Department of Radiological Technology, Tzu Chi College of Technology, Taiwan.
Med Phys. 2012 Apr;39(4):2013-20. doi: 10.1118/1.3694097.
The need for an accurate estimate of absorbed doses within and around irradiated thorax tissues necessitates the use of carefully selected materials from which phantoms are constructed. A lung substitute is more difficult to establish mostly due to its low physical density. Although many researchers have used cork as a lung substitute, very little research data address cork's characteristics to determine which type of cork is optimal as a substitute for lung tissue.
Natural cork, composition cork, rubber cork, ATOM, RANDO, and a reference lung material (ICRU-44 lung tissue) were investigated to establish comparisons of physical properties. Following the determination of the respective physical properties, the dose distributions from 6 MV photon beams in water/lung substitute/water phantoms were assessed using the Monte Carlo method. Physical and electron densities affecting the dose distributions through lung tissues in different field size conditions were investigated.
The physical properties (physical density, electronic density, and effective atomic number) of the composition cork are the most similar to those of the ICRU-44 lung, and the CT number of the composition cork is very similar to that of humans aged 30-60. PDD of the composition cork and the RANDO phantom are the most comparable to that of ICRU-44 lung in 1 × 1 cm(2) field size due to the combined properties of physical density (PD) and electron density per gram (EDG) of the studied lung materials. PD and EDG affect the lung dose primarily in small field size. The effects of PD are minimal in large fields, having a more rapid lateral electron equilibrium. EDG dominates PDD pattern in lung material when large fields are applied. Combined effects of PD and EDG are nonlinear for all field sizes.
The composition cork is the preferred lung substitute based on physical and dosimetric properties.
需要准确估计受照射胸腔组织内和周围的吸收剂量，这就需要使用精心挑选的材料来构建体模。由于肺的物理密度较低，因此建立肺替代品更加困难。尽管许多研究人员使用软木作为肺替代品，但很少有研究数据涉及软木的特性，以确定哪种类型的软木最适合替代肺组织。
研究了天然软木、合成软木、橡胶软木、ATOM、RANDO 和参考肺材料（ICRU-44 肺组织），以建立物理特性的比较。确定各自的物理特性后，使用蒙特卡罗方法评估水/肺替代物/水体模中 6MV 光子束的剂量分布。研究了不同射野条件下通过肺组织影响剂量分布的物理和电子密度。
合成软木的物理特性（物理密度、电子密度和有效原子序数）与 ICRU-44 肺最相似，且合成软木的 CT 数与人的 30-60 岁年龄非常相似。由于研究中肺材料的物理密度（PD）和每克电子密度（EDG）的综合特性，合成软木和 RANDO 体模在 1×1cm2 射野大小下的 PDD 与 ICRU-44 肺最接近。PD 和 EDG 主要在小射野中影响肺剂量。在大射野中，PD 的影响最小，具有更快的侧向电子平衡。当应用大射野时，EDG 主宰肺材料中的 PDD 模式。对于所有射野大小，PD 和 EDG 的综合影响是非线性的。
基于物理和剂量学特性，合成软木是首选的肺替代品。
