Technique factors and their relationship to radiation dose in pendant geometry breast CT
Technique factors and their relationship to radiation dose in pendant geometry breast CT
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DOI：
10.1118/1.2128126
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发表时间：
2005-12-01
期刊：
影响因子：
3.8
通讯作者：
Nelson, TR
中科院分区：
文献类型：
--
作者：
Boone, JM;Kwan, ALC;Nelson, TR
一些机构正在研究使用乳腺计算机断层扫描（CT）作为乳房X线摄影的替代方法。然而，与乳房CT相关的辐射剂量测定问题与乳房X线摄影的情况明显不同。在这项研究中，一个操作的乳房CT扫描仪的光谱特性，其特征在于从40至110 kVp（Be窗口W阳极与0.30 mm添加铜过滤）的kVp依赖的光谱的物理测量和计算机建模。先前报告的转换因子，标准化腺体剂量的CT-DgN（ct），来自蒙特卡罗方法，与乳腺扫描仪的输出光谱，以计算平均腺体剂量乳房的基础上的不同组合的X射线技术因素（kVp和mAs）。在我们机构的四种临床乳腺X射线摄影系统中，测量了平均腺体剂量（MGD）作为压缩乳房厚度（2-8 cm）和三种不同乳房成分（0%、50%和100%腺体分数）的函数。这四个系统的平均MGD用于计算乳腺CT系统的技术因子，该系统将匹配双视图乳腺摄影剂量水平。对于直径为14 cm的乳房（相当于乳房X线摄影中5 cm厚的压缩乳房），发现在80 kVp下，乳房CT扫描仪等中心（距源468 mm）处的空气比释动能水平为4.4、6.4和9.0 mGy，可分别为0%、50%和100%腺体乳房提供等效的乳房X线摄影剂量。在80 kVp（等中心处空气比释动能为11.3 mGy/100 mAs）时，需要57 mAs（整个扫描的积分）才能匹配14 cm 50%腺体乳腺的乳房X线摄影剂量。在50 kVp时，需要360 mAs才能匹配乳腺摄影剂量水平。表格中提供了等中心处的空气比释动能和0%、50%和100%腺体乳腺的mAs。影响乳腺CT技术因素的其他问题也进行了讨论。(c)2005年美国医学物理学家协会。
The use of breast computed tomography (CT) as an alternative to mammography in some patients is being studied at several institutions. However, the radiation dosimetry issues associated with breast CT are markedly different than in the case of mammography. In this study, the spectral properties of an operational breast CT scanner were characterized both by physical measurement and computer modeling of the kVp-dependent spectra, from 40 to 110 kVp (Be window W anode with 0.30 mm added Cu filtration). Previously reported conversion factors, normalized glandular dose for CT-DgN(ct), derived from Monte Carlo methods, were used in concert with the output spectra of the breast scanner to compute the mean glandular dose to the breast based upon different combinations of x-ray technique factors (kVp and mAs). The mean glandular dose (MGD) was measured as a function of the compressed breast thickness (2-8 cm) and three different breast compositions (0%, 50%, and 100% glandular fractions) in four clinical mammography systems in our institution. The average MGD from these four systems was used to compute the technique factors for breast CT systems that would match the two-view mammographic dose levels. For a 14 cm diameter breast (equivalent to a 5 cm thick compressed breast in mammography), air kerma levels at the breast CT scanner's isocenter (468 mm from the source) of 4.4, 6.4, and 9.0 mGy were found to deliver equivalent mammography doses for 0%, 50%, and 100% glandular breasts (respectively) at 80 kVp. At 80 kVp (where air kerma was 11.3 mGy/100 mAs at the isocenter), 57 mAs (integrated over the entire scan) was required to match the mammography dose for a 14 cm 50% glandular breast. At 50 kVp, 360 mAs is required to match mammographic dose levels. Tables are provided for both air kerma at the isocenter and mAs for 0%, 50%, and 100% glandular breasts. Other issues that impact breast CT technique factors are also discussed. (c) 2005 American Association of Physicists in Medicine.