拟，观察到的伽玛通过率在我们中心的预治疗 QA 容限内。
通过与体模测量结果的比较，发现与模拟固定控制点相比，包含真实直线加速器运动可提高模型的准确性。能够准确计算剂量作为计划系统的二次检查，并确定现实的传输特性，可能允许减少 VMAT 的基于机器的预治疗计划 QA。
