Fast, accurate photon beam accelerator modeling using BEAMnrc: A systematic investigation of efficiency enhancing methods and cross-section data
Fast, accurate photon beam accelerator modeling using BEAMnrc: A systematic investigation of efficiency enhancing methods and cross-section data
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DOI：
10.1118/1.3253300
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发表时间：
2009-12-01
期刊：
影响因子：
3.8
通讯作者：
Chetty, Indrin J.
中科院分区：
文献类型：
--
作者：
Fragoso, Margarida;Kawrakow, Iwan;Chetty, Indrin J.
在这项工作中，效率提高的方法和截面数据的BEAMnrc蒙特卡罗（MC）代码系统的调查。此外，还将BEAMnrc与VMC++进行了比较，VMC ++是另一种专用MC代码系统，最近已针对整个治疗头的模拟进行了增强。BEAMnrc和VMC++用于模拟来自Siemens Primus直线加速器（直线加速器）的6 MV光子束，并在10 x 10和40 x 40 cm（2）射野尺寸的100 cm源-表面距离处生成相空间（PHSP）文件。研究中的BEAMnrc参数/技术按（i）光子和韧致辐射截面，（ii）近似效率改进技术（AEIT），（iii）方差降低技术（VRT）和（iv）VRT（韧致辐射光子分裂）与AEIT（带电粒子距离抑制）组合进行分组。在没有研究中的效率增强技术的情况下获得的BEAMnrc PHSP文件，或者当不可能时，使用其默认值（例如，边界交叉算法的EXACT算法）和默认横截面数据（PEGS 4和Bethe-Heitler）用作前述不同组生成的PHSP文件准确度验证的“基线”。随后，选择PHSP文件作为基于DOSXYZnrc的水体模剂量计算的输入，并根据测量结果进行验证。BEAMnrc和VMC++中可用的不同VRT和AEIT的性能由相对效率指定，即。例如，通过MC模拟相对于BEAMnrc基线计算的效率。最高相对效率与935相似（类似于单个2.6 GHz处理器上的111分钟）和类似于200（类似于在单个处理器上的45分钟）分别对于具有5000万个历史的10 × 10场大小和具有1亿个历史的40 × 40 cm（2）场大小，使用VRT定向韧致辐射分裂（DBS）而没有电子分裂。当DBS与电子分裂一起使用并与增强带电粒子射程抑制（BEAMnrc中最近引入的一种技术）相结合时，对于10 x 10和40 x 40 cm（2）的场尺寸，相对效率分别类似于420（类似于单个处理器上的253 min）和175（类似于单个处理器上的58 min）。对于10 x 10和40 x 40 cm（2）射野尺寸，使用VMC++计算Siemens Primus治疗头产生的相对效率分别类似于1400（类似于单个处理器上的6 min）和60（类似于单个处理器上的4 min）。单独使用DBS或DBS与带电粒子范围抑制相结合的BEAMnrc PHSP计算比使用的其他效率增强技术更有效。使用VMC++，在单个处理器上在几分钟内完成了整个直线加速器治疗头的精确模拟。与Bethe-Heitler（BEAMnrc默认韧致辐射截面）相比，NIST韧致辐射截面的平均能量、平面注量以及角度和光谱分布存在显著差异（+1% -3%）。然而，MC计算的剂量分布在水幻影（使用VRT/AEIT和横截面数据的组合）同意在2%的测量。此外，MC使用NIST横截面计算的模拟水/空气/水体模中的剂量分布与BEAMnrc Bethe-Heitler默认情况的一致性在2%以内。(C)2009年美国医学物理学家协会。[DOI：10.1118/1.3253300]
In this work, an investigation of efficiency enhancing methods and cross-section data in the BEAMnrc Monte Carlo (MC) code system is presented. Additionally, BEAMnrc was compared with VMC++, another special-purpose MC code system that has recently been enhanced for the simulation of the entire treatment head. BEAMnrc and VMC++ were used to simulate a 6 MV photon beam from a Siemens Primus linear accelerator (linac) and phase space (PHSP) files were generated at 100 cm source-to-surface distance for the 10 x 10 and 40 x 40 cm(2) field sizes. The BEAMnrc parameters/techniques under investigation were grouped by (i) photon and bremsstrahlung cross sections, (ii) approximate efficiency improving techniques (AEITs), (iii) variance reduction techniques (VRTs), and (iv) a VRT (bremsstrahlung photon splitting) in combination with an AEIT (charged particle range rejection). The BEAMnrc PHSP file obtained without the efficiency enhancing techniques under study or, when not possible, with their default values (e.g., EXACT algorithm for the boundary crossing algorithm) and with the default cross-section data (PEGS4 and Bethe-Heitler) was used as the "base line" for accuracy verification of the PHSP files generated from the different groups described previously. Subsequently, a selection of the PHSP files was used as input for DOSXYZnrc-based water phantom dose calculations, which were verified against measurements. The performance of the different VRTs and AEITs available in BEAMnrc and of VMC++ was specified by the relative efficiency, i. e., by the efficiency of the MC simulation relative to that of the BEAMnrc base-line calculation. The highest relative efficiencies were similar to 935 (similar to 111 min on a single 2.6 GHz processor) and similar to 200 (similar to 45 min on a single processor) for the 10 x 10 field size with 50 million histories and 40 x 40 cm(2) field size with 100 million histories, respectively, using the VRT directional bremsstrahlung splitting (DBS) with no electron splitting. When DBS was used with electron splitting and combined with augmented charged particle range rejection, a technique recently introduced in BEAMnrc, relative efficiencies were similar to 420 (similar to 253 min on a single processor) and similar to 175 (similar to 58 min on a single processor) for the 10 x 10 and 40 x 40 cm(2) field sizes, respectively. Calculations of the Siemens Primus treatment head with VMC++ produced relative efficiencies of similar to 1400 (similar to 6 min on a single processor) and similar to 60 (similar to 4 min on a single processor) for the 10 x 10 and 40 x 40 cm(2) field sizes, respectively. BEAMnrc PHSP calculations with DBS alone or DBS in combination with charged particle range rejection were more efficient than the other efficiency enhancing techniques used. Using VMC++, accurate simulations of the entire linac treatment head were performed within minutes on a single processor. Noteworthy differences (+1% -3%) in the mean energy, planar fluence, and angular and spectral distributions were observed with the NIST bremsstrahlung cross sections compared with those of Bethe-Heitler (BEAMnrc default bremsstrahlung cross section). However, MC calculated dose distributions in water phantoms (using combinations of VRTs/AEITs and cross-section data) agreed within 2% of measurements. Furthermore, MC calculated dose distributions in a simulated water/air/water phantom, using NIST cross sections, were within 2% agreement with the BEAMnrc Bethe-Heitler default case. (C) 2009 American Association of Physicists in Medicine. [DOI: 10.1118/1.3253300]