School of Electronic Science and Application Physics, Hefei University of Technology, Hefei, China.
Cancer Biother Radiopharm. 2012 Aug;27(6):344-52. doi: 10.1089/cbr.2012.1173.
The organ or tumor activity is not uniform due to inhomogeneous expression/distributions of receptors/antigens and the nonuniform vascularization of the tumor tissue. However, most patient-specific three-dimensional Monte-Carlo methods for radionuclide dosimetry have dealt with quasi-homogeneous activity distributions. A voxel-by-voxel activity sample algorithm (VM) without artifacts is presented to calculate the dose of the heterogeneous activity distribution for radionuclide dosimetry.
The source particle location is sampled according to the activity spatial distribution. The source particle weight is imparted by the relative activity concentration of its origination voxel. This algorithm is applied to calculate the dose volume histogram for multiple independent activity regions with Gauss diffusion activity distributions and then compared with the level partition method (LM). The minimal response and the mean tolerant initial total activity threshold required by tumor control probability and normal tissue complication probability for radioimmunotherapy ((131)I-RIT) also were evaluated by the voxel-by-voxel sample algorithm and the LM. The effective clearance half-time is assumed to be equal to its physical half-life (i.e., 8.02 days for (131)I).
The result shows that the new algorithm is more consistent with the weighted superposition of the quasi-homogeneous activity distribution than the LM, especially for the multiple independent activity regions composed of different amounts of voxels. The new algorithm effectively avoids the leveling/binning artifacts to the heterogeneous activity distribution. The (131)I-RIT simulation also showed that the minimal response initial total activity threshold of tumors will be much more than the mean tolerant initial total activity threshold of normal organs (e.g., kidney) with the activity heterogeneous grade deteriorating.
A VM is presented to simulate the dose of the heterogeneous activity distribution for radionuclide dosimetry. The new algorithm effectively avoids the leveling/binning artifacts to the heterogeneous activity distribution.
由于受体/抗原的不均匀表达/分布以及肿瘤组织的非均匀血管化，器官或肿瘤的活性并不均匀。然而，大多数用于放射性核素剂量测定的特定于患者的三维蒙特卡罗方法都处理了准均匀活性分布。本文提出了一种无伪影的体素内活性样本算法（VM），用于计算放射性核素剂量测定中不均匀活性分布的剂量。
根据活性空间分布对源粒子位置进行采样。源粒子的权重由其起源体素的相对活性浓度赋予。该算法应用于具有高斯扩散活性分布的多个独立活性区域的剂量体积直方图的计算，并与水平分区方法（LM）进行比较。还通过体素内样本算法和 LM 评估了用于放射性免疫治疗（131I-RIT）的肿瘤控制概率和正常组织并发症概率的最小反应和平均耐受初始总活性阈值。有效清除半衰期假设与其物理半衰期相等（即 131I 的 8.02 天）。
结果表明，新算法比 LM 更符合准均匀活性分布的加权叠加，特别是对于由不同数量体素组成的多个独立活性区域。新算法有效地避免了对不均匀活性分布的水平/分箱伪影。131I-RIT 模拟还表明，随着活性异质性程度的恶化，肿瘤的最小反应初始总活性阈值将远高于正常器官（如肾脏）的平均耐受初始总活性阈值。
提出了一种 VM 来模拟放射性核素剂量测定中不均匀活性分布的剂量。新算法有效地避免了对不均匀活性分布的水平/分箱伪影。
