Zhang Juying, Bednarz Bryan, Xu X George
Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
Health Phys. 2006 Nov;91(5 Suppl):S59-65. doi: 10.1097/01.HP.0000234039.58356.de.
Voxelized geometry such as those obtained from medical images is increasingly used in Monte Carlo calculations of absorbed doses. One useful application of calculated absorbed dose is the determination of fluence-to-dose conversion factors for different organs. However, confusion still exists about how such a geometry is defined and how the energy deposition is best computed, especially involving a popular code, MCNP5. This study investigated two different types of geometries in the MCNP5 code, cell and lattice definitions. A 10 cm x 10 cm x 10 cm test phantom, which contained an embedded 2 cm x 2 cm x 2 cm target at its center, was considered. A planar source emitting parallel photons was also considered in the study. The results revealed that MCNP5 does not calculate total target volume for multi-voxel geometries. Therefore, tallies which involve total target volume must be divided by the user by the total number of voxels to obtain a correct dose result. Also, using planar source areas greater than the phantom size results in the same fluence-to-dose conversion factor.
体素化几何结构，例如从医学图像中获取的那些，在吸收剂量的蒙特卡罗计算中越来越常用。计算得到的吸收剂量的一个有用应用是确定不同器官的注量-剂量转换因子。然而，对于如何定义这样的几何结构以及如何最好地计算能量沉积，仍然存在困惑，特别是涉及到一个流行的代码MCNP5时。本研究调查了MCNP5代码中的两种不同类型的几何结构，即单元格和晶格定义。考虑了一个10 cm×10 cm×10 cm的测试体模，其中心包含一个2 cm×2 cm×2 cm的嵌入式靶区。该研究还考虑了一个发射平行光子的平面源。结果表明，MCNP5不会计算多体素几何结构的总靶区体积。因此，涉及总靶区体积的计数必须由用户除以体素总数，以获得正确的剂量结果。此外，使用大于体模尺寸的平面源面积会得到相同的注量-剂量转换因子。
