Institute of Medical Physics, School of Physics, The University of Sydney, Sydney, New South Wales, Australia; School of Medicine, Taif University, Taif, Saudi Arabia; Liverpool and Macarthur Cancer Therapy Centers, Liverpool, NSW, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia.
Liverpool and Macarthur Cancer Therapy Centers, Liverpool, NSW, Australia; South Western Sydney Clinical School, University of New South Wales, Sydney, NSW, Australia.
Phys Med. 2019 Mar;59:37-46. doi: 10.1016/j.ejmp.2019.02.007. Epub 2019 Feb 26.
To study the sensitivity of an Electronic Portal Imaging Device (EPID) in detecting delivery errors for VMAT lung stereotactic body radiotherapy (SBRT) using the Collapsed Arc method.
Baseline VMAT plans and plans with errors intentionally introduced were generated for 15 lung SBRT patients. Three types of errors were introduced by modifying collimator angles and multi-leaf collimator (MLC) field sizes (MLCFS) and MLC shifts by ±5, ±2, and ±1° or millimeters. A total of 103 plans were measured with EPID on an Elekta Synergy Linear Accelerator (Agility MLC) and compared to both the original treatment planning system (TPS) Collapsed Arc dose matrix and the no-error plan baseline EPID measurements. Gamma analysis was performed using the OmniPro-I'mRT (IBA Dosimetry) software and gamma criteria of 1%/1 mm, 2%/1 mm, 2%/2 mm, and 3%/3.
When the error-introduced EPID measured dose matrices were compared to the TPS matrices, the majority of simulated errors were detected with gamma tolerance of 2%/1 mm and 1%/1 mm. When the error-introduced EPID measured dose matrices were compared to the baseline EPID measurements, all the MLCFS and MLC shift errors, and ±5°collimator errors were detected using 2%/1 mm and 1%/1 mm gamma criteria.
This work demonstrates the feasibility and effectiveness of the collapsed arc technique and EPID for pre-treatment verification of lung SBRT VMAT plans. The EPID was able to detect the majority of MLC and the larger collimator errors with sensitivity to errors depending on the gamma tolerances.
使用 Collapsed Arc 方法研究电子射野影像装置（EPID）检测 VMAT 肺部立体定向体放射治疗（SBRT）剂量投递误差的灵敏度。
为 15 例肺部 SBRT 患者生成了基线 VMAT 计划和有意引入误差的计划。通过修改准直器角度和多叶准直器（MLC）野大小（MLCFS）以及 MLC 偏移±5、±2 和±1°或毫米的方式引入了三种类型的误差。使用 Elekta Synergy 直线加速器（Agility MLC）上的 EPID 对总共 103 个计划进行了测量，并将其与原始治疗计划系统（TPS）的 Collapsed Arc 剂量矩阵以及无误差计划基线 EPID 测量值进行了比较。使用 OmniPro-I'mRT（IBA 剂量学）软件进行伽马分析，并使用伽马标准 1%/1mm、2%/1mm、2%/2mm 和 3%/3mm 进行分析。
当将引入误差的 EPID 测量剂量矩阵与 TPS 矩阵进行比较时，大多数模拟误差都使用 2%/1mm 和 1%/1mm 的伽马容限检测到。当将引入误差的 EPID 测量剂量矩阵与基线 EPID 测量值进行比较时，使用 2%/1mm 和 1%/1mm 的伽马标准可以检测到所有的 MLCFS 和 MLC 偏移误差，以及±5°准直器误差。
这项工作证明了 Collapsed Arc 技术和 EPID 用于肺部 SBRT VMAT 计划的治疗前验证的可行性和有效性。EPID 能够以伽马容限为基础，检测到大多数 MLC 和较大的准直器误差。
