A REVISED MODEL FOR ELECTRON DOSIMETRY IN THE HUMAN SMALL INTESTINE
A REVISED MODEL FOR ELECTRON DOSIMETRY IN THE HUMAN SMALL INTESTINE
复制标题
人体小肠电子剂量测定的修正模型
DOI：
10.1097/01.hp.0000144569.42599.eb
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发表时间：
2005
期刊：
影响因子：
2.2
通讯作者：
John W. Poston
中科院分区：
文献类型：
--
作者：
Bhuiyan Nu;John W. Poston
在这项研究中，吸收剂量计算的成年人小肠（SI）壁从电子在其内腔内容物。还研究了由于管腔半径和壁厚的变化对剂量的影响。SI模型基于从成人SI的解剖学和组织学回顾中收集的值。SI的组织学和放射学分析表明，这种壁器官的微观复杂性可以避免用于剂量测定目的，并且可以使用一组同心圆柱体来模拟SI。该模型被输入到Monte Carlo N-Particle（MCNP）4A版计算软件包中，该软件包用于模拟SI中50个离散能量范围为10-500 keV的电子的能量沉积。源电子以及所有产生的粒子，如撞击电子、韧致辐射和由韧致辐射相互作用产生的电子，被传输直到粒子能量低于1 keV的低能截止。对次级光子进行了详细的物理处理。通过合理的历史数据，采用适当的方差缩减技术来提高Monte Carlo计算的精度。该模型使用非常小的理货区域，其厚度范围从0.5米到200米，这取决于所研究的电子能量和理货在壁中的位置。与这些计算相关的相对误差保持在5%以下。对于所研究的每种能量，在整个壁中的大量计数结果使得能够在壁中构建能量特定深度剂量曲线。这些曲线中的每一个都与预期的能量沉积模式一致。这些曲线表明，只有一小部分在内容物-粘液界面处吸收的能量到达干细胞层，因为细胞位于粘膜深处。在10-500 keV的能量范围内，这个分数从1.66 × 10−6到1.21 × 10−1不等。这些结果表明，界面剂量（通常被报告为“壁”剂量）明显高估了干细胞的实际剂量。与临界细胞深度的变化相关的剂量不确定性被证明是非常高的电子，其CSDA范围在软组织中超过了临界细胞的深度。该研究表明，壁厚的不确定性对深度剂量没有影响，而管腔半径的变化会显著改变深度剂量。结果表明，这些变化可以用管腔半径的平方倒数来近似。
In this study, the absorbed dose was calculated to the small intestine (SI) wall of an adult human from electrons in its lumen contents. The effects on dose due to variations in the lumen radius and wall-thickness also were studied. The SI model was based on values gleaned from anatomic and histologic reviews of the adult human SI. Histologic and radiological analyses of the SI suggested the microscopic intricacy of this walled organ could be avoided for dosimetric purposes and a set of concentric cylinders could be used to model the SI. The model was input into the Monte Carlo N-Particle (MCNP) version 4A computational package, which was used to simulate energy deposition in the SI by electrons of fifty discrete energies ranging 10–500 keV. The source electrons as well as all resulting particles, such as knock-on electrons, bremsstrahlung, and electrons created from bremsstrahlung interactions, were transported until the particle energies fell below the 1 keV low-energy cutoff. Detailed physics treatments for secondary photons were made. With a reasonable number of histories, appropriate variance reduction techniques were used to improve the precision of the Monte Carlo calculations. The model used very small tally regions, which ranged in thickness from 0.5 &mgr;m to 200 &mgr;m depending on the electron energy studied and tally location in the wall. Relative errors associated with these calculations were maintained at less than 5%. The large number of tally results across the wall for each of the energies studied enabled the construction of the energy-specific depth dose curves in the wall. Each of these curves was consistent with the anticipated energy deposition pattern. These curves showed that only a small fraction of the energy absorbed at the contents-mucus interface reaches the stem cell layers because the cells are located deep in the mucosa. This fraction was found to vary from 1.66 × 10−6 to 1.21 × 10−1 over the energy range 10–500 keV. These results demonstrated the interface dose, which has been routinely reported as the “wall” dose, is a significant overestimate of the actual dose to the stem cells. The dose uncertainties associated with variations of the critical cell depth were shown to be very high for electrons whose CSDA ranges in the soft tissue exceeded the depth of the critical cells. This study showed that the uncertainty in the wall-thickness had no effect on depth doses while variation in the lumen radius significantly changes depth doses. The results suggest that these changes could be approximated by the inverse square of the lumen radius.