基于体素的人体模型变形到患者后的快速蒙特卡罗模拟。
Fast Monte Carlo simulation on a voxelized human phantom deformed to a patient.
机构信息
E.T.S.I. Industriales, Universidad de Castilla-La Mancha, Avenida Camilo José Cela s/n, E-13071 Ciudad Real, Spain.
出版信息
Med Phys. 2009 Nov;36(11):5162-74. doi: 10.1118/1.3245877.
PURPOSE
A method for performing fast simulations of absorbed dose using a patient's computerized tomography (CT) scan without explicitly relying on a calibration curve is presented.
METHODS
The method is based on geometrical deformations performed on a standard voxelized human phantom. This involves spatially transforming the human phantom to align it with the patient CT image. Since the chemical composition and density of each voxel are given in the phantom data, a calibration curve is not used in the proposed method. For this study, the Monte Carlo (MC) code PENELOPE has been used as the simulation of reference. The results obtained with PENELOPE simulations are compared to those obtained with PENFAST and with the collapsed cone convolution algorithm implemented in a commercial treatment planning system.
RESULTS
The comparisons of the absorbed doses calculated with the different algorithms on two patient CTs and the corresponding deformed phantoms show a maximum distance to agreement of 2 mm, and in general, the obtained absorbed dose distributions are compatible within the reached statistical uncertainty. The validity of the deformation method for a broad range of patients is shown using MC simulations in random density phantoms. A PENFAST simulation of a 6 MV photon beam impinging on a patient CT reaches 2% statistical uncertainty in the absorbed dose, in a 0.1 cm3 voxel along the central axis, in 10 min running on a single core of a 2.8 GHz CPU.
CONCLUSIONS
The proposed method of the absorbed dose calculation in a deformed voxelized phantom allows for dosimetric studies in the geometry of a patient CT scan. This is due to the fact that the chemical composition and material density of the phantom are known. Furthermore, simulation using the phantom geometry can provide dosimetric information for each organ. The method can be used for quality assurance procedures. In relation to PENFAST, it is shown that a purely condensed-history algorithm (class I) can be used for absorbed dose estimation in patient CTs.
目的
提出了一种在不依赖校准曲线的情况下，使用患者的计算机断层扫描（CT）扫描进行快速吸收剂量模拟的方法。
方法
该方法基于对标准体素化人体模型进行几何变形。这涉及到将人体模型进行空间变换以使其与患者 CT 图像对齐。由于每个体素的化学成分和密度都在体模数据中给出，因此该方法不使用校准曲线。在这项研究中，蒙特卡罗（MC）代码 PENELOPE 被用作参考模拟。将 PENFAST 和商业治疗计划系统中实现的锥形束卷积算法的模拟结果与 PENELOPE 模拟结果进行比较。
结果
在两个患者 CT 和相应变形体模上，用不同算法计算的吸收剂量的比较显示最大差异为 2 毫米，并且通常，所得到的吸收剂量分布在达到的统计不确定性内是兼容的。使用 MC 在随机密度体模中对广泛的患者进行的变形方法的有效性模拟。在患者 CT 上的 6 MV 光子束的 PENFAST 模拟中，在中央轴上的 0.1 cm3 体素中，达到 2%的统计不确定性，在 2.8 GHz CPU 的单个核心上运行 10 分钟。
结论
提出的在变形体素化体模中计算吸收剂量的方法允许在患者 CT 扫描的几何形状中进行剂量学研究。这是因为体模的化学成分和材料密度是已知的。此外，使用体模几何形状的模拟可以为每个器官提供剂量信息。该方法可用于质量保证程序。与 PENFAST 相比，表明纯粹的凝聚历史算法（I 类）可用于患者 CT 中的吸收剂量估计。
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