Shami Nahid, Atarod Maryam, Shokrani Parvaneh, Najafizade Nadia
Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
School of Allied Medical Sciences, Shahrekord University of Medical Sciences, Shahrekord, Iran.
J Med Signals Sens. 2023 May 29;13(2):144-152. doi: 10.4103/jmss.jmss_152_21. eCollection 2023 Apr-Jun.
This study aimed to optimize efficiency in Monte Carlo (MC) simulation using sensitivity analysis of a beam model.
The BEAMnrc-based model of 6 MV beam of a Siemens Primus linac was developed. For sensitivity analysis, the effect of the electron source, treatment head, and virtual phantom specifications on calculated percent depth dose (PDD) and lateral dose profiles was evaluated.
The optimum mean energy (E) and the full width at half maximum (FWHM) of the intensity distribution of the electron beam were calculated as 6.7 MeV and 3 mm, respectively. Increasing E from 6.1 to 6.7 MeV, increased the PDD in the fall-off region by 4.70% and decreased the lateral profile by 8.76%. Changing the FWHM had a significant effect on the buildup region of PDD and the horns and out-of-field regions of the lateral profile. Increasing the collimators opening by 0.5 mm, PDD increased by 2.13% and the central and penumbra regions of profiles decreased by 1.98% and 11.40% respectively. Collimator properties such as thickness and density were effective in changing the penumbra (11.32% for 0.25 cm increment) and the out-of-field (22.82% for 3 g/cm) regions of the lateral profiles.
Analysis of a 6 MV model showed that PDD profiles were more sensitive to changes in energy than to FWHM of the electron source. The lateral profiles were sensitive to E, FWHM, and collimator opening. The density of the collimator affected only the out-of-field region of lateral profiles. The findings of this study may be used to make benchmarking of an MC beam model more efficient.
本研究旨在通过对射束模型进行敏感性分析来优化蒙特卡罗（MC）模拟的效率。
建立了基于BEAMnrc的西门子Primus直线加速器6 MV射束模型。为了进行敏感性分析，评估了电子源、治疗头和虚拟体模规格对计算出的百分深度剂量（PDD）和侧向剂量分布的影响。
计算得出电子束强度分布的最佳平均能量（E）和半高宽（FWHM）分别为6.7 MeV和3 mm。将E从6.1 MeV增加到6.7 MeV，剂量跌落区的PDD增加了4.70%，侧向剂量分布降低了8.76%。改变FWHM对PDD的剂量建成区以及侧向剂量分布的角部和射野外部区域有显著影响。将准直器开口增加0.5 mm，PDD增加了2.13%，剂量分布的中心区和半影区分别降低了1.98%和11.40%。准直器的厚度和密度等特性对侧向剂量分布的半影区（每增加0.25 cm为11.32%）和射野外部区域（每增加3 g/cm为22.82%）有影响。
对6 MV模型的分析表明，PDD分布对能量变化的敏感性高于对电子源FWHM的敏感性。侧向剂量分布对E、FWHM和准直器开口敏感。准直器的密度仅影响侧向剂量分布的射野外部区域。本研究结果可用于提高MC射束模型的基准测试效率。
