MONTE-CARLO EVALUATION OF KERMA AT A POINT FOR PHOTON TRANSPORT PROBLEMS
MONTE-CARLO EVALUATION OF KERMA AT A POINT FOR PHOTON TRANSPORT PROBLEMS
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DOI：
10.1118/1.596069
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发表时间：
1987-07-01
期刊：
影响因子：
3.8
通讯作者：
WILLIAMSON, JF
中科院分区：
文献类型：
--
作者：
WILLIAMSON, JF
散射光子产生的几何点碰撞角估计是蒙特卡罗模拟的一个潜在的重要含义，特别是在存在陡峭通量梯度的情况下。我们研究了从随机生成的光子轨迹中提取点kerma估计的常用方法，该方法包括计算在感兴趣点附近发生的光子碰撞所损失的能量。从单位体积和通量的轨道长度等效推导出的其他几种方法的精度和效率进行了评价。最后，讨论了下一次飞行估计器，其中每个模拟光子碰撞对该点的期望贡献。所有这些技术都涉及到统计精度和空间分辨率之间的权衡：增加贡献碰撞的数量需要在更大的体积上平均kerma。基于分析模型和现实的蒙特卡罗模拟，与模拟评分相比，使用下一段和轨迹长度估计器可以将增产效率提高2到20倍。给出了选择估计器和成功实施的实用指南。
Estimation of collision kerma at a geometric point arising from scattered photons is potentially important implication of Monte Carlo simulation, especially in the presence of steep flux gradients. We examine the usual method of extracting point-kerma estimates from randomly generated photon trajectories which consists of tallying the energy lost by photon collisions occurring in the vicinity of the point of interest. Several other methods derived from the equivalence of track length per unit volume and flux are evaluated as to accuracy and efficiency. Finally, a next-flight estimator is discussed in which the expected contribution of each simulated photon collision to the point. All of these techniques are shown to involve a trade-off between statistical precison and spatial resolution: increasing the number of contributing collisions requires averaging kerma over a larger volume. Based upon both analytic models and realistic Monte Carlo simulations, use of next-flight and track-length estimators is shown to improve stimulation efficiencies by factors of 2 to 20 compared to analog scoring. Practical guidelines as to choice of estimator and successful implementation are presented.