Department of Radiology, University of Florida College of Medicine, Gainesville, FL, USA.
Department of Radiology, University of New Mexico, Albuquerque, NM, USA.
J Appl Clin Med Phys. 2019 Jun;20(6):141-151. doi: 10.1002/acm2.12594. Epub 2019 May 2.
The purpose of this study was to investigate the frequency and impact of vertical mis-centering on organ doses in computed tomography (CT) exams and evaluate the effect of a commercially available positioning compensation system (PCS). Mis-centering frequency and magnitude was retrospectively measured in 300 patients examined with chest-abdomen-pelvis CT. Organ doses were measured in three postmortem subjects scanned on a CT scanner at nine different vertical table positions (maximum shift ± 4 cm). Organ doses were measured with optically stimulated luminescent dosimeters inserted within organs. Regression analysis was performed to determine the correlation between organ doses and mis-centering. Methods were repeated using a PCS that automatically detects the table offset to adjust tube current output accordingly. Clinical mis-centering was >1 cm in 53% and 21% of patients in the vertical and lateral directions, respectively. The 1-cm table shifts resulted in organ dose differences up to 8%, while 4-cm shifts resulted in organ dose differences up to 35%. Organ doses increased linearly with superior table shifts for the lung, colon, uterus, ovaries, and skin (R = 0.73-0.99, P < 0.005). When the PCS was utilized, organ doses decreased with superior table shifts and dose differences were lower (average 5%, maximum 18%) than scans performed without PCS (average 9%, maximum 35%) at all table shifts. Mis-centering occurs frequently in the clinic and has a significant effect on patient dose. While accurate patient positioning remains important for maintaining optimal imaging conditions, a PCS has been shown to reduce the effects of patient mis-centering.
本研究旨在调查在计算机断层扫描（CT）检查中垂直中心偏移的频率和对器官剂量的影响，并评估一种市售的定位补偿系统（PCS）的效果。通过对 300 例胸部-腹部-骨盆 CT 检查的患者进行回顾性测量，计算了中心偏移的频率和幅度。在 CT 扫描仪上对三个死后标本进行了九种不同垂直床面位置（最大偏移±4cm）的扫描，以测量器官剂量。通过插入器官内的光激励发光剂量计来测量器官剂量。通过回归分析确定器官剂量与中心偏移之间的相关性。方法在使用可自动检测床面偏移并相应调整管电流输出的 PCS 时重复进行。临床中心偏移在垂直和水平方向上分别超过 1cm 的患者占 53%和 21%。1cm 的床面偏移会导致器官剂量差异高达 8%，而 4cm 的床面偏移会导致器官剂量差异高达 35%。当使用 PCS 时，随着床面向上移动，器官剂量呈线性增加，对于肺、结肠、子宫、卵巢和皮肤（R = 0.73-0.99，P < 0.005）。当使用 PCS 时，随着床面向上移动，器官剂量减小，剂量差异降低（平均 5%，最大 18%），而在所有床面偏移情况下未使用 PCS 时的剂量差异更高（平均 9%，最大 35%）。在临床实践中，中心偏移经常发生，对患者剂量有显著影响。虽然准确的患者定位对于保持最佳成像条件仍然很重要，但 PCS 已被证明可以降低患者中心偏移的影响。
