McLean D
School of Medical Radiation Technology, University of Sydney, Lidcombe NSW.
Australas Phys Eng Sci Med. 1997 Mar;20(1):11-9.
The composition of the female breast is an elusive variable in screen-film mammography that has a vital role in determining both the radiographic image quality and breast radiation dose. Despite the large volume of research in mammography only two studies known to the author define the chemical composition of the two major breast constituents, fibrous glandular tissue and adipose tissue. Unfortunately there is not complete agreement between these two studies. Upon this basis, a variety of breast phantom materials have been suggested and developed. This paper examines the radiographic equivalence of some of these materials dealing notably with formulations given by Hammerstein et al and ICRU Report 44, as well as BR12, water, and lucite. Radiographic equivalence was calculated using a computer simulation of mammographic spectra (after the example of Birch and Marshall and Tucker et al, and fitted to available FDA data) applied to attenuation data of phantom materials, in turn based on elemental linear attenuation coefficient data. A software algorithm was written that iteratively calculates the thickness of a nominated material required to match the attenuation of another material of particular thickness. The equivalence of 2-8 cm of lucite to various phantom materials was calculated for molybdenum target, molybdenum filter (Mo/Mo) x-ray beams from 25 to 35 kVp and for Mo/Rh and Rh/Rh beams from 27 to 35 kVp. It was found that for Mo/Mo beams the equivalent thickness of breast phantom material for certain thicknesses of lucite was largely independent of x-ray beam energy with the range of thickness equivalences being less than 3% at 8 cm of lucite and less than 0.5% at 2 cm of lucite. The RMI 156 breast phantom was found to be equivalent to 42 mm of Hammerstein et al. 50% glandular/50% adipose phantom material for Mo/Mo beams at 27 kVp, increasing to 43 mm for the range of Rh/Rh beams. While some questions remain on the accuracy of the present composition of breast constituents, it is clear that various breast compositions can be successfully simulated by using an appropriate thickness of lucite material. The use of lucite breast phantoms is then seen as an effective and reliable way of evaluating mammographic image quality and for calculating breast dose for varying required breast compositions.
在屏-片乳腺摄影中，女性乳房的组成是一个难以捉摸的变量，它在决定射线图像质量和乳房辐射剂量方面都起着至关重要的作用。尽管乳腺摄影领域已有大量研究，但据作者所知，仅有两项研究对乳房的两种主要成分，即纤维腺组织和脂肪组织的化学成分进行了定义。遗憾的是，这两项研究之间并未达成完全一致。在此基础上，人们提出并开发了多种乳房体模材料。本文研究了其中一些材料的射线等效性，特别涉及Hammerstein等人给出的配方、ICRU报告44中的配方，以及BR12、水和有机玻璃。射线等效性是通过对乳腺摄影光谱进行计算机模拟（以Birch和Marshall以及Tucker等人的例子为基础，并与现有的FDA数据拟合）来计算的，该模拟应用于体模材料的衰减数据，而体模材料的衰减数据又基于元素线性衰减系数数据。编写了一个软件算法，用于迭代计算与特定厚度的另一种材料衰减相匹配的指定材料的厚度。针对钼靶、钼滤过（Mo/Mo）的X射线束（管电压从25到35 kVp）以及Mo/Rh和Rh/Rh的X射线束（管电压从27到35 kVp），计算了2 - 8厘米有机玻璃与各种体模材料的等效性。结果发现，对于Mo/Mo射线束，在一定厚度的有机玻璃下，乳房体模材料的等效厚度在很大程度上与X射线束能量无关，在8厘米有机玻璃时厚度等效范围小于3%，在2厘米有机玻璃时小于0.5%。研究发现，对于27 kVp的Mo/Mo射线束，RMI 156乳房体模相当于Hammerstein等人的50%腺组织/50%脂肪体模材料的42毫米厚度，对于Rh/Rh射线束范围，这一厚度增加到43毫米。虽然关于乳房成分当前组成的准确性仍存在一些问题，但显然通过使用适当厚度的有机玻璃材料可以成功模拟各种乳房成分。因此，使用有机玻璃乳房体模被视为评估乳腺摄影图像质量以及为不同所需乳房成分计算乳房剂量的一种有效且可靠的方法。
