Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Med Phys. 2012 Oct;39(10):6071-9. doi: 10.1118/1.4749966.
Patient exposure rate measurements verify published patient dose rate data and characterize dose rates near 2-18-fluorodeoxyglucose ((18)F-FDG) patients. A specific dose rate constant based on patient exposure rate measurements is a convenient quantity that can be applied to the desired distance, injection activity, and time postinjection to obtain an accurate calculation of cumulative external radiation dose. This study reports exposure rates measured at various locations near positron emission tomography (PET) (18)F-FDG patients prior to PET scanning. These measurements are normalized for the amount of administered activity, measurement distance, and time postinjection and are compared with other published data.
Exposure rates were measured using a calibrated ionization chamber at various body locations from 152 adult oncology patients postvoid after a mean uptake time of 76 min following injection with a mean activity of 490 MBq (18)F-FDG. Data were obtained at nine measurement locations for each patient: three near the head, four near the chest, and two near the feet.
On contact with, 30 cm superior to and 30 cm lateral to the head, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.482 (0.511), 0.135 (0.155), and 0.193 (0.223) μSv∕MBq h, respectively. On contact with, 30 cm anterior to, 30 cm lateral to and 1 m anterior to the chest, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.623 (0.709), 0.254 (0.283), 0.190 (0.218), and 0.067 (0.081) μSv∕MBq h respectively. 30 cm inferior and 30 cm lateral to the feet, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.024 (0.022) and 0.039 (0.044) μSv∕MBq h, respectively.
The measurements for this study support the use of 0.092 μSv m(2)∕MBq h as a reasonable representation of the dose rate anterior from the chest of patients immediately following injection. This value can then be reliably scaled to the desired time and distance for planning and staff dose evaluation purposes. At distances closer than 1 m, a distance-specific dose rate constant of 0.367 μSv∕MBq h at 30 cm is recommended for accurate calculations. An accurate patient-specific dose rate constant that accounts for patient-specific variables (e.g., distribution and attenuation) will allow an accurate evaluation of the dose rate from a patient injected with an isotope rather than simply utilizing a physical constant.
患者照射率测量验证已发表的患者剂量率数据，并对靠近 2-[18F] 氟代脱氧葡萄糖（18F-FDG）患者的剂量率进行特征描述。基于患者照射率测量的特定剂量率常数是一个方便的量，可以应用于所需的距离、注射活动和注射后时间，以准确计算累积外照射剂量。本研究报告了在正电子发射断层扫描（PET）18F-FDG 患者扫描前，在各种位置测量到的照射率。这些测量结果是根据给予的活动量、测量距离和注射后时间进行归一化的，并与其他已发表的数据进行了比较。
在 152 名成年肿瘤患者注射后平均 76 分钟进行排尿后，使用经过校准的电离室在各个身体部位测量照射率，平均活动量为 490MBq（18）F-FDG。对每位患者获得九个测量位置的数据：头部附近三个位置、胸部附近四个位置和脚部附近两个位置。
在接触头部、头部上方 30cm 处和头部侧面 30cm 处，注射后 60 分钟时单位注入活度的平均（75%分位数）剂量率分别为 0.482（0.511）、0.135（0.155）和 0.193（0.223）μSv/MBq h。在接触胸部、胸部前方 30cm 处、胸部侧面 30cm 处和胸部前方 1m 处，注射后 60 分钟时单位注入活度的平均（75%分位数）剂量率分别为 0.623（0.709）、0.254（0.283）、0.190（0.218）和 0.067（0.081）μSv/MBq h。在脚部下方 30cm 处和脚部侧面 30cm 处，注射后 60 分钟时单位注入活度的平均（75%分位数）剂量率分别为 0.024（0.022）和 0.039（0.044）μSv/MBq h。
本研究的测量结果支持使用 0.092μSv m2/MBq h 作为患者注射后立即胸部前剂量率的合理代表。然后，该值可以可靠地按所需的时间和距离进行缩放，以用于规划和工作人员剂量评估目的。在距离小于 1m 的地方，建议在 30cm 处使用特定于距离的剂量率常数 0.367μSv/MBq h 进行准确计算。一个准确的患者特异性剂量率常数，它考虑到患者特异性变量（例如分布和衰减），将允许对注入同位素的患者的剂量率进行准确评估，而不仅仅是简单地利用物理常数。
