McDermott Alanna, White R Allen, Mc-Nitt-Gray Mike, Angel Erin, Cody Dianna
Department of Bioinformatics and Computational Biology, UT MD Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 237, Houston, Texas 77030, USA.
Med Phys. 2009 May;36(5):1494-9. doi: 10.1118/1.3101817.
An anthropomorphic pediatric phantom (5-yr-old equivalent) was used to determine organ doses at specific surface and internal locations resulting from computed tomography (CT) scans. This phantom contains four different tissue-equivalent materials: Soft tissue, bone, brain, and lung. It was imaged on a 64-channel CT scanner with three head protocols (one contiguous axial scan and two helical scans [pitch = 0.516 and 0.984]) and four chest protocols (one contiguous axial scan and three helical scans [pitch = 0.516, 0.984, and 1.375]). Effective mA s [= (tube current x rotation time)/pitch] was kept nearly constant at 200 effective mA s for head and 290 effective mA s for chest protocols. Dose measurements were acquired using thermoluminescent dosimeter powder in capsules placed at locations internal to the phantom and on the phantom surface. The organs of interest were the brain, both eyes, thyroid, sternum, both breasts, and both lungs. The organ dose measurements from helical scans were lower than for contiguous axial scans by 0% to 25% even after adjusting for equivalent effective mA s. There was no significant difference (p > 0.05) in organ dose values between the 0.516 and 0.984 pitch values for both head and chest scans. The chest organ dose measurements obtained at a pitch of 1.375 were significantly higher than the dose values obtained at the other helical pitches used for chest scans (p < 0.05). This difference was attributed to the automatic selection of the large focal spot due to a higher tube current value. These findings suggest that there may be a previously unsuspected radiation dose benefit associated with the use of helical scan mode during computed tomography scanning.
使用一个拟人化的儿童体模（相当于5岁儿童）来确定计算机断层扫描（CT）扫描在特定体表和内部位置产生的器官剂量。该体模包含四种不同的组织等效材料：软组织、骨骼、脑和肺。在一台64通道CT扫描仪上对其进行成像，采用了三种头部扫描方案（一次连续轴向扫描和两次螺旋扫描 [螺距 = 0.516和0.984]）以及四种胸部扫描方案（一次连续轴向扫描和三次螺旋扫描 [螺距 = 0.516、0.984和1.375]）。有效毫安秒 [=（管电流×旋转时间）/螺距] 在头部扫描时保持在200有效毫安秒左右，在胸部扫描方案中保持在290有效毫安秒左右。使用置于体模内部位置和体模表面的胶囊中的热释光剂量计粉末进行剂量测量。感兴趣的器官包括脑、双眼、甲状腺、胸骨、双乳和双肺。即使在对等效有效毫安秒进行调整之后，螺旋扫描的器官剂量测量值仍比连续轴向扫描低0%至25%。对于头部和胸部扫描，螺距值为0.516和0.984时的器官剂量值之间没有显著差异（p>0.05）。在螺距为1.375时获得的胸部器官剂量测量值显著高于用于胸部扫描的其他螺旋螺距时获得的剂量值（p<0.05）。这种差异归因于由于管电流值较高而自动选择了大焦点。这些发现表明，在计算机断层扫描期间使用螺旋扫描模式可能存在先前未被怀疑的辐射剂量益处。
