Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC 29425-3230, USA.
Med Phys. 2011 Oct;38(10):5362-9. doi: 10.1118/1.3635222.
To estimate in-patient KERMA for specific organs in computed tomography (CT) scanning using ratios to isocenter free-in-air KERMA obtained using a Rando phantom.
A CT scan of an anthropomorphic phantom results in an air KERMA K at a selected phantom location and air kerma K(CT) at the CT scanner isocenter when the scan is repeated in the absence of the phantom. The authors define the KERMA ratio (R(K)) as K∕ K(CT), which were experimentally determined in a Male Rando Phantom using lithium fluoride chips (TLD-100). R(K) values were obtained for a total of 400 individual point locations, as well as for 25 individual organs of interest in CT dosimetry. CT examinations of Rando were performed on a GE LightSpeed Ultra scanner operated at 80 kV, 120 kV, and 140 kV, as well as a Siemens Sensation 16 operated at 120 kV.
At 120 kV, median R(K) values for the GE and Siemens scanners were 0.60 and 0.64, respectively. The 10th percentile R(K) values ranged from 0.34 at 80 kV to 0.54 at 140 kV, and the 90th percentile R(K) values ranged from 0.64 at 80 kV to 0.78 at 140 kV. The average R(K) for the 25 Rando organs at 120 kV was 0.61 ± 0.08. Average R(K) values in the head, chest, and abdomen showed little variation. Relative to R(K) values in the head, chest, and abdomen obtained at 120 kV, R(K) values were about 12% lower in the pelvis and about 58% higher in the cervical spine region. Average R(K) values were about 6% higher on the Siemens Sensation 16 scanner than the GE LightSpeed Ultra. Reducing the x-ray tube voltage from 120 kV to 80 kV resulted in an average reduction in R(K) value of 34%, whereas increasing the x-ray tube voltage to 140 kV increased the average R(K) value by 9%.
In-patient to isocenter relative KERMA values in Rando phantom can be used to estimate organ doses in similar sized adults undergoing CT examinations from easily measured air KERMA values at the isocenter (free in air). Conversion from in-patient air KERMA values to tissue dose would require the use of energy-appropriate conversion factors.
使用伦琴空气比释动能（KERMA）比值，从 Rando 体模中获得无体模空气比释动能（KERMA），估算特定器官的 CT 扫描住院 KERMA。
对人体模型进行 CT 扫描会在选定的模型位置产生空气 KERMA K，并在没有模型的情况下在 CT 扫描仪等中心处产生空气 KERMA K(CT)。作者将 KERMA 比（R(K)）定义为 K∕ K(CT)，使用氟化锂芯片（TLD-100）在男性 Rando 体模中进行了实验确定。在 CT 剂量学中，总共获得了 400 个点位置和 25 个感兴趣器官的 R(K) 值。在 GE LightSpeed Ultra 扫描仪（80kV、120kV 和 140kV）和 Siemens Sensation 16 扫描仪（120kV）上对 Rando 进行了 CT 检查。
在 120kV 时，GE 和 Siemens 扫描仪的中位数 R(K) 值分别为 0.60 和 0.64。第 10 百分位数 R(K) 值范围为 80kV 时的 0.34 至 140kV 时的 0.54，第 90 百分位数 R(K) 值范围为 80kV 时的 0.64 至 140kV 时的 0.78。120kV 时 25 个 Rando 器官的平均 R(K) 值为 0.61±0.08。120kV 时头部、胸部和腹部的平均 R(K) 值变化不大。与 120kV 时头部、胸部和腹部的 R(K) 值相比，骨盆的 R(K) 值低约 12%，颈椎区域的 R(K) 值高约 58%。西门子 Sensation 16 扫描仪上的平均 R(K) 值比 GE LightSpeed Ultra 扫描仪高约 6%。将 X 射线管电压从 120kV 降低到 80kV 会导致 R(K) 值平均降低 34%，而将 X 射线管电压升高到 140kV 会使平均 R(K) 值升高 9%。
伦琴体模中住院患者与等中心的相对 KERMA 值可用于估算在类似大小的成年人中进行 CT 检查时的器官剂量，这些值可从等中心（自由空气中）容易测量的空气 KERMA 值获得。将住院患者空气 KERMA 值转换为组织剂量将需要使用能量适当的转换因子。
