Etienne Thomas, Kim Joshua, Thind Kundan, Chetty Indrin J
Department of Radiation Oncology, Baylor Scott and White Health, Temple, Texas, USA.
Department of Radiation Oncology, Cedars-Sinai Medical Center, Los Angeles, California, USA.
Med Phys. 2025 Jan;52(1):673-684. doi: 10.1002/mp.17455. Epub 2024 Oct 10.
Monte Carlo (MC) modeling of MR-guided radiotherapy (MRgRT) treatment machines enables the characterization of photon/electron interactions in the presence of a magnetic field. The EGSnrc MC code system is a well-established system for radiation dose calculations. The multi-leaf collimator (MLC) component modules presently available within the EGSnrc MC code system do not include a model of the double-focused MLC available on a low-field (0.35T) MRI linear accelerator (MR linac).
Here we developed and validated a new component module (CM) for the low-field MRgRT MLC using the EGSnrc/BEAMnrc/DOSXYZnrc code system. We performed detailed modeling of the treatment head and validated the model using measurements and calculations from the vendor-specific treatment planning system (TPS).
The detailed geometry of the low-field MR linac MLC and other treatment head structures were modeled using BEAMnrc. Comparisons of DOSXYZnrc simulated dose against measurements and the low-field MR linac TPS for a variety of AAPM TG-53 task group report suggested square and shaped fields, as well as a step-and-shoot intensity-modulated radiotherapy (IMRT) plan, are presented.
Our model agrees with both measured and TPS calculated data on average within 2%/2 mm (dose/DTA) criterion for square field profiles. Output factors agreed within 1% for field sizes down to 2.49 × 2.49 cm and within 2% of TPS data for the smallest field size of 0.83 × 0.83 cm. Shaped field and IMRT MC calculations agreed with measured and TPS data such that the gamma pass rates (3%/2 mm) were 99.5% and (3%/3 mm) 96.2%, respectively.
We developed and validated an MLC CM (SYNCVRMLC) for the low-field MR linac using the EGSnrc MC code systems. This new CM will facilitate MC computation of fluence and dose distributions using BEAMnrc/DOSXYZnrc for patients treated on the low-field MR linac.
磁共振引导放疗（MRgRT）治疗机的蒙特卡罗（MC）建模能够表征在磁场存在情况下的光子/电子相互作用。EGSnrc MC代码系统是用于辐射剂量计算的成熟系统。目前EGSnrc MC代码系统中可用的多叶准直器（MLC）组件模块不包括低场（0.35T）MRI直线加速器（MR直线加速器）上可用的双聚焦MLC模型。
在此，我们使用EGSnrc/BEAMnrc/DOSXYZnrc代码系统为低场MRgRT MLC开发并验证了一个新的组件模块（CM）。我们对治疗头进行了详细建模，并使用特定供应商治疗计划系统（TPS）的测量和计算结果对模型进行了验证。
使用BEAMnrc对低场MR直线加速器MLC和其他治疗头结构的详细几何形状进行建模。针对各种AAPM TG - 53任务组报告中的方形和成形野，以及步进式强度调制放疗（IMRT）计划，给出了DOSXYZnrc模拟剂量与测量值以及低场MR直线加速器TPS的比较结果。
对于方形野轮廓，我们的模型与测量数据和TPS计算数据在平均2%/2毫米（剂量/剂量偏差）标准内达成一致。对于小至2.49×2.49厘米的野尺寸，输出因子在1%以内达成一致，对于最小野尺寸0.83×0.83厘米，与TPS数据在2%以内达成一致。成形野和IMRT的MC计算结果与测量数据和TPS数据一致，使得γ通过率（3%/2毫米）分别为99.5%和（3%/3毫米）96.2%。
我们使用EGSnrc MC代码系统为低场MR直线加速器开发并验证了一个MLC CM（SYNCVRMLC）。这个新的CM将便于使用BEAMnrc/DOSXYZnrc对在低场MR直线加速器上接受治疗的患者进行注量和剂量分布的MC计算。
