Ionizing Radiation Standards, National Research Council of Canada, Ottawa, Canada.
Phys Med Biol. 2010 Aug 21;55(16):4495-507. doi: 10.1088/0031-9155/55/16/S05. Epub 2010 Jul 29.
Several variance reduction techniques improving the efficiency of the Monte Carlo estimation of the scatter contribution to a cone beam computed tomography (CBCT) scan were implemented in egs_ctct, an EGSnrc-based application for CBCT-related calculations. The largest impact on the efficiency comes from the splitting + Russian Roulette techniques which are described in detail. The fixed splitting technique is outperformed by both the position-dependent importance splitting (PDIS) and the region-dependent importance splitting (RDIS). The superiority of PDIS over RDIS observed for a water phantom with bone inserts is not observed when applying these techniques to a more realistic human chest phantom. A maximum efficiency improvement of several orders of magnitude over an analog calculation is obtained. A scatter calculation combining the reported efficiency gain with a smoothing algorithm is already in the proximity of being of practical use if a medium size computer cluster is available.
几种降低方差的技术被应用于 egs_ctct 中，以提高蒙特卡罗模拟在锥形束 CT（CBCT）扫描中散射贡献估计的效率，egs_ctct 是一个基于 EGSnrc 的用于 CBCT 相关计算的应用程序。对效率影响最大的是分裂+俄罗斯轮盘赌技术，我们对其进行了详细描述。固定分裂技术不如位置相关重要性分裂（PDIS）和区域相关重要性分裂（RDIS）。在对更现实的人体胸部模型应用这些技术时，观察到在带有骨插入物的水模体上 PDIS 优于 RDIS，但并未观察到这种优势。与模拟计算相比，效率提高了几个数量级。如果有一个中等大小的计算机集群，那么将报告的效率增益与平滑算法相结合的散射计算已经接近实用。
