Vertical off-centering affects organ dose in chest CT: Evidence from Monte Carlo simulations in anthropomorphic phantoms
Vertical off-centering affects organ dose in chest CT: Evidence from Monte Carlo simulations in anthropomorphic phantoms
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DOI：
10.1002/mp.12519
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发表时间：
2017-11-01
期刊：
影响因子：
3.8
通讯作者：
Alkadhi, Hatem
中科院分区：
文献类型：
--
作者：
Saltybaeva, Natalia;Alkadhi, Hatem
目的探讨管电流调制胸部CT扫描中患者垂直偏心对器官剂量的影响。方法采用192层螺旋CT扫描仪，在11种不同的垂直位置(最大偏心5 cm)对成年男性、女性和超重男性的拟人模型进行扫描。使用从原始数据中提取的管电流值，对每个被调查的设置进行蒙特卡罗模拟，以获得3D剂量分布。器官剂量被计算为垂直偏离中心的函数，并与为位于门架等中心的体模计算的参考值进行比较。图像噪声也被计算为使用少量圆形感兴趣区域的模体垂直位置的函数。结果在体模垂直偏心扫描时，CT扫描仪所施加的管状电流与体模位于门架等中心位置时的管状电流有显著差异(P<；0.005)。对于所研究的所有体模构型，两个方向垂直偏心小于20 mm时，相对器官剂量差小于7%，而偏心大于40 mm时，器官剂量变化较大，约为20%。观察到最低台面位置的甲状腺的相对剂量差最大，为38%。乳房、心脏、肺、甲状腺和肝脏的器官剂量与垂直偏心显著相关(R-2=0.909-0.998，P<；0.005)。相对剂量增加与较低的桌子位置相关，在外周器官：乳房和甲状腺中更为明显。图像噪声与管电流和器官剂量成反比，且在床位越高，图像噪声越大。结论胸部CT管电流调制垂直偏心过大，会导致中医功能的误操作，影响辐射剂量和图像噪声。因此，必须特别注意患者的正确体位，以优化各自CT检查的器官剂量和图像质量。
PurposeThe objective of our study was to assess the effect of patient vertical off-centering on organ dose in chest CT with tube current modulation.MethodsFor this purpose, anthropomorphic phantoms representing adult male, female, and overweight male were scanned on 192-slice CT scanner at 11 different vertical positions (maximal off-centering 5 cm). Monte Carlo simulations were performed for each of the investigated setup, using tube current values extracted from the raw data, in order to obtain 3D dose distributions. Organ doses were calculated as a function of vertical off-centering and compared with the reference values, calculated for the phantoms positioned in the gantry isocenter. Image noise was also calculated as a function of phantoms vertical position using few circular regions of interest. Pearson statistical analysis was used to determine the correlation coefficient between image noise and organ dose values with vertical off-centering.ResultsResults of our study showed a significant difference in tube currents applied by the CT scanner when the phantom was scanned in off-centered vertical positions compared to those obtained when the phantom was positioned in the gantry isocenter (P < 0.005). For all investigated phantom configurations the vertical off-centering below 20 mm in both directions resulted in relative organ dose differences below 7%, while the off-centering above 40 mm was associated with higher organ dose changes of about 20%. The highest relative dose difference of 38% was observed for the thyroid gland at the lowest table positions. A significant correlation between organ doses for breasts, heart, lungs, thyroid, and liver, and vertical off-centering (R-2 = 0.909-0.998, P < 0.005) was found. The relative dose increase associated with lower table position was more pronounced in peripheral organs: breast and thyroid gland. Image noise behaved opposite to the tube current and organ doses and increased at higher table positions.ConclusionStrong vertical off-centering in chest CT with tube current modulation results in misoperation of the TCM function affecting both radiation dose and image noise. Therefore, special attention must be paid to a correct patient positioning in order to optimize organ doses and image quality of the respective CT examination.