Ali Khawaja Ranish Deedar, Singh Sarabjeet, Padole Atul, Otrakji Alexi, Lira Diego, Zhang Da, Liu Bob, Primak Andrew, Xu George, Kalra Mannudeep K
MGH Imaging, Massachusetts General Hospital, Fruit St, Boston, MA 02114, USA.
Siemens Healthcare USA, Malvern, PA, USA.
Radiat Prot Dosimetry. 2017 Aug 1;175(4):440-449. doi: 10.1093/rpd/ncw371.
To determine the effect of patient off-centering on point organ radiation dose measurements in a human cadaver scanned with routine abdominal CT protocol. A human cadaver (88 years, body-mass-index 20 kg/m2) was scanned with routine abdominal CT protocol on 128-slice dual source MDCT (Definition Flash, Siemens). A total of 18 scans were performed using two scan protocols (a) 120 kV-200 mAs fixed-mA (CTDIvol 14 mGy) (b) 120 kV-125 ref mAs (7 mGy) with automatic exposure control (AEC, CareDose 4D) at three different positions (a) gantry isocenter, (b) upward off-centering and (c) downward off-centering. Scanning was repeated three times at each position. Six thimble (in liver, stomach, kidney, pancreas, colon and urinary bladder) and four MOSFET dosimeters (on cornea, thyroid, testicle and breast) were placed for calculation of measured point organ doses. Organ dose estimations were retrieved from dose-tracking software (eXposure, Radimetrics). Statistical analysis was performed using analysis of variance. There was a significant difference between the trends of point organ doses with AEC and fixed-mA at all three positions (p < 0.01). Variation in point doses between fixed-mA and AEC protocols were statistically significant across all organs at all Table positions (p < 0.001). There was up to 5-6% decrease in point doses with upward off-centering and in downward off-centering. There were statistical significant differences in point doses from dosimeters and dose-tracking software (mean difference for internal organs, 5-36% for fixed-mA & 7-48% for AEC protocols; p < 0.001; mean difference for surface organs, >92% for both protocols; p < 0.0001). For both protocols, the highest mean difference in point doses was found for stomach and lowest for colon. Measured absorbed point doses in abdominal CT vary with patient-centering in the gantry isocenter. Due to lack of consideration of patient positioning in the dose estimation on automatic software-over estimation of the doses up to 92% was reported.
为确定在采用常规腹部CT扫描方案扫描的人体尸体中，患者偏心对器官点辐射剂量测量的影响。使用128层双源MDCT（Definition Flash，西门子）对一具人体尸体（88岁，体重指数20kg/m²）采用常规腹部CT扫描方案进行扫描。使用两种扫描方案共进行了18次扫描：（a）120kV - 200mAs固定毫安（CTDIvol 14mGy）；（b）120kV - 125参考毫安（7mGy）并采用自动曝光控制（AEC，CareDose 4D），在三个不同位置进行扫描：（a）机架等中心；（b）向上偏心；（c）向下偏心。在每个位置重复扫描三次。放置了六个指形电离室（分别位于肝脏、胃、肾脏、胰腺、结肠和膀胱）和四个MOSFET剂量仪（分别位于角膜、甲状腺、睾丸和乳房）以计算测量的器官点剂量。器官剂量估计值从剂量跟踪软件（eXposure，Radimetrics）中获取。采用方差分析进行统计分析。在所有三个位置，采用AEC和固定毫安时器官点剂量的趋势之间存在显著差异（p < 0.01）。在所有表格位置的所有器官中，固定毫安和AEC方案之间的点剂量变化具有统计学意义（p < 0.001）。向上偏心和向下偏心时，点剂量最多降低5 - 6%。剂量仪和剂量跟踪软件的点剂量存在统计学显著差异（内部器官的平均差异，固定毫安方案为5 - 36%，AEC方案为7 - 48%；p < 0.001；表面器官的平均差异，两种方案均>92%；p < 0.0001）。对于两种方案，点剂量的最高平均差异出现在胃部，最低出现在结肠。腹部CT中测量的吸收器官点剂量随患者在机架等中心的对中情况而变化。由于自动软件在剂量估计中未考虑患者定位，据报道剂量高估高达92%。
