Breast dose in mammography is about 30% lower when realistic heterogeneous glandular distributions are considered
Breast dose in mammography is about 30% lower when realistic heterogeneous glandular distributions are considered
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DOI：
10.1118/1.4931966
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发表时间：
2015-11-01
期刊：
影响因子：
3.8
通讯作者：
Boone, John M.
中科院分区：
文献类型：
--
作者：
Hernandez, Andrew M.;Seibert, J. Anthony;Boone, John M.
目的：目前的乳房X光摄影剂量学方法假定乳房由腺体和脂肪组织组成。以前使用三维(3D)专用乳腺CT(BCT)数据集来评估乳房内复杂的解剖结构，表征乳腺腺组织的统计分布。本研究的目的是探讨BCT获取的乳腺组织的非均匀分布对剂量学测量的影响。方法：使用BCT获取的乳腺直径、体积和三维纤维腺分布来设计由腺体组织的非均匀分布组成的逼真的压缩乳腺模型。由BCT得到的腺体分布符合双高斯函数，并作为概率密度图来分配压缩乳腺模型中的密度分布。使用MCNPX 2.6.0蒙特卡罗程序估算乳腺摄影几何图形中的单能归一化平均腺体剂量DGN(E)值。DGN(E)值随后通过典型的乳房X光摄影X射线谱加权，以确定异质(pDgN(异种))和同质(pDgN(高))病例的多能DGN(PDgN)系数。结果：在所有体模和体模中，当体模分布位于乳房体模的冠状平面内时，体模的pDgN异源系数分别为35.3%(SD，4.1)和24.2%(SD，3.0)，分别比pDgN(HOMO)系数低。在乳房尺寸不变的情况下，对于W-Rh谱，将VGF从7.3%增加到19.1%会导致pDgN(异种)比pDgN(HOMO)减少23.6%-27.4%。相对于Mo-Mo谱的中心分布，腺体分布在上下方向上的距离等于压缩乳房宽度的10%时，pDgN(杂化)系数分别变化了37.3%和-26.6%。乳房压缩宽度的10%的距离，腺体分布的横向移位导致W-Rh光谱的pDgN(异质)系数相对于中心分布改变1.5%。结论：将BCT导出的异质腺体分布引入乳房X光摄影模体设计中，相对于广泛使用的均匀假设，腺体剂量减少。均匀的分布高估了乳房入口面附近的腺体组织的数量，那里的剂量沉积呈指数级高。虽然这些发现是基于使用大量女性队列的临床测量的腺体组织分布，但未来的工作需要改进基于乳房大小和总腺比例的腺体分布的分类。(C)2015年美国医学物理学家协会。
Purpose: Current dosimetry methods in mammography assume that the breast is comprised of a homogeneous mixture of glandular and adipose tissues. Three-dimensional (3D) dedicated breast CT (bCT) data sets were used previously to assess the complex anatomical structure within the breast, characterizing the statistical distribution of glandular tissue in the breast. The purpose of this work was to investigate the effect of bCT-derived heterogeneous glandular distributions on dosimetry in mammography.Methods: bCT-derived breast diameters, volumes, and 3D fibroglandular distributions were used to design realistic compressed breast models comprised of heterogeneous distributions of glandular tissue. The bCT-derived glandular distributions were fit to biGaussian functions and used as probability density maps to assign the density distributions within compressed breast models. The MCNPX 2.6.0 Monte Carlo code was used to estimate monoenergetic normalized mean glandular dose "DgN(E)" values in mammography geometry. The DgN(E) values were then weighted by typical mammography x-ray spectra to determine polyenergetic DgN (pDgN) coefficients for heterogeneous (pDgN(hetero)) and homogeneous (pDgN(homo)) cases. The dependence of estimated pDgN values on phantom size, volumetric glandular fraction (VGF), x-ray technique factors, and location of the heterogeneous glandular distributions was investigated.Results: The pDgNhetero coefficients were on average 35.3% (SD, 4.1) and 24.2% (SD, 3.0) lower than the pDgN(homo) coefficients for the Mo-Mo and W-Rh x-ray spectra, respectively, across all phantom sizes and VGFs when the glandular distributions were centered within the breast phantom in the coronal plane. At constant breast size, increasing VGF from 7.3% to 19.1% lead to a reduction in pDgN(hetero) relative to pDgN(homo) of 23.6%-27.4% for a W-Rh spectrum. Displacement of the glandular distribution, at a distance equal to 10% of the compressed breast width in the superior and inferior directions, resulted in a 37.3% and a -26.6% change in the pDgN(hetero) coefficient, respectively, relative to the centered distribution for the Mo-Mo spectrum. Lateral displacement of the glandular distribution, at a distance equal to 10% of the compressed breast width, resulted in a 1.5% change in the pDgN(hetero) coefficient relative to the centered distribution for the W-Rh spectrum.Conclusions: Introducing bCT-derived heterogeneous glandular distributions into mammography phantom design resulted in decreased glandular dose relative to the widely used homogeneous assumption. A homogeneous distribution overestimates the amount of glandular tissue near the entrant surface of the breast, where dose deposition is exponentially higher. While these findings are based on clinically measured distributions of glandular tissue using a large cohort of women, future work is required to improve the classification of glandular distributions based on breast size and overall glandular fraction. (C) 2015 American Association of Physicists in Medicine.