Comparison of dose calculation algorithms in phantoms with lung equivalent heterogeneities under conditions of lateral electronic disequilibrium
Comparison of dose calculation algorithms in phantoms with lung equivalent heterogeneities under conditions of lateral electronic disequilibrium
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DOI：
10.1118/1.1788932
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发表时间：
2004-10-01
期刊：
影响因子：
3.8
通讯作者：
Ribas, M
中科院分区：
文献类型：
--
作者：
Carrasco, P;Jornet, N;Ribas, M
在异质层体模（包括肺等效异质性）中，通过几个探测器对PDD和射束轮廓进行了一组广泛的基准测量，并在两个治疗计划系统中通过不同的计算算法与预测剂量值进行了比较。使用TLD、平面平行电离室和圆柱形电离室以及带有薄膜的束剖面来测量PDD。此外，Monte Carlo模拟的PENMENTAL PE代码进行。研究了四种不同的射野尺寸（10 x 10、5 x 5、2 x 2和1 x 1 cm（2））和两种肺等效材料（CIRS，p（e）（w）= 0.195和St. Bartholomew Hospital，伦敦，P-e（w）= 0.244-0.322）。分析了四种基于校正的算法和一种基于卷积叠加的算法的性能。基于校正的算法是Cadplan（Varian）治疗计划系统中实现的TRAC、Modified TRAC和等效TAR以及Helax-TMS（Nucletron）治疗计划系统中的TMS TRAC Beam。卷积叠加算法是在Helax-TMS中实现的Collapsed Cone。唯一研究的计算方法，成功地与测量值与2%的平均值内的所有媒体是塌陷锥和蒙特卡洛模拟。在2 x 2 cm（2）18 MV X射线束中，CIRS肺等效材料内的EqTAR算法发现了射束轴上预测剂量和输送剂量之间的最大差异。在这些条件下，相对于重复测量的平均和最大差异分别为32%和39%。在体模的水当量部分，除了非常接近界面的地方，每个算法都正确预测了剂量（在2%以内），其中发现2 x 2 cm（2）18 MV光子束的差异高达24%。在参考检测器（水中的电离室和肺中的电离室）和Monte Carlo模拟之间发现了一致的值，产生最小差异（0.4% +/- 1.2%）。低密度介质中的半影展宽效应没有被任何基于校正的算法预测到，并且在估计的不确定性内与实验值和蒙特卡罗模拟相匹配的唯一算法是塌陷锥算法。(C)2004年美国医学物理学家协会。
An extensive set of benchmark measurement of PDDs and beam profiles was performed in a heterogeneous layer phantom, including a lung equivalent heterogeneity, by means of several detectors and compared against the predicted dose values by different calculation algorithms in two treatment planning systems. PDDs were measured with TLDs, plane parallel and cylindrical ionization chambers and beam profiles with films. Additionally, Monte Carlo simulations by means of the PENELOPE code were performed. Four different field sizes (10 x 10, 5 x 5, 2 x 2, and 1 x 1 cm(2)) and two lung equivalent materials (CIRS, p(e)(w) = 0.195 and St. Bartholomew Hospital, London, P-e(w) = 0.244-0.322) were studied. The performance of four correction-based algorithms and one based on convolution-superposition was analyzed. The correction-based algorithms were the Batho, the Modified Batho, and the Equivalent TAR implemented in the Cadplan (Varian) treatment planning system and the TMS Pencil Beam from the Helax-TMS (Nucletron) treatment planning system. The convolution-superposition algorithm was the Collapsed Cone implemented in the Helax-TMS. The only studied calculation methods that correlated successfully with the measured values with a 2% average inside all media were the Collapsed Cone and the Monte Carlo simulation. The biggest difference between the predicted and the delivered dose in the beam axis was found for the EqTAR algorithm inside the CIRS lung equivalent material in a 2 x 2 cm(2) 18 MV x-ray beam. In these conditions, average and maximum difference against the TLD measurements were 32% and 39%, respectively. In the water equivalent part of the phantom every algorithm correctly predicted the dose (within 2%) everywhere except very close to the interfaces where differences up to 24% were found for 2 x 2 cm(2) 18 MV photon beams. Consistent values were found between the reference detector (ionization chamber in water and TLD in lung) and Monte Carlo simulations, yielding minimal differences (0.4% +/- 1.2%). The penumbra broadening effect in low density media was not predicted by any of the correction-based algorithms, and the only one that matched the experimental values and the Monte Carlo simulations within the estimated uncertainties was the Collapsed Cone Algorithm. (C) 2004 American Association of Physicist in Medicine.