Rodrigues Anna, Sawkey Daren, Yin Fang-Fang, Wu Qiuwen
Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710 and Medical Physics Graduate Program, Duke University Medical Center, Durham, North Carolina 27705.
Varian Medical Systems, Palo Alto, California 94304.
Med Phys. 2015 May;42(5):2389-403. doi: 10.1118/1.4916896.
To develop a framework for accurate electron Monte Carlo dose calculation. In this study, comprehensive validations of vendor provided electron beam phase space files for Varian TrueBeam Linacs against measurement data are presented.
In this framework, the Monte Carlo generated phase space files were provided by the vendor and used as input to the downstream plan-specific simulations including jaws, electron applicators, and water phantom computed in the EGSnrc environment. The phase space files were generated based on open field commissioning data. A subset of electron energies of 6, 9, 12, 16, and 20 MeV and open and collimated field sizes 3 × 3, 4 × 4, 5 × 5, 6 × 6, 10 × 10, 15 × 15, 20 × 20, and 25 × 25 cm(2) were evaluated. Measurements acquired with a CC13 cylindrical ionization chamber and electron diode detector and simulations from this framework were compared for a water phantom geometry. The evaluation metrics include percent depth dose, orthogonal and diagonal profiles at depths R100, R50, Rp, and Rp+ for standard and extended source-to-surface distances (SSD), as well as cone and cut-out output factors.
Agreement for the percent depth dose and orthogonal profiles between measurement and Monte Carlo was generally within 2% or 1 mm. The largest discrepancies were observed within depths of 5 mm from phantom surface. Differences in field size, penumbra, and flatness for the orthogonal profiles at depths R100, R50, and Rp were within 1 mm, 1 mm, and 2%, respectively. Orthogonal profiles at SSDs of 100 and 120 cm showed the same level of agreement. Cone and cut-out output factors agreed well with maximum differences within 2.5% for 6 MeV and 1% for all other energies. Cone output factors at extended SSDs of 105, 110, 115, and 120 cm exhibited similar levels of agreement.
We have presented a Monte Carlo simulation framework for electron beam dose calculations for Varian TrueBeam Linacs. Electron beam energies of 6 to 20 MeV for open and collimated field sizes from 3 × 3 to 25 × 25 cm(2) were studied and results were compared to the measurement data with excellent agreement. Application of this framework can thus be used as the platform for treatment planning of dynamic electron arc radiotherapy and other advanced dynamic techniques with electron beams.
开发一个用于精确电子蒙特卡罗剂量计算的框架。在本研究中，针对瓦里安TrueBeam直线加速器，给出了供应商提供的电子束相空间文件与测量数据的全面验证。
在这个框架中，蒙特卡罗生成的相空间文件由供应商提供，并用作下游特定计划模拟的输入，包括在EGSnrc环境中计算的准直器、电子限光筒和水模体。相空间文件基于开放野调试数据生成。评估了6、9、12、16和20 MeV的部分电子能量以及3×3、4×4、5×5、6×6、10×10、15×15、20×20和25×25 cm²的开放野和准直野尺寸。对于水模体几何结构，比较了使用CC13圆柱形电离室和电子二极管探测器获得的测量结果以及该框架的模拟结果。评估指标包括百分深度剂量、在标准和扩展源皮距（SSD）下深度R100、R50、Rp和Rp+处的正交和对角线剂量分布，以及射野和限束装置输出因子。
测量值与蒙特卡罗计算的百分深度剂量和正交剂量分布的一致性一般在2%或1 mm以内。在距模体表面5 mm深度范围内观察到最大差异。在深度R100、R50和Rp处，正交剂量分布的射野尺寸、半值层和平坦度差异分别在1 mm、1 mm和2%以内。100和120 cm SSD处的正交剂量分布显示出相同程度的一致性。射野和限束装置输出因子一致性良好，6 MeV时最大差异在2.5%以内，其他能量时在1%以内。105、110、115和120 cm扩展SSD处的射野输出因子表现出相似程度的一致性。
我们提出了一个用于瓦里安TrueBeam直线加速器电子束剂量计算的蒙特卡罗模拟框架。研究了6至20 MeV电子束能量下3×3至25×25 cm²开放野和准直野尺寸，并将结果与测量数据进行比较，一致性良好。因此，该框架的应用可作为动态电子弧形放射治疗和其他先进电子束动态技术治疗计划的平台。
