Department of Radiology, Teikyo University School of Medicine, Tokyo, Japan.
AJNR Am J Neuroradiol. 2010 May;31(5):822-6. doi: 10.3174/ajnr.A1946. Epub 2009 Dec 31.
Some recent studies on radiation lens injuries have indicated much lower dose thresholds than specified by the current radiation protection guidelines. The purpose of this research was to measure the lens dose during brain CT scans with multidetector row CT and to assess methods for estimating the lens dose.
With 8 types of multidetector row CT scanners, both axial and helical scans were obtained for the head part of a human-shaped phantom by using normal clinical settings with the orbitomeatal line as the baseline. We measured the doses on both eyelids by using an RPLGD during whole-brain scans including the orbit with the starting point at the level of the inferior orbital rim. To assess the effect of the starting points on the lens doses, we measured the lens doses by using 2 other starting points for scanning (the orbitomeatal line and the superior orbital rim).
The CTDIvols and the lens doses during whole-brain CT including the orbit were 50.9-113.3 mGy and 42.6-103.5 mGy, respectively. The ratios of lens dose to CTDIvol were 80.6%-103.4%. The lens doses decreased as the starting points were set more superiorly. The lens doses during scans from the superior orbital rim were 11.8%-20.9% of the doses during the scans from the inferior orbital rim.
CTDIvol can be used to estimate the lens dose during whole-brain CT when the orbit is included in the scanning range.
一些最近的关于放射性晶状体损伤的研究表明，其剂量阈值远低于现行辐射防护指南规定的阈值。本研究旨在测量多层螺旋 CT 脑部 CT 扫描时晶状体的剂量，并评估估计晶状体剂量的方法。
使用 8 种多层螺旋 CT 扫描仪，以眶耳线为基线，采用正常临床设置，对人体头部进行轴位和螺旋扫描。在包括眶部的全脑扫描中，我们使用 RPLGD 测量整个眼睑的剂量，扫描起点位于眶下缘水平。为了评估扫描起点对晶状体剂量的影响，我们使用另外两个扫描起点（眶耳线和眶上缘）测量晶状体剂量。
包括眶部的全脑 CT 的 CTDIvol 和晶状体剂量分别为 50.9-113.3 mGy 和 42.6-103.5 mGy。晶状体剂量与 CTDIvol 的比值为 80.6%-103.4%。随着扫描起点位置越高，晶状体剂量越低。从眶上缘扫描的晶状体剂量为从眶下缘扫描的 11.8%-20.9%。
当眶部包括在扫描范围内时，CTDIvol 可用于估计全脑 CT 扫描时的晶状体剂量。
