Carrasco P, Jornet N, Duch M A, Weber L, Ginjaume M, Eudaldo T, Jurado D, Ruiz A, Ribas M
Servei de Radiofisica i Radioprotecció, Hospital de la Santa Creu i Sant Pau, St Antoni Maria Claret-167, 08025 Barcelona, Spain.
Med Phys. 2004 Oct;31(10):2899-911. doi: 10.1118/1.1788932.
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 cm2) and two lung equivalent materials (CIRS, p(w)e=0.195 and St. Bartholomew Hospital, London, p(w)e=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 cm2 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 cm2 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.
在包含肺等效不均匀性的非均匀层模体中，使用多种探测器对剂量深度分布（PDDs）和射野轮廓进行了广泛的基准测量，并与两个治疗计划系统中不同计算算法预测的剂量值进行了比较。PDDs使用热释光剂量计（TLDs）、平行平板电离室和圆柱形电离室进行测量，射野轮廓使用胶片进行测量。此外，还使用PENELOPE代码进行了蒙特卡罗模拟。研究了四种不同的射野尺寸（10×10、5×5、2×2和1×1 cm²）和两种肺等效材料（CIRS，p(w)e = 0.195；伦敦圣巴塞洛缪医院，p(w)e = 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。基于校正的算法包括Cadplan（瓦里安）治疗计划系统中实现 的巴托（Batho）算法、修正巴托算法和等效组织空气比（Equivalent TAR）算法，以及Helax - TMS（核通）治疗计划系统中的TMS笔形束算法。卷积叠加算法是Helax - TMS中实现的坍缩圆锥算法。在所有介质中，唯一与测量值成功相关且平均偏差在2%以内的研究计算方法是坍缩圆锥算法和蒙特卡罗模拟。在2×2 cm² 18 MV X射线束中，在CIRS肺等效材料内，发现EqTAR算法在射束轴线上预测剂量与实际 delivered剂量之间的最大差异。在这些条件下，与TLD测量相比，平均差异和最大差异分别为32%和39%。在模体的水等效部分，除了非常靠近界面的地方（对于2×2 cm² 18 MV光子束，差异高达24%），每种算法都能在各处正确预测剂量（在2%以内）。在参考探测器（水中的电离室和肺中的TLD）和蒙特卡罗模拟之间发现了一致的值（差异最小，为0.4%±1.2%）。任何基于校正的算法都未预测到低密度介质中的半影展宽效应，唯一在估计不确定度范围内与实验值和蒙特卡罗模拟匹配的算法是坍缩圆锥算法。
