Sprague David R, Chin Frederick T, Liow Jeih-San, Fujita Masahiro, Burns H Donald, Hargreaves Richard, Stubbs James B, Pike Victor W, Innis Robert B, Mozley P David
Molecular Imaging Branch, NIMH, National Institutes of Health, Bethesda, Maryland 20892-0135, USA.
J Nucl Med. 2007 Jan;48(1):100-7.
(18)F-Labeled substance P antagonist-receptor quantifier ([(18)F]SPA-RQ) [2-fluoromethoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-[(2S,3S)-2-phenyl-piperidin-3-yl)amine] is a selective radioligand for in vivo quantification of tachykinin NK(1) receptors with PET. The aims of this study were to estimate the radiation safety profile and relative risks of [(18)F]SPA-RQ with 3 different methods of image analysis.
Whole-body PET images were acquired in 7 healthy subjects after injection of 192 +/- 7 MBq (5.2 +/- 0.2 mCi) [(18)F]SPA-RQ. Emission images were serially acquired at multiple time-points from 0 to 120 min and approximately 180-240 min after injection. Urine samples were collected after each imaging session and for 24 h after the last scan to measure excreted radioactivity. Horizontal tomographic images were compressed to varying degrees in the anteroposterior direction to create 3 datasets: thin-slice, bisected, and 2-dimensional (2D) planar images. Regions of interest were drawn around visually identifiable source organs to generate time-activity curves for each dataset. Residence times were determined from these curves, and doses to individual organs and the body as a whole were calculated using OLINDA/EXM 1.0.
The lungs, upper large intestine wall, small intestine, urinary bladder wall, kidneys, and thyroid had the highest radiation-absorbed doses. Biexponential fitting of mean bladder and urine activity showed that about 41% of injected activity was excreted via urine. Assuming a 2.4-h urine voiding interval, the calculated effective doses from thin-slice, bisected, and 2D planar images were 29.5, 29.3, and 32.3 microSv/MBq (109, 108, and 120 mrem/mCi), respectively.
Insofar as effective dose is an accurate measure of radiation risk, all 3 methods of analysis provided quite similar estimates of risk to human subjects. The radiation dose was moderate and would potentially allow subjects to receive multiple PET scans in a single year. Individual organ exposures varied among the 3 methods, especially for structures asymmetrically located in an anterior or posterior position. Bisected and 2D planar images almost always provided higher organ dose estimates than thin-slice images. Thus, either the bisected or 2D planar method of analysis appears acceptable for quantifying human radiation burden, at least for radioligands with a relatively broad distribution in the body and not concentrated in a small number of radiation sensitive organs.
（18）F标记的P物质拮抗剂-受体定量剂（[(18)F]SPA-RQ）[2-氟甲氧基-5-(5-三氟甲基-四氮唑-1-基)-苄基]-[(2S,3S)-2-苯基-哌啶-3-基)胺]是一种用于通过PET在体内定量速激肽NK(1)受体的选择性放射性配体。本研究的目的是使用3种不同的图像分析方法评估[(18)F]SPA-RQ的辐射安全性和相对风险。
7名健康受试者注射192±7 MBq（5.2±0.2 mCi）[(18)F]SPA-RQ后进行全身PET成像。在注射后0至120分钟以及大约180-240分钟的多个时间点连续采集发射图像。每次成像后收集尿液样本，并在最后一次扫描后24小时内收集尿液样本以测量排泄的放射性。水平断层图像在前后方向上进行不同程度的压缩，以创建3个数据集：薄层图像、二等分图像和二维（2D）平面图像。在视觉上可识别的源器官周围绘制感兴趣区域，以生成每个数据集的时间-活度曲线。根据这些曲线确定停留时间，并使用OLINDA/EXM 1.0计算各个器官和整个身体的剂量。
肺、上大肠壁、小肠、膀胱壁、肾脏和甲状腺的辐射吸收剂量最高。膀胱和尿液平均活度的双指数拟合表明，约41%的注入活度通过尿液排泄。假设排尿间隔为2.4小时，从薄层图像、二等分图像和2D平面图像计算出的有效剂量分别为29.5、29.3和32.3 μSv/MBq（109、108和120 mrem/mCi）。
就有效剂量是辐射风险的准确衡量指标而言，所有3种分析方法对人类受试者的风险估计非常相似。辐射剂量适中，可能允许受试者在一年内接受多次PET扫描。3种方法之间各个器官的暴露情况有所不同，特别是对于不对称位于前部或后部位置的结构。二等分图像和2D平面图像几乎总是比薄层图像提供更高的器官剂量估计。因此，二等分或2D平面分析方法似乎可接受用于量化人类辐射负担，至少对于在体内分布相对广泛且不集中在少数辐射敏感器官的放射性配体是如此。
